Study On The Characteristics Of Inorganic Compositions In PM_2.5 And Source Apportionment During Haze And Non-haze Days In Beijing

PM_2.5.5 samples in Beijing urban area during haze and non-haze days were collected for a month in spring,summer,autumn and winter in 2016,respectively.The seasonal,daily and diurnalvariations were described for concentrations of PM_2.5 between haze and non-haze days,besides,the meteorological factors that affected the concentration were further analyzed,basing on long-term monitoring data.A method was developed for the determination of water-soluble ions in PM_2.5.5 by accelerated solvent extraction combined with ion chromatography.The pollution level and variation characteristics of 8 water-soluble ions and 11 heavy metal elements in PM_2.5were studied.The sources and transport pathway of PM_2.5.5 were analyzed by positive matrix factorization?PMF?model and hybrid single particle lagrangian integrated trajectory model?HYSPLIT?respectively,the contribution rate of each pollution source was calculated as well,the conclusions were as followed:The annual average concentration of PM_2.5 was 119.8?g/m³ in Beijing,almost 72.5%of which was accounted for by the PM_2.5 mass concentrations in the haze days representing 37.6%of the sampling days.Relatively more haze days occurred in aerosol sampling periods during winter and summer compared with other seasons,presenting obvious characteristics of double peak.There was a significant difference in the mass concentrations of the particles during the haze and non-haze days,the characteristic of distribution was winter>autumn>spring>summer.There were relatively stable influencing factors in diurnal PM_2.5 concentrations,and the higher its concentration,the greater the correlation coefficient.Temperature had little influence on the formation of haze days within seasons,the relative humidity in spring and winterhad more important impact on the haze formation,but it was less important in summer and autumn.It was also easy to form haze days in the case of southern and southwest winds with speed less than 1.2m/s and higher atmospheric pressure.The total mass concentration of ions in PM_2.5 was 55.6?g/m³,which accounted for 46.4%of PM_2.5.5 mass concentration.SO₄^2-,NO₃^-and NH₄⁺?SNA?were mostly from secondary transformation and was the most important water-soluble ions in PM_2.5,mainly in the form of NH₄NO₃ and?NH₄?₂SO₄,especially in haze days.The charge of water-soluble ions in PM_2.5appeared cationic loss in haze days,which was slightly acidic,whereas it was cation excess and showing alkalinein non-haze days.The total concentration of 11 heavy metal elements in PM_2.5 were 1719.4 ng/m³,accounting for 1.44%of PM_2.5 mass concentration,of which Fe,Znand Pb were the main heavy metal elements,accounting for 90.6%of the measured elements.There were obvious seasonal differences among theelements,with the highest concentration values of almost all elements appearing in winter,followed by autumn.The mass concentration of each element was significantly higher than that of non-haze days,the ratios of elements in haze days andnon-haze daysvaried greatly,ranging from 1.42?Cu?to 5.46?Pb?,the ratio of Pb was largest.The sources of secondary inorganic,coal combustion and vehicle exhaust were the main sources of PM_2.5 in Beijing,accounting for about 87.8%of the total emissions.It was greatly influenced by the northwest air mass in spring,autumn and winter,however in summer it was mainly influenced by local circulation in the Bohai Sea.The air mass transported from the south and the northwest over long distancescorrespond to lower PM_2.5mass concentrations,the PM_2.5mass concentration corresponding to airmass transported from the north and the northwest was relatively high,and it was easy to cause haze days in Beijing.