A Conceptual Framework for the Assessment of Cumulative Exposure to Air Pollution at a Fine Spatial Scale

1. Introduction

The World Health Organization has estimated that deaths attributed to outdoor air pollution are predominantly due to ischemic heart diseases and strokes (80%), followed by chronic obstructive pulmonary diseases or acute lower respiratory infections (14%) and lung cancer (6%) [1].

Several original papers, reviews and meta-analyses have documented that mortality (including mortality from all-causes) and chronic diseases (especially cancer, cardiovascular and respiratory disease) are associated with long-term exposure to particulate air pollution-notably to particles with diameters of 10 µm or less (PM₁₀), and particles with diameters of 2.5 µm or less (PM_2.5) and their constituents [2,3,4,5], as well as to nitrogen dioxide (NO₂) [2,4,5,6,7] and sulfur dioxide (SO₂) [2,4,5,6,7,8]. Regarding all-cause mortality, these studies have revealed an increase in mortality with long-term exposure to elemental carbon (pooled estimate: +6% per 1 μg/m³; CI95% (5%−7%)), NO₂ (pooled estimate: +5% per 10 μg/m³; CI95% (3%−8%)), and PM_2.5 (pooled estimate: +6% per 10 μg/m³; CI95% (4%−8%). Mortality from cardiovascular and non-malignant respiratory diseases was significantly associated with long-term exposure to NO₂ (pooled estimate:+11% per 10 μg/m³;CI95% [5%-16%]; +3% CI95% (6%−13%) respectively) [4]. Recently, Bentayeb et al. have shown that long-term exposure to PM₁₀, PM_2.5, NO₂, SO₂ and benzene is strongly associated with an increased risk of non-accidental mortality in France [7].

A Scientific Statement from the American Heart Association supports that long-term exposure to particulate matter has cardiovascular effects [9,10]. Regarding cancer, the International Agency for Research on Cancer (IARC) has classified air pollution, as a whole, as carcinogenic to humans, and had already determined that several components of outdoor air pollution were carcinogens, including diesel engine exhaust, solvents, metals, and dust [11].

Compared to the health effects of short-term exposures, the impact of air pollution on chronic diseases has given rise to a more limited body of literature. Since the seminal publications of the Harvard Six Cities Study, which examined the relationship between long-term ambient concentrations of particulates and mortality in a cohort of about 8000 adults between 1976 and 1989 [12], between 1979 and 1998 [13], and between 1974 and 2009 [3], results of other important cohort studies...