Chemical, microphysical and optical properties of primary particles from the combustion of biomass fuels

Abstract

Biomass fuel combustion for residential energy significantly influences both emissions and the atmospheric burden of aerosols in world regions, i.e., east and south Asia. This study reports measurements of climate-relevant properties of particles emitted from biomass fuels widely used for cooking in south Asia, in laboratory experiments simulating actual cooking in the region. Fuel burn rates of 1−2 kg h⁻¹ for wood species and 1.5−2 kg h⁻¹ for crop residues and dried cattle dung, influenced PM_2.5 emission factors which were 1.7−2 g kg⁻¹ at low burn rates but 5−9 g kg⁻¹ at higher burn rates. Total carbon accounted for 45−55% and ions and trace elements for 2−12% of PM_2.5 mass. The Elemental Carbon (EC) content was variable and highest (22−35%) in particles emitted from low burn rate combustion (wood and jute stalks) but significantly lower (2−4%) from high burn rate combustion (dried cattle dung and rice straw). The mass absorption cross-section (MAC, m² g⁻¹) correlated with EC content for strongly absorbing particles. Weakly absorbing particles, from straw and dung combustion, showed absorption that could not be explained by EC content alone. On average, the MAC of biofuel emission particles was significantly higher than reported measurements from forest fires but somewhat lower than those from diesel engines, indicating potential to significantly influence atmospheric absorption. Both for a given fuel and across different fuels, increased burn rates result in higher emission rates of PM_2.5, larger Organic Carbon (OC) content, larger average particle sizes and lower MAC. Larger mean particle size (0.42−1.31 μm MMAD) and organic carbon content, than in emissions from combustion sources like diesels, have potential implications for hygroscopic growth and cloud nucleation behavior of these aerosols. These measurements can be used to refine regional emission inventories and derive optical parametrizations, for climate modeling, representative of regions dominated by primary particles from biomass fuel combustion.