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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
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Research article
06 Jun 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).
Long-term trends of surface ozone and its influencing factors at the Mt. Waliguan GAW station, China, Part 2: Variation mechanism and links to some climate indices
Wanyun Xu1, Xiaobin Xu1, Meiyun Lin2, Weili Lin3, Jie Tang3, David Tarasick4, Jiangzhong Ma1, and Xiangdong Zheng1 1State Key Laboratory of Severe Weather &Key Laboratory for Atmospheric Chemistry, Institute of Atmospheric Composition, Chinese Academy of Meteorological Sciences, Beijing, 100081, China
2NOAA Geophysical Fluid Dynamics Laboratory and Program in Atmospheric and Oceanic Sciences in Princeton University, Princeton, New Jersey 08540, USA
3Meteorological Observation Center, China Meteorological Administration, Beijing, 100081, China
4Science and Technology Branch, Environment Canada, 4905 Du fferin Street, Downsview, Ontario, M3H 5T3, Canada
Abstract. Interannual variability and long-term trends of tropospheric ozone are both of environmental and climate concerns. Ozone measured at Mt. Waliguan Observatory (WLG, 3816 m asl) on the Tibetan Plateau over the period 19947ndash;2013 has increased significantly by 0.2–0.3 ppbv year-1 during spring and autumn, but shows a much smaller trend in winter and no significant trend in summer. Here we explore the factors driving the observed ozone changes at WLG using backward trajectory analysis, chemistry-climate model hindcast simulations (GFDL-AM3), a trajectory-mapped ozonesonde dataset and various climate indices. A stratospheric ozone tracer implemented in GFDL-AM3 indicates that stratosphere-to-troposphere transport (STT) can explain ~ 70 % of the observed springtime ozone increase at WLG, consistent with an increase in the NW air mass frequency inferred from the trajectory analysis. Enhanced STT associated with the strengthening of the mid-latitude jet stream contributes to the observed high-ozone anomalies at WLG during the springs of 1999 and 2012. During autumn, observations at WLG are more heavily influenced by polluted air masses originated from Southeast Asia than in the other seasons. Rising Asian anthropogenic emissions of ozone precursors is the key driver of increasing autumnal ozone observed at WLG, as supported by the GFDL-AM3 model with time-varying emissions, which captures the observed ozone increase (0.26 ± 0.11 ppbv year-1). AM3 simulates a greater ozone increase of 0.38 ± 0.11 ppbv year-1 at WLG in autumn under conditions with strong transport from Southeast Asia and shows no significant ozone trend in autumn when anthropogenic emissions are held constant in time. During summer, WLG is mostly influenced by easterly air masses but these trajectories do not extend to the polluted regions of eastern China and have decreased significantly over the last two decades, which likely explains why summertime ozone measured at WLG shows no significant trend despite ozone increases in Eastern China. Analysis of the Trajectory-mapped Ozonesonde dataset for the Stratosphere and Troposphere (TOST) and trajectory residence time reveals increases in direct ozone transport from the eastern sector during autumn, which adds to the autumnal ozone increase. We further examine the links of ozone variability at WLG to the QBO, the North Atlantic Oscillation (NAO), the East Asian summer monsoon (EASM) and the sunspot cycle. Our results suggest that the 2–3 year, 3–7 year and 11 year periodicities are linked to QBO, EASMI and NAO and the sunspot cycle, respectively. A multivariate regression analysis is performed to quantify the relative contributions of various factors to surface ozone concentrations at WLG. Through an observational and modelling analysis, this study demonstrates the complex relationships between surface ozone at remote locations and its dynamical and chemical influencing factors.

Citation: Xu, W., Xu, X., Lin, M., Lin, W., Tang, J., Tarasick, D., Ma, J., and Zheng, X.: Long-term trends of surface ozone and its influencing factors at the Mt. Waliguan GAW station, China, Part 2: Variation mechanism and links to some climate indices, Atmos. Chem. Phys. Discuss.,, in review, 2017.
Wanyun Xu et al.
Wanyun Xu et al.


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Short summary
Various periodicities and long-term trends of surface ozone measured at Mt. Waliguan (WLG) for the period of 1994 to 2013 is studied. We identify the key drivers of the periodicities and long-term trends of ozone at Waliguan. STT and rising emissions contribute to spring and autumnal trends, respectively. The periodicities in the ozone data are linked to various climate indices, including EASMI, NAO, sunspot cycle, etc. An empirical model is obtained for normalized monthly ozone at WLG.
Various periodicities and long-term trends of surface ozone measured at Mt. Waliguan (WLG) for...