Regional impact of biomass burning in southeast Asia on atmospheric aerosols during the 2013 seven South-East Asian studies project

A nested air quality prediction modeling system (NAQPMS) with an online tracer-tagged module was utilized to investigate the regional impact of biomass burning (BB) on aerosols and source–receptor relationships in Southeast Asia during March–April 2013. NAQPMS could reproduce the three-dimensional spatial distribution of aerosols. Both monthly and episodic analyses indicated that BB significantly contributed to surface and column aerosol concentrations in Southeast Asia along two long-range transport pathways. In the first pathway, aerosols from BB were blown northward from the Indochina peninsula to southwestern provinces in China. The mean contributions of BB decreased from 70%– 80% in the source regions to 10%–40% in southwestern China. Myanmar was the largest exporter. In the second pathway, PM_2.5 emitted by BB was uplifted into the mid-altitudes (2000 m) in the Indochina peninsula and transported eastward to the western Pacific at altitudes of 2500–4000 m, passing the South China Sea, southern China and western Pacific. In downwind regions, BB contributed 30%–60% of aerosols at altitudes of 2000–4000 m and 10%–30% below 2000 m. A simple estimation based on source–receptor relationships showed that BB emissions were likely overestimated by 35%– 50% in the Fire Inventory from National Center for Atmospheric Research (v1.5).