Secondary Aerosol Formation In Highly Polluted Urban Area: Field Study By Single Particle Mass Spectrometry In Shanghai

Particulate matter(or termed aerosol) draws much attention due to its health, climate and visibility effects.In order to control particulate matter pollution,it is important to know what aerosols come from and how they evolve in atmosphere. However,until now formation mechanisms of secondary aerosol components have not been clearly understood.Here we present the real-time single particle analysis of nitrate-containing aerosol particles in Shanghai by deploying an aerosol time-of-flight mass spectrometer(ATOFMS).The purpose of this work is to investigate how secondary aerosol components were formed in the urban area of Shanghai and the effects of gas phase pollutant(such as NO₂ and O₃) levels and meteorological conditions.Several conclusions were listed as follows:(1) The formation mechanisms of particulate nitrate were studied.Ammonium nitrate was not major component of aerosols in summer,2007.The heterogeneous reactions of N2O5 and NO3 on aerosol surface dominated the particulate nitrate formation on heavily polluted days.(2) The temporal profiles of particulate sulfate were studied.The relative intensity of sulfate signals showed a pronounced diurnal profile in summer 2007, peaking in the midday.In winter 2008,particulate sulfate did not show any identical diurnal pattern probably due to unstable meteorology condition.(3) The formation mechanisms of high molecular weight species(high-MW) in aerosol were studied.It is found that the molecular mass of high-MW ranges up to 400 Da.Organic matters which contain C-N bond were shown to play an important role in high-MW formation.And good correlation between high-MW and aerosol acidity suggests that high-MW formation favors acidic environment.