Significant ultrafine particle emissions from residential solid fuel combustion

Abstract When addressing particulate matter (PM) emissions from residential solid fuel combustion, ultrafine particles are usually merged into PM2.5, while whose mass concentration is applied as the index in evaluating PM pollution as well as assessing PM-induced health risk. This may not effectively represent the risk from ultrafine particles. In this study, we explored ultrafine particle emissions during residential combustion under both laboratory-controlled and real-world rural household conditions. Significant ultrafine particle emissions (i.e. with emission factors between 2 × 1015 to 2 × 1016 particles per kg of fuel) are found for both coal and biomass. High emissions of particle mass concentration often occur at the beginning of the combustion (i.e. the first 30 min after fire start) while high emissions of particle number concentration occur in a later combustion period (60–150 min). Ultrafine particles account for over 90% of the emitted total particle number concentration from 3 nm to 10 μm. These emissions elevate ultrafine particle number concentration by more than a decade in indoor environment under which household residents are directly exposed. In addition, we show that there is notable inconsistency between reducing PM2.5 mass based emissions and reducing ultrafine particle number based emissions among various control strategies that were proposed for reducing pollution from residential combustion. Both “cleaner” fuels and stoves that are designed to reduce PM2.5 emissions are found to be not necessarily effective in reducing ultrafine particle emissions, even increase their emissions in some cases. These findings indicate that the overlook of ultrafine particle emissions from residential solid fuel combustion can lead to potential health risk to household residents, especially to those vulnerable ones (e.g., the elderly and children) who are more sensitive to indoor air pollution. More attentions are needed on ultrafine particle pollution and its potential health risk in comparison to using the PM mass concentration index alone.