Abstract

Abstract. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed along with other online instruments to study the highly time resolved chemistry and sources of submicron aerosols (PM1) at Waliguan (WLG) Baseline Observatory, a high-altitude (3816 m a.s.l.) background station located at the northeast edge of the Qinghai–Tibet Plateau (QTP), during 1–31 July 2017. The average PM1 mass concentration during this study was 9.1 µg m−3 (ranging from 0.3 to 28.1 µg m−3), which was distinctly higher than those (2.0–5.7 µg m−3) measured with the Aerodyne AMS at other high-elevation sites in the southern or central QTP. Sulfate showed a dominant contribution (38.1 %) to PM1 at WLG followed by organics (34.5 %), ammonium (15.2 %), nitrate (8.1 %), BC (3.0 %) and chloride (1.1 %). Accordingly, bulk aerosols appeared to be slightly acidic throughout this study, mainly related to the enhanced sulfate contribution. All chemical species peaked at the accumulation mode, indicating the well-mixed and highly aged aerosol particles at WLG from long-range transport. Positive matrix factorization (PMF) on the high-resolution organic mass spectra resolved four distinct organic aerosol (OA) components, including a traffic-related hydrocarbon-like OA (HOA), a relatively fresh biomass burning OA (BBOA), an aged biomass burning OA (agBBOA) and a more-oxidized oxygenated OA (OOA). On average, the two relatively oxidized OAs, OOA and agBBOA, contributed 34.4 % and 40.4 % of organics, respectively, while the rest were 18.4 % for BBOA and 6.8 % for HOA. Source analysis for air masses showed that higher mass concentrations of PM1 and enhanced contributions of sulfate and biomass-burning-related OA components (agBBOA + BBOA) were from the northeast of the WLG with shorter transport distance, whereas lower PM1 mass concentrations with enhanced OOA contribution were from the west after long-range transport, suggesting their distinct aerosol sources and significant impacts of regional transport on aerosol mass loadings and chemistry at WLG.

Highlights

  • The Qinghai–Tibet Plateau (QTP) is one of the most remote and pristine regions in the world

  • An overview of temporal variations of mass concentrations and fractions of PM1 chemical species as well as meteorological conditions (T, relative humidity (RH), wind speed (WS), wind direction (WD) and Precip.), mass concentrations of relevant particulate matters (PM2.5 and PM10) and gaseous pollutants (O3 and carbon monoxide (CO)), and mass fractions of organic components are shown in Fig. 2, respectively

  • The missing data are due to hardware or software malfunction, maintenance of the instrument, or removal of large spikes and the unique burning event in data processing

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Summary

Introduction

The Qinghai–Tibet Plateau (QTP) is one of the most remote and pristine regions in the world. Air pollutants from southern and southeastern Asia, two of the major regions with enhanced biomass burning emissions in the world, stacked up in the southern foothills of the Himalayas during the pre-monsoon season, climbed over the Himalayas using topographic lifting and the mountain-valley breeze circulation, and moved upward to the QTP (Lüthi et al, 2015) These long-range transports followed by deposition of polluted air masses, especially for the two important lightabsorbing substances of black carbon (BC) and brown carbon (BrC), have significant impacts on climate, the environment and hydrology in the QTP (Xu et al, 2009; Kang et al, 2010; Qian et al, 2011; Yang et al, 2014)

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