Pollutant Emissions and Oxidative Potentials of Particles from the Indoor Burning of Biomass Pellets

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, NO_x, PM_2.5 (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 PM_2.5, and compared with those from raw biomass burning. For most targets, except for SO₂ and NO_x, the mass-based emission factors for pelletized biomass were 62-96% lower than those for raw biomass. SO₂ and NO_x levels 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, PM_2.5, OC, EC, PAHs, and EPFRs compared to those using raw biomass, while the differences in emissions of NO_x and SO₂ were 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.