Contributions Of Emission Sources To The Air Quality During Heavy Haze Episodes In Beijing-Tianjin-Hebei (BTH) And Guanzhong Basin (GZB),China

Since the reform and opening up,with the accelerating process of industrialization,urbanization and modernization,China has experienced rapid socio-economic development.This extensive economic growth model,which focuses on energy consumption,has led to increasing emissions of pollutants and consequent prominent problem of air pollution.Entering the 21st century,China's air pollution has changed from traditional coal-burning pollution to complex regional pollution with high concentrations of PM_2.5 and O₃.Especially since the end of 2011,large-scale haze episodes occurred frequently in China,especially in Beijing-Tianjin-Hebei?BTH?,Yangtze River Delta?YRD?,and Pearl River Delta?PRD?.Therefore,it is imperative to investigate the formation,transformation,transport,diffusion,and removal of the air pollutants in the atmosphere for the sustainable development of China's social economy and ecological health.In the present study,the WRF-Chem model is used to evaluate the contribution of residential coal combustion emissions in BTH to the local air quality during persistent heavy haze episodes in the winter of 2014,providing a reasonable basis for the development of air pollution control strategies and emission reduction measures.Additionally,the WRF-Chem model is also applied to simulate the formation of PM_2.5during heavy air pollution episodes in Guanzhong Basin?GZB?in the autumn and winter of 2016 and evaluate contributions of various emission sources to the local air quality,providing an effective basis for local authorities to take measures for the air pollution control.The thesis includes the following scientific activities:?1?Evaluation of contributions of residential coal combustion emissions in BTH to the air quality during heavy haze episodes in the winter of 2014;?2?Assessment of impacts of local emissions in Weicheng District of Xianyang and major emission sources in GZB on the local air quality.Compared to observations and measurements over the ambient monitoring sites,the WRF-Chem model reasonably well reproduces the temporal variations and spatial distributions of the major air pollutants and the time series of aerosol species during the simulation period.The main results obtained through sensitivity simulations by the WRF-Chem model are as follows:?1?The WRF-Chem model is used to evaluate contributions of residential coal combustion emissions to the air quality in BTH during persistent air pollution episodes from 9 to 25 January 2014.The sensitivity simulations reveal that residential coal combustion emission plays an important role in the haze formation in BTH.During the simulation period,the contribution of residential coal combustion emission in BTH to local PM_2.5 mass concentrations is about 23.1%.The main component of PM_2.5 from residential coal combustion emission in BTH is organic aerosol?OA?,with a contribution of 42.8%,followed by sulfate?17.1%?.When the residential coal combustion emission in BTH is excluded in the model simulation,the PM_2.5 mass concentration in Beijing decreases by approximately 30%,but if only residential coal combustion emission in Beijing is not considered,the PM_2.5 mass concentration in Beijing decreases by around 18.0%.Therefore,the residential coal replacement by clean energy sources carried out in BTH and its surrounding areas would be beneficial to the air quality improvement in Beijing.?2?The WRF-Chem model is applied to evaluate the contribution of the emissions at Weicheng District of Xianyang to the local PM_2.5 pollution levels and the impact of major emission sources in GZB on the PM_2.5 mass concentrations at Weicheng District during persistent heavy haze episodes from 12 to 18 November2016 and 16 to 21 December 2016.The sensitivity simulations show that the emissions at Weicheng District contribute about 30%of the local PM_2.5 mass concentration during the simulation period in the autumu and winter of 2016.The contribution of the regional transport to the PM_2.5 mass concentration at Weicheng District is as high as 60%.Among the various emission sources in GZB,the residential source is the main contributor to the PM_2.5 levels at Weicheng District in the autumn and winter.During the haze episode in the autumn of 2016,the residential emissions in GZB contribute about 37.4%to the PM_2.5 pollution level at Weicheng District;the contribution of industrial and transportation emissions in GZB to the PM_2.5 at Weicheng District is 22.1%and 11.2%,respectively;and the contribution of power emissions is only 2.0%.The contribution of residential emissions in GZB to the PM_2.5 mass concentration at Weicheng District during the winter haze episode is up to 60.6%;the contribution of industry and transportation in GZB to the PM_2.5 mass concentration at Weicheng District is 15.6%and 9.8%,respectively;and the contribution of power emissions to the mass concentration of PM_2.5 is equivalent to that in autumn.The above results will provide a reasonable basis for local environment protection agencies to formulate air pollution control strategies and emission reduction measures.