The Spatio-temporal Distribution Of Atmospheric Gaseous PAHs Concentration And Numerical Simulation In Nanjing

With the rapid urbanization and industrialization in China,large numbers of persistent organic pollutants(POPs)were emitted into atmosphere by human activities(for example,industrial production and residential coal consumption),and widely distributed all over the world through long-range atmospheric transport and transfer across multimedia.As a kind of Persistent Toxic Substances(PTS),polycyclic aromatic hydrocarbons(PAHs)have a large amount of emission,and was ubiquitous in the environment media.PAHs have threatened the environment and human health seriously.Concerns were raised regarding the contamination and fate of PAHs.Recently,studies mainly focused on the transport,transfer and the fate of PAHs at regional or national scale,and the atmospheric PAHs analysis through laying small amount of sampling sites in urban areas.However,there is still a long way to go with PAHs studies in China,even in the world.The spatio-temporal distribution of PAHs through laying intensive sampling sites in urban area and the atmospheric PAHs numerical simulation are relatively insufficient.Moreover,lots of studies concentrated on the contamination of particle phase PAHs.There is not much researches on the gaseous PAHs analysis.Researches on the urban gaseous PAHs distribution and simulation are vital to human health and urban sustainability.Based on the present status and deficiency of PAHs studies in China,we monitored the atmospheric gaseous PAHs through laying intensive sampling sites using the PUFPAS technology.Totally 28 air sampling sites were selected in urban area of Nanjng during January-October,2015.The collected PUF were extracted by Soxhlet,concentrated by rotary vacuum and cleaned using silica gel column,lastly PAHs were determined by GC-MS.Firstly,the spatial distribution and temporal variation of gaseous PAHs were analyzed.Four emissions sources were identified using the PMF model,and the temporal change of sources was also discussed.Then we developed a PAHs emission inventory with 1km×1km solution,which also considered the seasonal change of emission.Moreover,we employed a two dimensional advection-diffusion equation,which added the emission source,depositon,degredation,transfer and transform processes,and used this equation to simulate the PAHs concentration.The sensitivity of gaseous PAHs to meteorological factors were also analyzed based on setting different scenarios.Lastly,the model accuracy were vertified based on the measured data,and we determined uncertainty using Monte Carlo method.The main results in this paper are as follows:The concentration of gaseous PAHs had obvious spatial-temporal variation.Western PAHs>eastern PAHs,and PAHs in winter>autumn>spring and summer.We monitored the gaseous PAHs in Nanjing.The main concentration of gaseous PAHs was 31.6ng/m3 in Nanjing during January-October,2015.The 3-4 rings PAHs occupied 84%of the total PAHs.The western gaseous PAHs was higher(36.1 ng/m3)than the eastern gaseous PAHs(27.3 ng/m3),which mainly influenced by emission sources and meteorological factors.The obvious seasonal variation of gaseous PAHs was found in urban area of Nanjing.PAHs was highest in winter,and lowest in spring and summer.The ratio gaseous PAHs between in winter and in summer was 1.6,lower than the 2 in the North Chinese Plain.It mainly because the energy structure had a difference between these two regions.The emissions of residential coal combustion and biomass combustion relatively small in Nanjing.About the urban-suburban gradient,although the average PAHs in urban core area were higher than in suburban,it cannot found an obviously gradient decrease because lots of industrial parks was settled in Jiangning that have a high urbanization and industrization.The gaseous PAHs emission sources were mainly related with industrial activities.Four main emission sources were identified using the PMF model:coke production,coal and biomass combustion,oil and petroleum refinery,transport oil combustion,and the average contributions of four sources were 31%,25%,25%,19%,respectively.The coal combustion was mainly originated the industrial coal.The gaseous PAHs emission sources was mainly related with industrial activities.Coal and biomass combustion had a seasonal change in our study area.Maybe it mainly because of the monthly variation of staw burning.We also found that the coal and biomass combustion in winter had some contribution to the gaseous PAHs.Transportation had a small contribution to gaseous PAHs(19%)in Nanjing.PAHs emission inventory with 1km×1km solution was established at urban scale.Through establishing 1km ×1km PAHs emission inventory,PAHs emissions were 126.1t,including 7.5%carcinogenic PAHs(8.8t)yearly.The PAHs emission density was 19.1 kg/km2.PAHs emissions in Nanjing were lower than in Shanghai and Taiyuan,but significantly higher than the Suzhou,Wuxi and other citys of Yangtze River Delta.The areas where have a high emission were mainly concentrated on the Qixia,Jiangning and Yuhua which mainly belong to the suburban region.Petroleum refinery(34%),coal and biomass combustion(24%)were the dominated emission sources.Compared with the PAHs emissions in 2013,the PAHs emissions only decreased 0.5%in 2014.The contribution rate of transportation,and of coal and biomass combustion were relatively similar to the results identified by PMF.But contributions of the other two main sources(coke production,oil and petroleum refinery)had some differents using PMF and emission inventory,which might caused by the comprehensive influence of the different properties of gaseous PAHs and total PAHs,oil volatility and the statistical data uncertainty of coak production.The spatio-temporal variation model of atmospheric PAHs was developed based on the advenction-diffusion equation coupling with emission inventory and atmospheric transportation process.Multimedia model had a widespread use about the PAHs studies,but it also have some limits in the detailed spatial-temporal simulation.Previous studies mainly concentrated on the simulation at a national or regional scale.We simulated the spatialtemporal distribution of PAHs in Nanjing.Two gaseous PAHs(ACE and FLO)were selected to simulate using our model.The average stimulated PAHs in weastern region were higher than in eastern region,which is similar to our spatial distribution of measured PAHs.Because of the effect of main wind in Nanjing,ACE and FLO obviously transferred from east to west in our sampling periods.The seasonal variation of ACE and FLO was also similar to the seasonal change of measured data.The wind velocity was the most important meteorological parameter through the scenario analysis.Based on the sensitivity analysis,emission inventory and wind velocity were identified two key parameters.Improving their accuracy can significantly improve the model precision.We verified the model accuracy based on the measured data.The correlation between stimulated and measured data of ACE and FLO were 0.57 and 0.58,respectively(P<0.01).Lastly we clarified the model uncertainty based on the Monte Carlo method,and found the ACE concentration follow the log-normal distribution.