| Handan was a typical industrial city and also one of“2+26”cities of air pollution transmission channel in Beijing-Tianjin-Hebei region.To identify the air pollution in Handan and explore the characteristics and variations of water-soluble inorganic ions at different air pollution levels,PM2.5 and PM10 samples were collected in four seasons of 2018,the mass concentrations of water-soluble inorganic ions were analyzed by ion chromatography.To understand the formation mechanism of particles,characteristics of PM1 and ions and aerosol scattering properties,PM1 samples and aerosol scattering coefficients were also observed in winter of Handan.The results showed that the annual average concentrations of PM2.5 and PM-0 was 99.10±78.18?g/m3 and 173.37±99.89?g/m3,respectively.PM2.5 concentrations accounts for 55.2%,which was the main chemical components of PM10.The proportion of secondary ions SNA(SO42-,NO3-and NH4+)in PM2.5 was 45.69%,much higher than that in PM10(33.68%),however,Ca2+ and Mg2+ were mainly distributed in PM10.The analysis of backward trajectory indicates that the dust pollution in spring mainly comes from Inner Mongolia.Compare to January 2016,the concentration of PM2.5 in January 2018 was decreased,but the contributions of secondary source and mobile source increased.The average mass concentration of PM1 was 78.26±35.30?g/m3,accounting for 50%of the PM1 mass.The formation of NO3-was mainly though homogeneous reactions,while heterogeneous reactions dominated the formation of SO42-.The air pollution was divided in to 3 levels:clean(PM2.5?75?g/m3),light/medium polluted(75?g/m3<PM2.5?150?g/m3)and heavy polluted(PM2.5>150?g/m3)according to the ambient national standard.The mass concentration of PM2.5 in clean,light/medium and severe polluted period was 51.21±15.55,91.96±25.44 and 241.44±69.70?g/m3,respectively.The ratio of PM2.5 to PM10 elevated with the increase of air pollution,and PM2.5/PM10 was as high as 75%in heavy polluted period,indicated that fine particle playing a leading role in the formation of heavy pollution in Handan.At light/medium levels,NO3-reached the highest level,accounted for 23.6%of PM2.5,the contributions of NO3-and NH4+ to the growth of PM2.5(31%and 14%)were notable higher than SO42-.With the increase of air pollution levels,sulfur oxidation ratios(SOR)decreased first and then increased,while nitrogen oxidation ratios(NOR)increased significantly.At the pollution levels from light to severe,Cl-appeared remarkable increased,and the contributions of coal consumption and secondary transform shows strongly elevated in severe polluted days by principal component analysisThe average aerosol scattering coefficients at 635,525 and 450 nm was 610.6,713.6 and 851.5 Mm-1,respectively.The scattering coefficients and hourly concentrations of PM2.5 showed a doubled peak trend of evening peaks and valley value during afternoon The diurnal variations of scattering coefficient were different at different pollution levels,and the mass scattering efficiency(MSE)of PM2.5 increased with air pollution. |
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