Pollution Characteristics And Source Analysis Of Inorganic Components In Atmospheric PM_2.5 In Mt. Huang

East China is one of the most densely populated and economically developed regions in China.It is of great significance to study the molecular compositions and sources of PM_2.5 at its mountainous background（Mt.Huang）.In this study,the source and composition of inorganic components in aerosols were observed by high-time resolution measurement method at the foot of Mt.Huang.PM_2.5 quartz filter samples were collected in Mt.Huang in summer（July 27 to August 3）and winter（January 6 to January 17）in2019,respectively.8 kinds of water^–soluble inorganic ions and 16 kinds of trace elements were analyzed by ion chromatograph（Dionex-aquion and dionex-600）and energy dispersive X-ray fluorescence spectrometer（ED-XRF）.Combined with meteorological conditions and high^–time resolution data of pollutants,the diurnal variations of inorganic components in Mt.Huang in different seasons were discussed from biogenic and anthropogenic factors.Finally,the source of inorganic components in PM_2.5in Mt.Huang was analyzed by enrichment factors（EFs）、positive matrix factorization（PMF）and potential source contribution function（PSCF）analysis.The main results are listed as follows:（1）The average mass concentration of PM_2.5 in summer during the sampling period was 13.97±6.85μg·m^-3,and the average mass concentration of PM_2.5 in winter is25.11±19.75μg·m^-3.The concentration in winter increased by 79.74%compared with that in summer.The daily average mass concentrations of PM_2.5 in summer and winter are both lower than the first-class standard limit of China’s ambient air quality standard(35μg·m^-3).PM_2.5 mass concentration is higher at night than during the day,reaching the peak in the early morning.Such diurnal variation is more significant in winter than in summer.（2）During the sampling period,the mass concentrations of water-soluble inorganic ions in PM_2.5 at the foot of Mt.Huang in summer and winter were 5.00±2.46μg·m^-3 and13.47±13.78μg·m^-3,accounting for 35.82%and 53.67%of PM_2.5 mass concentration,respectively.Secondary inorganic ions（SNA）are the most important water-soluble inorganic ions,accounting for 59.95%（summer）and 77.41%（winter）of the total concentration of inorganic ions respectively,indicating that the secondary pollution in winter is more serious than that in summer.The concentration level of inorganic ions at night is higher than that during the day.The diurnal variation of SNA mass concentration is significant with the peak occurring from 4:00-7:00 in the morning.The overall composition of atmospheric PM_2.5 in Mt.Huang is alkaline,and the slope in winter（0.71）is less than that in summer（0.95）.The results of thermodynamic equilibrium model ISORROPIA-II show that the p H_is values of Mt.Huang in summer and winter are3.92±1.57 and 4.60±1.90 respectively,indicating that PM_2.5 in Mt.Huang is more alkaline in winter than in summer.NH₄⁺mainly exists in the form of NH₄HSO₄ and NH₄NO₃ in summer and（NH₄）₂SO₄ and NH₄NO₃ in winter,respectively.（3）During the sampling period,the mean mass concentrations of trace elements in Mt.Huang in summer and winter were 2835.19±674.39 ng·m^-3 and 3131.45±672.07 ng·m^-3,respectively.The seasonal variation of trace element mass concentration was not as significant as inorganic ions,indicating that their source was stable.The daily variation trend of trace elements was basically consistent with the change of PM_2.5 mass concentration,with the low value in the day and the high value at night.The mass concentration of crustal elements was obviously affected by valley wind during some periods,indicating that the effect of valley wind circulation on the concentration level of crustal elements in mountainous areas was more obvious than that of the increase of boundary layer height.The heavy metals including Ba,Cr,Zn,Cu and Pb were obviously affected by anthropogenic activities and have complex sources.The daily variation trend of heavy metals（Ba,Cr and Cu）from traffic emissions presented a“double-peaks”characteristic,which was similar to that in urban areas.The average enrichment factors（EFs）of elements varied from 2.9 to 356.3.Trace elements with high EFs were mainly originated from dust,transportation,coal combustion and industrial emissions.（4）The source analysis results based on PMF model showed that the inorganic components in Mt.Huang summer PM_2.5 mainly came from secondary inorganic sources（35.52%）and traffic sources（23.44%）,and the sum of the two contribution rates was 59%,while the contribution of coal,industrial sources（21.55%）and dust sources（19.49%）was relatively lower.The inorganic components of PM_2.5 in Mt.Huang in winter mainly came from secondary inorganic sources（36.34%）and coal-fired and industrial sources（29.63%）,while the contribution of dust sources（18.63%）and traffic sources（15.40%）was lower.The results of potential source analysis based on PSCF model showed that Anhui Province,Zhejiang Province,Jiangxi Province,Guangdong Province and Fujian Province were the main potential source areas of most inorganic components in Mt.Huang in summer;Anhui Province,Shandong Province,Henan Province,Shanxi Province and Shaanxi Province were the main potential source areas of most inorganic components in Mt.Huang in winter.There were significant North-South differences in the distribution of potential source areas in Mt.Huang between in summer and winter,indicating that the source of PM_2.5 in Mt.Huang was significantly affected by monsoon in different seasons.