Analysis Of The Chemical Components And Source Contribution Of Water-soluble Ions In PM_2.5 In The Northern Suburb Of Nanjing Based On Online Observation

Continuous observation was conducted at the 12th floor of the meteorological building in Nanjing University of Information Science and Technology,from July 2016 to June 2017.Based on the analysis of the online observation data,the balance and seasonal,monthly and daily variationsof water-soluble ions in PM2.5 are analyzed.The source contribution is analyzed by PMF model and the spatial distribution of the main components in local wind is discussed.Also,we analyse a typical aerosol pollution process in winter and compare the observation results of MARGA and SPAMS.The research shows that NH3 is abundant in the northern suburb of Nanjing,and the main combination form of water-soluble ions in PM2.5 is(NH4)2 SO4 and NH4NO3.The annual mean value of total concentration is 37.55 ?g/m3.The annual average of each component is arranged from large to small:NO3->SO42->NH4+>Cl->K+>Ca2+>Na+>Mg2+.The main components NO3-,SO42-.NH4+ and Cl-account for more than 90%of the total concentration.The total concentration is highest in winter for 47.32 ?g/m3 and 33.72 ?g/m3 for spring.It is both about 28 ?g/m3 in summer and autumn.The concentration of Ca2+ and Mg2+ in spring is obviously higher than that of other seasons,and the concentration of other ions is generally the highest in winter.The monthly variation conform to the seasonal variation.In January,the total concentration is the highest in the whole year and the concentration of NO3-is obviously affected by temperature.The daily variation of meteorological elements has peak and valley values at about 6:00?7:00 and 15:00?16:00,because of the daily variation of atmospheric boundary layer.Hence,the concentrations of all kinds of pollutants.especially NO3-,SO42-and NH4+.have significant diurnal variation.In general,the daily variation in winter is the most significant,and there may be a constant accumulation of concentration in the night.The main contributors to water-soluble ions in PM2.5 can be divided into 4 factors:waste incineration+biomass buring,secondary aerosol+traffic emissions,secondary aerosol+coal combustion and dust.The contribution ratio of each factor is 46.8%,39.4%,8.6%and 5.3%,respectively.The secondary aerosol+traffic emissions and secondary aerosol+coal combustion play a dominant role in contribution and the proportion of them is complementary.The proportion of former for July to October is lower than that of the latter,and the contribution of the former is relatively higher in other months.The monthly variation in the contribution of waste incineration+biomass burning is smaller,and the change of the dust factor is in line with the common dust pollution in spring.The high value of the concentration of NO3-,SO42-and NH4+ in each direction vary with the seasons.Pollutant often will be transported by the southeast wind with the speed of 1?3 m/s.The spatial distribution of the average concentration of the 3 main components in different seasons also reflects their combination form and source information to some extent.Due to the influence of meteorological conditions,the condition of local pollutant diffusion is not good enough,resulting in the accumulation of pollutants.It is an important reason for winter typical pollution process in the northern suburb of Nanjing.In this case,the concentration of the main components of water-soluble ions in PM2.5 increase significantly,reaching 2?3 times of the general case,especially the NO3.The relative contribution of the mobile source was much higher than that of the fixed source.The increasing concentration of NO2,and the ample NH3 in the local atmosphere playe a significant role in promoting the formation of NO3.Generally,there is a strong correspondence between MARGA mass concentration and SPAMS number concentration.The SPAMS concentration of main components can be extracted by characteristic ion method,and the mass concentration of corresponding ions in PM2.5 can be qualitatively determined.However,when SPAMS concentration is used to qualitatively determine the mass concentration of corresponding components,NO3 are overestimated and Cl-are underestimated,because of the different principles of the 2 instruments.