The evolution of open biomass burning during summer crop harvest in the North China Plain

Open biomass burning (OBB) negatively impacts air quality by discharging abundant fine particulate matter (PM2.5, aerodynamic diameter ≤2.5 µm) and trace gases. The statistical methods and numerical simulations have been used to estimate emissions from OBB. The former is poor in producing reliable distributions and transport of emissions, while studies with the latter have focused on cases analysis over short periods. This study investigates the multi-year evaluation of OBB and its contribution to PM2.5 and black carbon (BC) based on satellite observations and numerical modeling over the North China Plain. The number of fires increased by 206% from 2008 to 2012, and decreased by 84% from 2012 to 2016, indicating that the implementation of straw burning ban policy had achieved significant positive effects. The simulation from Weather Research and Forecasting model coupled with chemistry showed that the surface concentrations of PM2.5 and BC emitted by OBB in the burning source area increased from 22 and 3.22 μg/m3, respectively, in 2008 to 45.77 and 6.47 μg/m3, respectively, in 2012, and then decreased to 1.41 and 0.22 μg/m3, respectively, in 2016. The differentiated impacts on air quality of policies across provinces are also investigated. Open crop straw burning was banned early in Shandong and Henan provinces, but they suffer from poor air quality due to open straw burning until the effective straw burning ban in Anhui and Jiangsu provinces, which suggests the need for interregional collaboration for pollution control.