Seasonal variations of high time-resolved chemical compositions, sources and
evolution for atmospheric submicron aerosols in the megacity Beijing
Wei Hu, Min Hu, Wei-Wei Hu, Jing Zheng, Chen Chen, Yusheng Wu, and Song Guo
State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
Received: 06 Feb 2017 – Accepted for review: 10 Feb 2017 – Discussion started: 16 Feb 2017
Abstract. Severe regional haze problem in the megacity Beijing and surrounding areas, caused by fast formation and growth of fine particles, has attracted much attention in recent years. In order to investigate the secondary formation and aging process of urban aerosols, four intensive campaigns were conducted in four seasons between March 2012 and March 2013 at an urban site in Beijing (116.31° E, 37.99° N). An Aerodyne high resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) and other relevant instrumentations for gaseous and particulate pollutants were deployed. The average mass concentrations of submicron particulate matter (PM1) were 45.1±45.8, 37.5±31.0, 41.3±42.7, and 81.7±72.4 μg m−3 in spring, summer, autumn and winter, respectively. Organic aerosol (OA) was the most abundant component in PM1, accounting for 31, 33, 44 and 36 % seasonally, and secondary inorganic aerosol (SNA, sum of sulfate, nitrate and ammonium) accounted for 59, 57, 43, and 55 % of PM1 correspondingly. Based on the application of positive matrix factorization (PMF), the sources of OA were obtained, including the primary ones of hydrocarbon-like (HOA), cooking (COA), biomass burning OA (BBOA) and coal combustion OA (CCOA), and secondary component oxygenated OA (OOA). OOA, usually composed of more-oxidized (MO-OOA) and less-oxidized OOA (LO-OOA), accounted for 63, 69, 47 and 50 % in four seasons, respectively. Totally, the fraction of secondary components (OOA+SNA) contributed about 60–80 % to PM1, suggesting that secondary formation played an important role in the PM pollution in Beijing, and primary sources were also non-negligible. The evolution process of OA in different seasons was investigated with multiple metrics and tools. The average carbon oxidation states and other metrics show that the oxidation state of OA was the highest in summer, probably due to both strong photochemical and aqueous-phase oxidations. BBOA and CCOA were only resolved in autumn and winter, respectively, consistent with the agricultural activities (e.g., straw burning after the harvest in suburban areas) in autumn and domestic heating in winter, signifying that the comprehensive management for the emissions from biomass burning and coal combustion are needed. High concentrations of chemical components in PM1 in Beijing, especially in winter or in adverse meteorological conditions, suggest that further strengthening the regional emission control of primary particulate and precursors of secondary species is expected.
Hu, W., Hu, M., Hu, W.-W., Zheng, J., Chen, C., Wu, Y., and Guo, S.: Seasonal variations of high time-resolved chemical compositions, sources and
evolution for atmospheric submicron aerosols in the megacity Beijing, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-115, in review, 2017.