Semi-volatile Organic Compounds(SOCS) In Atmosphere Under Different Weather Conditions And In Different Regions

Haze-fog pollution is one of the most prominent environmental issues in recent decade in China.Although the government have done a lot of work in air pollution control in recent years,the haze-fog pollution is still an important challenge,especially in northern China.Semivolatile organic compounds?SOCs?are important constituent of atmospheric pollutants,many SOCs has the characteristics of persistent organic pollutants,which are have attracted great attentions for many years.Many efforts have been carried out on the origin,formation and evolution of haze or fog at home and abroad,as well as the pollution,sources and long-distance transport of SOCs in the atmosphere.The atmospheric physical and chemical processes under different weather conditions and in differnet regions have very an important influence on the fate of SOCs,but there is still a lack of research in this aspect.Here daily fine particulate matter(PM_2.5)in winter atmosphere were collected in the suburb of Beijing in 2014 to analyze the concentration,composition,fate,and potential source areas of polycyclic aromatic hydrocarbons?PAHs?,brominated flame retardants?BFRs?,and organic phosphorus flame retardants?OPFRs?.In addition,Beijing and Guangzhou are the typical cities in the northern and southern China,which have been suffering from the harm of air pollution for a long time.Therefore,atmospheric samples?including particle and gas phase?in 2014 winter and in 2015summer were also collected,to compare the pollution characteristics,gas-particle partitioning and possible sources of PAHs.In addition,the health risks of human exposure to PAHs were assessed by ordinary residents due to its threat to human.The concentrations of total PAHs,OPFRs,and BFRs in PM_2.5 in Beijing winter were in the ranges of 1.0-167 ng/m³,257-8358 pg/m³,and 17.0-301 pg/m³,with a median of 42.8 ng/m³,1347 pg/m³ and 46.7 pg/m³,respectively.The concentration of PAHs in heating period was obviously higher than that in non-heating period,which was dependent on regional coal combustion for residential heating.Nevertheless,the changed OPFR compositions in the colder period were probably related to enhance indoor emissions of some OPFRs due to heating,BFRs are mainly from industrial activities,and had no relations with residential heating.The mean concentrations of SOCs in haze and fog days were generally 2-10 times higher than those in clear days,indicating the increased contamination of these chemicals during haze or fog events.Most SOCs during fog days were all higher than those during haze days,due to the increased sorption to PM_2.5 via gas-particle partitioning with high relative huminity.However,the lack of RH dependence for PAHs could be due to the dominant combustion sources?e.g.,increased during haze episodes?.Concentrations of low brominated BFRs and OPFRs had been significantly influenced by the fractions in PM_2.5,which are easily distributed between gas-particle phases.The results also indicated that BFRs with lower octanol-air partition coefficients tend to be accumulated onto PM_2.5 in haze and fog episodes and/or to be removed from PM_2.5 in clear episodes,in which gas-particle partitioning may be the main mechanism.The differences between fog/haze and clear days for PAHs and OPFRs concentrations,however,were significantly associated with their overall persistence in the environment and atmospheric half-lives,respectively,suggesting pollutants that are more recalcitrant to degradation are prone to accumulate in haze and fog days.Source identification of SOCs in the atmosphere was conducted by principal component anapyses showed that SOCs at this site are related to the source of diffusive pollution,industrial source and indoor heating.The potential source contribution function?PSCF?model showed that the southern and eastern cities are the major source regions of the SOCs.PAH concentrations in Beijing atmosphere?8.34-524 ng/m³?were much higher than those in Guangzhou?11.8-64.0 ng/m³?.Signigicant differences in PAH concentrations and compositions were observed between summer and winter in Beijing,which were related to the emission sources and the gas-particle partitioning of PAHs.However,the insignificant difference in Guangzhou indicates the similarity of the source.Junge-Pankow adsorption model based on cold vapor pressure?P_L⁰?and octanol-gas partitioning coefficient(K_OA)absorption model were used to compare the gas-particle partition of PAHs in the two site.Increasing emission sources in Beijing winter made the gas-particle partitioning of PAHs was closer to equilibration.PAHs in TSPs were in good correlation with the OC and EC in winter in both regions,suggesting the similar sources?the primary emissions?.OC and EC had significant influence on 3-4 ring PAHs?products of straw and coal combustion,respectively?in Beijing winter atmosphere.Molecular diagnostic ratios suggested that the PAHs in Beijing was more affected by biomass and coal combustion,but liquid fuel combustion in Guangzhou.The carcinogenic equivalent concentrations of PAHs in the atmosphere were higher than the limit of BaP concentration in atmosphere,and the loss of life expectancy for ordinary residents in the Beijing air is four times greater than that in Guangzhou.