| Carbon fractions are major components in fine particulate matters (PM2.5), and has adverse effects on environment, visibility, climate and human health. However, understandings about carbon fractions in atmospheric particles are still inadequate at present. Due to the lack of systematic observation data, majority of existing research is fragment and lacking of representative. This study basing on the observation data of fine particles and its’components which were sampled at multi-sites in Nanjing in recent five years, systematically studied the characteristics of seasonal and spatial variations of carbon fractions, as well as correlations between carbon fractions and other components, and analyzed the influence of different pollution process on carbon fractions. In this study, primary discussions of major sources of carbon fractions and control countermeasures were also proposed.The results indicated that, compared to 2011 and 2012, concentrations of PM2.5, Organic Carbon (OC) and Elemental Carbon (EC) showed obvious drop tendency in recent three years. The annual contribution of Total Carbon (TC) to PM2.5 reached 22%, suggesting that carbon fractions are still major components of PM2.5.Differences on annual concentrations of OC and EC among six sites are minor, implying that spatial distribution of concentrations of carbon fractions were well-proportioned. All annual ratios of OC/EC in six sites were greater than 2.0, indicating the significant influence of secondary organic aerosol (SOA) on carbon fractions in Nanjing region. The concentrations of OC, EC, Primary Organic Carbon (POC), and Secondary Organic Carbon (SOC) showed similar seasonal fluctuation, which were higher in winter and autumn while lower in summer and spring, and average concentrations of carbon fractions in winter were almost twice of the concentrations in summer, indicating carbon aerosol pollution was more severe in winter than other three seasons.In spring, significant correlations existed among OC, EC, Nss-K+ and NO2, implying that biomass burning and motor vehicle emission made a certain contribution to concentrations of carbon fractions. Both OC and EC showed well correlations with SO42-、NH4+ and SO2 in summer, indicating that industrial coal combustion was one of the dominant sources of carbon fractions in summer. In autumn, significant correlations among OC, EC, SO42-、NO2、SO2 indicated the contributions of vehicle emission and coal combustion. At the same time, SOC、NO2 and SO2 showed remarkable correlations in autumn, implying secondary transformation of pollutant was an origin of carbon fractions as well. In winter, besides O3, carbon fractions, secondary inorganic ions and gaseous pollutant all well correlated with each other, and correlations were higher than in other three seasons, implying each pollutant may have common sources in winter, such as coal combustion, vehicle emission and secondary transformation.From clean weather to heavily polluted, the growth of EC and POC concentrations were the most notable (306.1% and 299.5%), while the growth of SOC concentration was less notable than that of EC and POC, which could imply that the primary emission and accumulation of pollutants made greater contributions to carbon fractions than secondary transformation. In addition, there was weak correlation between OC and EC in heavily polluted weather, implying the pollution sources of carbon fractions may change a lot in heavy polluted weather.Temporary emission reduction and pollution control measurements were carried out during the Asian Youth Games and Youth Olympic Games in Nanjing, and accounted for significant reductions on concentrations of PM2.5, carbon fractions and gaseous pollutant, which implying that high-intensitive pollution control countermeasures decreased contributions of industrial coal combustion, vehicle emission and secondary transformation to carbon fractions.This study made use of carbon profiles and ratios between carbon fractions and other components of particle matters to identify the pollution sources of carbon fractions. Results showed that secondary transformation made more significant contributions to carbon fractions in winter than in other three seasons. In summer, contributions of secondary transformation were less remarkable than industrial coal combustion and vehicle emission. Carbon fractions suffered from the impact of biomass burning in spring, and road dust was also an emission source of carbon fractions. The contributions of secondary transformation may also be significant in autumn. |
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