Characterization of submicron particles during biomass burning and coal combustion periods in Beijing, China.

An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed along with other observation instruments to measure the characteristics of PM1 (particulate matter with a vacuum aerodynamic diameter of ≤1μm) during the biomass burning period (October 1 to 27; BBP) and the coal combustion period (December 10 to 31; CCP) in Beijing in 2014. The average PM1 mass concentrations during the BBP and CCP were 82.3 and 37.5μgm(-3), respectively. Nitrate, ammonium and other pollutants emitted by the burning processes, especially coal combustion, increased significantly in association with increased pollution levels. Positive matrix factorization (PMF) was applied to a unified high-resolution mass spectra database of organic species with NO(+) and NO2(+) ions to discover the relationships between organic and inorganic species. One inorganic factor was identified in both periods, and another five and four distinct organic factors were identified in the BBP and CCP, respectively. Secondary organic aerosols (SOAs) accounted for 55% of the total organic aerosols (OAs) during the BBP, which is higher than the proportion during the CCP (oxygenated OA, 40%). The organic nitrate and inorganic nitrate were first successfully separated through the PMF analysis based on the HR-ToF-AMS observations in Beijing, and organic nitrate components accounted for 21% and 18% of the total nitrate mass during the BBP and CCP, respectively. Although the PM1 mass concentration during the CCP was much lower than in the BBP, the average concentration of polycyclic aromatic hydrocarbons (PAHs) during the CCP (107.3±171.6ngm(-3)) was ~5 times higher than that in the BBP (21.9±21.7ngm(-3)).