| In order to explore the formation mechanism of air pollution in the Yangtze River Delta region,and provide a certain scientific basis for the prevention and control of air pollution,PM2.5 samples were collected at Lin'an regional atmosphere background station from March 1,2018 to February 28,2019.We analyzed carbonaceous components,water-soluble inorganic ions,and heavy metal elements to investigate time distribution characteristics and existence forms of each component.Principal component analysis and Multiple Linear Regression?PCA-MLR?was uesd to trace the sources of environmental pollution in the background area of the Yangtze River Delta.The result show:The average annual concentration of PM2.5 in Lin'an is 42.72?g/m3,showing a trend of winter>spring>autumn>summer.The average temperature is 17.3°C,the average humidity is 78%,the average pressure is 999.6 h Pa,and the annual precipitation is 1744.9 mm,with an average of 2.2 m/s.The average wind speed in each season does not change much,and northerly winds prevail throughout the year.The four trace gas pollutants SO2,NO2,CO and O3?8h all reached the national secondary standard.HYSLIPT showed that,under the influence of monsoon climate,the remote input of PM2.5 in Lin'an has obvious seasonal changes.The average annual concentration of OC and EC in Lin'an was?7.70±0.41??g/m3 and?0.69±0.0.06??g/m3.OC,EC,and TC were highest in autumn and lowest in summer.The mass concentration of TC in Lin'an area accounts for an average of 24.27%of PM2.5,and the total carbon aerosol?TCA?accounts for an average of 36.67%of PM2.5.The ratio of OC/EC in each season is summer>autumn>spring>winter,mainly distributed between 4?16,indicating that a large amount of secondary organic carbon?SOC?is generated in the area.The correlation between OC and EC is good,showing that they have similar or consistent sources of pollution.The SOC and SOA were determined by the EC tracer method.The results show that the annual SOC in Lin'an area accounts for 41.56%of OC and SOA accounts for 11.98%of PM2.5.Both of them reached the highest value in summer.The average annual concentration of water-soluble ions in PM2.5 in Lin'an is 20.25?g/m3,accounting for 46.15%of PM2.5.The annual average concentration is?(SO42-)>??NO3-?>??NH4+?>?(Ca2+)>??Na+?>??K+?>?(Mg2+)>??Cl-?>??F-?,and it has obvious seasonal changes.SNA is the main component of water-soluble ions in atmospheric aerosols,with an average annual mass of 15.92?g/m3,accounting for 78.61%of the mass concentration of water-soluble ions.The results of ion balance analysis show that the average annual AE/CE in Lin'an area is 0.68,indicating that the atmospheric particulate matter in this area is weakly alkaline.By measuring the ratio of NO3-/SO42-,it is shown that the spring-summer-autumn season is dominated by fixed sources and the winter is dominated by mobile sources.By analyzing the sulfur oxidation rate?SOR?and nitrogen oxidation rate?NOR?,we found that there was obvious conversion of SO2 and NO2 to SO42-and NO3-in this area.By analyzing the correlation between the water-soluble ions,it was found that there was a significant correlation between NH4+,SO42-,and NO3-.Analysis of the existence forms of NH4+found that Linan's summer NH4+mainly existed in the form of?NH4?2SO4 and NH4HSO4,and spring,autumn and winter NH4+mainly existed in the form of?NH4?2SO4 and NH4NO3.The average annual mass concentration of heavy metal elements in PM2.5 in Lin'an is2992.72 ng/m3,accounting for 5.65%of PM2.5 mass concentration.The average mass concentration of each metal element is Fe>Al>Cu>Pb>Ni>Mn>Cr>Sr>V>Ba.Fe,Al,and Pb belong to the three elements with a higher content,and the total mass accounts for about 90%of the metal elements.Cu,Ni,Mn,Cr,Sr,V,and Ba are less in the seven elements,accounts for about 10%of the metal elements.The average mass concentration of metal elements and the mass ratio of PM2.5 in the four seasons are winter>summer>spring>autumn.The enrichment factor calculations show that Cu,Pb,and Ni are seriously enriched and are strongly affected by humans;Cr,V,Sr,and Mn are slightly enriched and are obviously affected by human activities;Ba and Fe are affected by natural sources and The common contribution of anthropogenic sources.Principal component analysis and Multiple Linear Regression?PCA-MLR?was used to conduct a comprehensive analysis,it was found that there are six main sources of PM2.5 in Lin'an area,which are traffic sources,industrial sources,combustion sources,secondary sources,sea salt sources,and dust sources. |
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