Characterization of submicron particles during autumn in Beijing, China

In this study, we performed a highly time-resolved chemical characterization of non-refractory submicron particles (NR-PM₁) in Beijing by using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The results showed the average NR-PM₁ mass concentration to be 56.4±58.0μg/m³, with a peak at 307.4μg/m³. Due to the high frequency of biomass burning in autumn, submicron particles significantly increased in organic content, which accounted for 51% of NR-PM₁ on average. Secondary inorganic aerosols (sulfate+nitrate+ammonium) accounted for 46% of NR-PM₁, of which sulfate, nitrate, and ammonium contributed 15%, 20%, and 11%, respectively. To determine the intrinsic relationships between the organic and inorganic species, we used the positive matrix factorization (PMF) model to merge the high-resolution mass spectra of the organic species and NO⁺ and NO₂⁺ ions. The PMF analysis separated the mixed organic and nitrate (NO⁺ and NO₂⁺) spectra into four organic factors, including hydrocarbon-like organic aerosol (HOA), oxygenated organic aerosol (OOA), cooking organic aerosol (COA), and biomass burning organic aerosol (BBOA), as well as one nitrate inorganic aerosol (NIA) factor. COA (33%) and OOA (30%) contributed the most to the total organic aerosol (OA) mass, followed by BBOA (20%) and HOA (17%). We successfully quantified the mass concentrations of the organic and inorganic nitrates by the NO⁺ and NO₂⁺ ions signal in the organic and NIA factors. The organic nitrate mass varied from 0.01-6.8μg/m³, with an average of 1.0±1.1μg/m³, and organic nitrate components accounted for 10% of the total nitrate mass in this observation.