Abstract
Abstract. Atmospheric aerosols exert highly uncertain impacts on radiative forcing and also have detrimental effects on human health. While aerosol particles are widely characterized in megacities in China, aerosol composition, sources and particle growth in rural areas in the Tibetan Plateau remain less understood. Here we present the results from an autumn study that was conducted from 5 September to 15 October 2013 at a national background monitoring station (3295 m a.s.l.) in the Tibetan Plateau. The submicron aerosol composition and particle number size distributions were measured in situ with an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) and a Scanning Mobility Particle Sizer (SMPS). The average mass concentration of submicron aerosol (PM1) is 11.4 μg m−3 (range: 1.0–78.4 μg m−3) for the entire study, which is much lower than observed at urban and rural sites in eastern China. Organics dominated PM1, accounting for 43 % on average, followed by sulfate (28 %) and ammonium (11 %). Positive Matrix Factorization analysis of ACSM organic aerosol (OA) mass spectra identified an oxygenated OA (OOA) and a biomass burning OA (BBOA). The OOA dominated OA composition, accounting for 85 % on average, 17 % of which was inferred from aged BBOA. The BBOA contributed a considerable fraction of OA (15 %) due to the burning of cow dung and straw in September. New particle formation and growth events were frequently observed (80 % of time) throughout the study. The average particle growth rate is 2.0 nm h−1 (range: 0.8–3.2 nm h−1). By linking the evolution of particle number size distribution to aerosol composition, we found an elevated contribution of organics during particle growth periods and also a positive relationship between the growth rate and the fraction of OOA in OA, which potentially indicates an important role of organics in particle growth in the Tibetan Plateau.
Highlights
High concentration of atmosphere aerosol associated with the rapid economic growth, urbanization and industrialization has become a major environmental concern in China
By linking the evolution of particle number size distribution to aerosol composition, we found an elevated contribution of organics during particle growth periods and a positive relationship between the growth rate and the fraction of oxygenated OA (OOA) in organic aerosol (OA), which potentially indicates an important role of organics in particle growth in the Tibetan Plateau
The relative contributions of sulfate and organics during Ep 2 and Ep 3 are different the nitrate contribution is similar. These results suggest that the national background site is subject to the influences of air masses from different sources, some of which are enriched with OA, while others are dominated with aerosols mainly composed of ammonium sulfates
Summary
High concentration of atmosphere aerosol associated with the rapid economic growth, urbanization and industrialization has become a major environmental concern in China. A large number of studies have been conducted to investigate the sources, chemical and physical properties and evolution processes of aerosol particles at urban and rural sites in China during the last decade (Cao et al, 2007; Wu et al, 2007; He et al, 2011; Gong et al, 2012; Huang et al, 2013; Sun et al, 2013, 2015; Jiang et al, 2015). An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was first deployed at a national background monitoring site (Menyuan, Qinghai) in the Tibetan Plateau for the real-time characterization of submicron aerosol composition including organics, sulfate, nitrate, ammonium and chloride from 5 September to 15 October, 2013.
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