A high-resolution inventory of air pollutant emissions from crop residue burning in China

Crop residue burning is an important source of air pollutants and strongly affects the regional air quality and global climate change. This study presents a detailed emission inventory of major air pollutants from crop residue burning for the year of 2014 in China by the bottom-up method. Activity data were investigated for 296 prefecture-level cities. Emission factors were determined for indoor and in-field burning separately. Regional differences were considered for the proportion of residue burned (PCRB), the ratio between indoor and in-field burning, and the ratio of straw to grain production. The emissions were estimated at prefecture-city level as the first step; then they were redistributed within a city based on 1-km resolution land-use, MODIS fire counts, and rural population. Temporal variation was determined according to farming practices in different regions and MODIS fire counts. Uncertainties were estimated using the Monte Carlo method. The total emissions from crop residue burning in China were estimated to be 0.13 ( - 47-92%) for BC, 0.71 ( - 48-92%) for OC, 1.77 ( - 48-91%) for PM2.5, 2.04 (- 50-100%) for PM10, 0.16 (- 59-133%) for SO2, 0.53 ( - 55-105%) for NOx, 0.12 ( - 47-93%) for NH3, 1.07 ( - 55-102%) for CH4, 1.85 ( - 43-74%) for NMVOC, 18.33 ( - 46-85%) for CO and 305.20 ( - 45-80%) for CO2, in unit of Tg yr(-1). Our results are remarkably lower than those reported in previous studies, mainly because of the PCRB has decreased significantly in recent years. For most of the pollutants, indoor burning accounted for about 50-70% of the emissions. Rice, wheat and corn contributed more than 85% of the emissions, but their relative contributions varied a lot with region and season. High emissions were mostly located in the eastern China, central China and northeastern China, and temporally peaked in April, June and October, with different intensities in the north and the south. This study provides a useful basis for air quality modeling and the policy making of pollution control strategies.