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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-587
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
01 Sep 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).
Chemical characteristics of submicron particles at the central Tibet Plateau: influence of long-range transport
Jianzhong Xu1, Qi Zhang2, Jinsen Shi3, Xinlei Ge4, Conghui Xie1, Junfeng Wang4, Shichang Kang1, Ruixiong Zhang5, and Yuhang Wang5 1State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-Environment and Resources, CAS, Lanzhou 730000, China
2Department of Environmental Toxicology, University of California, Davis, CA 95616, USA
3Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China
4Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China
5School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
Abstract. Recent studies have revealed a significant influx of air pollution from south Asia to Himalayas and Tibet Plateau (TP) during pre-monsoon period. In order to characterize the chemical composition, sources, and transport mechanism of polluted air mass in this pristine area, we performed a field study during June 2015 by deploying a suite of online instruments including an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-AMS) and a multi-angle absorption photometer (MAAP) at Nam Co Station (90°57' E, 30°46 ' N 4730 m a.s.l.) at the central of the TP. The measurements were made at a time when the transition from pre-monsoon to monsoon occurred. The average ambient mass concentration of submicron particulate matter (PM1) over the whole campaign period was 2.0 µg m−3, with organics accounting for 64 %, followed by sulfate (16 %), black carbon (9 %), ammonium (8 %), and nitrate (3 %). This mass loading and composition were comparable with most of AMS results in remote sites worldwide. Air pollution episodes were observed during the pre-monsoon period, while consistently low aerosol concentrations were observed during the monsoon period. However, the chemical composition of aerosol during the air pollution episodes in the pre-monsoon season was on a case-by-case basis, depending on the prevailing meteorological conditions and air mass transport routes. Most of the chemical species exhibited significant diurnal variations with higher values occurring during afternoon and lower values during early morning time whereas nitrate peaked during early morning in association with higher relative humidity and lower air temperature. Organic aerosol (OA) was more oxidized with an oxygen-to-carbon ratio (O / C) of 0.94 during the pre-monsoon period than during monsoon (average O / C of 0.48). The average O / C of OA was 0.88 over the entire campaign period. Positive matrix factorization of the high resolution mass spectra of OA identified two oxygenated organic aerosol (OOA) factors: a less oxidized OOA (LO-OOA) and a more oxidized OOA (MO-OOA). The MO-OOA dominated during the pre-monsoon period, while LO-OOA dominated during the monsoon. The sensitivity of air pollution transport with synoptic process was also evaluated with a 3-D chemical transport model.

Citation: Xu, J., Zhang, Q., Shi, J., Ge, X., Xie, C., Wang, J., Kang, S., Zhang, R., and Wang, Y.: Chemical characteristics of submicron particles at the central Tibet Plateau: influence of long-range transport, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-587, in review, 2017.
Jianzhong Xu et al.
Jianzhong Xu et al.
Jianzhong Xu et al.

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Short summary
This manuscript presents results from a comprehensive field study using an HR-AMS coupled with a suite of other instruments in Central Tibetan Plateau. The study discusses the chemical composition, sources, and processes of submicron aerosol during the transition from pre-monsoon to monsoon. Organic aerosol was overall highly oxidized during the entire study with higher O / C ratios during the pre-monsoon period. The sensitivity of air pollution transport with synoptic process was also evaluated.
This manuscript presents results from a comprehensive field study using an HR-AMS coupled with a...
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