Fractions of smoke leakage into indoor space from residential solid fuel combustion in chimney stoves

Severe indoor air pollution from solid-fuel combustion is a global health concern. Although stove chimneys can expel most of the smoke to outside, unignorable amounts can remain indoors, known as indoor fugitive emissions. Quantitative analyses of indoor emission rates (IER) and indoor fugitive fractions (IFF) are limited, particularly in field settings. This study quantified the IERs and IFFs of particulate matters (PMs) from residential solid fuel combustion, covering different fuel-stove combinations in rural China. The study showed that both IERs and IFFs were not normally distributed. The median IER for PM_2.5, which peaked at 860 mg/min, was 32 mg/min. IERs very significantly among different fuel and stove types, with biomass pellets and improved stoves demonstrating lower IERs than traditional biomass and coal. Approximately 27% of PM_2.5 was leaked into indoor air, but this fraction ranged largely from a low percentage to 80%. Higher IFFs were observed for coals burned in traditional stoves. The median IFFs of organic carbon and elemental carbon were 26% (12%-43% as the interquartile range) and 19% (9%-40%), respectively. The chimney lifting effect significantly affected the degree of indoor leakage, with relatively low IFFs under high gas velocity conditions. Chimney exhaust and fugitive smoke had distinct size distributions, and small particles exhibited fewer leakages than coarse particles. The study provides valuable datasets for quantifying internal combustion impacts on indoor air quality and consequently human health.