The Characteristics And Source Of PM₁₀ At Background Stations Of Eastern China

The characteristics of PM₁₀ and its chemical composition December 2015 to December 2017 were studied at three regional atmospheric background stations in central and eastern China.During the period,the PM₁₀mass concentration was the highest at Lin’an(62.2±36.6mg·m^-3),followed by Jinsha(57.6±31.8mg·m^-3)and Longfengshan(57.5±55.3mg·m^-3).Compared with 2013,the PM₁₀mass concentration at Lin’an and Jinsha decreased by 29.3%and 26.2%,respectively.The average concentrations of SO₄^2-(9.9,10.2mg·m^-3),NO₃^-(8.2,6.7mg·m^-3),and NH₄⁺(3.7,2.6mg·m^-3)in Lin’an and Jinsha were higher than those in Longfengshan(5.9,4.9,2.1mg·m^-3).The average NO₃^-/SO₄^2-ratios at Longfengshan and Lin’an were relatively high（0.86 and 0.84）,while those at Jinsha were relatively low（0.62）.The OC was the highest at Longfengshan and the lowest at Jinsha.The average PM₁₀,NO₃^-,EC mass concentrations and the NO₃^-/SO₄^2-ratio at the three sites in summer were the lowest.There was good agreement between the observed PM₁₀and the reconstructed PM₁₀at all the stations indicating that the chemical compositions could well represent the major components of PM₁₀.The comparison of the fractions of different aerosol types in winter and summer with the earlier studies at Lin’an station indicated that the fraction of OM declined by 3%～9%.Motor vehicle emissions and secondary formation were the major contributors of PM₁₀at Lin’an Station and Longfengshan Station.Biomass buring and secondary formation were the dominant contributors of PM₁₀at Jinsha Station.At Longfenshan Station,the contribution of secondary source to PM₁₀increased from 36%in 2016 to42%in 2017.At Lin’an Station,the contribution of vehicle exhausts decreased from22%in 2016 to 14%in 2017.On the contrary,secondary formation contributed36%in 2016 and increased to 45%in 2017.At Jinsha Station,secondary source contributed 35%and 43%to PM₁₀in 2016 and 2017,respectively.In addition,the contribution of coal combustion deceased from 22% in 2016 to 10% in 2017.