Characterization Of Carbonaceous Aerosols In PM₂₅ And PM₁₀ During Haze Pollution Episodes In Winter In Taiyuan,China

PM2.5 and PM10 samples were collected using TH-150C middle volume sampler at five sampling sites to study pollution characteristics of carbonaceous aerosols in Taiyuan during haze pollution episodes in winter.Organic carbon(OC)and elemental carbon(EC)were analyzed by Elementar Analysensysteme GmbH vario EL cube,and the characteristics including pollution levels,spatial distributions of TCA、OC and EC,OC/EC ratios as well as correlation parameters were investigated in detail.The correlation analysis of carbonaceous aerosols characteristics and meteorological factors was made,while using the back ward trajectory model(HYSPLIT)to simulate and analyze the haze pollution process.The results has provided extremely scientific value for controlling carbonaceous aerosols pollution effectively in Taiyuan.The pollution characteristics of carbonaceous aerosols concentrations in Taiyuan during haze pollution episodes of winter were as following:TCA,OC and EC mass concentrations of PM2.5 were(133.56±41.8)μg·m-3,(53.27±17.71)μg·m-3 and(48.33±16.07)μg·m-3 respectively.TCA,OC and EC mass concentrations of PM10 were(150.93±46.85)μg·m-3,(62.96±20.86)μg·m-3 and(50.19±15.07)μg·m-3.The concentrations of total carbon aerosol(TCA)accounted for(38.73%-54.84%)of PM2.5 and(21.87%-34.50%)of PM10.Carbonaceous aerosol was an important component of air particulate matter in Taiyuan.The concentrations of TCA,OC and EC in PM2.5 at JY site during sampling period were higher than ones at four other sites,and this trend was consistent with the ones in PM10.TCA,OC and EC concentrations in PM2.5 at YZ site were the lowest,while the ones in PM2.5 at SD site were the lowest,which indicated that the spatial distributions of TCA,OC and EC were different obviously.The average values of OC/EC ratios were all less than 2,which indicated that the primary pollution was predominant,and the secondary pollution was not serious.The correlation between OC and EC in PM2.5 was good with the R2 of 0.81,indicating the emission sources were relatively simple and the coal combustion and vehicle exhaust were influencing factors of carbonaceous aerosols.The low correlation coefficient(RM=0.69)between OC and EC in PM10 revealed emission sources of OC and EC were complicated,and the emission sources,pollution transport and meteorological factors played important roles.The carbonaceous aerosols concentrations and meteorological factors had a close relationship.The increase of carbonaceous aerosols concentrations could cause the visibility depression.The correlation coefficient(r=-0.49)between visibility and TCA in PM2.5 was better than the r of-0.38 in PM10,which was mainly because OC light scattering and the particles of different chemical compositions and sources attached to the surface of the carbonaceous aerosols to light scattering,absorption,refraction influence.The humidity that had a positive correlation with OC and EC concentrations was the leading factor affecting carbonaceous aerosols in PM2.5 and PM10 during winter in Taiyuan.The partial correlation coefficients between humidity and OC,EC in PM2.5 were both 0.60,while the partial correlation coefficients between humidity and OC,EC in PM10 were 0.45 and 0.41 respectively.The partial correlation coefficients between wind speed and OC in PM2.5 and PM10 were-0.46 and-0.34 respectively,while the partial correlation coefficient between wind speed and EC in PM2.5 and PM10 were both-0.22.The humidity had a weak negative correlation with OC and EC concentrations.The temperature and OC,EC concentrations were positively correlated.The partial correlation coefficient between temperature and OC,EC in PM2.5 were 0.44 and 0.46,while the partial correlation coefficient between temperature and OC,EC in PM10 were 0.43 and 0.31 respectively.The temperature also had an impact on the concentrations of carbonaceous aerosols,and the meteorological factors had different effects on PM2.5 and PM10.The back ward trajectory model was made to simulate and analyze the haze pollution process in Taiyuan.The analyses based on the HYSPLIT trajectory model indicated that the haze pollution was not only caused by the local emissions,but also the China’s remote northwest transmission of dust.Carbonaceous aerosols pollution should be reduced by controlling the primary emissions such as coal combustion and vehicle exhaust to improve the air quality in Taiyuan City.