The Temporal-Spatial Characteristics Of PM_2.5 And O₃ In Shandong Province And The Pollution Processes Analysis In Typical Areas

With the development of economy and industry and the acceleration of urbanization,Shandong province becomes an important area of air pollution research gradually.Air pollution is becoming more and more serious in Shandong,so it is urgent to improve air quality.The major air pollutants data from China National Environmental Monitoring Centre were used to investigate the spatial-temporal distribution characteristics of fine particulate matter(PM_2.5)and ozone?O₃?and the synergism and difference of PM_2.5.5 and O₃ pollution in Shandong province in 2015.Meanwhile,a nested grid air quality prediction modeling system?NAQPMS?was used to simulate PM_2.5.5 and O₃ during June2015.Using the simulated data,the causes of PM_2.5.5 and O₃ compound pollution in typical region?Jinan,Dezhou and Liaocheng?of Shandong were analyzed.The analysis of observation data showed that the air quality of Shandong peninsula is the best.In most other areas,PM_2.5 pollution was severe,especially in western cities.Dezhou was the city with serious PM_2.5 and O₃ pollution.The characteristics of compound air pollution in Shandong are obvious.The concentration of PM_2.5 and O₃have been found to exceed the standard simultaneously in almost all areas,and the phenomenon mainly occurs in summer.There are 10 cities which the number of days that PM_2.5.5 and O₃ both exceeding the standard are more than 20 days and 6 cities are more than 30 days.The maximum of the number is 65 days in Dezhou.The correlation of PM_2.5 and O₃ concentration and meteorological factors indicates that the condition of high temperature and low humidity is more advantageous to O₃ and PM_2.5 superposition coexistence and achieve a high concentration simultaneously.The condition of high temperature and low humidity first guarantees the generation of O₃.Under this condition,the improvement of relative humidity will be more conducive to the increase of PM_2.5 concentration.The verification of simulation results by observation data showed that the main meteorological factors simulation result of WRF is good.The simulation result of temperature is the best,followed by relative humidity.For relative humidity,the simulation result is not ideal for high value.Moreover,Nudging has an optimized effect on the simulation results of WRF.The simulation results of NAQPMS can reasonably reproduce the trend of pollutants.The mean deviation between the simulated values and observed values of the main pollutants is also within the reasonable range.The analysis of simulated concentration of PM_2.5 component showed that in O₃polluted days,the concentration of inorganic salt ions ammonium?NH₄⁺?,sulfate(SO₄^2-),nitrate?NO₃^-?and PM2.5 were significantly higher than that of O₃ clean days.The proportion of BC and OC in PM_2.5 component was between 6%and 9%.The total amount of sulfate,nitrate and ammonium salt can be 35%to 50%of PM_2.5concentration,and the proportion in O₃ polluted days was higher than that of O₃ clean days.The analysis of compound pollution processes in typical region showed that in the first pollution process?from June 8 to 12?,the O₃ concentration was affected by regional transport,and the pollutants mainly came from Henan,Hubei.The pollutants were then cleared by the strong northwest wind.In the second pollution process?from June 14 to 26?,the increase of O₃ concentration was mainly affected by the cumulative effect of local pollutants,and the degree of pollution was more serious than the first one.The control of the high-pressure system and the uniform pressure field were the most important weather pattern which lead to the long duration of pollution.In addition,in the vertical direction,PM_2.5 and O₃ concentration showed a consistent trend over time.The occurrence time of maximum PM_2.5 concentration was slightly slower than that of maximum O₃ concentration.Compared with the clean time,the temperature and relative humidity in the vertical direction of the pollution period were also high,which provides favorable conditions for the generation of new particles and the generation of secondary aerosols.