Characteristics Of PM₁ Chemical Composition And Role Of Meteorological Factors During Heavy Aerosol Pollution Episodes In Northern Beijing Area In Autumn And Winter

In this study,we conducted an investigation of size-resolved chemical components of PM₁ from a site in northern China background area by high resolution time of flight aerosol mass spectrometry?HR-TOF-AMS?.This field campaign covers the autumn and winter of 2015,spring and summer of 2016.The characteristics of heavy pollution during autumn and winter of 2015 were emphatically studied among them.The result shows that the mass concentrations of NR-PM₁?None-Refractory PM₁?was 25.2 ?g/m3.The results show that the main composition of PM₁ was organic aerosol?OA?,nitrate,sulfate,ammonium and chloride,and the average mass concentrations of the five components were 9.9,6.4,4.4,4.0,and 0.5 ?g/m3.Organics was the main component of PM₁,and the proportion of nitrate was higher than sulfate in autumn and winter.Heavy aerosol pollution episodes?HPEs?usually start from late autumn and become more serious in winter in Beijing and its vicinity?BIV?,and the reasons for the formation and change of HPEs in background areas of northern BIV was discussed.We investigated the chemical composition of NR-PM₁ and meteorological conditions during HPEs in autumn and winter of 2015.Stable regional atmosphere and higher atmospheric condensation processes associated with southerly and lower wind dominated a doubling of the mass concentration of PM₁ within a few hours.The positive feedback of meteorological condition caused ⁷0�80% increased hourly PM₁ in the formation and developing stages of HPE because of the more stable atmosphere and increased condensation occurred,leading to more serious and sustained HPEs.According to the analysis methods of positive matrix factor?PMF?,correlation analysis and backward trajectory,we found that in addition to the lower southerly wind carrying the pollutants from southern part of BIV,which derived from motor vehicles,biomass burning and industrial emissions,leading to greater gains of nitrate,westerly wind from central Inner Mongolia and north Shanxi were also found to carry air pollutants mostly derived from coal combustion,contributing to the PM₁ mass in the northern BIV area in winter,resulted higher sulfate,and organic aerosol mass.Inferred from positive matrix factor analysis of OA for the two heavy pollution events,we found that biomass burning and coal-combustion had the great contribution to the primary organic aerosols in autumn and winter,respectively,and the secondary organic aerosols dominated the total OA mass?67%?,mainly containing oxidizing organic aerosols?LVOOA and SVOOA?.In addition to the two typical heavy pollution events,the article also further discussed other pollution periods and clean periods in the whole autumn and winter time.The average mass concentration of PM₁ during pollution periods was about 10 times as much as clean periods,and nitrate concentration and has more contribution during pollution time,while its average particle size was the largest among all species.According to the classifying and element analysis of organic aerosols,during pollution time,the oxidation of organic matter was significantly higher than the clean period,but the aging mechanism was not active,which indicated that oxidation process was slower.The backward trajectory result shows that air mass had more complex source in pollution time,including the air masses from the west,south and northeast.During the clean periods,BIV area was mainly affected by purify air from Siberia,which was helped for the elimination of pollution.