Characteristics Evolution And Optical Properties In High Time-Resolved Chemical Compositions Of Atmospheric Submicron Aerosols In Shanghai

As a characteristic pollutant of urban compound pollution,submicron particulate matter has significantly impacted on human health and climate change.In this study,four intensive campaigns were conducted to investigate the seasonal characteristics of submicron particles in Shanghai.The time series,chemical composition and size distributions of different species are obtained based on high-resolution time-of-flight aerosol-mass-spectrometer measurement in four seasons.The detailed seasonal variations and diurnal patterns of chemical compositions were investigated.Then the evolution process of major species and influencing factors in different seasons were revealed.In addition,the optical properties in high time-resolved chemical compositions of submicron particles through combining with optical measurements.The main conclusions are as follows:（1）The average mass concentrations of submicron particulate matter during spring,summer,autumn and winter observations in Shanghai are 23.9±20.7μg/m³,28.5±17.6μg/m³,22.0±17.2μg/m³ and 31.9±22.7μg/m³,respectively.The major chemical components in submicron particulate matter showed obvious seasonal and daily variations.The increase of submicron particulate matter is mainly due to the contribution of nitrate in spring,autumn and winter,while the photochemical reaction promotes the rapid growth of sulfate in summer.（2）Detailed source apportionment of organic aerosol showed that the fraction of more oxidized oxygenated organic aerosol in organic aerosol in spring was much lower than primary organic aerosol.In summer and autumn,oxygenated organic aerosol was higher than primary organic aerosol.Oxygenated organic aerosol dominated organic aerosol in summer（69%）.More oxidized oxygenated organic aerosol account for 28%in autumn,suggesting that organic aerosol was aging.（3）The ambient secondary components aging processes and influencing mechanism were studied.It was found that the sulfate concentration and sulfur conversion rate increased with the increase of relative humidity in spring and winter,indicating that the formation of sulfate may be dominated by liquid phase.The liquid phase oxidation and the strong photochemical reaction concentration have a significant contribution to the formation of more oxidized oxygenated organic aerosol and less oxidized oxygenated organic aerosol in the spring,summer and winter observations,respectively.Unlike the other three seasons,the photochemical reaction process dominated the formation of more oxidized oxygenated organic aerosol in autumn.（4）The results of extinction contribution to particulate components indicate that the mass scattering efficiency of major chemical species（Organic,NH₄NO₃ and（NH₄）₂SO₄）were 5.3±0.5 m²/g,4.3±1.0 m²/g and4.2±0.6 m²/g,respectively in this study.The MSEs for three scattering species enhanced rapidly with the increase of mass concentrations when mass concentration was low but it tended to be constant after the mass concentration reached a certain value.The scattering contribution estimation formula were further investigated.The result showed that the formula fitted in this study can well predict scattering coefficient of PM₁ based on chemical composition data in typical urban areas in China.