Seasonal Variation And Source Of Atmospheric Carbonaceous Particles In Lushan Forest Park

The rapid economic development in our country has brought about outstanding environmental problems,such as the pollution of particulate matter(PM_2.5),which has a series of impacts on human health,and has received widespread attentions.As one of the important components of PM_2.5,carbonaceous component accounts for a high proportion in mid-latitude terrestrial areas,and a higher proportion in forest areas.It has become the most important part of PM_2.5 under high pollution conditions.Carbonaceous components can not only directly absorb and scatter solar radiation,and play an important role in regional environment and global climate;but also can affect human health.Therefore,this article conducted a one-year observation of the pollutants in Lushan Forest Park（December 2019～December 2020）to evaluate the air quality of Lushan Forest Park and the pollution characteristics of carbonaceous components in PM_2.5.Also,the backward airflow software（Meteolnfo）was used to analyze the source of PM_2.5 and potential source areas.The main conclusions are as follows:（1）During the sampling period,the concentration of SO₂ varied from 1.54 to 22μg·m^-3,and the average concentration was（5.95±0.31）μg·m^-3.The concentration of NO₂varied from 2.38 to 23μg·m^-3,and the average concentration was（5.75±0.33）μg·m^-3.The overall range of O₃ concentration varied from 19.44 to 163.5μg·m^-3,and the highest concentration of O₃ in spring and summer was the 1.635 times and 1.02 times of the first level standard(100μg·m^-3).The concentration of PM_2.5 varied from 3 to 64.75μg·m^-3,and the average concentration was（21.61±1.02）μg·m^-3.The seasonal variation trend of PM_2.5was winter（24.43±2.53）μg·m^-3>autumn（24.12±1.85）μg·m^-3>spring（23.31±1.96）μg·m^-3>summer（14.69±1.19）μg·m^-3.（2）Meteorological elements will have an impact on air pollutants.The magnitude of precipitation will have an impact on the concentration of NO₂,SO₂ and PM_2.5.When the precipitation is large,the concentration will be reduced,indicating that precipitation has a certain cleaning effect on it.The wind speed has a certain influence on the air pollutants.When the wind speed was greater than 6 m·s^-1,the pollutant concentration decreased.The summer temperature is high,and the O₃ concentration will also increase.This is due to the higher temperature,which causes the solar radiation to become stronger,thereby increasing the O₃ concentration.The content of gaseous pollutants SO₂,NO₂ and O₃ in the atmosphere can promote the production of PM2.5.（3）The organic carbon（OC）concentration in PM_2.5 in Lushan Forest Park was between 1.38～8.16μg·m^-3,the average concentration was（4.08±0.52）μg·m^-3.The elemental carbon（EC）concentration in PM_2.5 was between 0.09～0.50μg·m^-3,and the average concentration was（0.23±0.04）μg·m^-3.The OC concentration was higher than the EC concentration.Temporal changes in the OC concentrations were characterized by spring（4.73±1.58）μg·m^-3>winter（4.33±1.86）μg·m^-3>autumn（4.26±1.59）μg·m^-3>summer（2.98±0.88）μg·m^-3,while the temporal changes in the EC concentrations were characterized by spring（0.29±0.11）μg·m^-3>winter（0.25±0.08）μg·m^-3>autumn（0.25±0.12）μg·m^-3>summer（0.14±0.03）μg·m^-3.Moreover,the concentration of EC and OC in the PM_2.5 of Lushan Forest Park were lower than those in urban areas.In addition,the concentrations of EC and OC in the atmosphere have negative correlation with the relative humidity,precipitation,wind speed and temperature of the air,and positive correlation with the relationship with air pressure.The influence of meteorological elements on the EC and OC in PM_2.5 is not single,but is the result of the interaction of various meteorological factors.（4）The OC/EC value of Lushan Forest Park was between 8.3 and 27.6,all of which were greater than 2,indicating that SOC was generated in Lushan during the sampling period.Using the OC/EC ratio to estimate the concentration of SOC,it was found that the average SOC concentration was 1.19μg·m^-3,of which the average SOC concentration was2.22μg·m^-3 in autumn and the average SOC concentration was 0.53μg·m^-3in summer.The average SOC conversion rate（α）of Lushan Forest Park was 33.2%,indicating that SOC accounted for a large part of the OC.Analyzing the correlation between SOC concentration and SOC conversion rate（α）,and O₃ concentration,it can be found that there was no direct relationship between them in spring and summer.However,there was a good correlation between the SOC concentration and the O₃ concentration in autumn and winter.It showed that,in addition to oxidizing O₃,there were other oxidants such as hydroxyl radicals and nitric acid free radicals in the air,leading to an increase in the concentration of SOC.（5）The correlation analysis between PM_2.5,OC and EC in Lushan Forest Park showed that the sources of OC,EC and PM_2.5 were consistent in summer,the sources of EC and PM_2.5 in autumn were the same,and the sources of EC and OC in winter were similar.According to the results of the OC/EC ratio,it was speculated that during the sampling period,the sources of the carbonaceous components in Lushan Forest Park were mainly biomass burning,coal burning,wood burning and dust.Principal component analysis of different carbon components revealed that EC and OC in PM2.5 were mainly derived from biomass combustion,coal-burning,automobile exhaust emissions and road dust diesel vehicle exhaust during the sampling period.（6）The airflow trajectory cluster analysis,potential source contribution factor analysis（PSCF）and concentration weighted trajectory analysis（CWT）were used to analyze the contribution of different surrounding source areas to PM_2.5 in the Lushan Forest Park.The cluster analysis results show that there are five clusters in spring,summer,autumn and winter,but there are some differences in the results of the four seasons.The northwest air mass is the main transport path that affects the PM_2.5 concentration in spring,autumn and winter.The autumn and winter seasons are mainly affected by the heating period in the north,and the summer seasons are mainly affected by the southwest air mass,which mainly comes from the ocean,The concentration of particles is reduced.The analysis results of potential source area（PSCF）show that there are some seasonal variations in pscf.The concentration of PM_2.5 is related to human factors and coal emission.The results of CWT showed that the CWT value was the highest in winter and the lowest in summer.The local and surrounding areas of Lushan,Southern Anhui and Southeastern Hubei are the main potential sources of PM_2.5.