Identification of Factors Determining Household PM 2.5 Variations at Regional Scale and Their Implications for Pollution Mitigation.

Indoor PM 2.5 , particulate matter no more than 2.5 μm in aerodynamic equivalent diameter, has very high spatiotemporal variabilities; and exploring the key factors influencing the variabilities is critical for purifying air and protecting human health. Here, we conducted a longer-term field monitoring campaign using low-cost sensors and evaluated inter- and intra-household PM 2.5 variations in rural areas where energy or stove stacking is common. Household PM 2.5 varied largely across different homes but also within households. Using generalized linear models and dominance analysis, we estimated that outdoor PM 2.5 explained 19% of the intrahousehold variation in indoor daily PM 2.5 , whereas factors like the outdoor temperature and indoor-outdoor temperature difference that was associated with energy use directly or indirectly, explained 26% of the temporal variation. Inter-household variation was lower than intrahousehold variation. The inter-household variation was strongly associated with distinct internal sources, with energy-use-associated factors explaining 35% of the variation. The statistical source apportionment model estimated that solid fuel burning for heating contributed an average of 31%-55% of PM 2.5 annually, whereas the contribution of sources originating from the outdoors was ≤10%. By replacing raw biomass or coal with biomass pellets in gasifier burners for heating, indoor PM 2.5 could be significantly reduced and indoor temperature substantially increased, providing thermal comforts in addition to improved air quality.