Impacts of stove use patterns and outdoor air quality on household air pollution and cardiovascular mortality in southwestern China

Background: Decades of intervention programs that replaced traditional biomass stoves with cleaner-burning technologies have failed to meet the World Health Organization (WHO) interim indoor air quality target of 35-μg m⁻³ for PM_2.5. Many attribute these results to continued use of biomass stoves and poor outdoor air quality, though the relative impacts of these factors have not been empirically quantified. Methods: We measured 496 days of real-time stove use concurrently with outdoor and indoor air pollution (PM_2.5) in 150 rural households in Sichuan, China. The impacts of stove use patterns and outdoor air quality on indoor PM_2.5 were quantified. We also estimated the potential avoided cardiovascular mortality in southwestern China associated with transition from traditional to clean fuel stoves using established exposure-response relationships. Results: Mean daily indoor PM_2.5 was highest in homes using both wood and clean fuel stoves (122 μg m⁻³), followed by exclusive use of wood stoves (106 μg m⁻³) and clean fuel stoves (semi-gasifiers: 65 μg m⁻³; gas or electric: 55 μg m⁻³). Wood stoves emitted proportionally higher indoor PM_2.5 during ignition, and longer stove use was not associated with higher indoor PM_2.5. Only 24% of days with exclusive use of clean fuel stoves met the WHO indoor air quality target, though this fraction rose to 73% after subtracting the outdoor PM_2.5 contribution. Reduced PM_2.5 exposure through exclusive use of gas or electric stoves was estimated to prevent 48,000 yearly premature deaths in southwestern China, with greater reductions if local outdoor PM_2.5 is also reduced. Conclusions: Clean stove and fuel interventions are not likely to reduce indoor PM_2.5 to the WHO target unless their use is exclusive and outdoor air pollution is sufficiently low, but may still offer some cardiovascular benefits.