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Residential solid fuel combustion significantly impacts air quality and human health. Pelletized biomass fuels are promoted as a cleaner alternative, particularly for those who cannot afford the high costs of gas/electricity, but their emission characteristics and potential effects remain poorly understood. The present laboratory-based study evaluated pollution emissions from pelletized biomass burning, including CH4(methane), NMHC (nonmethane hydrocarbon compounds), CO, SO2, NOx, PM2.5(particulate matter with an aerodynamic diameter ≤2.5 μm), OC (organic carbon), EC (element carbon), PAHs (polycyclic aromatic hydrocarbons), EPFRs (environmentally persistent free radicals), and OP (oxidative potential) of PM2.5, and compared with those from raw biomass burning. For most targets, except for SO2and NOx, the mass-based emission factors for pelletized biomass were 62–96% lower than those for raw biomass. SO2and NOxlevels were negatively correlated with other air pollutants (p< 0.05). Based on real-world daily consumption data, this study estimated that households using pelletized biomass could achieve significant reductions (51–95%) in emissions of CH4, NMHC, CO, PM2.5, OC, EC, PAHs, and EPFRs compared to those using raw biomass, while the differences in emissions of NOxand SO2were statistically insignificant. The reduction rate of benzo(a)pyrene-equivalent emissions was only 16%, much lower than the reduction in the total PAH mass (78%). This is primarily attributed to the more PAHs with high toxic potentials, such as dibenz(a,h)anthracene, in the pelletized biomass emissions. Consequently, impacts on human health associated with PAHs might be overestimated if only the mass of total PAHs was counted. The OP of particles from the pellet burning was also significantly lower than that from raw biomass by 96%. The results suggested that pelletized biomass could be a transitional substitution option that can significantly improve air quality and mitigate human exposure.

Household air pollution associated with solid fuel use is a long-standing public concern. The global population mainly using solid fuels for cooking remains large. Besides cooking, large amounts of coal and biomass fuels are burned for space heating during cold seasons in many regions. In this study, a wintertime multiple-region field campaign was carried out in north China to evaluate indoor PM2.5variations. With hourly resolved data from ∼1600 households, key influencing factors of indoor PM2.5were identified from a machine learning approach, and a random forest regression (RFR) model was further developed to quantitatively assess the impacts of household energy transition on indoor PM2.5. The indoor PM2.5concentration averaged at 120 μg/m3but ranged from 16 to ∼400 μg/m3. Indoor PM2.5was ∼60% lower in families using clean heating approaches compared to those burning traditional coal or biomass fuels. The RFR model had a good performance (R2= 0.85), and the interpretation was consistent with the field observation. A transition to clean coals or biomass pellets can reduce indoor PM2.5by 20%, and further switching to clean modern energies would reduce it an additional 30%, suggesting many significant benefits in promoting clean transitions in household heating activities.

Rising environmental concerns associated with the domestic use of solid biofuels have driven the search for clean energy alternatives. This study investigated the in vitrotoxicological characteristics of PM2.5emissions from residential biomass pellet burning using the A549 epithelial cell line. The potential of modern pellet applications to reduce PM2.5emissions was evaluated by considering both mass reduction and toxicity modification. PM2.5emissions from raw and pelletized biomass combustion reduced cell viability, indicative of acute toxicity, and also protein expression associated with epithelial barrier integrity, implying further systemic toxicity, potentially via an oxidative stress mechanism. Toxicity varied between PM2.5emissions from raw biomass and pellets, with pelletized straw and wood inducing cytotoxicity by factors of 0.54 and 1.30, and causing epithelial barrier damage by factors of 1.76 and 2.08, respectively, compared to their raw counterparts. Factoring in both mass reduction and toxicity modifications, PM2.5emissions from pelletized straw and wood dropped to 1.83 and 5.07 g/kg, respectively, from 30.1 to 9.32 g/kg for raw biomass combustion. This study underscores the effectiveness of pelletized biomass, particularly straw pellets, as a sustainable alternative to traditional biofuels and highlights the necessity of considering changes in toxicity when assessing the potential of clean fuels to mitigate emissions of the PM2.5complex.

Indoor PM2.5, 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 PM2.5variations in rural areas where energy or stove stacking is common. Household PM2.5varied largely across different homes but also within households. Using generalized linear models and dominance analysis, we estimated that outdoor PM2.5explained 19% of the intrahousehold variation in indoor daily PM2.5, 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 PM2.5annually, 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 PM2.5could be significantly reduced and indoor temperature substantially increased, providing thermal comforts in addition to improved air quality.