Impact of Crop Straw Burning on Urban Air Quality Based on WRF-Chem Simulations

Smoke from open crop straw burning has a notable impact on ambient, regional, and global air quality. The crop straw burning smoke event of 1 October 2015 in Huaihe River basin of China has been simulated using the WRF-Chem (Weather Research and Forecasting Model coupled with Chemistry). This study focused on the evolution of the fire plume composition and its impact on urban air quality in 83 cities in Henan, Shangdong, Jiangsu, and Anhui provinces. Two simulations were conducted in this study. The first simulation referred to as WRF-FIRE included the FINN (Fire Inventory from NCAR) fire emission dataset, EDGAR-HTAP (Emission Database for Global Atmospheric Research on Hemispheric Transport of Air Pollution) anthropogenic emissions and MEGAN (Model of Emission of Gases and Aerosols from Nature) while the other referred to as WRF-NOFIRE, which was conducted without the FINN fire emission. The results show that WRF-FIRE simulation could reveal most of the locations of fires and the spreading of the fire plume was properly captured. WRF-FIRE simulation agreed well with ground-based measurements of O₃, CO, PM2.5, and PM10. The total correlation coefficient between simulation and observations was up to 0.50. Based on the difference between simulations with and without fire emission, the concentrations of O₃, CO, PM2.5, and PM10 increased differently in different cities. The maximum hourly biases (MHB) of CO, PM2.5, and PM10 were up to triple standard deviations of simulations without fire emission near the source. Emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs) from fire tended to increase modeled O₃ concentrations downwind of the fire location, and MHB was almost triple standard deviations of simulation without fire emission. Meanwhile, the impacts of fires were different for individual components of urban air pollutants. The basic concentrations of NO₂ and SO₂ probably decreased due to the high level surface O₃ far downwind of the fire location.