Study On The Physical Properties Of Aerosols In Hefei Area

In recent years,aerosols have attracted the attention of many scholars due to their important effects on climate change and public health.The rapid economic,industrial development and urbanization process have caused many serious environmental problems in Chinese cities.Although the Chinese government has implemented various emission reduction measures,large-scale and intermittent air pollution in cities in the Yangtze River Delta is still a problem.The size distribution,sources and sinks of atmospheric aerosols are key factors for understanding and managing their impact on health,visibility and climate.Information on the number concentration and particle size distribution of aerosols is of great significance for understanding the environmental and health effects of aerosols.New particle formation(NPF)is an important source of secondary aerosols in the atmospheric environment.Its formation mechanism and its impact on air quality are a topic of increasing concern in atmospheric science.In addition,most of the aerosols released by human activities are confined to the atmospheric boundary layer.In addition,different meteorological conditions may also cause frequent changes in the regional transport sources of aerosols,which can be identified from the vertical distribution of aerosols in different atmospheres.,Evaluating the vertical distribution of aerosols in the atmosphere is of great significance for understanding its sources and sinks,as well as the possible source regions of aerosols of different heights.Evaluating the vertical distribution of aerosols in the atmosphere is very important for understanding the environmental behavior of aerosols and the source regions of aerosols of different heights.In this study,aerosols in the Hefei area were used as the research object.The FMPS was used to observe the aerosol particle size distribution in different seasons.The annual aerosol vertical distribution data,combined with the black carbon meter and turbidity meter to observe the changes in the optical properties of winter aerosols,explored the seasonal variation of aerosol number concentration,the formation conditions of new particle generation events and their impact on air quality,The seasonal and diurnal variations of the vertical distribution of sol,the dependence of optical properties on meteorological factors,etc.The main conclusions obtained are as follows:(1)In this study,the particle number size distributions,and the frequency of NPF events over Hefei were investigated from November 2018 to February 2019.The proportions of the nucleation mode,Aitken mode,and accumulation mode were 24.59%,53.10%,and 22.30%,respectively,which indicates the presence of abundant ultrafine particles in Hefei.Forty-six NPF events occurred during the observation days,accounting for 41.82%of the entire observation period.Moreover,the favorable meteorological conditions,potential precursor gases,and PM_2.5 range of the NPF events were analyzed.Compared to non-NPF days,the NPF events preferentially occurred on days with lower relative humidity,higher wind speeds,and higher temperatures.When the PM_2.5 was 15-20,70-80,and 105-115?g�m^-3,the frequency of the NPF events was higher.Nucleation mode particles were positively related to atmospheric oxidation indicated by ozone when PM_2.5ranged from 15 to 20?g�m^-3,and related to gaseous precursors like SO₂ and NO₂ when PM_2.5was located at 70-80 and 105-115?g�m^-3.On pollution days,NPF events did not directly contribute to the increase in the PM_2.5in the daytime,however,NPF events would occur during the night and the growth of particulate matter contributes to the nighttime PM_2.5 contents.This could lead to pollution that lasted into the next day.These findings are significant to the improvement of our understanding of the effects of aerosols on air quality.(2)The particle number size distributions of aerosols(5.6-560 nm)were measured using FMPS from 1 to 11 May 2019.The clean atmosphere was one of the basic conditions for the occurrence of this continuous new particle generation event.It started between 9:00 a.m.and12:00 a.m.,and it mainly ended after 20:00.The GR and CS values in Hefei were 2.98nm�h^-1and 3.0�10^-2 s^-1,respectively.Back trajectory clustering analysis revealed that the mass concentration of the air masses from the southeastern part of Henan Province and the southern part of Anhui Province surrounding the study area was relatively high.In addition to local pollution,the long-distance transportation of pollutants in the Yangtze River Delta area contributes significantly to the accumulation of modal particles in Hefei.In addition,the health risks of PM_2.5 deserve the attention of relevant departments.In this case,there were835 premature deaths related to PM_2.5.The population affected by PM_2.5 accounts for 1.08%of the total population of Hefei.(3)In this study,the vertical aerosol distribution in Hefei was analyzed continuously for one year(from March 2018 to February 2019)using MAX-DOAS.The aerosol extinction coefficient near the ground is the highest in winter(0.94 km^-1),followed by autumn and spring,and the lowest in summer.Local pollution caused the accumulation of aerosols near the surface.The rate of decrease of the aerosol extinction coefficient was higher in autumn and winter than in spring and summer.The diurnal variations of aerosol extinction coefficient in the different seasons were affected by the planetary boundary layer height,and we observed notable high-altitude transport of aerosols in autumn.We assessed the vertical distribution of the aerosol extinction coefficient under different pollution concentrations and identified peak values mainly below a height of 0.5 km.With increasing height,the extinction coefficient decreased linearly and slowly under low PM_2.5 concentrations,whereas decreased more rapidly under high PM_2.5 concentrations.Clustering analysis,the PSCF,and the CWT model inferred different seasonal characteristics in the potential source areas of aerosols at different heights.In addition to local pollution sources,Jiangsu Province was found to be the main source of pollution in Hefei at a height of 0.4 km,whereas Hubei Province was the main source of pollution at a height of 2 km.(4)A field study was carried out using aethelometer and nephelometer from 5 November to 10 December 2019 in Hefei.Based on the meteorological data,diurnal variation and wind dependence of the optical properties of aerosols were analyzed.The average PM_2.5,aerosol scattering coefficient(?_sp),absorption coefficient(?_ap)in autumn in Hefei were 43�25?g�m-3,238.70�161.52 Mm^-1,and 32.04�17.01 Mm^-1,respectively,and the trend of time variation of?_sp and?_ap was consistent with PM_2.5.PM_2.5,?_sp,and?_ap have significant double-peak daily variation characteristics,peaking at 8:00 and 20:00,which was mainly related to traffic emissions and meteorological conditions.Under weather conditions where temperature,relative humidity and wind speed are all relative,pollutants are more likely to accumulate.But the higher wind speed is also easy to transport pollutants around.?_apand?_spare mainly affected by the pollution air mass in the northwest wind direction.Based on the HYSPLIT backward trajectory model,the spatial characteristics of different transport pathways were analyzed by cluster analysis,and the PSCF and CWT method were used to investigate the potential source area distribution of Hefei.Air pollution mainly comes from the northwest of Hefei.PSCF larger value was mainly distributed in the northwest and southwest of Hefei.The northeastern area of Henan Province,the southwestern area of Shandong Province,and the northern area of Anhui Province are areas with high CWT values.In particular,Jining city in Shandong Province and Shangqiu city in Henan Province are the potential sources of air quality in Hefei.