Gas/Particle Partitioning Mechanisms And Prediction Of Partitioning Coefficients Of Polycyclic Aromatic Hydrocarbons In Atmosphere

Polycyclic aromatic hydrocarbons（PAHs）are originated from the incomplete combustion of fossil fuels and biomass by natural processes and anthropogenic activities.PAHs had been received widespread attention due to their serious harm to the ecological environment and human health.As a typical atmospheric semi-volatile organic compounds（SVOCs）,PAHs can exist both in gas phase and particle phase in atmosphere.The processes of dry/wet deposition and long-range atmospheric transport of PAHs can be affected by the distribution between the gas phase and particle phase.Furthermore,the harmful risk to human health is also different for different phases of PAHs.Therefore,the study of the gas/particle（G/P）partitioning mechanism and the prediction of the G/P partitioning coefficient（K_P）of PAHs are important scientific issues.In the present study,based on the monitoring data of G/P partitioning of PAHs from different dimensions,the variation characteristics and influencing factors of the G/P partitioning descriptors and mechanism of PAHs were discussed,and the empirical equations of K_P for PAHs were established for the better predication of K_P.The results of the present study provided a theoretical basis for the study of the environmental behavior and the pollution control of PAHs in atmosphere.In order to study the variation characteristics and the influencing factors of G/P partitioning descriptors of PAHs,three different dimensions monitoring data with gas phase and particle phase of 15 PAHs（from daytime and nighttime,from different years,and from 11 cities across China）were used for the study on the diurnal variation,seasonal variation,interannual variation,and spatial variation of the particulate phase fraction（ф_P）and the G/P partitioning coefficient（K_P）.Furthermore,the correlations with two influencing factors（total suspended particles（TSP）and ambient temperature）of the two G/P partitioning descriptors were also studied.The results indicated that the diurnal variation with lower values of G/P partitioning descriptors in the daytime than those in the nighttime were found for most PAHs.However,an opposite diurnal variation was observed for the three 3-rings PAHs（Acy,Ace,and Flu）.Significant seasonal variations were observed for the two G/P partitioning descriptors of 15 PAHs.A significant increasing temporal trend with the values of G/P partitioning descriptors was observed for the eight 3-rings to 5-rings PAHs（Phe,Ant,Fluo,Pyr,Ba A,Chr,Bb F,and Bk F）.The values of G/P partitioning descriptors for the 15 PAHs were different among different cities.The correlation analysis was conducted betweenф_P and log K_P with temperature,which indicated that temperature was the primary influencing factor on the variation of the G/P partitioning descriptors.The G/P partitioning mechanism of PAHs was comprehensively studied in three different perspectives（the analysis of monitoring data,the assessment of predicting models,and the study of the G/P partitioning theories）.The linear relationships between log K_P and the octanol-air partitioning coefficient(log K_OA)indicated that the G/P partitioning mechanisms of the three 3-rings PAHs were different between daytime and nighttime;the G/P partitioning mechanisms of the eight 3-rings to 5-rings PAHs were different among different years,and the G/P partitioning mechanisms of the 15 PAHs were different among different cities.The results indicated that the temperature and pollution sources were the primary influencing factors on the difference of the G/P partitioning mechanisms of PAHs.The root mean square error and the prediction precision were used to assess the performance of the three G/P partitioning coefficients prediction models.The bad performance on the low molecular weight and high molecular weight PAHs was observed for all the three models.The results indicated that other influencing factors were not considered in the three models for the prediction of the G/P partitioning of PAHs.The theoretical equation for the G/P partitioning coefficients of PAHs was established,and the influence of parameters in the theoretical equation were discussed.The results indicated that the particulate fraction of source emission and the degradation rate of PAHs in gas phase were the key parameters for the G/P partitioning of PAHs.The results further improve the theory of G/P partitioning of PAHs in the atmosphere.In order to achieve the accurate prediction of the G/P partitioning coefficients of PAHs,the relationships between slopes and intercepts from the linear relationships between log K_P and log K_OA with temperature were analyzed.Then the empirical prediction equation with temperature as the independent variable was established for the prediction of the G/P partitioning coefficients of PAHs.The results indicated that that the major difference between the predications of the empirical equation and the current prediction models were observed only for the low molecular weight（3-rings PAHs）and the high molecular weight PAHs（5-rings and 6-rings PAHs）.Based on the monitoring data from Harbin and literature,the performance of the empirical equation was validated using the evaluation methods of the root mean square error and the prediction precision.The results indicated that the performance of the empirical equation was good,whicn was more suitable for the low molecular weight PAHs and the high molecular weight PAHs.The effectively improves the accuracy of the prediction of the G/P partitioning coefficient of PAHs.