Study On Variation Of Polycyclic Aromatic Hydrocarbons Pollution Characteristics In Atmosphere After Wet Deposition

Polycyclic aromatic hydrocarbons（PAHs）belongs to a category of semi-volatile organic compounds（SVOCs）.They have a wide range of sources,mainly from human activities such as industrial production,agricultural planting,etc.,as well as have certain carcinogenicity.PAHs in the atmosphere can migrate over long distances,which aggravates the degree of pollution.In recent years,they have caused extensive research all around the world.There are frequent rainfall in summer and autumn in Harbin,and also frequent snowfall in winter and spring,which presents special climatic conditions.Therefore,the study of PAHs in the atmosphere after wet deposition is worthwhile.This research aims at the analysis of time variation of the pollution characteristics of PAHs in the atmosphere in 24h after rainfall and snowfall in Harbin.The receptor model are applied to analyze the source of PAHs.The health risks of PAHs are evaluated in viewed of the higher pollution stage in winter.Finally,the parameters of the gas-particle partitioning of PAHs are discussed,and three models are used to predict the gas-particle partitioning.Collect atmospheric samples after rainfall and snowfall,after which analyze their concentration and composition characteristics,and find that the overall level of PAHs after rainfall is low,and there is no correlation between wind speed and changes in PAHs concentration.It is found that the concentration level of PAHs in the atmosphere after snowfall is higher than that after rainfall.The highest concentration of PAHs in the gas phase reaches 1292ng/m³,and it presents a good negative correlation of wind speed and the concentration change in two phases.For both rainfall and snowfall,some PAHs will have a large change in concentration over time.Different PAHs have different changing trends,while most of the remaining PAHs maintain a relatively stable concentration.In terms of composition,the composition of low-rings PAHs fluctuates greatly over time,among which the proportion of 4-rings PAHs in two phases is relatively large.The health risk assessment of PAHs during the snowfall sampling period was carried out through two ways of respiratory inhalation exposure and dermal exposure.The average cancer risk values of youth,adults and children are 1.447×10^-4,1.044×10^-4 and 9.658×10^-5.In the evening rushhour,the emission of vehicle exhaust and the combustion of coal for heating have significantly increased the risk of carcinogenesis.Through characteristic compounds diagnostic ratio method and principal component analysis method,combined with the actual situation of Harbin,it is concluded that after rainfall,coal combustion are the main sources of PAHs in Harbin;after snowfall,heating coal,straw incineration,and emission of vehicle exhaust are the main sources of PAHs.Emissions are its main source.Through the backward trajectory model to analyze the air movement path during the sampling period,it is found that the airflow after rainfall mainly comes from the northwest region,and the airflow after snowfall mainly comes from the northwest and southwest regions.For the study of the distribution of PAHs in the atmosphere of Harbin,the relationship between log K_P and log K_OA as well as the relationship between log P_L⁰ and log K_OA are first studied respectively,and the distribution of PAHs in the atmosphere 24h after snowfall is analyzed in time series.It presents that the distribution is very unstable,and it’s difficult to approach the stage of equilibrium.The PAHs in the atmosphere were predicted 24 hours after snowfall,and it was concluded that the HB model,DE model,and LMY model had better prediction effects for 4-rings PAHs;for 2-3 rings PAHs,the HB model and DE model were not very effective while the LMY model has a good predictive effect;for 5-6 rings PAHs,the HB model and the DE model are no longer applicable,and the LMY model is more suitable for describing its trend.