Simulation Study On The Impact Of Local Anthropogenic Emission And Traffic Emission Reduction On PM_2.5 In Shanghai

Shanghai is a center of science and technology,trade,information,finance and shipping China.With the development of the economy and society,the public is paying more and more attention to the air pollution problems in Shanghai.Anthropogenic emissions and synoptic weather systems are the two major factors affecting PM_2.5 pollution.As prerequisites for the development and refinement of emission reduction policies and emergency response strategies,evaluating the contribution of anthropogenic sources under various unfavorable weather systems and assessing the implementation of emission reduction policies are essential.First of all,surface meteorological observation data and air quality monitoring data from 2013 to 2017 were used to classify different weather systems.According to the classification results,numerical simulation studies were conducted based on typical PM_2.5 pollution events?February 4-6,2016,February 19-20,2016?to evaluate the contribution of anthropogenic emissions in Shanghai.The results show that:?1?The historical haze days of Shanghai from 2013 to 2017 were classified according to the weather systems,among which high pressure and cold front are the most typical weather systems.?2?WRF-Chem model successfully reproduced the pollution events of two typical weather systems.For the high pressure affected event,the average temperature and the dew point temperature MB of four stations is 0.83°C,-0.57°C,the average RMSE is 1.48°C,1.44°C,and the average IOA is 0.91,0.92.The wind speed of the four stations is overestimated,MB reaches 1.47 m·s-1,RMSE reaches 2.14 m·s-1,and IOA is 0.6.For the cold front affected event,the average temperature and the dew point temperature MB is 0.69°C,-1.64°C,the average RMSE is 1.05°C,2.14°C,and the average IOA is 0.89 and 0.96.The wind speed of the four stations was also overestimated,MB reaches 1.82 m·s-1,RMSE reaches 2.14 m·s-1,and IOA is 0.6.For the simulation of pollutants,the simulation of the two cases are consistent with the observation.The MB of PM_2.5 concentration is 58.09?g·m^-3,1.07?g·m^-3,and the IOA is 0.69 and 0.91 respectively.?3?In the sensitivity experiment,the contribution of anthropogenic emissions in Shanghai to PM_2.5 concentration shows different characteristics under different weather systems.For the high pressure affected event,anthropogenic emissions in Shanghai is a major contributor of the local PM_2.5 mass concentration?58.6%?.For the cold front affected event,the contribution is 22.3%.Therefore,under high-pressure weather system,the emergency response measures should focus on the local emission control,and the emergency response measures for the cold front affected event should attach importance to regional joint emission reduction measures.In addition,this paper used the historical data from 2013 to 2017 to calculate the variation of PM_2.5 mass concentration in Shanghai.On this basis,a typical case?April 16-18,2014?was selected to be conduct a numerical simulation study on,the following conclusions were drawn:?1?In Shanghai PM_2.5 mass concentration showed a significant downward trend in 2013-2017.The average annual mass concentration in 2017 decreased by 23?g·m^-3 compared with 2013,and during the morning and evening peak periods the average concentration decreased by 27?g·m^-3.?2?The model simulated the meteorological field well,although the simulation results of PM_2.5 mass concentration are slightly different from observation(MB is-44.0?g·m^-3,RMSE is 58.7?g·m^-3),WRF-Chem model successfully simulated the temporal and spatial variation of PM_2.5 mass concentration in Shanghai,and IOA reaches 0.65.?3?According to the sensitivity experiment of Shanghai's traffic emissions reduction in recent years,the results show that during the study period,PM_2.5 concentration in Shanghai decreased by 3.29?g·m^-3 on average.The monitoring station locates in Hongkou,in the northern part of Shanghai is most affected by traffic reduction.The maximum hourly average mass concentration reduces up to 26?g·m^-3,which exceeds 13% of the monitoring station PM_2.5 mass concentration.The results of this study can provide guidance for policy makers to implement effective control strategies.