Chemical Characterization Of Submicron Aerosols In Beijing And A Typical Case Of APEC

Atmospheric aerosols are a major pollutant in the megacity of Beijing, China.The haze formation is closely related to the chemical composition of fine particles. Monitoring for submicron particles and the chemical components of it can help us researching on the secondary aerosol formation,evolution process and insighting into the reason of haze. It is important to known the formation reason of haze and take measures to control the issue of haze events.In this study, An Aerodyne Compact Aerosol Mass Spectrometer was deployed in urban Beijing to characterize the chemical compositions and sources of autumn and winter submicron aerosol particles.We also analysed the influence of secondary aerosol formationto the visibility reduction. After that, we focusd on the influence of emission reduction measures during the APEC to the chemical compositions and sources of submicron aerosol particles.The main conclusions are as follows:(1)Compared the results of the autumn and winter of 2012,the growth rate of the PM1 mass concentrations is relatively flat.Nitrate was the most important inorganic component, also an important source of pollution in autumn, especially during the pollution accumulation process. While sulfate was the most important inorganic component in winter.(2)The occurrence frequency of heavy pollution was higher in winter than in autumn. The concentration of sulfate always increased to a very high value in a short time and lead to poor visibility. The research also indicated that high concentration of aerosols and the high humidity were the main reason for the reduction of the visibility in winter.(3)The results during the APEC(2014/10/24-2014/11/26) showed that Organics was the most abundant chemical component accounting for 36% of total NR-PM1 mass, followed by nitrate(28%), ammonium(16%), sulfate(14%), and chloride(7%). The fraction of nitrate significantly increased with total PM1 mass loading, indicating the important roles of traffic emission and secondary aerosols formation in urban Beijing. Recent studies showed that, both aerosol concentrations and RH had important effects on the reduction of visibility,causing the occurrence of the haze event. Positive Matrix Factorization(PMF) of the C-ToF-AMS organic mass spectra differentiated the organic aerosol(OA) into three primary components, i.e., hydrocarbon-like OA( HOA), cooking-related OA( COA), and coal combustion OA(CCOA), and one secondary component, i.e., oxygenated OA(OOA), which on average accounted for 15%, 21%, 26%, and 38% of the total OA mass loadings, respectively. So it was obvious that the formation of the second aerosols played a dominant role in the pollution, compared with the primary aerosols.(4)The “APEC blue” can be attribute to the favorablemeteorological condition and lessened sources emission. During this period, aerosol concentrations reduced obviously and second components reduced more than primary components. The horizontal and vertical transport of aerosols were strong during the APEC, but the low humidity condition was not conducive tosecondary aerosols formation. The emission of primary aerosols was decresed, but reduction of second aerosol was more apparent, influenced by the meteorological condition, such as relative humidity and temperature, and that the main reason for the drop of PM1 during APEC. In addition, the OOA occupied largest in organic aerosol during the APEC period, while CCOA takes dominance after that for heating.