Characteristics Of Temporal And Spatial Distribution Of PM_2.5 And Its Chemical Composition In Suzhou

Suzhou is located in the center of the Yangtze River Delta.With rapid development of economy,air quality of Suzhou was influenced by regional complex pollution.On this condition,the concentration of particulate and the spatial distribution and temporal variation of the chemical composition need to be clear.In this study,ambient PM_2.5 samples have been collected for one year at four different sites in Suzhou,which were Nanmen,Gaoxinqu,Gongyeyuanqu and Jinting,representing urban residential district,mixing zone,industrial environment,and controlled district respectively.Data of PM_2.5 mass concentration,water-soluble inorganic ions,organic carbon and elemental carbon in different seasons were collected and analyzed.The aims of this study is to determine the temporal and spatial variation characteristics of PM_2.5 and chemical composition.Moreover,the characterization,source and potential source regions of pollution events in winter and summer were also explored in this paper.The main conclusions of this research are as follows:?1?The daily concentrations of PM_2.5 ranged from 18.32 to 215.87 ?g·m^-3.The annual average mass concentration of PM_2.5 was 69.00±28.19 ?g·m^-3,70.19±31.97 ?g·m^-3,74.08±37.67 ?g·m^-3,72.15±36.80 ?g·m^-3 in Nanmen,Gaoxinqu,Gongyeyuanqu,and Jinting respectively.There was no significant differences among these sites.The highest concentration of PM_2.5 was observed in winter.There were obvious fluctuation in winter.The lowest concentration of PM_2.5 was observed in summer.?2?The major chemical components in PM_2.5 were SO₄^2-,NO₃^-,NH₄⁺,organic carbon?OC?and elemental carbon?EC?which accounted from 50% to 80% of PM_2.5.The seasonal variations were different with from chemical components while the spatial distributions were similar.SOR?sulfur oxidation ratio?values were higher than 0.25 and NOR?nitrogen oxidation ratio?values were higher than 0.10 during the sampling period,which demonstrated that the secondary formation of SO₂ and NO₂ was significant.The average mass ratio of NO₃^-/SO₄^2-was 1.00,and mass ratio of NO₂/SO₂ was 3.15.These ratio indicates that emissions from mobile and stationary sources were both important in Suzhou.SO₄^2-and NO₃^-were neutralized by NH₄⁺.SO₄^2-,NO₃^-and NH₄⁺ were mostly in the form of NH₄NO3 and?NH₄?2SO4.?3?Seasonal variations of OC and EC were consistent with that of PM_2.5.The ratio of OC/EC ranged from 1.00 to 2.50,with the average value of 1.82.The highest concentration of secondary organic aerosol was observed in winter,and the lowest concentration of secondary organic aerosol was observed in summer.The differences of secondary organic aerosol levels between spring and autumn were negigible.Concentrations of secondary organic aerosol were significantly lower than primary organic aerosol.OC2,OC3,OC4 and EC1 occupied a bigger proportion of TC in PM_2.5.They were major carbon fraction of PM_2.5.?4?The light extinction coefficients of PM_2.5 showed no significant difference among sites.The light extinction coefficients of Jinting site was higher than urban sites in summer.The light extinction coefficients were obvious fluctuation in winter.The light extinction coefficient in winter more than 2 times compared to summer and autumn in Jinting.Ammonium sulfate and ammonium nitrate were the major light extinction components.?5?In the pollution events,the major secondary inorganic ions(SO₄^2-,NO₃^-and NH₄⁺)played an important role.Pollution events were affected by the different pathways of air masses in winter and summer.Unfavorable weather conditions?low wind speed and tempreture,high RH?aggravated the air quality in urban area of Suzhou.This study is useful to understand the characterization and sources of PM_2.5 in the urban areas of Suzhou.