Numerical study on source contributions to PM_2.5 over Beijing-Tianjin-Hebei area during a severe haze event

Identification of the source regions of PM_2.5 and quantification of theircontributions are critical for efficient haze pollution control. In this study, the Nested Air Quality Prediction Model System (NAQPMS) coupled with an online source-tagging module was employed to simulate an extreme severe haze episode over Beijing-Tianjin-Hebei (BTH) area in January 2013. A detailed quantification of the source contributions from different regions was provided. The simulation was validated through comparisonwith surface observations, which suggested that the model could reasonably reproduce the temporal and spatial variations of PM_2.5 concentrations during this episode. The results of the source-tagging calculation suggested that local emissions were the dominated sources of the surface PM_2.5, accounting for 29.8% to 63.7% contributions of the surface PM_2.5 concentrations. On the other hand, PM_2.5 at 800 m layer was mainly contributed by the sources of the surrounding areas with the contributed ratio from 69.3% to 86.3%. For the most polluted southeast BTH area (including Xingtai, Handan, Cangzhou and Hengshui), emissions from Shandong and Henan provinces had significant contribution to the PM_2.5 pollution with the largest contributions 25.2% and 31.5% at surface and 800 m layer, respectively. Therefore, the control of haze pollution over BHT areas should not only focus on the collaborative emission control within BHT areas but also take into account the joint emission control for BHT regions, Shandong and Henan Provinces.