Spatial and temporal distributions of air pollutant emissions from open crop straw and biomass burnings in China from 2002 to 2016

Open biomass burning (OBB) with a main contribution from open crop straw burning (OCSB) plays a key role in the formation of heavy haze episodes during harvest seasons in China through release of particulate matter (PM) and gaseous pollutants. Here we analyze spatial and temporal distributions of air pollutant emissions from OCSB and OBB in China from 2002 to 2016 on the basis of daily and highly resolved (1 km) emissions from the latest FINNv1.5 inventory. Estimated annual emissions of black carbon, organic carbon, PM2.5, PM10, CH4, CO, CO2, NH3, NOx, SO2 and NMVOCS from OBB in China from 2002 to 2016 have increased by 192, 180, 191, 196, 212, 199, 173, 208, 185, 184 and 225%, respectively, whereas emissions from OCSB have increased consistently by 200% for each species. Estimated PM2.5 annual emissions from OCSB increased significantly by 245.7% from 14.9 Gg/year in 2012 to 51.5 Gg/year in 2016 in Northeast China, whereas decreasing by 76.1% from 76.3 Gg/year in 2012 to 18.2 Gg/year in 2016 in East China. Contributions of OCSB in OBB emissions increased from 25.4% in 2002 to 56.4% in 2016 in North China and from 31.0% in 2002 to 66.4% in 2016 in Northeast China. Spatial distributions for the period of 2002-2016 indicate that the largest PM2.5 annual mean emissions from OCSB (37.0 Gg/year) occur in East China, followed by Northeast China (20.0 Gg/year) and Central China (13.5 Gg/year), whereas Southwest China has the largest PM2.5 annual mean emissions from OBB (286.5 Gg/year), following by East China (273.7 Gg/year), South China (237.3 Gg/year) and Central China (126.1 Gg/year). Contributions of OCSB in OBB emissions for PM2.5 have increased significantly to 56.4-66.4% in North and Northeast China in 2016.