| The frequent outbreaks and unprecedentedly high particulate matter concentrations of haze pollution in China has drawn worldwide attention.Zhengzhou and Xinxiang are two representative cities in the central plains city group in China.Due to their rapid economic and urbanization development,the atmospheric environment is also affected,and the pollution of particulate is becoming more and more serious.In this study,PM2.5 samples were collected from Zhengzhou in 2016 and Xinxiang in 2017,as well as the PM1 and PM10 samples from Xinxiang in winter.The mass concentration and seasonal variation characteristic of PM2.5 and water-soluble ions were analyzed.The impact of meteorological factors on PM2.5 was explored.According to the backward trajectory and cluster analysis,the transmission path of PM2.5 was obtained.At the same time,the main sources of the two cities atmospheric pollution were obtained by correlation analysis and principal component analysis.Particulate pollution is more serious in winter,and the smaller the particle size is,the greater the threat to human health.Therefore,a comprehensive understanding of each haze formation process was acquired according to the size-dependent mass concentration and carbonaceous components measurement in Xinxiang 2017.The study drew the following main conclusions:1.The annual average concentration of PM2.5 in Zhengzhou,2016 and Xinxiang,2017 were 150.72±85.39μg/m3 and 75.83±47.88μg/m3,the annual standard rates of PM2.5 were 14.3%and 58.8%,respectively.The pollution of PM2.5 is still serious,but the PM2.5 concentrations in Zhengzhou and Xinxiang decreased by 13.9%and 24.6%with previous years.External source transport has certain influence on PM2.5pollution in Zhengzhou and Xinxiang.In Xinxiang,34.42%of the air mass was affected from the direction of Zhengzhou in the south.Through cluster analysis,it is found that the whole north China plain in 2016 has a high potential pollution level.The narrowing of the range of high PM2.5concentration in 2017 also reflects the decline of regional pollution level from the side,which indirectly proves the effectiveness of the air treatment action in 2017.2.There was a certain correlation between the mass concentration of PM2.5 and meteorological conditions.In general,high wind speed was conducive to the dilution and diffusion of pollutants,while high relative humidity increases the concentration of PM2.5.The influence of air temperature on atmospheric particles was complex.In winter,PM2.5 is positively correlated with temperature and negatively correlated with air pressure.The phenomenon of temperature inversion caused the accumulation of particulate matter and the increase of PM2.5 concentration.In summer,PM2.5 concentration is negatively correlated with temperature and positively correlated with air pressure.The vertical movement of airflow is conducive to the diffusion of particulate matter and the reduction of PM2.5 concentration.3.The 7 water-soluble ions concentrations of PM2.5 in Zhengzhou and Xinxiang were 54.20 μg/m3and 42.98μg/m3,and accounted for 36.0%and 58.3%of PM2.5,respectively.Water-soluble ions are the most important components of PM2.5 in Xinxiang.The concentration of water-soluble ions had obvious seasonal characteristics,both of which were winter>spring>autumn>summer.SO42-,NO3-and NH4+were the main water-soluble ions of PM2.5 in the two cities,and accounted for 92.9%and 81.3%of the 7 ions concentrations.Secondary pollution has a more serious impact on Zhengzhou.The concentration of Ca2+in Xinxiang was 4.2 times of Zhengzhou,so attention should be paid to the prevention and control of dust.4.PM2.5 of Zhengzhou and Xinxiang were alkaline in general,and the alkalinity of Xinxiang was greater than that of Zhengzhou.According to SOR and NOR,the high concentration of SO42-and NO3-in the two cities were not only caused by the primary emission,but also the strong secondary transformation process of SO2 and NO2 exists in the atmosphere.There is a high correlation between NH4+and NO3-,SO42-and Cl-in Zhengzhou and Xinxiang,with a correlation coefficient of 0.648～0.911.The correlation coefficient between NH4+and NO3-in Zhengzhou is greater than that between NH4+and SO42-,indicating that NH4+preferentially combines with NO3-to form NH4NO3,while in Xinxiang,NH4+preferentially combines with SO42-.According to the results of principal component analysis,the main sources of water-soluble ions of PM2.5 in Zhengzhou 2016 and Xinxiang 2017 were secondary transformation,combustion source and the mixed source of natural source and building source.Water-soluble ions in PM2.5 in Zhengzhou 2016 were also affected by agricultural activities.According to the value of NO3-/SO42-,mobile sources have a greater impact on PM pollution in Zhengzhou and Xinxiang,indicating that the impact of vehicle emissions on air pollution cannot be ignored.5.The average proportions of TM for the three particle sizes of PM1,PM2.5 and PM10 were 43%,36%and 26%,respectively.These results revealed that the carbonaceous components in fine particles is high,and that the decreasing trend with the increase in particle size.During the one-month sampling period,four pollution events（PE）were observed,among which PE1 and PE3 were short-term PE with low PM concentrations,and PE2 and PE4 were long-term PE with high particulate concentrations.The stagnant meteorological conditions made the pollutions last longer.In the drier environment,the carbonaceous components had great contributions to the formation of PE1 and PE2,but they were not the main components of the explosive growth of PM in the environment with higher relative humidity.The snowfall lasted for three days during the sampling period had the best removal effect on PM10,but the removal rate of carbon components in PM1 was the highest.More than 85%of SOC was removed by wet deposition in PM1 and PM2.5. |
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