Analysis Of PM_2.5 Pollution Characteristics And Influencing Factors In Jinan City

With the improvement of urbanization and industrialization,the continuous haze events of high-intensity,long-term,and wide-ranging have occurred in urban areas of China,especially the atmospheric environmental problems in urban areas.Jinan is located in the center of the area with severe air pollution such as SO₂,NO_X and fine particles in the Bohai Rim,whose air pollution is serious and PM_2.5 is one of the primary pollutants.Through analyzing the characteristics and influencing factors of PM_2.5 of Jinan,it is possible to strengthen the understanding of the processes and causes of heavy pollution in Jinan,and provide scientific theoretical basis for the scientific planning and healthy development of the city.Based on the daily site monitoring data of Jinan from 2014 to 2018,the characteristics of PM_2.5 mass concentration was studied in Jinan.For the typical heavy pollution process,the circulation field characteristics and the relationship between PM_2.5 mass concentration and meteorological elements were analyzed.By constructing the backward trajectory tracking model and the localized air quality model,the effect factors of regional transport on PM_2.5 mass concentration were explored from the perspective of directional and quantitative.The main conclusions are as follows:（1）On the annual scale,PM_2.5 mass concentration in Jinan from high to low are winter,autumn,spring,and summer,with the corresponding average concentrations are 104?g/m³,69?g/m³,67?g/m³,55?g/m³ respectively.The frequency of heavy pollution is 30%,which in winter accounts for 63%of the whole year.On the monthly scale,the mean change is in"U"shaped.November-February of the following year is the period,when the average PM_2.5 mass concentration is relatively high.And January and December are the most severely polluted months.On the daily scale,the diurnal variation is"double peaks and double valleys"type,with peaks appearing at approximately 23:00and 10:00 and valleys appearing at approximately 6:00 and 16:00.The daily changes in spring,autumn,and winter are consistent with the mean diurnal variation,especially in the winter,the curve is most significant.The characteristics of"double peaks and double valleys"in summer are not obvious,only a significant peak appeared at 10:00,and its diurnal curve undulation degree was the most gentle.（2）From the perspective of the atmospheric circulation,the ground was mainly controlled by weak high pressure and average pressure field,and the situation in front of the ridge behind the trough at 850 hPa was likely to cause heavy pollution.The ground was located on the periphery of the high-pressure system,the isobaric dense area and the surface air flow convergence area.The 850hPa circulation field was a low pressure trough,which guided the cold air southward.The high wind speed was conducive to the diffusion of pollutants and provides favorable circulation conditions for the improvement of air quality in Jinan.（3）From the influence of meteorological elements,the fluctuation range of temperature and relative humidity was large,while the fluctuation range of air pressure and wind speed was small.And the meteorological elements within each concentration level were evenly distributed.On the whole,the surface temperature,relative humidity,air pressure and other factors in the period of heavy pollution were higher than the mean values in the period of non-pollution.However,when the pollution concentration was low,the relationship between them was uncertain.The analysis based on the elastic coefficient showed that changes in temperature,pressure,and relative humidity caused the positive increase in PM_2.5 mass concentration,while the wind speed was reversed.From the wind direction,during the heavy pollution process,the dominant wind was southerly,and the peak of PM_2.5 mass concentration in the pollution process occured in the period of small wind,when the dominant wind direction was opposite.（4）Through the optimization of the scheme,the localized air quality model,WRF-Chem was constructed.A comparative analysis of the simulated and observed values showed that the correlation coefficients of the observed and simulated air temperature,pressure,and relative humidity at meteorological stations in Jinan were above 0.8,and those of wind speed were between 0.6-0.7.The correlation coefficients of simulated and observed PM_2.5 mass concentration at monitoring stations were around 0.8,the consistency index was above 0.85,and the root mean square error was between 30-45.The model had the better simulation performance for the severely polluted weather process in the study area.（5）The influence of regional transportation on PM_2.5 mass concentration in Jinan showed that the transport direction of the near-surface air mass affected the contribution rate of each province in the heavy pollution process.The contribution rate of external sources to the monitoring stations in Jinan was 64.7%-80.7%.The average contribution rate of Shandong Province is 31.7%,most of which were concentrated in the southwest of Shandong.Inside,the average contribution rate of Jing-Jin-Ji was 13.2%,11.5%in Henan Province,5.9%in Jiangsu Province,5.2%in Anhui Province.（6）The vertical structural characteristics of PM_2.5 pollution transport in Jinan showed that the slow movement of near-surface air masses and the subsidence of middle and high-level air masses caused the heavy pollution.1km was the main conveyor belt for pollutants,and most of which were distributed below 600m.In the process of heavy pollution in Jinan,there was a big difference in the transport flux（0-450?g/m³）,while the direction corresponding to the high-flux area was consistent with the direction of air mass transportation at the corresponding height at the time of heavy pollution.