PM2.5 Emissions from Biomass Burning in South/Southeast Asia – Uncertainties and Trade-Offs
Kristofer Lasko, Krishna Prasad Vadrevu, Varaprasad Bandaru, Thi Nhat Thanh Nguyen, Quang Hung Bui
Abstract
Biomass burning leads to significant air pollutant emissions, which impact air quality, human health, and soil carbon. In this study, we quantify total fine particulate matter (PM2.5) emissions in South/Southeast Asia (S/SEA), with emphasis on the biomass burning. Major vegetation types burnt include shrublands, tropical forests, agriculture, peatlands, and temperate forest. Research shows that biomass burning PM2.5 emissions are underestimated, especially rice straw burning emissions due to variation resulting from different harvest and burning practices (pile burning or open burning), which especially affect residue fuel-loads and amounts burned combustion efficiency and detection of burning. This is compounded by the difficulty of detecting and quantifying agricultural fires from satellite remote sensing. To overcome underestimation, we use a bottom-up approach using a subnational spatial database of rice-harvested area, region-specific fuel-loading factors, region, and burning-practice-specific emission and combustion factors, including literature-derived estimates of straw and stubble burned. Most previous research does not use field-derived, region-specific factors. We incorporate rice straw and rice standing stalks (stubble), which are generally not accounted for in combination. For non-rice biomass burning emissions, we leverage the Global Fire Emissions Database (GFED); however, we incorporate region-specific emission factors (EFs), and for urban transport and human activities, we use the Regional Emission inventory in ASia (REAS). From our studies, for S/SEA, we estimate 26.2 million tons of PM2.5 annually, with about 22% attributed to agricultural burning (21% from rice, 1% from non-rice), 21% to temperate and tropical forest burning, and 20% to peatlands, 8% to shrublands, and 28% to urban areas (REAS). The most PM2.5 emissions occur in India, Indonesia, Bangladesh, Myanmar, and Vietnam. A difference of a factor of 28 was found by comparing our emissions with the standard GFED EFs for agriculture, suggesting missed satellite-based emissions (5.9 million tons vs. 0.2 million tons). We also demonstrate the need to reduce uncertainty in agricultural emissions assessments.