Are cleaner cooking solutions clean enough? A systematic review and meta-analysis of particulate and carbon monoxide concentrations and exposures

Abstract

Globally, approximately 3 billion primarily cook using inefficient and poorly vented combustion devices, leading to unsafe levels of household air pollution (HAP) in and around the home. Such exposures contribute to nearly 4 million deaths annually (WHO 2018a, 2018b ). Characterizing the effectiveness of interventions for reducing HAP concentration and exposure is critical for informing policy and programmatic decision-making on which cooking solutions yield the greatest health benefits. This review synthesizes evidence of in-field measurements from four cleaner cooking technologies and three clean fuels, using field studies aimed at reducing HAP concentration and personal exposure to health damaging pollutants (particulate matter (PM_2.5) and carbon monoxide (CO)). Fifty studies from Africa, Asia, South and Latin America, provided 168 estimates synthesized through meta-analysis. For PM_2.5 kitchen concentrations, burning biomass more cleanly through improved combustion stoves (ICS) with (n = 29; 63% reduction) or without (n = 12; 52%) venting (through flue or chimney) and through forced-draft combustion (n = 9; 50%) was less effective than cooking with clean fuels including ethanol (n = 4; 83%), liquefied petroleum gas (LPG) (n = 11; 83%) and electricity (n = 6; 86%). Only studies of clean fuels consistently achieved post-intervention kitchen PM_2.5 levels at or below the health-based WHO interim target level 1 (WHO-IT1) of 35 μg m⁻³. None of the advanced combustion stoves (gasifiers) achieved WHO-IT1, although no evidence was available for pellet fuelled stoves. For personal exposure to PM_2.5, none of the ICS (n = 11) were close to WHO-IT1 whereas 75% (n = 6 of 8) of LPG interventions were at or below WHO-IT1. Similar patterns were observed for CO, although most post-intervention levels achieved the WHO 24 h guideline level. While clean cooking fuel interventions (LPG, electric) significantly reduce kitchen concentrations and personal exposure to PM_2.5 in household settings, stove stacking and background levels of ambient air pollution, have likely prevented most clean fuel interventions from approaching WHO-IT1. In order to maximize health gains, a wholistic approach jointly targeting ambient and HAP should be followed in lower-and-middle income countries.