A Study On The Indicative Significance Of PAHs In Snow From Two Pollution Events In Harbin City For Atmospheric Pollution

In recent years,with the rapid development of society,urbanization,and industrialization,the amount of pollutants discharged into the natural environment by human activities has been increasing,posing a considerable threat to the natural ecological environment and human health.Polycyclic aromatic hydrocarbons（PAHs）are toxic pollutants that exist widely in the natural environment.PAHs pollutants mainly come from pollution generated by human life and many industrial activities.Due to the extremely serious"three carcinogenic,teratogenic,and mutagenic effects"of polycyclic aromatic hydrocarbons,they have received more attention from people from all aspects of society.Harbin,as an important city in the old industrial base of Northeast China,has had a significant impact on atmospheric quality through years of industrial development and urban construction.At the same time,atmospheric pollutants not only come from local pollution sources,but also are affected by the cross regional transport of pollutants in neighboring areas.The issue of atmospheric pollution and pollutant transport routes has received widespread attention from relevant scholars.Urban areas in Northeast China often face serious air pollution problems in winter,especially the impact of particulate pollutants,which has led to an increase in human incidence rate and mortality.These particulate PAHs are toxic pollutants that exist widely in the natural environment.PAHs pollutants mainly come from pollution generated by human life and many industrial activities.Due to their extremely serious"three carcinogenic effects"of carcinogenesis,teratogenicity,and mutagenicity,PAHs have received more attention from various sectors of society.Harbin,as an important city in the old industrial base of Northeast China,has had a significant impact on atmospheric quality through years of industrial development and urban construction.At the same time,atmospheric pollutants not only come from local pollution sources,but also are affected by the cross regional transport of pollutants in neighboring areas.The issue of atmospheric pollution and pollutant transport routes has received widespread attention from relevant scholars.Therefore,it is of great significance to study the characteristics of air pollution in Northeast China and its relationship with increased anthropogenic heat source emissions.Snow is considered one of the most effective wet removal processes for atmospheric pollutants,and its chemical composition provides important information about air quality and pollution sources.This study takes Harbin,one of the provincial capitals in Northeast China,as an example to analyze the different PAHs,air quality indicators,meteorological factors,and six major atmospheric pollutants(PM_2.5,PM₁₀,CO,NO₂,SO₂,and O₃)under two pollution events in December 2019,and studies the air quality index and air pollutants during the two typical pollution periods in Harbin in winter 2019,And PAHs in snow after each pollution to explore similar environmental behavior.This study determined the spatial distribution of PAHs concentrations in snow after two different air pollution events;Spatially identify the sources of PAHs and compare the differences in PAHs levels and sources between two snowfalls;evaluate the relationship between PAHs and air pollutants and meteorological factors,investigate transmission routes and potential pollution source areas;discuss the impact of air pollution and human activities on PAH pollution,The results showed that:（1）In December 2019,the daily average value of the air quality index in Harbin was between 29 and 294,with 42%of the days being lightly,moderately,and heavily polluted.The high pollution rate indicates that the air pollution in major cities in Northeast China is serious.During the study period,PM_2.5was the most common major pollutant.In addition,there was a highly positive correlation between PM2.5 and AQI（R=0.999,P<0.01）,and more attention should be paid to atmospheric fine particles.The air quality from December 9-14（pollution event I）and December 25-30（pollution situation II）belonged to mild to moderate pollution and moderate to severe pollution,respectively.After two snowfalls,AQI significantly decreased,indicating a high removal rate of atmospheric pollutants by snow.It is worth noting that the heavier the pollution,the wider the range of AQI changes,and the better the snow removal effect.The characteristic radar images of the most polluted days during the two pollution periods indicate that the main type of atmospheric pollution is secondary particulate matter pollution,as PM_2.5has exceeded the upper limit of the standard.This pollution event was caused by secondary particulate matter generated by fine particulate matter in the atmosphere,which adsorbed major pollutants from human and biological emissions and promoted the conversion of gas to particulate matter under adverse weather conditions.（2）Considering that snowfall can effectively remove PAHs from the atmosphere,the concentration of PAHs in snowfall can be used as an indicator of atmospheric pollution levels.The correlation analysis results during pollution events I and II show that the correlation between PAHs and air pollutants in snowfall identifies industrial and household coal burning and vehicle emissions.The most significant positive correlations between air pollutants and PAHs are PM_2.5and 4-ring PAHs,indicating that they may have common environmental behaviors.This indicates that PAHs in snowfall can be used as an indicator of atmospheric pollution levels,and PAHs are more easily adsorbed onto atmospheric particulates.The results show that particulate matter and PAHs in the air are jointly emitted and transported by fine atmospheric particles emitted from coal burning and vehicles.SO₂,NO₂,CO,and 3-6 ring PAHs are commonly considered to be the main pollutants produced by coal combustion,biomass combustion,and fossil fuel combustion.Based on the PM_2.5/PM₁₀ratio,PM_2.5is the main air pollutant in both events,which is attributed to the secondary particulate matter converted from the gas to particles process.Low temperature and high humidity meteorological conditions may lead to secondary generation of PM_2.5from PAHs,SO₂,NO₂,and CO.（3）Using 72 hour backward trajectory clustering,the main source directions and transport paths of air masses during the phase I and II pollution processes in Harbin were identified.In addition,WPSCF and WCWT based on backward trajectory are used to determine possible source areas and their contributions to air pollutants,and to compare the impact of pollution levels on the distribution characteristics of source areas.The sources of PAHs in the snowfall in Harbin,the capital city of the northeastern province,are mainly from the combustion of coal and wood,which is also consistent with the fact that Harbin enters the heating period in winter.At the same time,it is also dominated by fossil fuel combustion sources,which may be caused by factors such as the complex traffic conditions in the main urban area of Harbin City and the large amount of exhaust emissions from automobiles.These characteristics reflect that the long-distance transportation of coal and biomass combustion comes from surrounding areas,while vehicle exhaust mainly comes from local emissions.High WPSCF and WCWT values were found in the second pollution,and air pollutants were transported from southern Russia,northeastern Inner Mongolia,northern Liaoning,Jilin,and southwestern Heilongjiang provinces.Backward trajectory and potential pollution source contribution analysis indicate that in addition to the impact of local pollution source emissions,regional transportation may make greater contributions when more serious pollution events occur in Harbin.