Contribution Of Sea Salt Aerosol To Atmospheric Particulate Matter In Tianjin

Atmospheric particulate matter（PM）is generally defined as a mixture of solid and/or liquid particles that remains individually dispersed in the air.Various atmospheric particles are evenly dispersed in the air to form a relatively stable and massive suspension system,namely an aerosol system.Therefore,PM is sometimes called atmospheric aerosol.PM is suspended in the atmospheric environment on which human beings depend,which causes serious environmental pollution problems,including global climate change,haze,and ozone layer destruction.Sea salt aerosol（SSA）,dust,and volcanic ash are the three primary natural sources of atmospheric aerosol.SSA has received widespread attention because of its large generation area,wide influence range,long duration,and relatively stable seasonality.In this work,the samples were collected in the coastal city of Tianjin from October 2020 to December 2021.The sampling sites were distributed uniformly from the seaside to the inland.The samples of PM include PM_2.5,PM₁₀,and TSP.The concentration of atmospheric particulate matter,cations,anions,and heavy metals in PM were determined.The contribution of SSA to PM and component source of PM are investigated by correlation analysis and PMF analysis.The backward trajectory clustering is used to inquire into the potential source area of PM in Tianjin.（1）The PM concentrations in Tianjin generally present the characteristics of winter>autumn>spring.The concentration of heavy metals and water-soluble ions in PM is both TSP>PM₁₀>PM_2.5.The larger the particle size,the higher the concentration of heavy metal elements and water-soluble ions.The concentrations of total heavy metals are 9.43～70.20μg/m~3,with an average concentration of 24.42μg/m~3,accounting for 19.7%of PM.The concentrations of total water-soluble ions concentrations are 16.17～137.6μg/m~3,with an average concentration of52.11μg/m~3,accounting for 38.0%of PM,which is the main component of PM.（2）The calculations of the concentration,proportion,and components of SSA in PM indicate that the contribution of SSA to the concentration of PM is spring>autumn>winter.The contributions of SSA to the mass of particulate matter and the total ion concentration decrease with the increase of distance from the sea.Namely,the farther away from the sea,the less PM is affected by the sea.For atmospheric particles with different particle sizes,the proportion of sea salt aerosols and the proportion of sea salt components in aerosols in PM_2.5 and PM₁₀ are higher than TSP,which also confirms that SSA is mainly concentrated in 1～10μm section.（3）Source apportionment of PM was fulfilled via correlation analysis and PMF source analysis.The results show that the sources of PM in Tianjin are mainly included coal combustion,fuel oil,secondary particles,mixed source,soil dust,and sea salt source.However,the sea salt is only observed at S1（1.51km away from the sea）and S2（10.08km away from the sea）.The contributions of sea salt sources are 9.8%and 1.6%in there,respectively.There is no obvious sea salt in PM at S3～S7 sampling sites.That illuminates that the contribution of sea salt to PM decreases with the increase of distance from the coastline.（4）The pollutants in spring,autumn,and winter are mainly affected by the northwest airflow that is concluded by the backward trajectory clustering of airflow and the analysis of pollutant concentration.In spring,pollutants are also affected by the northern airflow which passes through the Bohai Bay and strengthens the impact of SSA on atmospheric particles.The path with the highest pollution level in spring and winter comes from Russia,passing through Mongolia,Inner Mongolia,Hebei,and Beijing to Tianjin.The path with the highest pollution level in autumn comes from Inner Mongolia,passing through Hebei and Beijing to Tianjin.From the perspective of spatial distribution,with the increase of distance from the sea,the contribution of the northern airflow（passing through the Bohai Bay）to its airflow trajectory and the carried pollutants(PM_2.5 and PM₁₀)are gradually decreasing,which are S1（16.67%,19μg/m~3,43.25μg/m~3）,S2（16.66%,19μg/m~3,43.25μg/m~3）,S3（15.00%,17μg/m~3,44.83μg/m~3）,S4（14.58%,15μg/m~3,42.83μg/m~3）,S5（10.83%,14μg/m~3,40.53μg/m~3）,S6（10.23%,12.47μg/m~3,18.26μg/m~3）.That is,the farther away from the sea,the smaller the impact of sea salt aerosol on it.