Numerical Simulation Study On The Distribution And Source Of Black Carbon In Autumn In Mid-eastern China

Mid-eastern China has a much higher black carbon(BC)concentration.Due to the uneven distribution of BC emissions and complex variable atmospheric diffusion conditions,the spatial distribution of BC and its source contributions are quite variable and uncertain.In order to deeply understand the distribution and source characteristics of BC,and make targeted emission reduction policies.In this study,the Weather Research and Forecasting model coupled to Chemistry(WRF-Chem model),coupled with an online BC source-tagging method,and sensitivity experiments was used to quantitatively analyze the distribution characteristics and regional and industry source contributions of average BC concentration in autumn in China.In addition,we analyzed the source region contributions to BC in the Yangtze river delta during an air pollution event,hoping to understand the distribution and source contribution characteristics of BC,under the different weather conditions.The results are shown as follows:(1)In autumn,BC pollution was serious in Mid-eastern China,BC was mainly distributed in the north China plain,Yangtze river delta,two lakes region,eastern Sichuan,which were all low-altitude areas and shown a wide range of high BC concentration characteristics.In the area with high BC concentration,2/3 of the BC concentration was contributed by local sources,and the remaining 1/3 was contributed by external transport.The contribution of external source region mainly included BC transportation of neighboring provinces and cities,but less long-distance transport.The distribution of BC concentration and proportion contributed by different types of emission sources has obvious difference.Industry sources,residential sources and transport sources contributed a similar proportion of BC to Beijing-tianjin-hebei and Fenwei regions,among which industry sources accounted for the largest proportion.Pollution treatment should coordinate and control the emissions of the three industries,and focus on the emission reduction of industry production;The BC in the Yangtze river delta was mainly contributed by the transport source(42.5%),which needs to be controlled.Two lakes region was mainly contributed by the residential source(46.5%),and the living fuels such as fuelwood still used in those regions were considered to be replaced with cleaner fuels.(2)The distribution and source of BC concentration vary greatly under different weather conditions.In this pollution event,the high concentration of BC in the YRD occurred during two distinct synoptic situations: during cold front passed through,the YRD was controlled by a northerly wind,the surface BC concentration in YRD increased,and the contribution of upwind source region to the surface BC in the YRD was significant(32.3%);after the cold front passed through,the YRD was under a high-pressure center with stable weather conditions,causing regional BC pollution,and the local contributions to BC in the YRD was mainly contribution(80.3%).There were differences in the sources of vertical BC between the near surface and the upper middle layer.The contributions of outside transport to BC in the YRD increased with height due to higher layers having higher wind speeds and a larger transport flux of BC from outside of the YRD.Under the outside transport of air pollution accompanied by a cold front,local contributions were mainly dominant several hundred meters near the surface,but contributions outside the YRD were dominant above the surface in the whole vertical direction.Under stable weather conditions,high concentrations of BC in YRD were associated with higher local source contributions.