Characteristics Of Water-soluble Components Of Atmospheric Particles During Heavy Air Pollution

In recent years,air pollution problem has become increasingly serious in China.Water-soluble components,which played an important role in the environment,climate and human health,are the main component of atmospheric particulate matter,accounting for more than one third of fine particulate matter.Therefore,it is of great significance to analyze the variation characteristics,particle size distribution and optical characteristics of water-soluble components for a better understanding of the formation mechanism of secondary aerosols and the formulation of pollutant control measures.In this paper,the water-soluble components of atmospheric particles in winter were studied.Two representative cities(Hefei and Beijing)in eastern China were selected to study water-soluble inorganic ions and Water-Soluble Organic Carbon(WSOC).(1)In this study,size-segregated airborne particles were collected in Yangtze River Delta Region(YRD)from Dec.5,2016 to Jan.2,2017.The results are highlighted as follows:Secondary water-soluble ions SO42-,NO3-,NH4-composed 70.2%of the total ions in fine particles on heavy polluted days.The size distributions of SO42-,NO3-,NH4-were bimodal with maxima at 1.1-2.1 ?m and 9.0-10.0 ?m.They had similar size distributions from clear to heavy polluted days.The mass rations of NO3-/SO42-during sampling days all exceeded 1.0 suggesting the vehicle exhaust currently makes a greater contribution to aerosol pollution than stationary sources in Hefei and might be considered much more serious compared to a few years ago.Hence,controlling NO.,emissions from vehicles should be a priority in urban Hefei and other regions with serious air pollution.SOR(sulfur oxidation ratios)increased more rapidly than NOR(nitrogen oxidation ratios).The SOR and NOR showed an increasing trend while RH increases.The secondary formation of sulfate(0.43-0.65 ?m)could be favored by both high temperature and high RH,while in the 0.65-1.1 ?m and 1.1-2.1 ?m only be favored by RH,(2)A regional severe pollution weather process occurred in Beijing from Dec.24,2014 to Dec.30,2014.The average daily mass concentration of PM2.5 on polluted days was three times than that of non-polluted days.Secondary and light absorption properties of water-soluble organic carbon(WSOC)in Beijing were investigated by 12 h-averaged fine particulate matter(PM1.0)samples.The concentration of WSOC in PM2.5 on polluted days(6.8 ?g C/m3)was 4 times higher than that on non-polluted days(1.7 ?g C/m3).WSOC and SOC(Secondary Organic Carbon,SOC)had a high correlation(R=0.82).The SOC concentration on polluted days was higher than that on non-polluted days.The high correlation indicated that the source and formation mechanism of WSOC and SOC were similar,and most of the high WSOC concentration in winter in Beijing comes from secondary generation.The high correlation between WSOC and biomass combustion tracer(K+)indicates that biomass combustion is also an important source of WSOC in winter in Beijing.The average light absorption(Abs365)of WSOC at 360-370 run is adopted to measure the light absorption intensity of water-soluble brown carbon in the sample.The light absorption at 365 nm(Abs365)was approximately 3.42 Mm-1,with a range of 1.8 to 7.7 Mm-1.Abs365 is typically used as a proxy of water-soluble brown carbon,which showed a strongly correlation with WSOC(R=0.81,p<0.01).The value of Absorption Angstrom Exponent(AAE)was 3.42 during sampling days.The mass absorption efficiency(MAE)of WSOC in Beijing was 1.96 m2/g on the polluted days and 1.86 m2/g on the non-polluted days.