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Sources and photochemistry of volatile organic compounds in the remote atmosphere of western China: Results from the Mt. Waliguan Observatory

by L. K. Xue, T. Wang, H. Guo, D. R. Blake, J. Tang, X. C. Zhang, S. M. Saunders, W. X. Wang
Atmospheric Chemistry and Physics ()


The chem. of the natural atm. and the influence by long-range transport of air pollution are key issues in the atm. sciences. Here we present two intensive field measurements of volatile org. compds. (VOCs) in late spring and summer of 2003 at Mt. Waliguan (WLG, 36.28° N, 100.90° E, 3816ma.s.l.), a baseline station in the northeast part of the Qinghai-Tibetan Plateau. Most VOC species exhibited higher concns. in late spring than in summer. A typical diurnal variation was obsd. with higher nighttime levels, in contrast to results from other mountainous sites. Five different air masses were identified from backward trajectory anal. showing distinct VOC speciation. Air masses originating from the central Eurasian continent contained the lowest VOC levels compared to the others that were impacted by anthropogenic emissions from China and the Indian subcontinent. A photochem. box model based on the Master Chem. Mechanism (version 3.2) and constrained by a full suite of measurements was developed to probe the photochem. of atm. at WLG. Our results show net ozone prodn. from in situ photochem. during both late spring and summer. Oxidn. of nitric oxide (NO) by the hydroperoxyl radical (HO2) dominates the ozone prodn. relative to the oxidn. by the org. peroxy radicals (RO2), and the ozone is primarily destroyed by photolysis and reactions with the HOx (HOx = OH + HO2) radicals. Ozone photolysis is the predominant primary source of radicals (ROx = OH + HO2+RO2), followed by the photolysis of secondary oxygenated VOCs and hydrogen peroxides. The radical losses are governed by the self and cross reactions among the radicals. Overall, the findings of the present study provide insights into the background chem. and the impacts of pollution transport on the pristine atm. over the Eurasian continent. on SciFinder(R)]

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