| It has significant influences to understand the composition,sources and pollution causes of urban aerosols and formulate corresponding measures by studying on the physical and chemical characteristics of aerosols from outside of the city.In order to understand the source of PM2.5 in dry season of Kunming and the possible causes of extremely polluted weather,this study collected the atmospheric samples from the main urban area of Kunming and Chenggong district from November 2017 to March 2019,analyzed the characteristics of PM2.5 mass concentration and main chemical components?water-soluble ions,carbon components and mineral elements?.Besides,the enrichment factor method,ratio method,backward airflow trajectory analysis method and orthogonal Matrix factor method were used to analyze the sources of PM2.5,and the differences of PM2.5.5 in the main urban area and Chenggong district were discussed.What's more,based on the analysis of the chemical composition of the Chenggong district,the external atmospheric gas in the dry season was extracted.Finally,the information on the composition of PM2.5;quantitatively estimate the contribution of external sources to various chemical components in the main urban area of Kunming.The conclusions are as follow:The PM2.5 concentrations in Chenggong district during the dry season were between 11.1-58.1?g·m-3,with an average value of 24.5±10.3?g·m-3,which was slightly higher than the atmospheric background station.It indicated that there was an atmosphere pollution in Chenggong district atmosphere.The average content of total carbon?TC?was 5.6±2.6?g·m-3,accounting for 22.7%of the mass concentration of PM2.5.The range of char/soot was 2.2-25.8?average 7.8?,and the range of OC/EC was 2.6-6.4?average 4.4?,which was close to the carbon component characteristics of biomass combustion emissions.The average value of the total concentration of water-soluble ions was 8.0±4.4?g·m-3,accounting for 32.3%of the mass concentration of PM2.5.The cation amount was more than the anion amount,indicating that the fine particles in the atmosphere were alkaline.It was estimated that the soil component content during the sampling period was about 15.8%of PM2.5.PMF source analysis showed that biomass combustion was the primary source of PM2.5 in the Chenggong district,contributing 31.7%,followed by geological dust,accounting for 26.9%.The atmospheric particulate matter Chenggong district mainly came from long-distance transportation,and the local impact on the sampling point was relatively small from 2017 to 2019.In the dry season from 2017 to 2019,the average PM2.5.5 concentration in the main urban area of Kunming was 32.6?g·m-3,which was about 30%higher than the average PM2.5.5 concentration in Chenggong district(24.5?g·m-3).Atmospheric particulate matter PM2.5 was affected by certain human activities and had the characteristics of diurnal variation.The range of OC/EC ratio was 2.4-5.5,with an average value of 3.3,which was lower than the upwind aerosol OC/EC ratio?average 4.4?in Kunming.The range of char/soot was 3.7-25.8?average 13.1?,which was close to the characteristics of carbon components of biomass combustion emissions but higher than the Chenggong district char/soot ratio?average 7.8?.So,the carbon component of aerosols in the main urban area of Kunming were affected by biomass burning.The average value of water-soluble ions in the main urban area was 9.1±4.2?g·m-3,accounting for 28.2%of the PM2.5 mass concentration.The anions were completely neutralized by the cations,and the fine particles exhibit alkaline characteristics.PMF source analysis showed that soil dust was the primary source of Kunming urban area,with a contribution of 31.7%,followed by biomass combustion source,accounting for 24.7%.Therefore,local emissions had a significant impact on the main urban area of Kunming from 2017 to 2019.The mass concentration of PM2.5 from external transportation to Kunming was24.0±10.5?g·m-3 on average.There were many differences between the aerosol PM2.5 input and wind directions.When the wind direction was eastward,the particulate matter concentration was higher.The average value of the total mass concentration of water-soluble inorganic ions was 7.8±4.3?g·m-3,accounting for32.0%of the mass concentration of PM2.5.In addition,the estimated average content of soil components was 3.2±2.2?g·m-3,accounting for PM2.5 14.5%;the average content of SO42-,NO3-and NH4+in PM2.5 sourced from the northeast were18.0±4.3%,5.2±2.0%and 6.2±3.3%.The ratio of Ca/Ti and K/Ti in aerosols from the northeast were 17.0±9.4 and 21.8±6.1 on average.Furthermore,Ca/Ti?17.4±7.4?and K/Ti?19.7±10.3?ratio can be used as the tracking index for aerosols in different wind directions in Kunming.Finally,there was a good correlation relationship in PM2.5 mass concentration in24 hours between Chenggong district and the main urban area of Kunming City.The main urban area was affected by the external transportation.The results shows that the contribution of external input to SO42-in the main urban area was as high as76.3%,followed by NO3-?73.0%?,organic carbon?66.3%?,elemental carbon?47.8%?,Ca2+?42.0%?,which indicates that the atmospheric pollutants in the main urban area of Kunming are controlled by regional transport. |
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