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.