Chemical oxidative potential of secondary organic aerosol (SOA) generated from the photooxidation of biogenic and anthropogenic volatile organic compounds

Abstract

Particulate matter (PM), of which a significant fraction is comprised of secondary organic aerosols (SOA), has received considerable attention due to its health implications. In this study, the water-soluble oxidative potential (OP^WS) of SOA generated from the photooxidation of biogenic and anthropogenic hydrocarbon precursors (isoprene, α-pinene, β-caryophyllene, pentadecane, m-xylene, and naphthalene) under different reaction conditions (<q>RO₂+HO₂</q> vs. <q>RO₂+NO</q> dominant, dry vs. humid) was characterized using dithiothreitol (DTT) consumption. The measured intrinsic OP^WS-DTT values ranged from 9 to 205pmolmin^-1µg^-1 and were highly dependent on the specific hydrocarbon precursor, with naphthalene and isoprene SOA generating the highest and lowest OP^WS-DTT values, respectively. Humidity and RO₂ fate affected OP^WS-DTT in a hydrocarbon-specific manner, with naphthalene SOA exhibiting the most pronounced effects, likely due to the formation of nitroaromatics. Together, these results suggest that precursor identity may be more influential than reaction condition in determining SOA oxidative potential, demonstrating the importance of sources, such as incomplete combustion, to aerosol toxicity. In the context of other PM sources, all SOA systems, with the exception of naphthalene SOA, were less DTT active than ambient sources related to incomplete combustion, including diesel and gasoline combustion as well as biomass burning. Finally, naphthalene SOA was as DTT active as biomass burning aerosol, which was found to be the most DTT-active OA source in a previous ambient study. These results highlight a need to consider SOA contributions (particularly from anthropogenic hydrocarbons) to health effects in the context of hydrocarbon emissions, SOA yields, and other PM sources.

Atmos. Chem. Phys., 17, 839853, 2017 www.atmos-chem-phys.net/17/839/2017/ doi:10.5194/acp-17-839-2017 Author(s) 2017. CC Attribution 3.0 License.

Wing Y. Tuet1, Yunle Chen2, Lu Xu1, Shierly Fok1, Dong Gao3, Rodney J. Weber4, and Nga L. Ng1,4

1School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA

2School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, USA

3School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA

4School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

Correspondence to: Nga L. Ng ([email protected])

Received: 26 September 2016 Published in Atmos. Chem. Phys. Discuss.: 7 October 2016 Revised: 26 December 2016 Accepted: 28 December 2016 Published: 19 January 2017

Abstract. Particulate matter (PM), of which a signicant fraction is comprised of secondary organic aerosols (SOA), has received considerable attention due to its health implications. In this study, the water-soluble oxidative potential (OPWS) of SOA generated from the photooxidation of biogenic and anthropogenic hydrocarbon precursors (isoprene, -pinene, -caryophyllene, pentadecane, mxylene, and naphthalene) under different reaction conditions (RO2+ HO2 vs. RO2+ NO dominant, dry vs. humid)

was characterized using dithiothreitol (DTT) consumption.

The measured intrinsic OPWS-DTT values ranged from 9 to

205 pmol min1 g1 and were highly dependent on the specic hydrocarbon precursor, with naphthalene and isoprene SOA generating the highest and lowest OPWS-DTT values,

respectively. Humidity and RO2 fate affected OPWS-DTT in a hydrocarbon-specic manner, with naphthalene SOA exhibiting the most pronounced effects, likely due to the formation of nitroaromatics. Together, these results suggest that precursor identity may be more inuential than reaction condition in determining SOA oxidative potential, demonstrating the importance of sources, such as incomplete combustion, to aerosol toxicity. In the context of other PM sources, all SOA systems, with the exception of naphthalene SOA, were less DTT active than ambient sources related to incomplete combustion, including diesel and gasoline combustion as well as biomass burning. Finally, naphthalene SOA was as DTT active as biomass burning aerosol, which was found to be the most DTT-active OA source in a previous ambient

Chemical oxidative potential of secondary organic aerosol (SOA) generated from the photooxidation of biogenic and anthropogenic volatile organic compounds

study. These results highlight a need to consider SOA contributions (particularly from anthropogenic hydrocarbons) to health effects in the context of hydrocarbon emissions, SOA yields, and other PM sources.

1 Introduction

Numerous epidemiological studies have found associations between elevated particulate matter (PM) concentrations and increased incidences of cardiopulmonary disease, including increases in lung cancer, asthma, chronic obstructive pulmonary disease, arrhythmia, and ischemic heart disease (Li et al., 2008; Pope III and Dockery, 2006; Brunekreef and Hol-gate, 2002; Dockery et al., 1993; Hoek et al., 2013; Anderson et al., 2011; Pope et al., 2002). Furthermore, ambient PM pollution ranked among the top 10 global risk factors in the 2010 Global Burden of Disease Study, with signicant contributions from cardiopulmonary diseases and lower respiratory infections (Lim et al., 2012). Recent epidemiological studies have also found an association between particle oxidative potential and various cardiopulmonary health endpoints (Bates et al., 2015; Fang et al., 2016; Yang et al., 2016; Weichenthal et al., 2016). Furthermore, results from toxicology studies suggest that PM-induced oxidant production, including reactive oxygen and nitrogen species (ROS/RNS), is a possible mechanism by which PM exposure results in adverse health effects (Li et al., 2003a; Tao et al., 2003; Castro and Freeman,

Published by Copernicus Publications on behalf of the European Geosciences Union.

840 W. Y. Tuet et al.: Chemical oxidative potential of SOA

2001; Gurgueira et al., 2002). These species can initiate inammatory cascades, which may ultimately lead to oxidative stress and cellular damage (Wiseman and Halliwell, 1996;Hensley et al., 2000). Prolonged stimulation of inammatory cascades may also lead to chronic inammation, for which there is a well-established link between chronic inammation and cancer (Philip et al., 2004). Collectively, these ndings suggest a possible link between PM exposure and epidemiologically associated health endpoints since PM can contain ROS/RNS and generate ROS/RNS via redox reactions and by inducing cellular pathways that produce ROS/RNS.

Chemical assays in which an antioxidant is used to simulate redox reactions that would occur in biological systems have been developed to study the oxidative potential of PM samples (Kumagai et al., 2002; Cho et al., 2005). In these assays, redox-active species in PM samples catalyze electron transfer from the antioxidant (dithiothreitol, DTT; ascorbic acid, AA; etc.) to oxygen, and antioxidant decay provides a measure of the concentration of redox-active species in the sample (Fang et al., 2015b). These assays have been utilized extensively to characterize ambient PM samples, and source apportionment regressions have been applied to DTT activity results to identify PM sources that may be detrimental to health (Bates et al., 2015; Fang et al., 2015a; Verma et al., 2014, 2015a). Results from these regressions, as well as inhalation and exposure studies, suggest that organic carbon constituents may play a signicant role in PM-induced health effects (Li et al., 2003b; Kleinman et al., 2005; Hamad et al., 2015; Verma et al., 2015b). In particular, humic-like substances (HULIS) and oxygenated polyaromatic hydrocarbons (PAHs) have been shown to contribute signicantly to the redox activity of water-soluble PM samples (Verma et al., 2012, 2015a, b; Dou et al., 2015; Lin and Yu, 2011). Recently, Tuet et al. (2016) also showed that there is a signi-cant correlation between intracellular ROS/RNS production and organic species (water-soluble organic carbon and brown carbon) for summer ambient samples, which suggests that photochemically driven secondary organic aerosols (SOA) may be important in PM-induced oxidative stress.

Many prior studies have focused on the health effects of primary emissions, such as PM directly emitted from diesel and gasoline engines (Bai et al., 2001; Kumagai et al., 2002;McWhinney et al., 2013a; Turner et al., 2015). Conversely, few studies have explored the potential health implications of SOA, which are formed from the oxidation of volatile organic compounds (VOCs; McWhinney et al., 2013b; Rattanavaraha et al., 2011; Kramer et al., 2016; Lund et al., 2013; McDonald et al., 2010, 2012; Baltensperger et al., 2008; Arashiro et al., 2016; Platt et al., 2014), even though eld studies have shown that SOA often dominate over primary aerosols even in urban environments (Zhang et al., 2007; Jimenez et al., 2009; Ng et al., 2010). The few studies that exist focus on SOA generated from a single class of hydrocarbon precursor or on SOA formed in a simulated urban background (Kramer et al., 2016; McWhinney et al., 2013b;

Rattanavaraha et al., 2011; Arashiro et al., 2016; McDonald et al., 2012). While studies on oxidative potential have shown that SOA is indeed redox active, the combined range of oxidative potentials observed for individual SOA systems is quite large and remains unexplored (McWhinney et al., 2013b; Kramer et al., 2016). Furthermore, results from cellular exposure studies are inconclusive, with some studies nding signicant response from SOA exposure and others nding little to no response. The exposure dose also differed from study to study, which may result in inconclusive results. This also highlights a need to consider doseresponse relationships as demonstrated recently in Tuet et al. (2016).Comparisons between the observed cellular endpoints from exposure to SOA formed from individual precursors are also lacking (Baltensperger et al., 2008; Lund et al., 2013; Mc-Donald et al., 2010, 2012; Arashiro et al., 2016). As such, there is a lack of perspective in terms of different individual SOA systems and their contributions to PM-induced health effects, making it unclear whether certain responses are indeed toxic for a range of sources and subtypes of PM. However, as cellular assays and animal inhalation experiments are more complex, a systematic study on the oxidative potential of individual SOA systems may be warranted rst.

In the present study, the water-soluble oxidative potential of SOA generated from various precursors under different reaction conditions was measured using the DTT assay (henceforth referred to as OPWS-DTT). While numerous cell-free

assays have been developed to measure oxidative potential, the DTT assay is well-suited for the purposes of this study due to its proven sensitivity to organic carbon constituents and its correlation with organic carbon (Janssen et al., 2014;Visentin et al., 2016). Furthermore, there are many previous studies reporting the DTT activities of laboratory-generated SOA and ambient samples for comparison purposes (Kramer et al., 2016; Bates et al., 2015; McWhinney et al., 2013a, b;Verma et al., 2015a; Xu et al., 2015a, b; Fang et al., 2015b;Lu et al., 2014). VOCs were chosen to represent the major classes of compounds known to produce SOA upon oxidation by atmospheric oxidants and to include precursors of both anthropogenic and biogenic origins (Table S1 in the Supplement). Biogenic precursors include isoprene, -pinene, and -caryophyllene, while anthropogenic precursors include pentadecane, m-xylene, and naphthalene. Isoprene was chosen since it is the most abundant non-methane hydrocarbon, with estimated global emissions around 500 Tg yr1 (Guenther et al., 2006). -pinene and -caryophyllene were chosen as representative, well-studied monoterpenes and sesquiterpenes, respectively. Both classes of compounds contribute signicantly to ambient aerosol (Eddingsaas et al., 2012;Hoffmann et al., 1997; Tasoglou and Pandis, 2015; Goldstein and Galbally, 2007). -pinene emissions ( 50 Tg yr1) are

also on the same order of global anthropogenic emissions ( 110 Tg yr1; Guenther et al., 1993; Piccot et al., 1992).

Similarly, anthropogenic precursors were chosen to include a long-chain alkane (pentadecane), a single-ring aromatic (m-

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W. Y. Tuet et al.: Chemical oxidative potential of SOA 841

Table 1. Experimental conditions.

Experiment Compound OH Relative [HC]0 [SOA]c precursor humidity (%) (ppb) (g m3)

1a isoprene H2O2 < 5 % 97 5.73 2a -pinene H2O2 < 5 % 191 119 3a -caryophyllene H2O2 < 5 % 36 221 4a pentadecane H2O2 < 5 % 106 9.71 5a m-xylene H2O2 < 5 % 450 89.3 6a naphthalene H2O2 < 5 % 178 128 7 isoprene H2O2 < 5 %b 97 17.1 8 -pinene H2O2 40 % 334 154 9 -caryophyllene H2O2 42 % 63 230 10 pentadecane H2O2 45 % 106 23.5 11 m-xylene H2O2 45 % 450 13.9 12 naphthalene H2O2 44 % 431 132 13 isoprene HONO < 5 % 970 148 14 -pinene HONO < 5 % 174 166 15 -caryophyllene HONO < 5 % 21 80.8 16 pentadecane HONO < 5 % 74 35.7 17 m-xylene HONO < 5 % 431 153 18 naphthalene HONO < 5 % 145 142

a These experiments were repeated to establish reproducibility. b Acidic seed (8 mM MgSO4 and16 mM H2SO4) was used instead of 8 mM (NH4)2SO4. c Average SOA concentration in the chamber during lter collection.

xylene), and a poly-aromatic (naphthalene). These classes of compounds are emitted as products of incomplete combustion (Robinson et al., 2007; Jia and Batterman, 2010; Bruns et al., 2016) and have been shown to have considerable SOA yields (e.g., Chan et al., 2009; Ng et al., 2007b; Lambe et al., 2011). In addition to precursor identity, the effects of humidity (dry vs. humid) and NOx (differing peroxy radical (RO2)

fates, RO2+ HO2 vs. RO2+ NO) on OPWS-DTT were inves

tigated because these conditions have been shown to affect the chemical composition and mass loading of formed SOA (Chhabra et al., 2010, 2011; Eddingsaas et al., 2012; Ng et al., 2007a, b; Loza et al., 2014; Chan et al., 2009; Boyd et al., 2015). Finally, intrinsic OPWS-DTT was compared with bulk

aerosol composition, specically elemental ratios, to investigate whether there is a link between OPWS-DTT and aerosol

composition.

2 Methods

2.1 Chamber experiments

SOA from the photooxidation of biogenic and anthropogenic VOCs were generated in the Georgia Tech Environmental Chamber (GTEC) facility. Details of the facility are described elsewhere (Boyd et al., 2015). Briey, the facility consists of two 12 m3 Teon chambers suspended inside a 6.4 m 3.7 m (21 ft 12 ft) temperature-controlled enclo

sure surrounded by black lights (Sylvania 24922) and natural sunlight uorescent lamps (Sylvania 24477). Multiple sam-

pling ports from each chamber allow for gas- and aerosol-phase measurements as well as introduction of reagents. Gas-phase measurements include O3, NO2, and NOx concentrations as measured by an O3 analyzer (Teledyne T400), a cavity-attenuated phase shift (CAPS) NO2 monitor (Aero-dyne), and a chemiluminescence NOx monitor (Teledyne 200EU), respectively. Additionally, a gas chromatography-ame ionization detector (GC-FID, Agilent 7890A) was used to monitor hydrocarbon decay and estimate hydroxyl radical (OH) concentration. In terms of aerosol-phase measurements, aerosol volume concentrations and distributions were measured using a scanning mobility particle sizer (SMPS, TSI), while bulk aerosol composition was determined using a high-resolution time-of-ight aerosol mass spectrometer (HR-ToF-AMS, Aerodyne; henceforth referred to as the AMS) (DeCarlo et al., 2006). AMS data were analyzed using the data analysis toolkits SQUIRREL (v. 1.57) and PIKA(v. 1.16). Elemental ratios (O : C, H : C, and N : C) were obtained using the method outlined by Canagaratna et al. (2015) and were used to calculate the average carbon oxidation state (OSc) (Kroll et al., 2011). Temperature and relative humidity (RH) were monitored using a hydro-thermometer (Vaisala HMP110).

Experimental conditions, given in Table 1, were designed to probe the effects of humidity, RO2 fate, and precursor hydrocarbon on OPWS-DTT. All experiments were performed at

25 C under dry (RH < 5 %) or humid (RH 45 %) condi

tions. Prior to each experiment, the chambers were ushed with pure air for 24 h. For humid experiments, the cham-

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842 W. Y. Tuet et al.: Chemical oxidative potential of SOA

bers were also humidied by means of a bubbler lled with deionized (DI) water during this time. Seed aerosol was then injected by atomizing a 15 mM (NH4)2SO4 seed solution (Sigma Aldrich) until the seed concentration was approximately 20 g m3. It is noted that for experiment 7 (isoprene

SOA under RO2+ HO2-dominant, humid conditions), ex

perimental conditions deviated due to extremely low SOA mass yields. For this experiment, an acidic seed solution (8 mM MgSO4 and 16 mM H2SO4) was used under dry conditions to promote SOA formation via the IEPOX (isoprene epoxydiols) uptake pathway, which has a higher SOA mass yield compared to the IEPOX + OH pathway and contributes

signicantly to ambient OA (Surratt et al., 2010; Lin et al., 2012).

Once the seed concentration stabilized, hydrocarbon was added by injecting a known volume of hydrocarbon solution (isoprene, 99 %; -pinene, 99 %; -caryophyllene,

> 98.5 %; pentadecane, 99 %; m-xylene, 99 %; naphtha

lene, 99 % (Sigma Aldrich)) into a glass bulb and passing zero air at 5 L min1 over the solution until fully evaporated ( 10 min). For pentadecane and -caryophyllene, the glass

bulb was gently heated to ensure full evaporation (Tasoglou and Pandis, 2015). Naphthalene was injected by passing pure air over the solid, as outlined in previous studies (Chan et al., 2009). After hydrocarbon injection, OH precursor was added to the chamber. Experiments were conducted under various NOx conditions where different RO2 reaction pathways prevailed. For RO2+ HO2 experiments, hydrogen peroxide

(H2O2) was used as the OH precursor. H2O2 (50 % aqueous solution, Sigma Aldrich) was injected using the method described for hydrocarbon injection to achieve an H2O2 concentration of 3 ppm, which yielded OH concentrations on the order of 106 molec cm3. For RO2+ NO experiments, ni

trous acid (HONO) was used as the OH precursor. HONO was prepared by adding 10 mL of 1 % wt aqueous NaNO2 (VWR International) dropwise into 20 mL of 10 % wt H2SO4 (VWR International) in a glass bulb. Zero air was then passed over the solution to introduce HONO into the chamber (Chan et al., 2009; Kroll et al., 2005). Photolysis of HONO yielded OH concentrations on the order of 107 molec cm3. NO and

NO2 were also formed as byproducts of HONO synthesis.

Once all the H2O2 evaporated (RO2+ HO2 experiments) or

NOx concentrations stabilized (RO2+ NO experiments), the

UV lights were turned on to initiate photooxidation.

2.2 Aerosol collection and extraction

Aerosol samples were collected onto 47 mm Teon lters(0.45 m pore size, Pall Laboratory) for approximately 1.5 h at a ow rate of 28 L min1. For each experiment, two lters (front lter and backing lter) were loaded in series to account for possible sampling artifacts (Conny and Slater, 2002). Total mass collected was determined by integrating the SMPS volume concentration as a function of time over the lter collection period and using the total volume of air

400

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Gas-phase concentration (ppb)

Mo (g m

-3)

0

20

60

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100

120

140

160

180

40 Reaction time (min)

100

80

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40

20

0

Figure 1. Typical reaction prole for a chamber experiment under RO2 + NO-dominant conditions. NO and NO2 concentrations

were monitored by CAPS NO2 and chemiluminescence NOx monitors, respectively. Hydrocarbon decay was monitored using GC

FID, while initial hydrocarbon (naphthalene) concentrations were determined using the chamber volume and mass of hydrocarbon injected. Aerosol mass concentrations were determined using volume concentrations obtained from SMPS and assuming an aerosol density of 1 g cm3. While typical SOA density is about 1.4 g cm3, it varies with hydrocarbon precursor identity and reaction conditions, and a density between 1.0 and 1.6 g cm

3 has been reported in previous studies (Ng et al., 2006, 2007a, b; Chan et al., 2009; Tasoglou and Pandis, 2015; Bahreini et al., 2005). The use of a density of 1 g cm3 is to facilitate easier comparisons with past and future studies. Results from future studies can be scaled accordingly for comparison with the current work. Mass concentrations have been corrected for particle wall loss (Nah et al., 2016).

collected. Volume concentrations were integrated using time-dependent data. Background lters containing seed and an OH precursor (H2O2 or HONO) only at experimental conditions were also collected to account for potential H2O2 or

HONO uptake, which may inuence oxidative potential. Collected lter samples were placed in sterile petri dishes, sealed with Paralm M, and stored at 20 C until extraction and

analysis (Fang et al., 2015b). Prior to determining OPWS-DTT,

collected particles were extracted in DI water by submerging the lter and sonicating for 1 hr using an Ultrasonic Cleanser (VWR International; Fang et al., 2015a). Sonication steps were performed in 30 min intervals with water replacement after each interval to reduce bath temperature. After sonication, extracts were ltered using 0.45 m PTFE (polytetrauoroethylene) syringe lters (Fisherbrand) to remove insoluble material (Fang et al., 2015b). All lter samples were extracted within 12 days of collection and analyzed immediately following extraction.

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W. Y. Tuet et al.: Chemical oxidative potential of SOA 843

250

200

150

100

50

0

+ HO

Humid, RO

+ HO

Dry, RO

Dry, RO

+ NO

-1 )

-1 g

DTT activity (pmol min

H:C

ISO AP BCAR PD MX NAPH

SOA system

Figure 2. Intrinsic DTT activities for SOA generated from various hydrocarbon precursors (ISO: isoprene, AP: -pinene, BCAR: -caryophyllene, PD: pentadecane, MX: m-xylene, and NAPH: naphthalene) under various conditions (red circles: dry, RO2+ HO2; blue

squares: humid, RO2+ HO2; and black triangles: dry, RO2+ NO).

Dry RO2+ HO2 experiments were repeated to ensure reproducibil

ity in SOA generation and collection. Error bars represent a 15 % coefcient of variation (Fang et al., 2015b).

2.3 Oxidative potential

The decay of DTT, a chemical species that reacts with redox-active species in a sample via electron transfer reactions, was used as a measure of oxidative potential (Cho et al., 2005; Kumagai et al., 2002). The intrinsic OPWS-DTT of aerosol

samples, as well as method blanks and positive controls (9,10-phenanthraquinone), was determined using a semiautomated DTT system. Specics of the high-throughput system are detailed in Fang et al. (2015b) Briey, the method consisted of three main steps: (1) oxidation of DTT by redox-active species in the sample, (2) reaction of residual DTT with DTNB (5,5-dithiobis(2-nitrobenzoic acid)) to form 2-nitro-5-mercaptobenzoic acid (TNB), repeated at specic time intervals, and (3) measurement of TNB to determine DTT consumption. After each time interval and between samples, the system was ushed with DI water.

3 Results and discussion

3.1 Laboratory-generated aerosol

Over the course of each experiment, gas and aerosol composition was continuously monitored. A typical time series for NO, NO2, gas-phase hydrocarbon concentration, and aerosol mass concentration is shown in Fig. 1 for naphthalene photooxidation under RO2+ NO-dominant reaction conditions.

Hydrocarbon decay was monitored using GC-FID, while initial gas-phase hydrocarbon concentrations were determined using the chamber volume and mass of hydrocarbon in-

2.0

1.5

1.0

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0.0

0.0

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O:C

Figure 3. Van Krevelen plot for various SOA systems. Data points are colored by SOA system (red: isoprene, yellow: -pinene, green: -caryophyllene, light blue: pentadecane, blue: m-xylene, and purple: naphthalene), shaped according to reaction conditions (circle: dry, RO2 + HO2; square: humid, RO2+ HO2; and triangle: dry,

RO2+ NO), and sized by intrinsic DTT activity. OA factors re

solved from PMF analysis of ambient AMS data are shown as black markers, also sized by intrinsic DTT activity. Hydrocarbon precursors are shown as stars, colored by SOA system. Specics on site locations and factor resolution methods are described elsewhere. COA: cooking OA, BBOA: biomass burning OA, Isoprene-OA: isoprene-derived OA, MO-OOA: more-oxidized oxygenated OA (Verma et al., 2015a; Xu et al., 2015a, b).

jected. Following irradiation, NO decreased due to reaction with RO2 from hydrocarbon oxidations. Nevertheless, ozone formation was suppressed owing to the high NO concentration throughout the experiment. Aerosol growth is ob-served shortly after initiation of photooxidation (i.e., turning on the lights) due to the efcient photolysis of HONO, which produced a high OH concentration on the order of 107 molec cm3. Once HONO was completely consumed, no further decay in the parent hydrocarbon and growth in aerosol mass were observed.

For each experiment, aerosol chemical composition was also monitored using the AMS. The average AMS mass spectra (Fig. S1 in the Supplement) for all VOC systems were consistent with those reported in previous studies (Chhabra et al., 2010, 2011). For RO2+ NO-dominant experiments, the

NO+ : NO+2 ratio has been used extensively in previous studies to differentiate between organic and inorganic nitrates (Farmer et al., 2010; Fry et al., 2009; Boyd et al., 2015;Xu et al., 2015b). The observed NO+ : NO+2 ratio for all

RO2+ NO-dominant experiments (4.26.1) was higher than

that observed for inorganic (ammonium) nitrates ( 2.3),

which indicates that these peaks are likely from organic nitrates rather than inorganic nitrates. The observed range is

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844 W. Y. Tuet et al.: Chemical oxidative potential of SOA

also consistent with values measured in previous organic nitrate studies for similar VOC systems and ambient studies (Bruns et al., 2010; Sato et al., 2010; Xu et al., 2015b). Elemental ratios (O : C, H : C, and N : C) were also obtained for each SOA system using the AMS. The aerosol systems investigated span a wide range of O : C ratios, as observed in previous laboratory and eld studies (Chhabra et al., 2011;Lambe et al., 2011; Jimenez et al., 2009; Ng et al., 2010).

3.2 Effect of hydrocarbon precursor and reaction condition on oxidative potential

To investigate whether different types of SOA differ in toxi-city, the OPWS-DTT, a measure of the concentration of redox-

active species present in a sample, was measured for SOA generated from six VOCs under three conditions (see Table 1 for specics). The blank-corrected OPWS-DTT values,

represented on a per mass (g) basis, are shown in Fig. 2.

Uncertainties associated with OPWS-DTT determination were approximated using a 15 % coefcient of variation, in accordance with previous studies using the same semiautomated system (Fang et al., 2015b). The OPWS-DTT values of all

backing lters and background lters were also measured and found to be within the uncertainty for blank Teon lters, which indicates that there were no observable sampling artifacts, gaseous absorption onto Teon lters, or H2O2 or

HONO uptake onto seed particles.

Overall, it is clear that the hydrocarbon precursor identity inuenced OPWS-DTT, with naphthalene having the highest intrinsic DTT activity (Fig. 2). All other hydrocarbon precursors investigated produced SOA with relatively low intrinsic OPWS-DTT ( 945 pmol min1 g1). For isoprene, the

SOA in this study was generated through different reaction pathways, including isoprene photooxidation under different RO2 fates and IEPOX reactive uptake to acidic seed particles. Although these different conditions produced different products and SOA compositions (Xu et al., 2014; Surratt et al., 2010; Chan et al., 2010), the OPWS-DTT is very similar.

It is important to note that the intrinsic OPWS-DTT values for

SOA generated under all conditions in this study are in agreement with the isoprene-derived OA factor resolved from positive matrix factorization (PMF) analysis of ambient AMS data (Fig. 4; Xu et al., 2015a, b; Verma et al., 2015a). The isoprene-derived OA from ambient measurements is largely attributed to IEPOX uptake, but it possibly contains some contribution from other isoprene oxidation pathways (Xu et al., 2015a, b). The similarity between laboratory-generated and ambient isoprene SOA suggests that isoprene SOA may have low OPWS-DTT regardless of reaction conditions. A previous laboratory chamber study by Kramer et al. (2016) also measured the DTT activity of isoprene SOA produced via different pathways, including SOA formed from direct photooxidation of isoprene. It was found that isoprene SOA formed under high-NOx conditions was more DTT active than that formed under low-NOx conditions. These re-

sults are in contrast with those obtained in this study, where

the OPWS-DTT of isoprene SOA was similar regardless of

reaction condition. However, we caution that (1) the SOA measured in Kramer et al. (2016) was formed under different experimental conditions, and (2) they utilized a different method for measuring DTT consumption (i.e., different extraction solvent, different initial DTT concentration, different method for quantifying DTT activity); therefore, the results from their study and ours may not be directly comparable. For instance, for isoprene photooxidation experiments, the low-NOx conditions in Kramer et al. (2016) corresponded to 5 ppm isoprene and 200 ppb NO, where the reaction regime was largely dened by the VOC / NOx ratio. It has been shown previously that SOA formed under the same VOC / NOx conditions can be drastically different and the use of this metric might not necessarily reect the actual peroxy radical fate (Ng et al., 2007b; Kroll and Seinfeld, 2008; Wennberg, 2013). In our study, the low-NOx experimental condition is dened by the fate of peroxy radicals directly, i.e., no NOx added, but with the presence of H2O2 to enhance the RO2+ HO2 reaction pathway, which is domi

nant in ambient environments when NOx levels are low.

-pinene, -caryophyllene, and pentadecane produced low OPWS-DTT across all conditions explored in this study (Fig. 2). Specically, the SOA formed under different reaction conditions do not appear to have signicantly different OPWS-DTT, even though different NOx conditions have been

shown to affect SOA loading and composition due to competing RO2 chemistry (Chan et al., 2009; Eddingsaas et al., 2012; Loza et al., 2014; Ng et al., 2007a). For instance, under conditions that favor RO2+ NO, organic nitrates are formed,

whereas under conditions that favor RO2+ HO2, organic per

oxides are the predominant products. In this study, the formation of organic nitrates is evident in the RO2+ NO experi

ments with the relatively higher NO+ : NO+2 ratio in the AMS mass spectra. It is possible that neither the organic peroxides or organic nitrates formed from the oxidation of these precursors are highly redox active, such that the overall OPWS-DTT

is similar even though the products differ. Further studies are required to establish this.

Similarly, the OPWS-DTT of SOA formed from m-xylene

under conditions that favor different RO2 fates were not signicantly different. Since OPWS-DTT is intended as a mea

sure of redox activity, the reaction products ability to participate in electron transfer may explain this lack of difference (e.g., lack of conjugated systems and associated pi bonds with unbound electrons). Under both RO2+ HO2 and

RO2+ NO pathways, a large number of m-xylene oxida

tion products do not retain the aromatic ring (Vivanco and Santiago, 2010; Jenkin et al., 2003). Therefore, these products may have similar OPWS-DTT as reaction products of -

pinene, -caryophyllene, and pentadecane, which also do not contain an aromatic ring. Under humid conditions, aerosols formed from the oxidation of m-xylene were more DTT active than those formed under dry conditions. The AMS mass

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W. Y. Tuet et al.: Chemical oxidative potential of SOA 845

-1 )

-1 )

This study (dry, RO + HO ) Kramer et al. (2016)

This study (dry, RO + HO ) Kramer et al. 2016

Bates et al. (2015) Fang et al. (2015)

Bates et al. 2015 Fang et al. 2015

McWhinney et al. (2013) (ACP) McWhinney et al. (2013) (ES&T)

(Dry, RO + NO) Verma et al. (2015)

Lu et al. (2014)

(Humid, RO + HO )

(umid, RO + HO ) McWhinney et al. 2013 (ACP)

McWhinney et al. 2013 (ES&T)

(dry, RO + NO) Verma et al. 2015

Lu et al. 2014

-1 g

-1 g

DTT activity (pmol min

DTT activity (pmol min

250 200 150 100

50 0

250 200 150 100

50 0

Chamber study

Chamber study

Ambient study

Ambient study

Isoprene SOA

a-pinene SOA

b-caryophyllene SOA

Pentadecane SOA

m-xylene SOA

Naphthalene SOA

Isoprene SOA

a-pinene SOA

b-caryophyllene SOA

Pentadecane SOA

m-xylene SOA

Naphthalene SOA

Isoprene SOA

Isoprene SOA

Naphthalene SOA

Naphthalene SOA

Isoprene-OA

MO-OOA

Biomass burning OA

Cooking OA

Isoprene-OA

MO-OOA

Biomass Burning OA

Cooking OA

LD gasoline vehicles

HD diesel vehicles

BURN

Other OC

LD Gasoline Vehicles

HD Diesel Vehicles

BURN

Other OC

DEP

DEP

Beijing

Beijing

Atlanta

Atlanta

m

m

For naphthalene, the OPWS-DTT measured for SOA generated under dry, RO2+ HO2-dominant conditions is in agree

ment with that measured by McWhinney et al. (2013b) (Fig. 4), which generated naphthalene SOA under similar chamber conditions using the same OH radical precursor.These values should be directly comparable since the same standard method described by Cho et al. (2005) was used to obtain the oxidative potentials in both McWhinney et al. (2013b) and this study. The OPWS-DTT of naphthalene

aerosol also appears to be strongly inuenced by humidity and RO2 fate (Fig. 2), with higher toxicities observed for aerosol formed under both humid and RO2+ NO-dominant

conditions. The effect of RO2 fate may be explained by the different products known to form from RO2+ HO2 and

RO2+ NO reaction pathways. Many of the same products, in

cluding naphthoquinones and all of the ring-opening derivatives of 2-formylcinnamaldehyde, are formed under both reaction conditions (Kautzman et al., 2010). Naphthoquinones are also known to be DTT active and have been shown to account for approximately 21 % of the DTT activity ob-served for naphthalene SOA (Charrier and Anastasio, 2012;McWhinney et al., 2013b). In addition to these products, ni-

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Figure 4. Intrinsic DTT activities for chamber SOA, various PM subtypes resolved from ambient data, and diesel exhaust particles. It should be noted that the DTT activity for isoprene SOA in Kramer et al. (2016) was determined using a different DTT method and may not be directly comparable. All other studies shown used the method outlined in Cho et al. (2005). DTT activities obtained in this study are shaped by reaction condition (circle: dry, RO2+ HO2; square: humid, RO2+ HO2; triangle: dry, RO2+ NO). Specics on site locations and

factor resolution methods are described elsewhere. DTT activities for Beijing and Atlanta are averages obtained across multiple seasons. Isoprene-OA: isoprene-derived OA, MO-OOA: more-oxidized oxygenated OA, BBOA: biomass burning OA, COA: cooking OA, LDGV: light-duty gasoline vehicles, HDDV: heavy-duty diesel vehicles, BURN: biomass burning, DEP: diesel exhaust particles (Kramer et al., 2016; McWhinney et al., 2013b; Verma et al., 2015a; Bates et al., 2015; McWhinney et al., 2013a; Xu et al., 2015a, b; Lu et al., 2014; Fang et al., 2015b).

spectra for aerosol formed under humid conditions also differs notably for several characteristic fragments (Fig. S2), which may explain the difference observed in OPWS-DTT.

More specically, m/z 44, which serves as an indication of oxidation (O : C ratio) (Ng et al., 2010), is very different for this experiment (dry signal: 0.098 vs. humid signal: 0.15).It is possible that the degree of oxidation may be an important factor for SOA formed from the same hydrocarbon, and systematic chamber studies investigating changes in O : C for SOA formed from a single hydrocarbon precursor would be valuable. Previous studies involving the effect of humidity on SOA composition also yield mixed results, with some nding signicant changes in SOA composition and yields (Nguyen et al., 2011; Wong et al., 2015; Healy et al., 2009; Stirnweis et al., 2016) and others reporting little difference (Boyd et al., 2015; Edney et al., 2000; Cocker et al., 2001). Humidity effects are therefore highly hydrocarbon-dependent. Further study into the specic oxidation mechanisms and products in the photooxidation of aromatic hydrocarbon under dry and humid conditions may be warranted to understand the difference in DTT activity.

846 W. Y. Tuet et al.: Chemical oxidative potential of SOA

troaromatics including nitronaphthols and nitronaphthalenes are formed under RO2+ NO conditions (Kautzman et al.,

2010). The nitrite group next to the aromatic ring in these products may further promote electron transfer between nitroaromatics and DTT, resulting in more DTT consumption and a higher OPWS-DTT. This effect was not observed for m-xylene SOA due to the formation of predominantly ring-opening products (Vivanco and Santiago, 2010; Jenkin et al., 2003). The presence of an aromatic ring in SOA products may therefore be important for determining oxidative potentials, and polyaromatic precursors may yield products of substantial toxicity. This is further supported by the observation that the AMS mass spectra for highly DTT-active naphthalene SOA contain peaks at m/z 77 and m/z 91, which are indicative of aromatic phenyl and benzyl ions (Chhabra et al., 2010; McLafferty and Tureek, 1993). Additionally, peaks indicative of aromatic compounds greater than m/z 120 were observed with similar mass spectral features as those reported for aerosol generated from naphthalene oxidation by OH radicals in previous studies (Riva et al., 2015). Aromatic species are also exclusive to HULIS (Sannigrahi et al., 2006), and ambient data have shown that HULIS are a signicant aerosol component contributing to OPWS-DTT (Verma et al.,

2012, 2015b; Dou et al., 2015; Lin and Yu, 2011).

Bulk aerosol elemental ratios (O : C, H : C, and N : C) were also determined for each SOA system since different types of aerosol are known to span a wide range of O : C (Chhabra et al., 2011; Lambe et al., 2011). All elemental ratios were stable during the lter collection period and could thus be represented by a single value. To visualize these differences in oxidation, the van Krevelen diagram was utilized (Fig. 3) because changes in the slope of data points within the van Krevelen space can provide information on SOA functionalization (Heald et al., 2010; Van Krevelen, 1950; Ng et al., 2011). Starting from the precursor hydrocarbon, a slope of 0 indicates addition of alcohol groups, a slope of 1 indi

cates addition of carbonyl and alcohol groups on separate carbons or addition of carboxylic acids, and a slope of 2

indicates addition of ketones or aldehydes. Previous studies show that both laboratory-generated and ambient OA occupy a narrow van Krevelen space with a slope of 1 to 0.5

(Heald et al., 2010; Ng et al., 2011). Ambient data included in Fig. 3 are for different organic aerosol subtypes resolved from PMF analysis of AMS data collected in the southeastern US (Verma et al., 2015a; Xu et al., 2015a, b).

The laboratory-generated aerosols span the range of H : C and O : C observed in the ambient. As seen in Fig. 3 (data points sized by intrinsic OPWS-DTT), while different re

action conditions produced aerosol of differing composition (i.e., different O : C and H : C), the intrinsic OPWS-DTT

does not appear to be affected by these differences. On the other hand, the hydrocarbon precursor identity inuences OPWS-DTT substantially. It has been shown that ambient OA from different sources can become increasingly oxidized (increasing O : C ratio) with atmospheric aging (Jimenez et al.,

2009; Ng et al., 2011). Based on the results shown in Fig. 3, it appears that a higher O : C ratio did not correspond to a higher OPWS-DTT. This is true for both the laboratory-

generated SOA in this study and the different OA subtypes resolved from ambient data (Verma et al., 2015a; Xu et al., 2015a, b). Nevertheless, the O : C ratios for individual systems (i.e., SOA formed from the same hydrocarbon precursor) may affect the intrinsic OPWS-DTT. Indeed, for sev

eral SOA systems ( -caryophyllene, pentadecane, and mxylene), SOA with higher O : C ratios also had a higher intrinsic OPWS-DTT (Figs. 2, 3). For SOA systems formed un

der RO2+ NO-dominant conditions, N : C ratios were also

determined to investigate if there is a link between N : C and intrinsic DTT activity (Fig. S3). Again, with the exception of naphthalene SOA, the intrinsic OPWS-DTT does not appear to

be affected by N : C ratio even though the systems explored span a wide range of N : C. This is consistent with the results observed in the van Krevelen diagram and further emphasizes the importance of hydrocarbon identity in determining oxidative potentials.

3.3 Comparison to other types of PM

In order to evaluate how the oxidative potential of individual SOA systems compares to other sources and subtypes of PM, the intrinsic OPWS-DTT values from this study are com

pared to values reported in the literature (Fig. 4). Comparatively, SOA formed from the photooxidation of isoprene, -pinene, -caryophyllene, pentadecane, and m-xylene were not very DTT active and produced low intrinsic OPWS-DTT.

The OPWS-DTT values of these aerosol systems were also

within the range of various OA subtypes resolved from ambient data. The method for determining intrinsic OPWS-DTT

for various OA subtypes is provided in the Supplement. As noted earlier, the OPWS-DTT for isoprene SOA generated in

this study is similar to the isoprene-derived OA factor from ambient data. The other ambient OA factors include a highly oxidized MO-OOA (more-oxidized oxygenated OA) factor resolved from PMF analysis of ambient OA data, as well as an oxidized organic aerosol factor containing contributions from biogenic SOA (other OC) resolved using the chemical mass balance (CMB) method with ensemble-averaged source impact proles (Bates et al., 2015; Xu et al., 2015a, b; Verma et al., 2014). While sources of MO-OOA have not been identied, studies have shown that the aerosol mass spectra for various sources of OA approach those of MO-OOA as it ages (Ng et al., 2010), and it has been speculated that MOOOA may contain aerosol from multiple aged sources (Xu et al., 2015b). Furthermore, MO-OOA has been shown to have widespread contributions across urban and rural sites, as well as different seasons (Xu et al., 2015a, b). Conversely, naphthalene SOA was highly DTT active with an OPWS-DTT

on the order of biomass burning OA (BBOA (Verma et al., 2015a), BURN (Bates et al., 2015)). The BBOA and BURN factors were resolved using different source apportionment

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W. Y. Tuet et al.: Chemical oxidative potential of SOA 847

methods and as such, the range for comparison is large. Here, we focus on BBOA since Verma et al. (2015a) previously showed that BBOA had the highest intrinsic DTT activity among all OA subtypes resolved from PMF analysis of ambient AMS data collected in the southeastern US (see Fig. 4 for comparison). Because naphthalene aerosols formed under RO2+ NO-dominant conditions may be even more redox

active than BBOA and anthropogenic emissions are more abundant in urban environments with higher NOx, this system warrants further systematic studies. It should however be noted that comparisons of intrinsic DTT activities between SOA from a pure VOC and an ambient source are difcult.BBOA is a source that contains many compounds, some of which may not be redox active. Thus, although it may contain highly DTT-active components with high intrinsic activities, the overall intrinsic activity will be much lower. As a result, a direct comparison with pure naphthalene SOA on a per mass basis is tenuous. However, naphthalene SOA formed under urban conditions (RO2+ NO) also produces nitroaromatics,

which may induce DNA breaks and other mutagenic effects (Baird et al., 2005; Helmig et al., 1992). As such, aerosols formed from photooxidation of PAHs may be a particularly important OA source in terms of PM health effects.

Other common sources of PM are those related to trafc.

Previous studies have determined that products of incomplete combustion include quinones capable of participating in redox reactions, including the oxidation of DTT (Kumagai et al., 2002; McWhinney et al., 2013a). The SOA systems investigated, including isoprene, -pinene, -caryophyllene, pentadecane, and m-xylene produced SOA that were less DTT active than diesel exhaust particles (DEPs) collected from light-duty diesel vehicle (LDDV) engines operated under various conditions (McWhinney et al., 2013a) and resolved for heavy-duty diesel vehicles (HDDVs) from ambient data (Bates et al., 2015). It should be noted that the DTT activity reported for DEPs includes both water-soluble and water-insoluble fractions (total DTT activity), whereas the DTT activity measured for SOA is water-soluble. However, there should be very little contribution from water-insoluble species to SOA (McWhinney et al., 2013a). Conversely, the intrinsic OPWS-DTT of naphthalene SOA was on par with that of light-duty gasoline vehicles (LDGVs) and higher than that of HDDVs and DEPs (Verma et al., 2014; Bates et al., 2015).Since naphthalene may also be emitted from gasoline and diesel combustion (Jia and Batterman, 2010), trafc-related controls may be extremely important to control these highly DTT-active sources. Furthermore, since SOA often dominate over POA (primary organic aerosols) even in urban centers (Zhang et al., 2007; Ng et al., 2011), even SOA that is only slightly DTT active may contribute signicantly to PM-induced health effects.

3.4 Implications

The water-soluble oxidative potential, as measured by DTT consumption, was determined for SOA generated from six different hydrocarbon precursors under three conditions of varying humidity and RO2 fate. Results from this study demonstrate that hydrocarbon precursor identity inuenced intrinsic SOA oxidative potential substantially. The biogenic and anthropogenic precursors investigated yielded SOA with OPWS-DTT values ranging from 9 to 205 pmol min1 g1, with isoprene SOA and naphthalene SOA having the lowest and highest intrinsic OPWS-DTT, respectively. In general, OPWS-DTT values for biogenic SOA were lower than those

for anthropogenic SOA. Therefore, to evaluate overall oxidative potentials of ambient SOA, hydrocarbon precursor emissions and their corresponding SOA formation potential must be considered. Moreover, it may be possible to roughly estimate regional oxidative potentials using individual intrinsic OPWS-DTT of different types of SOA in conjunction with VOC emissions and SOA loadings in models. For instance, DTT activities of aerosols collected in Beijing, China (77111 pmol min1 g1; Lu et al., 2014), where anthropogenic emissions dominate, more closely resemble the OPWS-DTT of naphthalene SOA. Conversely, ambient aerosols collected in the southeastern US have DTT activities (2536 pmol min1 g1; Fang et al., 2015b) that more closely resemble those of biogenic SOA. It may therefore be informative to investigate whether concentration addition can be applied to DTT consumption by exploring well-characterized PM mixtures.

Chamber reaction conditions, including relative humidity and specic RO2 fate, inuenced SOA elemental composition substantially and affected OPWS-DTT in a hydrocarbon

specic manner, although hydrocarbon identity was by far

the most inuential in determining OPWS-DTT. For several

VOCs (isoprene, -pinene, -caryophyllene, and pentade-cane), the reaction conditions had a negligible effect on OPWS-DTT, which suggests that the organic peroxides and or

ganic nitrates formed from the oxidation of these precursors may have similarly low redox activity. An investigation into the redox activity of individual known photooxidation products, including organic peroxides and organic nitrates, may elucidate further information on the lack of reaction condition effect. Similarly, nitroaromatics may explain the difference observed between naphthalene aerosol formed under different RO2 reaction pathways since the nitrite group may promote electron transfer and result in a higher OPWS-DTT.

This effect was not observed for m-xylene SOA due to the formation of predominantly ring-opening products. The loss of the aromatic ring may also explain the differences in intrinsic OPWS-DTT. For instance, naphthalene SOA, which

contains many aromatic ring-retaining products, is as redox active as BBOA, one of the most DTT-active aerosol subtypes found in ambient studies. Conversely, m-xylene SOA with predominantly aromatic ring-breaking products

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848 W. Y. Tuet et al.: Chemical oxidative potential of SOA

is much less redox active and the measured OPWS-DTT is

lower than that of trafc-related sources and several OA sub-types (BBOA and cooking OA, COA). This further supports earlier ndings (Verma et al., 2015b) that the polyaromatic ring structure may be an important consideration for understanding SOA redox activity, which may have implications for cellular redox imbalance (Tuet et al., 2016). Furthermore, nitroaromatics and polyaromatics may also have signicant health effects beyond redox imbalance, including various mutagenic effects (Baird et al., 2005; Helmig et al., 1992). As such, hydrocarbon precursors forming aromatic ring-retaining products may be the most important to consider in PM-induced health effects in terms of oxidative potential. This is consistent with many studies using DTT to show oxidative potential associated with sources related to incomplete combustion (Bates et al., 2015; Verma et al., 2014; McWhinney et al., 2013b) and the identication of HULIS (Verma et al., 2015b; Dou et al., 2015; Lin and Yu, 2011), and more specically, quinones as key components contributing to oxidative potential (Verma et al., 2014). Finally, redox-active metals are also emitted by trafc through mechanical processes, such as brake and tire wear (Charrier and Anastasio, 2012; Fang et al., 2015a). These species were not considered in the chamber experiments explored in this study. Inclusion of redox-active metals in future SOA experiments may be valuable to further understand the roles of SOA and metal species in overall redox activity.

Abbreviations

PM: particulate matter, SOA: secondary organic aerosol, ROS/RNS: reactive oxygen and nitrogen species, DTT: dithiothreitol, OPWS: oxidative potential of water-soluble species.

4 Data availability

Data are available upon request to the corresponding author ([email protected]).

The Supplement related to this article is available online at http://dx.doi.org/10.5194/acp-17-839-2017-supplement

Web End =doi:10.5194/acp-17-839-2017-supplement .

References

Anderson, J. O., Thundiyil, J. G., and Stolbach, A.: Clearing the Air: A Review of the Effects of Particulate Matter Air Pollution on Human Health, Journal of Medical Toxicology, 8, 166175, doi:http://dx.doi.org/10.1007/s13181-011-0203-1

Web End =10.1007/s13181-011-0203-1 http://dx.doi.org/10.1007/s13181-011-0203-1

Web End = , 2011.

Arashiro, M., Lin, Y.-H., Sexton, K. G., Zhang, Z., Jaspers, I., Fry,R. C., Vizuete, W. G., Gold, A., and Surratt, J. D.: In vitro exposure to isoprene-derived secondary organic aerosol by direct deposition and its effects on COX-2 and IL-8 gene expression, Atmos. Chem. Phys., 16, 1407914090, doi:http://dx.doi.org/10.5194/acp-16-14079-2016

Web End =10.5194/acp- http://dx.doi.org/10.5194/acp-16-14079-2016

Web End =16-14079-2016 , 2016.

Bahreini, R., Keywood, M. D., Ng, N. L., Varutbangkul, V., Gao,S., Flagan, R. C., Seinfeld, J. H., Worsnop, D. R., and Jimenez, J.L.: Measurements of Secondary Organic Aerosol from Oxidation of Cycloalkenes, Terpenes, and m-Xylene Using an Aerodyne Aerosol Mass Spectrometer, Environ. Sci. Technol., 39, 5674 5688, doi:http://dx.doi.org/10.1021/es048061a

Web End =10.1021/es048061a http://dx.doi.org/10.1021/es048061a

Web End = , 2005.

Bai, Y., Suzuki, A. K., and Sagai, M.: The cytotoxic effects of diesel exhaust particles on human pulmonary artery endothelial cells in vitro: role of active oxygen species, Free Radical Bio. Med., 30, 555562, doi:http://dx.doi.org/10.1016/S0891-5849(00)00499-8

Web End =10.1016/S0891-5849(00)00499-8 http://dx.doi.org/10.1016/S0891-5849(00)00499-8

Web End = , 2001.

Baird, W. M., Hooven, L. A., and Mahadevan, B.: Carcinogenic polycyclic aromatic hydrocarbon-DNA adducts and mechanism of action, Environ. Mol. Mutagen., 45, 106114, doi:http://dx.doi.org/10.1002/em.20095

Web End =10.1002/em.20095 http://dx.doi.org/10.1002/em.20095

Web End = , 2005.

Baltensperger, U., Dommen, J., Alfarra, R., Duplissy, J., Gaeggeler,K., Metzger, A., Facchini, M. C., Decesari, S., Finessi, E., Reinnig, C., Schott, M., Warnke, J., Hoffmann, T., Klatzer, B., Puxbaum, H., Geiser, M., Savi, M., Lang, D., Kalberer, M., and Geiser, T.: Combined determination of the chemical composition and of health effects of secondary organic aerosols: The POLYSOA project, J. Aerosol Med. Pulm. Drug Deliv., 21, 145 154, doi:http://dx.doi.org/10.1089/jamp.2007.0655

Web End =10.1089/jamp.2007.0655 http://dx.doi.org/10.1089/jamp.2007.0655

Web End = , 2008.

Bates, J. T., Weber, R. J., Abrams, J., Verma, V., Fang, T., Klein,M., Strickland, M. J., Sarnat, S. E., Chang, H. H., Mulholland, J.A., Tolbert, P. E., and Russell, A. G.: Reactive Oxygen Species Generation Linked to Sources of Atmospheric Particulate Matter and Cardiorespiratory Effects, Environ. Sci. Technol., 49, 1360513612, doi:http://dx.doi.org/10.1021/acs.est.5b02967

Web End =10.1021/acs.est.5b02967 http://dx.doi.org/10.1021/acs.est.5b02967

Web End = , 2015.

Boyd, C. M., Sanchez, J., Xu, L., Eugene, A. J., Nah, T., Tuet, W.Y., Guzman, M. I., and Ng, N. L.: Secondary organic aerosol formation from the pinene+NO3 system: effect of humidity

and peroxy radical fate, Atmos. Chem. Phys., 15, 74977522, doi:http://dx.doi.org/10.5194/acp-15-7497-2015

Web End =10.5194/acp-15-7497-2015 http://dx.doi.org/10.5194/acp-15-7497-2015

Web End = , 2015.

Brunekreef, B. and Holgate, S. T.: Air pollution and health, Lancet,360, 12331242, 2002.

Bruns, E. A., Perraud, V., Zelenyuk, A., Ezell, M. J., Johnson, S.N., Yu, Y., Imre, D., Finlayson-Pitts, B. J., and Alexander, M.L.: Comparison of FTIR and Particle Mass Spectrometry for the Measurement of Particulate Organic Nitrates, Environ. Sci. Technol., 44, 10561061, doi:http://dx.doi.org/10.1021/es9029864

Web End =10.1021/es9029864 http://dx.doi.org/10.1021/es9029864

Web End = , 2010.

Bruns, E. A., El Haddad, I., Slowik, J. G., Kilic, D., Klein, F., Baltensperger, U., and Prvt, A. S. H.: Identication of signicant precursor gases of secondary organic aerosols from residential wood combustion, Sci. Rep., 6, 27881, doi:http://dx.doi.org/10.1038/srep27881

Web End =10.1038/srep27881 http://dx.doi.org/10.1038/srep27881

Web End = , 2016.

Canagaratna, M. R., Jimenez, J. L., Kroll, J. H., Chen, Q., Kessler,S. H., Massoli, P., Hildebrandt Ruiz, L., Fortner, E., Williams, L.R., Wilson, K. R., Surratt, J. D., Donahue, N. M., Jayne, J. T.,

Atmos. Chem. Phys., 17, 839853, 2017 www.atmos-chem-phys.net/17/839/2017/

Acknowledgement. This work was supported by the Health Effects Institute under research agreement no. 4943-RFA13-2/14-4. Wing Y. Tuet acknowledges support by the National Science Foundation Graduate Research Fellowship under Grant no. DGE-1148903.

Edited by: A. S. H. PrvtReviewed by: two anonymous referees

W. Y. Tuet et al.: Chemical oxidative potential of SOA 849

and Worsnop, D. R.: Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications, Atmos. Chem. Phys., 15, 253272, doi:http://dx.doi.org/10.5194/acp-15-253-2015

Web End =10.5194/acp-15-253-2015 http://dx.doi.org/10.5194/acp-15-253-2015

Web End = , 2015.

Castro, L. and Freeman, B. A.: Reactive oxygen species in human health and disease, Nutrition, 17, 161165, 2001.

Chan, A. W. H., Kautzman, K. E., Chhabra, P. S., Surratt, J. D., Chan, M. N., Crounse, J. D., Krten, A., Wennberg, P. O., Flagan, R. C., and Seinfeld, J. H.: Secondary organic aerosol formation from photooxidation of naphthalene and alkylnaphthalenes: implications for oxidation of intermediate volatility organic compounds (IVOCs), Atmos. Chem. Phys., 9, 30493060, doi:http://dx.doi.org/10.5194/acp-9-3049-2009

Web End =10.5194/acp-9-3049-2009 http://dx.doi.org/10.5194/acp-9-3049-2009

Web End = , 2009.

Chan, A. W. H., Chan, M. N., Surratt, J. D., Chhabra, P. S., Loza,C. L., Crounse, J. D., Yee, L. D., Flagan, R. C., Wennberg, P. O., and Seinfeld, J. H.: Role of aldehyde chemistry and NOx concentrations in secondary organic aerosol formation, Atmos. Chem.Phys., 10, 71697188, doi:http://dx.doi.org/10.5194/acp-10-7169-2010

Web End =10.5194/acp-10-7169-2010 http://dx.doi.org/10.5194/acp-10-7169-2010

Web End = , 2010.Charrier, J. G. and Anastasio, C.: On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals, Atmos. Chem. Phys., 12, 93219333, doi:http://dx.doi.org/10.5194/acp-12-9321-2012

Web End =10.5194/acp-12-9321-2012 http://dx.doi.org/10.5194/acp-12-9321-2012

Web End = , 2012.

Chhabra, P. S., Flagan, R. C., and Seinfeld, J. H.: Elemental analysis of chamber organic aerosol using an aerodyne high-resolution aerosol mass spectrometer, Atmos. Chem. Phys., 10, 41114131, doi:http://dx.doi.org/10.5194/acp-10-4111-2010

Web End =10.5194/acp-10-4111-2010 http://dx.doi.org/10.5194/acp-10-4111-2010

Web End = , 2010.

Chhabra, P. S., Ng, N. L., Canagaratna, M. R., Corrigan, A. L., Russell, L. M., Worsnop, D. R., Flagan, R. C., and Seinfeld, J. H.: Elemental composition and oxidation of chamber organic aerosol, Atmos. Chem. Phys., 11, 88278845, doi:http://dx.doi.org/10.5194/acp-11-8827-2011

Web End =10.5194/acp-11-8827- http://dx.doi.org/10.5194/acp-11-8827-2011

Web End =2011 , 2011.

Cho, A. K., Sioutas, C., Miguel, A. H., Kumagai, Y., Schmitz,D. A., Singh, M., Eiguren-Fernandez, A., and Froines, J.R.: Redox activity of airborne particulate matter at different sites in the Los Angeles Basin, Environ. Res., 99, 4047, doi:http://dx.doi.org/10.1016/j.envres.2005.01.003

Web End =10.1016/j.envres.2005.01.003 http://dx.doi.org/10.1016/j.envres.2005.01.003

Web End = , 2005.

Cocker III, D. R., Mader, B. T., Kalberer, M., Flagan, R. C., and Seinfeld, J. H.: The effect of water on gasparticle partitioning of secondary organic aerosol: II. m-xylene and 1,3,5-trimethylbenzene photooxidation systems, Atmos. Environ., 35, 60736085, doi:http://dx.doi.org/10.1016/S1352-2310(01)00405-8

Web End =10.1016/S1352-2310(01)00405-8 http://dx.doi.org/10.1016/S1352-2310(01)00405-8

Web End = , 2001.Conny, J. M. and Slater, J. F.: Black carbon and organic carbon in aerosol particles from crown res in the Canadian bo-real forest, J. Geophys. Res.-Atmos., 107, AAC 4-1AAC 4-12, doi:http://dx.doi.org/10.1029/2001JD001528

Web End =10.1029/2001JD001528 http://dx.doi.org/10.1029/2001JD001528

Web End = , 2002.

DeCarlo, P. F., Kimmel, J. R., Trimborn, A., Northway, M. J., Jayne,J. T., Aiken, A. C., Gonin, M., Fuhrer, K., Horvath, T., Docherty,K. S., Worsnop, D. R., and Jimenez, J. L.: Field-Deployable, High-Resolution, Time-of-Flight Aerosol Mass Spectrometer, Anal. Chem., 78, 82818289, doi:http://dx.doi.org/10.1021/ac061249n

Web End =10.1021/ac061249n http://dx.doi.org/10.1021/ac061249n

Web End = , 2006.Dockery, D. W., Pope, C. A., Xu, X., Spengler, J. D., Ware,J. H., Fay, M. E., Ferris, B. G., and Speizer, F. E.: An Association between Air Pollution and Mortality in Six U.S.Cities, New England Journal of Medicine, 329, 17531759, doi:http://dx.doi.org/10.1056/NEJM199312093292401

Web End =10.1056/NEJM199312093292401 http://dx.doi.org/10.1056/NEJM199312093292401

Web End = , 1993.

Dou, J., Lin, P., Kuang, B.-Y., and Yu, J. Z.: Reactive Oxygen Species Production Mediated by Humic-like Substances in Atmospheric Aerosols: Enhancement Effects by Pyridine, Imida-

zole, and Their Derivatives, Environ. Sci. Technol., 49, 6457 6465, doi:http://dx.doi.org/10.1021/es5059378

Web End =10.1021/es5059378 http://dx.doi.org/10.1021/es5059378

Web End = , 2015.

Eddingsaas, N. C., Loza, C. L., Yee, L. D., Chan, M., Schilling, K.A., Chhabra, P. S., Seinfeld, J. H., and Wennberg, P. O.: -pinene photooxidation under controlled chemical conditions Part 2: SOA yield and composition in low- and high-NOx environments, Atmos. Chem. Phys., 12, 74137427, doi:http://dx.doi.org/10.5194/acp-12-7413-2012

Web End =10.5194/acp-12-7413- http://dx.doi.org/10.5194/acp-12-7413-2012

Web End =2012 , 2012.

Edney, E. O., Driscoll, D. J., Speer, R. E., Weathers, W. S., Kleindienst, T. E., Li, W., and Smith, D. F.: Impact of aerosol liquid water on secondary organic aerosol yields of irradiated toluene/propylene/NOx/(NH4)2SO4/air mixtures, Atmos.Environ., 34, 39073919, doi:http://dx.doi.org/10.1016/S1352-2310(00)00174-6

Web End =10.1016/S1352-2310(00)00174-6 http://dx.doi.org/10.1016/S1352-2310(00)00174-6

Web End = , 2000.

Fang, T., Guo, H., Verma, V., Peltier, R. E., and Weber, R. J.: PM2.5 water-soluble elements in the southeastern United States: automated analytical method development, spatiotemporal distributions, source apportionment, and implications for heath studies, Atmos. Chem. Phys., 15, 1166711682, doi:http://dx.doi.org/10.5194/acp-15-11667-2015

Web End =10.5194/acp-15- http://dx.doi.org/10.5194/acp-15-11667-2015

Web End =11667-2015 , 2015a.

Fang, T., Verma, V., Guo, H., King, L. E., Edgerton, E. S., and Weber, R. J.: A semi-automated system for quantifying the oxidative potential of ambient particles in aqueous extracts using the dithiothreitol (DTT) assay: results from the Southeastern Center for Air Pollution and Epidemiology (SCAPE), Atmos. Meas.Tech., 8, 471482, doi:http://dx.doi.org/10.5194/amt-8-471-2015

Web End =10.5194/amt-8-471-2015 http://dx.doi.org/10.5194/amt-8-471-2015

Web End = , 2015b.

Fang, T., Verma, V., Bates, J. T., Abrams, J., Klein, M., Strickland,M. J., Sarnat, S. E., Chang, H. H., Mulholland, J. A., Tolbert, P.E., Russell, A. G., and Weber, R. J.: Oxidative potential of ambient water-soluble PM2.5 in the southeastern United States: contrasts in sources and health associations between ascorbic acid (AA) and dithiothreitol (DTT) assays, Atmos. Chem. Phys., 16, 38653879, doi:http://dx.doi.org/10.5194/acp-16-3865-2016

Web End =10.5194/acp-16-3865-2016 http://dx.doi.org/10.5194/acp-16-3865-2016

Web End = , 2016.

Farmer, D. K., Matsunaga, A., Docherty, K. S., Surratt, J. D., Seinfeld, J. H., Ziemann, P. J., and Jimenez, J. L.: Response of an aerosol mass spectrometer to organonitrates and organosulfates and implications for atmospheric chemistry, P. Natl. Acad. Sci.USA, 107, 66706675, doi:http://dx.doi.org/10.1073/pnas.0912340107

Web End =10.1073/pnas.0912340107 http://dx.doi.org/10.1073/pnas.0912340107

Web End = , 2010.Fry, J. L., Kiendler-Scharr, A., Rollins, A. W., Wooldridge, P. J.,

Brown, S. S., Fuchs, H., Dub, W., Mensah, A., dal Maso,M., Tillmann, R., Dorn, H.-P., Brauers, T., and Cohen, R.C.: Organic nitrate and secondary organic aerosol yield from NO3 oxidation of -pinene evaluated using a gas-phase kinetics/aerosol partitioning model, Atmos. Chem. Phys., 9, 1431

1449, doi:http://dx.doi.org/10.5194/acp-9-1431-2009

Web End =10.5194/acp-9-1431-2009 http://dx.doi.org/10.5194/acp-9-1431-2009

Web End = , 2009.

Goldstein, A. H. and Galbally, I. E.: Known and Unexplored Organic Constituents in the Earths Atmosphere, Environ. Sci.Technol., 41, 15141521, doi:http://dx.doi.org/10.1021/es072476p

Web End =10.1021/es072476p http://dx.doi.org/10.1021/es072476p

Web End = , 2007.Guenther, A., Karl, T., Harley, P., Wiedinmyer, C., Palmer, P. I., and Geron, C.: Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature), Atmos. Chem. Phys., 6, 31813210, doi:http://dx.doi.org/10.5194/acp-6-3181-2006

Web End =10.5194/acp-6- http://dx.doi.org/10.5194/acp-6-3181-2006

Web End =3181-2006 , 2006.

Guenther, A. B., Zimmerman, P. R., Harley, P. C., Monson, R. K., and Fall, R.: Isoprene and monoterpene emission rate variability: Model evaluations and sensitivity analyses, J. Geophys. Res.-Atmos., 98, 1260912617, doi:http://dx.doi.org/10.1029/93JD00527

Web End =10.1029/93JD00527 http://dx.doi.org/10.1029/93JD00527

Web End = , 1993.Gurgueira, S. A., Lawrence, J., Coull, B., Murthy, G. G. K., and

Gonzalez-Flecha, B.: Rapid increases in the steady-state concen-

www.atmos-chem-phys.net/17/839/2017/ Atmos. Chem. Phys., 17, 839853, 2017

850 W. Y. Tuet et al.: Chemical oxidative potential of SOA

tration of reactive oxygen species in the lungs and heart after particulate air pollution inhalation, Environ. Health Persp., 110, 749755, 2002.

Hamad, S. H., Shafer, M. M., Kadhim, A. K. H., Al-Omran, S. M., and Schauer, J. J.: Seasonal trends in the composition and ROS activity of ne particulate matter in Baghdad, Iraq, Atmos. Environ., 100, 102110, doi:http://dx.doi.org/10.1016/j.atmosenv.2014.10.043

Web End =10.1016/j.atmosenv.2014.10.043 http://dx.doi.org/10.1016/j.atmosenv.2014.10.043

Web End = , 2015.Heald, C. L., Kroll, J. H., Jimenez, J. L., Docherty, K. S., DeCarlo,P. F., Aiken, A. C., Chen, Q., Martin, S. T., Farmer, D. K., and Artaxo, P.: A simplied description of the evolution of organic aerosol composition in the atmosphere, Geophys. Res. Lett., 37, L08803, doi:http://dx.doi.org/10.1029/2010GL042737

Web End =10.1029/2010GL042737 http://dx.doi.org/10.1029/2010GL042737

Web End = , 2010.

Healy, R. M., Temime, B., Kuprovskyte, K., and Wenger, J. C.:

Effect of Relative Humidity on Gas/Particle Partitioning and Aerosol Mass Yield in the Photooxidation of p-Xylene, Environ.Sci. Technol., 43, 18841889, doi:http://dx.doi.org/10.1021/es802404z

Web End =10.1021/es802404z http://dx.doi.org/10.1021/es802404z

Web End = , 2009.Helmig, D., Arey, J., Harger, W. P., Atkinson, R., and Lopez-

Cancio, J.: Formation of mutagenic nitrodibenzopyranones and their occurrence in ambient air, Environ. Sci. Technol., 26, 622 624, doi:http://dx.doi.org/10.1021/es00027a028

Web End =10.1021/es00027a028 http://dx.doi.org/10.1021/es00027a028

Web End = , 1992.

Hensley, K., Robinson, K. A., Gabbita, S. P., Salsman, S., and Floyd, R. A.: Reactive oxygen species, cell signaling, and cell injury, Free Radical Bio. Med., 28, 14561462, doi:http://dx.doi.org/10.1016/S0891-5849(00)00252-5

Web End =10.1016/S0891-5849(00)00252-5 http://dx.doi.org/10.1016/S0891-5849(00)00252-5

Web End = , 2000.

Hoek, G., Krishnan, R. M., Beelen, R., Peters, A., Ostro, B.,

Brunekreef, B., and Kaufman, J. D.: Long-term air pollution exposure and cardio-respiratory mortality: a review, Environ Health, 12, 43, doi:http://dx.doi.org/10.1186/1476-069x-12-43

Web End =10.1186/1476-069x-12-43 http://dx.doi.org/10.1186/1476-069x-12-43

Web End = , 2013.Hoffmann, T., Odum, J., Bowman, F., Collins, D., Klockow, D., Flagan, R., and Seinfeld, J.: Formation of Organic Aerosols from the Oxidation of Biogenic Hydrocarbons, J. Atmos. Chem., 26, 189 222, doi:http://dx.doi.org/10.1023/A:1005734301837

Web End =10.1023/A:1005734301837 http://dx.doi.org/10.1023/A:1005734301837

Web End = , 1997.

Janssen, N. A. H., Yang, A., Strak, M., Steenhof, M., Hellack,B., Gerlofs-Nijland, M. E., Kuhlbusch, T., Kelly, F., Harrison, R., Brunekreef, B., Hoek, G., and Cassee, F.: Oxidative potential of particulate matter collected at sites with different source characteristics, Sci. Total Environ., 472, 572581, doi:http://dx.doi.org/10.1016/j.scitotenv.2013.11.099

Web End =10.1016/j.scitotenv.2013.11.099 http://dx.doi.org/10.1016/j.scitotenv.2013.11.099

Web End = , 2014.

Jenkin, M. E., Saunders, S. M., Wagner, V., and Pilling, M. J.: Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part B): tropospheric degradation of aromatic volatile organic compounds, Atmos. Chem. Phys., 3, 181193, doi:http://dx.doi.org/10.5194/acp-3-181-2003

Web End =10.5194/acp-3-181-2003 http://dx.doi.org/10.5194/acp-3-181-2003

Web End = , 2003.

Jia, C. and Batterman, S.: A Critical Review of Naphthalene Sources and Exposures Relevant to Indoor and Outdoor Air, International Journal of Environ. Res. Public Health, 7, 29032939, doi:http://dx.doi.org/10.3390/ijerph7072903

Web End =10.3390/ijerph7072903 http://dx.doi.org/10.3390/ijerph7072903

Web End = , 2010.

Jimenez, J. L., Canagaratna, M. R., Donahue, N. M., Prevot, A. S.H., Zhang, Q., Kroll, J. H., DeCarlo, P. F., Allan, J. D., Coe,H., Ng, N. L., Aiken, A. C., Docherty, K. S., Ulbrich, I. M., Grieshop, A. P., Robinson, A. L., Duplissy, J., Smith, J. D., Wilson, K. R., Lanz, V. A., Hueglin, C., Sun, Y. L., Tian, J., Laaksonen, A., Raatikainen, T., Rautiainen, J., Vaattovaara, P., Ehn,M., Kulmala, M., Tomlinson, J. M., Collins, D. R., Cubison, M.J., Dunlea, J., Huffman, J. A., Onasch, T. B., Alfarra, M. R., Williams, P. I., Bower, K., Kondo, Y., Schneider, J., Drewnick,F., Borrmann, S., Weimer, S., Demerjian, K., Salcedo, D., Cottrell, L., Grifn, R., Takami, A., Miyoshi, T., Hatakeyama, S., Shimono, A., Sun, J. Y., Zhang, Y. M., Dzepina, K., Kimmel,

J. R., Sueper, D., Jayne, J. T., Herndon, S. C., Trimborn, A.M., Williams, L. R., Wood, E. C., Middlebrook, A. M., Kolb,C. E., Baltensperger, U., and Worsnop, D. R.: Evolution of Organic Aerosols in the Atmosphere, Science, 326, 15251529, doi:http://dx.doi.org/10.1126/science.1180353

Web End =10.1126/science.1180353 http://dx.doi.org/10.1126/science.1180353

Web End = , 2009.

Kautzman, K. E., Surratt, J. D., Chan, M. N., Chan, A. W.H., Hersey, S. P., Chhabra, P. S., Dalleska, N. F., Wennberg,P. O., Flagan, R. C., and Seinfeld, J. H.: Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene, J. Phys. Chem. A, 114, 913934, doi:http://dx.doi.org/10.1021/jp908530s

Web End =10.1021/jp908530s http://dx.doi.org/10.1021/jp908530s

Web End = , 2010.

Kleinman, M. T., Hamade, A., Meacher, D., Oldham, M., Sioutas,C., Chakrabarti, B., Stram, D., Froines, J. R., and Cho, A. K.: Inhalation of concentrated ambient particulate matter near a heavily trafcked road stimulates antigen-induced airway responses in mice, J. Air Waste Manage. Assoc., 55, 12771288, 2005. Kramer, A. J., Rattanavaraha, W., Zhang, Z., Gold, A., Surratt, J.D., and Lin, Y.-H.: Assessing the oxidative potential of isoprene-derived epoxides and secondary organic aerosol, Atmos. Environ., 130, 211218, doi:http://dx.doi.org/10.1016/j.atmosenv.2015.10.018

Web End =10.1016/j.atmosenv.2015.10.018 http://dx.doi.org/10.1016/j.atmosenv.2015.10.018

Web End = , 2016. Kroll, J. H., Ng, N. L., Murphy, S. M., Flagan, R. C., and Seinfeld,J. H.: Secondary organic aerosol formation from isoprene photooxidation under high-NOx conditions, Geophys. Res. Lett., 32, L18808, doi:http://dx.doi.org/10.1029/2005GL023637

Web End =10.1029/2005GL023637 http://dx.doi.org/10.1029/2005GL023637

Web End = , 2005.

Kroll, J. H. and Seinfeld, J. H.: Chemistry of secondary organic aerosol: Formation and evolution of low-volatility organics in the atmosphere, Atmos. Environ., 42, 35933624, doi:http://dx.doi.org/10.1016/j.atmosenv.2008.01.003

Web End =10.1016/j.atmosenv.2008.01.003 http://dx.doi.org/10.1016/j.atmosenv.2008.01.003

Web End = , 2008.

Kroll, J. H., Donahue, N. M., Jimenez, J. L., Kessler, S. H., Canagaratna, M. R., Wilson, K. R., Altieri, K. E., Mazzoleni, L. R., Wozniak, A. S., Bluhm, H., Mysak, E. R., Smith, J. D., Kolb,C. E., and Worsnop, D. R.: Carbon oxidation state as a metric for describing the chemistry of atmospheric organic aerosol, Nat. Chem., 3, 133139, 2011.

Kumagai, Y., Koide, S., Taguchi, K., Endo, A., Nakai, Y., Yoshikawa, T., and Shimojo, N.: Oxidation of proximal protein sulfhydryls by phenanthraquinone, a component of diesel exhaust particles, Chem. Res. Toxicol., 15, 483489, doi:http://dx.doi.org/10.1021/tx0100993

Web End =10.1021/tx0100993 http://dx.doi.org/10.1021/tx0100993

Web End = , 2002.

Lambe, A. T., Onasch, T. B., Massoli, P., Croasdale, D. R., Wright,J. P., Ahern, A. T., Williams, L. R., Worsnop, D. R., Brune, W. H., and Davidovits, P.: Laboratory studies of the chemical composition and cloud condensation nuclei (CCN) activity of secondary organic aerosol (SOA) and oxidized primary organic aerosol (OPOA), Atmos. Chem. Phys., 11, 89138928, doi:http://dx.doi.org/10.5194/acp-11-8913-2011

Web End =10.5194/acp- http://dx.doi.org/10.5194/acp-11-8913-2011

Web End =11-8913-2011 , 2011.

Li, N., Hao, M. Q., Phalen, R. F., Hinds, W. C., and Nel, A. E.:

Particulate air pollutants and asthma A paradigm for the role of oxidative stress in PM-induced adverse health effects, Cl. Immunol., 109, 250265, doi:http://dx.doi.org/10.1016/j.clim.2003.08.006

Web End =10.1016/j.clim.2003.08.006 http://dx.doi.org/10.1016/j.clim.2003.08.006

Web End = , 2003a. Li, N., Sioutas, C., Cho, A., Schmitz, D., Misra, C., Sempf,J., Wang, M. Y., Oberley, T., Froines, J., and Nel, A.: Ultrane particulate pollutants induce oxidative stress and mitochondrial damage, Environ. Health Persp., 111, 455460, doi:http://dx.doi.org/10.1289/ehp.6000

Web End =10.1289/ehp.6000 http://dx.doi.org/10.1289/ehp.6000

Web End = , 2003b.

Li, N., Xia, T., and Nel, A. E.: The role of oxidative stress in ambient particulate matter-induced lung diseases and its implications in the toxicity of engineered nanoparticles, Free Radical Bio. Med.,

Atmos. Chem. Phys., 17, 839853, 2017 www.atmos-chem-phys.net/17/839/2017/

W. Y. Tuet et al.: Chemical oxidative potential of SOA 851

44, 16891699, doi:http://dx.doi.org/10.1016/j.freeradbiomed.2008.01.028

Web End =10.1016/j.freeradbiomed.2008.01.028 http://dx.doi.org/10.1016/j.freeradbiomed.2008.01.028

Web End = , 2008.

Lim, S. S., Vos, T., Flaxman, A. D., Danaei, G., Shibuya, K., Adair-Rohani, H., AlMazroa, M. A., Amann, M., Anderson, H. R., Andrews, K. G., Aryee, M., Atkinson, C., Bacchus, L. J., Bahalim,A. N., Balakrishnan, K., Balmes, J., Barker-Collo, S., Baxter,A., Bell, M. L., Blore, J. D., Blyth, F., Bonner, C., Borges, G.,

Bourne, R., Boussinesq, M., Brauer, M., Brooks, P., Bruce, N.G., Brunekreef, B., Bryan-Hancock, C., Bucello, C., Buchbinder,R., Bull, F., Burnett, R. T., Byers, T. E., Calabria, B., Carapetis,J., Carnahan, E., Chafe, Z., Charlson, F., Chen, H., Chen, J. S., Cheng, A. T.-A., Child, J. C., Cohen, A., Colson, K. E., Cowie,B. C., Darby, S., Darling, S., Davis, A., Degenhardt, L., Dentener, F., Des Jarlais, D. C., Devries, K., Dherani, M., Ding, E.L., Dorsey, E. R., Driscoll, T., Edmond, K., Ali, S. E., Engell, R.E., Erwin, P. J., Fahimi, S., Falder, G., Farzadfar, F., Ferrari, A., Finucane, M. M., Flaxman, S., Fowkes, F. G. R., Freedman, G., Freeman, M. K., Gakidou, E., Ghosh, S., Giovannucci, E., Gmel,G., Graham, K., Grainger, R., Grant, B., Gunnell, D., Gutierrez,H. R., Hall, W., Hoek, H. W., Hogan, A., Hosgood III, H. D., Hoy, D., Hu, H., Hubbell, B. J., Hutchings, S. J., Ibeanusi, S. E., Jacklyn, G. L., Jasrasaria, R., Jonas, J. B., Kan, H., Kanis, J. A., Kassebaum, N., Kawakami, N., Khang, Y.-H., Khatibzadeh, S., Khoo, J.-P., Kok, C., Laden, F., Lalloo, R., Lan, Q., Lathlean, T., Leasher, J. L., Leigh, J., Li, Y., Lin, J. K., Lipshultz, S. E., London, S., Lozano, R., Lu, Y., Mak, J., Malekzadeh, R., Mallinger,L., Marcenes, W., March, L., Marks, R., Martin, R., McGale, P., McGrath, J., Mehta, S., Memish, Z. A., Mensah, G. A., Merriman, T. R., Micha, R., Michaud, C., Mishra, V., Hanaah, K.M., Mokdad, A. A., Morawska, L., Mozaffarian, D., Murphy,T., Naghavi, M., Neal, B., Nelson, P. K., Nolla, J. M., Norman,R., Olives, C., Omer, S. B., Orchard, J., Osborne, R., Ostro, B., Page, A., Pandey, K. D., Parry, C. D. H., Passmore, E., Patra, J., Pearce, N., Pelizzari, P. M., Petzold, M., Phillips, M. R., Pope,D., Pope III, C. A., Powles, J., Rao, M., Razavi, H., Rehfuess, E.A., Rehm, J. T., Ritz, B., Rivara, F. P., Roberts, T., Robinson, C., Rodriguez-Portales, J. A., Romieu, I., Room, R., Rosenfeld, L.C., Roy, A., Rushton, L., Salomon, J. A., Sampson, U., Sanchez-Riera, L., Sanman, E., Sapkota, A., Seedat, S., Shi, P., Shield,K., Shivakoti, R., Singh, G. M., Sleet, D. A., Smith, E., Smith,K. R., Stapelberg, N. J. C., Steenland, K., Stckl, H., Stovner, L.J., Straif, K., Straney, L., Thurston, G. D., Tran, J. H., Van Dingenen, R., van Donkelaar, A., Veerman, J. L., Vijayakumar, L., Weintraub, R., Weissman, M. M., White, R. A., Whiteford, H., Wiersma, S. T., Wilkinson, J. D., Williams, H. C., Williams, W., Wilson, N., Woolf, A. D., Yip, P., Zielinski, J. M., Lopez, A. D., Murray, C. J. L., and Ezzati, M.: A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 19902010: a systematic analysis for the Global Burden of Disease Study 2010, Lancet, 380, 22242260, doi:http://dx.doi.org/10.1016/S0140-6736(12)61766-8

Web End =10.1016/S0140-6736(12)61766-8 http://dx.doi.org/10.1016/S0140-6736(12)61766-8

Web End = , 2012.

Lin, P. and Yu, J. Z.: Generation of Reactive Oxygen Species Mediated by Humic-like Substances in Atmospheric Aerosols, Environ. Sci. Technol., 45, 1036210368, doi:http://dx.doi.org/10.1021/es2028229

Web End =10.1021/es2028229 http://dx.doi.org/10.1021/es2028229

Web End = , 2011.

Lin, Y.-H., Zhang, Z., Docherty, K. S., Zhang, H., Budisulistiorini, S. H., Rubitschun, C. L., Shaw, S. L., Knipping, E. M., Edgerton, E. S., Kleindienst, T. E., Gold, A., and Surratt, J.D.: Isoprene Epoxydiols as Precursors to Secondary Organic

Aerosol Formation: Acid-Catalyzed Reactive Uptake Studies with Authentic Compounds, Environ. Sci. Technol., 46, 250 258, doi:http://dx.doi.org/10.1021/es202554c

Web End =10.1021/es202554c http://dx.doi.org/10.1021/es202554c

Web End = , 2012.

Loza, C. L., Craven, J. S., Yee, L. D., Coggon, M. M., Schwantes,R. H., Shiraiwa, M., Zhang, X., Schilling, K. A., Ng, N. L., Canagaratna, M. R., Ziemann, P. J., Flagan, R. C., and Seinfeld,J. H.: Secondary organic aerosol yields of 12-carbon alkanes, Atmos. Chem. Phys., 14, 14231439, doi:http://dx.doi.org/10.5194/acp-14-1423-2014

Web End =10.5194/acp-14-1423- http://dx.doi.org/10.5194/acp-14-1423-2014

Web End =2014 , 2014.

Lu, Y., Su, S., Jin, W., Wang, B., Li, N., Shen, H., Li, W.,

Huang, Y., Chen, H., Zhang, Y., Chen, Y., Lin, N., Wang,X., and Tao, S.: Characteristics and cellular effects of ambient particulate matter from Beijing, Environ. Pollut., 191, 6369, doi:http://dx.doi.org/10.1016/j.envpol.2014.04.008

Web End =10.1016/j.envpol.2014.04.008 http://dx.doi.org/10.1016/j.envpol.2014.04.008

Web End = , 2014.

Lund, A. K., Doyle-Eisele, M., Lin, Y. H., Arashiro, M., Surratt, J. D., Holmes, T., Schilling, K. A., Seinfeld, J. H., Rohr, A. C., Knipping, E. M., and McDonald, J. D.: The effects of alpha-pinene versus toluene-derived secondary organic aerosol exposure on the expression of markers associated with vascular disease, Inhal. Toxicol., 25, 309324, doi:http://dx.doi.org/10.3109/08958378.2013.782080

Web End =10.3109/08958378.2013.782080 http://dx.doi.org/10.3109/08958378.2013.782080

Web End = , 2013.

McDonald, J. D., Doyle-Eisele, M., Campen, M. J., Seagrave, J.,

Holmes, T., Lund, A., Surratt, J. D., Seinfeld, J. H., Rohr, A. C., and Knipping, E. M.: Cardiopulmonary response to inhalation of biogenic secondary organic aerosol, Inhal. Toxicol., 22, 253 265, doi:http://dx.doi.org/10.3109/08958370903148114

Web End =10.3109/08958370903148114 http://dx.doi.org/10.3109/08958370903148114

Web End = , 2010.

McDonald, J. D., Doyle-Eisele, M., Kracko, D., Lund, A., Surratt,J. D., Hersey, S. P., Seinfeld, J. H., Rohr, A. C., and Knipping,E. M.: Cardiopulmonary response to inhalation of secondary organic aerosol derived from gas-phase oxidation of toluene, Inhal. Toxicol., 24, 689697, doi:http://dx.doi.org/10.3109/08958378.2012.712164

Web End =10.3109/08958378.2012.712164 http://dx.doi.org/10.3109/08958378.2012.712164

Web End = , 2012.

McLafferty, F. W. and Tureek, F.: Interpretation of mass spectra,

University science books, 1993.

McWhinney, R. D., Badali, K., Liggio, J., Li, S.-M., and Abbatt, J. P. D.: Filterable Redox Cycling Activity: A Comparison between Diesel Exhaust Particles and Secondary Organic Aerosol Constituents, Environ. Sci. Technol., 47, 33623369, doi:http://dx.doi.org/10.1021/es304676x

Web End =10.1021/es304676x http://dx.doi.org/10.1021/es304676x

Web End = , 2013a.

McWhinney, R. D., Zhou, S., and Abbatt, J. P. D.: Naphthalene

SOA: redox activity and naphthoquinone gas-particle partitioning, Atmos. Chem. Phys., 13, 97319744, doi:http://dx.doi.org/10.5194/acp-13-9731-2013

Web End =10.5194/acp-13- http://dx.doi.org/10.5194/acp-13-9731-2013

Web End =9731-2013 , 2013b.

Nah, T., McVay, R. C., Pierce, J. R., Seinfeld, J. H., and Ng, N. L.:

Constraining uncertainties in particle wall-deposition correction during SOA formation in chamber experiments, Atmos. Chem.Phys. Discuss., doi:http://dx.doi.org/10.5194/acp-2016-820

Web End =10.5194/acp-2016-820 http://dx.doi.org/10.5194/acp-2016-820

Web End = , in review, 2016.

Ng, N. L., Kroll, J. H., Keywood, M. D., Bahreini, R., Varutbangkul, V., Flagan, R. C., Seinfeld, J. H., Lee, A., and Goldstein,A. H.: Contribution of First- versus Second-Generation Products to Secondary Organic Aerosols Formed in the Oxidation of Biogenic Hydrocarbons, Environ. Sci. Technol., 40, 22832297, doi:http://dx.doi.org/10.1021/es052269u

Web End =10.1021/es052269u http://dx.doi.org/10.1021/es052269u

Web End = , 2006.

Ng, N. L., Chhabra, P. S., Chan, A. W. H., Surratt, J. D., Kroll, J.H., Kwan, A. J., McCabe, D. C., Wennberg, P. O., Sorooshian,A., Murphy, S. M., Dalleska, N. F., Flagan, R. C., and Seinfeld,J. H.: Effect of NOx level on secondary organic aerosol (SOA) formation from the photooxidation of terpenes, Atmos. Chem.Phys., 7, 51595174, doi:http://dx.doi.org/10.5194/acp-7-5159-2007

Web End =10.5194/acp-7-5159-2007 http://dx.doi.org/10.5194/acp-7-5159-2007

Web End = , 2007a.

www.atmos-chem-phys.net/17/839/2017/ Atmos. Chem. Phys., 17, 839853, 2017

852 W. Y. Tuet et al.: Chemical oxidative potential of SOA

Ng, N. L., Kroll, J. H., Chan, A. W. H., Chhabra, P. S., Flagan,R. C., and Seinfeld, J. H.: Secondary organic aerosol formation from m-xylene, toluene, and benzene, Atmos. Chem. Phys., 7, 39093922, doi:http://dx.doi.org/10.5194/acp-7-3909-2007

Web End =10.5194/acp-7-3909-2007 http://dx.doi.org/10.5194/acp-7-3909-2007

Web End = , 2007b.

Ng, N. L., Canagaratna, M. R., Zhang, Q., Jimenez, J. L., Tian,J., Ulbrich, I. M., Kroll, J. H., Docherty, K. S., Chhabra, P.S., Bahreini, R., Murphy, S. M., Seinfeld, J. H., Hildebrandt,L., Donahue, N. M., DeCarlo, P. F., Lanz, V. A., Prvt, A. S.H., Dinar, E., Rudich, Y., and Worsnop, D. R.: Organic aerosol components observed in Northern Hemispheric datasets from Aerosol Mass Spectrometry, Atmos. Chem. Phys., 10, 4625 4641, doi:http://dx.doi.org/10.5194/acp-10-4625-2010

Web End =10.5194/acp-10-4625-2010 http://dx.doi.org/10.5194/acp-10-4625-2010

Web End = , 2010.

Ng, N. L., Canagaratna, M. R., Jimenez, J. L., Chhabra, P. S., Seinfeld, J. H., and Worsnop, D. R.: Changes in organic aerosol composition with aging inferred from aerosol mass spectra, Atmos. Chem. Phys., 11, 64656474, doi:http://dx.doi.org/10.5194/acp-11-6465-2011

Web End =10.5194/acp-11-6465- http://dx.doi.org/10.5194/acp-11-6465-2011

Web End =2011 , 2011.

Nguyen, T. B., Roach, P. J., Laskin, J., Laskin, A., and Nizkorodov,S. A.: Effect of humidity on the composition of isoprene photooxidation secondary organic aerosol, Atmos. Chem. Phys., 11, 69316944, doi:http://dx.doi.org/10.5194/acp-11-6931-2011

Web End =10.5194/acp-11-6931-2011 http://dx.doi.org/10.5194/acp-11-6931-2011

Web End = , 2011.

Philip, M., Rowley, D. A., and Schreiber, H.: Inammation as a tumor promoter in cancer induction, Seminars in Cancer Biology, 14, 433439, doi:http://dx.doi.org/10.1016/j.semcancer.2004.06.006

Web End =10.1016/j.semcancer.2004.06.006 http://dx.doi.org/10.1016/j.semcancer.2004.06.006

Web End = , 2004.Piccot, S. D., Watson, J. J., and Jones, J. W.: A global inventory of volatile organic compound emissions from anthropogenic sources, J. Geophys. Res.-Atmos., 97, 98979912, doi:http://dx.doi.org/10.1029/92JD00682

Web End =10.1029/92JD00682 http://dx.doi.org/10.1029/92JD00682

Web End = , 1992.

Platt, S. M., Haddad, I. E., Pieber, S. M., Huang, R. J., Zardini, A. A., Clairotte, M., Suarez-Bertoa, R., Barmet, P., Pfaffenberger, L., Wolf, R., Slowik, J. G., Fuller, S. J., Kalberer,M., Chirico, R., Dommen, J., Astorga, C., Zimmermann, R., Marchand, N., Hellebust, S., Temime-Roussel, B., Baltensperger,U., and Prvt, A. S. H.: Two-stroke scooters are a dominant source of air pollution in many cities, Nat. Commun., 5, 3749, doi:http://dx.doi.org/10.1038/ncomms4749

Web End =10.1038/ncomms4749 http://dx.doi.org/10.1038/ncomms4749

Web End = , 2014.

Pope, C. A., Burnett, R. T., Thun, M. J., Calle, E. E., Krewski,D., Ito, K., and Thurston, G. D.: Lung cancer, cardiopulmonary mortality, and long-term exposure to ne particulate air pollution, Jama-J. Am. Med. Assoc., 287, 11321141, doi:http://dx.doi.org/10.1001/jama.287.9.1132

Web End =10.1001/jama.287.9.1132 http://dx.doi.org/10.1001/jama.287.9.1132

Web End = , 2002.

Pope III, C. A. and Dockery, D. W.: Health effects of ne particulate air pollution: Lines that connect, J. Air Waste Manage. Assoc., 56, 709742, 2006.

Rattanavaraha, W., Rosen, E., Zhang, H., Li, Q., Pantong,K., and Kamens, R. M.: The reactive oxidant potential of different types of aged atmospheric particles: An outdoor chamber study, Atmos. Environ., 45, 38483855, doi:http://dx.doi.org/10.1016/j.atmosenv.2011.04.002

Web End =10.1016/j.atmosenv.2011.04.002 http://dx.doi.org/10.1016/j.atmosenv.2011.04.002

Web End = , 2011.

Riva, M., Robinson, E. S., Perraudin, E., Donahue, N. M., and Villenave, E.: Photochemical Aging of Secondary Organic Aerosols Generated from the Photooxidation of Polycyclic Aromatic Hydrocarbons in the Gas-Phase, Environ. Sci. Technol., 49, 5407 5416, doi:http://dx.doi.org/10.1021/acs.est.5b00442

Web End =10.1021/acs.est.5b00442 http://dx.doi.org/10.1021/acs.est.5b00442

Web End = , 2015.

Robinson, A. L., Donahue, N. M., Shrivastava, M. K., Weitkamp,E. A., Sage, A. M., Grieshop, A. P., Lane, T. E., Pierce, J. R., and Pandis, S. N.: Rethinking Organic Aerosols: Semivolatile Emissions and Photochemical Aging, Science, 315, 12591262, doi:http://dx.doi.org/10.1126/science.1133061

Web End =10.1126/science.1133061 http://dx.doi.org/10.1126/science.1133061

Web End = , 2007.

Sannigrahi, P., Sullivan, A. P., Weber, R. J., and Ingall, E. D.: Characterization of Water-Soluble Organic Carbon in Urban Atmospheric Aerosols Using Solid-State 13C NMR Spectroscopy, Environ. Sci. Technol., 40, 666672, doi:http://dx.doi.org/10.1021/es051150i

Web End =10.1021/es051150i http://dx.doi.org/10.1021/es051150i

Web End = , 2006.

Sato, K., Takami, A., Isozaki, T., Hikida, T., Shimono,A., and Imamura, T.: Mass spectrometric study of secondary organic aerosol formed from the photo-oxidation of aromatic hydrocarbons, Atmos. Environ., 44, 10801087, doi:http://dx.doi.org/10.1016/j.atmosenv.2009.12.013

Web End =10.1016/j.atmosenv.2009.12.013 http://dx.doi.org/10.1016/j.atmosenv.2009.12.013

Web End = , 2010.

Stirnweis, L., Marcolli, C., Dommen, J., Barmet, P., Frege, C., Platt, S. M., Bruns, E. A., Krapf, M., Slowik, J. G., Wolf, R., Prvt, A. S. H., El-Haddad, I., and Baltensperger, U.: -Pinene secondary organic aerosol yields increase at higher relative humidity and low NOx conditions, Atmos. Chem. Phys. Discuss., doi:http://dx.doi.org/10.5194/acp-2016-717

Web End =10.5194/acp-2016-717 http://dx.doi.org/10.5194/acp-2016-717

Web End = , in review, 2016.

Surratt, J. D., Chan, A. W. H., Eddingsaas, N. C., Chan, M., Loza, C.L., Kwan, A. J., Hersey, S. P., Flagan, R. C., Wennberg, P. O., and Seinfeld, J. H.: Reactive intermediates revealed in secondary organic aerosol formation from isoprene, P. Natl. Acad. Sci. USA, 107, 66406645, doi:http://dx.doi.org/10.1073/pnas.0911114107

Web End =10.1073/pnas.0911114107 http://dx.doi.org/10.1073/pnas.0911114107

Web End = , 2010.

Tao, F., Gonzalez-Flecha, B., and Kobzik, L.: Reactive oxygen species in pulmonary inammation by ambient particulates, Free Radical Bio. Med., 35, 327340, doi:http://dx.doi.org/10.1016/S0891-5849(03)00280-6

Web End =10.1016/S0891- http://dx.doi.org/10.1016/S0891-5849(03)00280-6

Web End =5849(03)00280-6 , 2003.

Tasoglou, A. and Pandis, S. N.: Formation and chemical aging of secondary organic aerosol during the -caryophyllene oxidation, Atmos. Chem. Phys., 15, 60356046, doi:http://dx.doi.org/10.5194/acp-15-6035-2015

Web End =10.5194/acp-15-6035- http://dx.doi.org/10.5194/acp-15-6035-2015

Web End =2015 , 2015.

Tuet, W. Y., Fok, S., Verma, V., Tagle Rodriguez, M. S., Grosberg, A., Champion, J. A., and Ng, N. L.: Dose-dependent intracellular reactive oxygen and nitrogen species production from particulate matter exposure: comparison to oxidative potential and chemical composition, Atmos. Environ., 144, 335344, doi:http://dx.doi.org/10.1016/j.atmosenv.2016.09.005

Web End =10.1016/j.atmosenv.2016.09.005 http://dx.doi.org/10.1016/j.atmosenv.2016.09.005

Web End = , 2016.

Turner, J., Hernandez, M., Snawder, J. E., Handorean, A., and Mc-Cabe, K. M.: A Toxicology Suite Adapted for Comparing Parallel Toxicity Responses of Model Human Lung Cells to Diesel Exhaust Particles and Their Extracts, Aerosol Sci. Technol., 49, 599610, doi:http://dx.doi.org/10.1080/02786826.2015.1053559

Web End =10.1080/02786826.2015.1053559 http://dx.doi.org/10.1080/02786826.2015.1053559

Web End = , 2015.

Van Krevelen, D.: Graphical-statistical method for the study of structure and reaction processes of coal, Fuel, 29, 269284, 1950. Verma, V., Rico-Martinez, R., Kotra, N., King, L., Liu, J. M., Snell,T. W., and Weber, R. J.: Contribution of Water-Soluble and Insoluble Components and Their Hydrophobic/Hydrophilic Sub-fractions to the Reactive Oxygen Species-Generating Potential of Fine Ambient Aerosols, Environ. Sci. Technol., 46, 11384 11392, doi:http://dx.doi.org/10.1021/es302484r

Web End =10.1021/es302484r http://dx.doi.org/10.1021/es302484r

Web End = , 2012.

Verma, V., Fang, T., Guo, H., King, L., Bates, J. T., Peltier, R. E., Edgerton, E., Russell, A. G., and Weber, R. J.: Reactive oxygen species associated with water-soluble PM2.5 in the southeastern United States: spatiotemporal trends and source apportionment, Atmos. Chem. Phys., 14, 1291512930, doi:http://dx.doi.org/10.5194/acp-14-12915-2014

Web End =10.5194/acp- http://dx.doi.org/10.5194/acp-14-12915-2014

Web End =14-12915-2014 , 2014.

Verma, V., Fang, T., Xu, L., Peltier, R. E., Russell, A. G., Ng, N. L., and Weber, R. J.: Organic Aerosols Associated with the Generation of Reactive Oxygen Species (ROS) by Water-Soluble PM2.5, Environ. Sci. Technol., 49, 46464656, doi:http://dx.doi.org/10.1021/es505577w

Web End =10.1021/es505577w http://dx.doi.org/10.1021/es505577w

Web End = , 2015a.

Atmos. Chem. Phys., 17, 839853, 2017 www.atmos-chem-phys.net/17/839/2017/

W. Y. Tuet et al.: Chemical oxidative potential of SOA 853

Verma, V., Wang, Y., El-A, R., Fang, T., Rowland, J., Russell, A. G., and Weber, R. J.: Fractionating ambient humic-like substances (HULIS) for their reactive oxygen species activity Assessing the importance of quinones and atmospheric aging, Atmos. Environ., 120, 351359, doi:http://dx.doi.org/10.1016/j.atmosenv.2015.09.010

Web End =10.1016/j.atmosenv.2015.09.010 http://dx.doi.org/10.1016/j.atmosenv.2015.09.010

Web End = , 2015b.

Visentin, M., Pagnoni, A., Sarti, E., and Pietrogrande, M. C.: Urban

PM2.5 oxidative potential: Importance of chemical species and comparison of two spectrophotometric cell-free assays, Environ.Pollut., 219, 7279, doi:http://dx.doi.org/10.1016/j.envpol.2016.09.047

Web End =10.1016/j.envpol.2016.09.047 http://dx.doi.org/10.1016/j.envpol.2016.09.047

Web End = , 2016.Vivanco, M. G. and Santiago, M.: Secondary Organic Aerosol

Formation from the Oxidation of a Mixture of Organic Gases in a Chamber, Air Quality, edited by: Kumar, A., InTech, doi:http://dx.doi.org/10.5772/9761

Web End =10.5772/9761 http://dx.doi.org/10.5772/9761

Web End = , 2010.

Weichenthal, S. A., Lavigne, E., Evans, G. J., Godri Pollitt, K.J., and Burnett, R. T.: Fine Particulate Matter and Emergency Room Visits for Respiratory Illness. Effect Modication by Oxidative Potential, Am. J. Resp. Crit. Care, 194, 577586, doi:http://dx.doi.org/10.1164/rccm.201512-2434OC

Web End =10.1164/rccm.201512-2434OC http://dx.doi.org/10.1164/rccm.201512-2434OC

Web End = , 2016.

Wennberg, P.: Lets abandon the high NOx and low NOx terminology, IGAC news, 50, 34, 2013.

Wiseman, H. and Halliwell, B.: Damage to DNA by reactive oxygen and nitrogen species: role in inammatory disease and progression to cancer, Biochem. J., 313, 1729, 1996.

Wong, J. P. S., Lee, A. K. Y., and Abbatt, J. P. D.: Impacts of Sulfate Seed Acidity and Water Content on Isoprene Secondary Organic Aerosol Formation, Environ. Sci. Technol., 49, 1321513221, doi:http://dx.doi.org/10.1021/acs.est.5b02686

Web End =10.1021/acs.est.5b02686 http://dx.doi.org/10.1021/acs.est.5b02686

Web End = , 2015.

Xu, L., Kollman, M. S., Song, C., Shilling, J. E., and Ng, N. L.: Effects of NOx on the Volatility of Secondary Organic Aerosol from Isoprene Photooxidation, Environ. Sci. Technol., 48, 2253 2262, doi:http://dx.doi.org/10.1021/es404842g

Web End =10.1021/es404842g http://dx.doi.org/10.1021/es404842g

Web End = , 2014.

Xu, L., Guo, H., Boyd, C. M., Klein, M., Bougiatioti, A., Cerully,K. M., Hite, J. R., Isaacman-VanWertz, G., Kreisberg, N. M., Knote, C., Olson, K., Koss, A., Goldstein, A. H., Hering, S.V., de Gouw, J., Baumann, K., Lee, S.-H., Nenes, A., Weber,R. J., and Ng, N. L.: Effects of anthropogenic emissions on aerosol formation from isoprene and monoterpenes in the southeastern United States, P. Natl. Acad. Sci. USA, 112, 3742, doi:http://dx.doi.org/10.1073/pnas.1417609112

Web End =10.1073/pnas.1417609112 http://dx.doi.org/10.1073/pnas.1417609112

Web End = , 2015a.

Xu, L., Suresh, S., Guo, H., Weber, R. J., and Ng, N. L.: Aerosol characterization over the southeastern United States using high-resolution aerosol mass spectrometry: spatial and seasonal variation of aerosol composition and sources with a focus on organic nitrates, Atmos. Chem. Phys., 15, 73077336, doi:http://dx.doi.org/10.5194/acp-15-7307-2015

Web End =10.5194/acp- http://dx.doi.org/10.5194/acp-15-7307-2015

Web End =15-7307-2015 , 2015b.

Yang, A., Janssen, N. A. H., Brunekreef, B., Cassee, F. R., Hoek,G., and Gehring, U.: Childrens respiratory health and oxidative potential of PM2.5: the PIAMA birth cohort study, Occupational and Environmental Medicine, doi:http://dx.doi.org/10.1136/oemed-2015-103175

Web End =10.1136/oemed-2015-103175 http://dx.doi.org/10.1136/oemed-2015-103175

Web End = , 2016.

Zhang, Q., Jimenez, J. L., Canagaratna, M. R., Allan, J. D., Coe,H., Ulbrich, I., Alfarra, M. R., Takami, A., Middlebrook, A.M., Sun, Y. L., Dzepina, K., Dunlea, E., Docherty, K., De-Carlo, P. F., Salcedo, D., Onasch, T., Jayne, J. T., Miyoshi,T., Shimono, A., Hatakeyama, S., Takegawa, N., Kondo, Y., Schneider, J., Drewnick, F., Borrmann, S., Weimer, S., Demerjian, K., Williams, P., Bower, K., Bahreini, R., Cottrell, L., Grifn, R. J., Rautiainen, J., Sun, J. Y., Zhang, Y. M., and Worsnop, D. R.: Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-inuenced Northern Hemisphere midlatitudes, Geophys. Res. Lett., 34, L13801, doi:http://dx.doi.org/10.1029/2007GL029979

Web End =10.1029/2007GL029979 http://dx.doi.org/10.1029/2007GL029979

Web End = , 2007.

www.atmos-chem-phys.net/17/839/2017/ Atmos. Chem. Phys., 17, 839853, 2017