Study On Physicochemical Properties Of Carbonaceous Aerosols And Single Particles In Handan City

Carbonaceous aerosols are important components of atmospheric particulate matter and have important environmental and climatic effects.It is estimated that about 7500Gg of black carbon is emitted annually worldwide.Because of its biochemical inertness,it has an important impact on the marine carbon cycle,the balance of radiative heat on the earth,soil carbon cycling,and human health.In recent years,North China has become one of the most heavily polluted areas in China and even in the world,in which Hebei Shanxi and Shandong Provinces rank the first three places in terms of smoke and dust emissions.Therefore,this study selected severely polluted plutonium in the North China Plain-Handan to study physicochemical characteristics of carbon aerosol and single particles.Handan is a typical coal-fired heavy industry and has a certain representativeness.Through the study,it was found that the concentration of PM_2.5,PM₁₀ particulate matter in the four seasons of 2016 was seriously polluted.The highest rate of PM_2.5exceeds the standard in the winter,which is 68.75%,followed by spring?62.50%?,and the lowest in summer?60.00%?.Compared with different(PM_2.5,PM₁₀,TSP)stages,it can be clearly found that fine particulates are exceeding the standard more seriously.The OC and EC in PM_2.5,PM₁₀,and TSP reached the maximum in winter,with the average OC of PM_2.5,PM₁₀ and TSP in winter being 35.55?g·m^-3 70.29?g·m^-374.59?g·m^-3.The mean values of EC were 10.41?g·m^-3 21.11?g·m^-3 25.16?g·m^-3.The mass concentration trends of OC and EC in the four seasons in 2016 presented as winter>autumn>spring>summer.The proportions of OC EC in PM_2.5,PM₁₀ and TSP also presented the rules of winter>autumn>spring>summer reflecting the effect of heating coal on OC and EC emissions in winter.Compared with major cities in the northern plains,the concentration of OC in PM_2.5 in Handan belonging to serious pollution city in the North China Plain of is slightly lower than that in Shijiazhuang and Zhengzhou,which are heavily polluted,and higher than Beijing,Tianjin,Jinan,Urumqi and other northern cities.Compared with the coastal cities in the south,the concentration of carbon aerosols in Handan is significantly higher than that in the southern cities,which is closely related to the climate and topography of Handan.Data analysis showed that the correlations of OC and EC in PM_2.5,PM₁₀ and TSP in winter?heating period?in Handan were 0.68,0.88,and 0.88,respectively.In contrast to winter,the correlation between OC and EC in spring PM_2.5 is significantly higher than that of PM₁₀ and TSP,which may be affected by the spring monsoon dust,and the correlation of coarse particulate matter is relatively low.The correlations between OC and EC in PM_2.5,PM₁₀ and TSP in summer and autumn were relatively low,indicating that OC and EC were also affected by local pollution emissions in summer and autumn and secondary generation and monsoon long-distance transmission.As a whole,the average value of OC/EC in Handan City is between 2.78 to 4.39,indicating that the pollutants mainly come from the three major sources:motor vehicles,coal combustion and biomass combustion.Winter SOC accounted for 16.33%,21.97%and 9.09%of PM_2.5,PM₁₀ and TSP,respectively,and summer accounted for the smallest SOC for4.46%,11.11%and 11.60%,respectively.Winter pollution is the most serious indicating that the gas emission of pollutants in winter is large,which is beneficial to the generation of SOC.The morphology and energy spectrum of airborne particulates during the winter typical polluted process were analyzed by transmission electron microscopy?TEM?.The main types of particulate matter observed were:soot aggregates,organic,fly ash,mineral particles,sulphate particles,metal particles.The secondary chemical reaction during the haze produces a large number of secondary particles such as nitrates,sulfates,and ammonium salts.After other reactions,the particles eventually form a nearly spherical core-shell structure.The particle dilution phenomenon is not obvious and outline is clean in non-haze day.Most of the particulate matter is dominated by internal mixing,and particularly,some fine soot fly ash and organic particles are mixed with sulfate.Occasionally,a small amount of fresh soot particles,calcium sulfate,and mineral particles are seen.The quantity-particle size distribution map shows a bimodal distribution,with the main peak being between 0.4-0.5?m,the second peak being between 0.6-0.7?m during haze day,and the single-peak distribution in the non-haze day and the peak at 0.2-0.3?m.Compared with non-haze day,the particle size is lager in haze day.Particles are mainly contributed by the near-spherical particles in the small particle size stage,and mainly contributed by minerals and soot aggregates in the large particle size stage.