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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-906
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
18 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Lower tropospheric ozone over India and its linkage to the South Asian monsoon
Xiao Lu1,2, Lin Zhang1, Xiong Liu3, Meng Gao2, Yuanhong Zhao1, and Jingyuan Shao1 1Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China
2School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
3Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138, USA
Abstract. Lower tropospheric (surface to 600 hPa) ozone over India poses serious risks to local human and crops, and potentially affects global ozone distribution through frequent deep convection in tropical regions. Our current understanding of processes controlling seasonal to long-term variations in lower tropospheric ozone over this region is rather limited due to spatially and temporally sparse observations. Here we present an integrated process analysis of the seasonal cycle, interannual variability, and long-term trends of lower tropospheric ozone over India and its linkage to the South Asian Monsoon using the Ozone Monitoring Instrument (OMI) satellite observations for years 2006–2014 interpreted with a global chemical transport model (GEOS-Chem) simulation for 1990–2010. OMI observed lower tropospheric ozone over India averaged for 2006–2010 show the highest concentrations (54.1 ppbv) in the pre-summer monsoon season (May) and the lowest concentrations (40.5 ppbv) in the summer monsoon season (August). Process analyses in GEOS-Chem show that hot and dry meteorological conditions and active biomass burning together contribute to 5.8 Tg more ozone produced in the lower troposphere of India in May than January. The onset of the summer monsoon brings ozone-unfavorable meteorological conditions and strong upward transport, all lead to large decreases in the lower tropospheric ozone burden. Interannually, we find that both OMI and GEOS-Chem indicate strong interannual positive correlations (r = 0.55–0.58) between ozone and surface temperature in pre-summer monsoon seasons, with larger correlations found in high NOx emission regions reflecting NOx-limited production conditions. Summer monsoon seasonal mean ozone levels are strongly controlled by monsoon strengths. Lower ozone concentrations are found in stronger monsoon seasons mainly due to less ozone net chemical production. Furthermore, model simulations over 1990–2010 estimate a mean annual trend of 0.19 ± 0.07 (p-value < 0.01) ppbv year-1 in Indian lower tropospheric ozone over this period, which are mainly driven by increases in anthropogenic emissions with small contribution (about 7 %) from global methane concentration increases.

Citation: Lu, X., Zhang, L., Liu, X., Gao, M., Zhao, Y., and Shao, J.: Lower tropospheric ozone over India and its linkage to the South Asian monsoon, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-906, in review, 2017.
Xiao Lu et al.
Xiao Lu et al.

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Short summary
Deteriorating tropospheric ozone pollution over India may not only affect local human health and vegetation, but also perturb global ozone distribution. This study analyzes the processes controlling lower tropospheric ozone over India using OMI satellite observations (2006–2014) and model simulations (1990–2010). We show that the South Asian monsoon largely controls the seasonal cycle and interannual variability of Indian lower tropospheric ozone via changes in ozone production and transport.
Deteriorating tropospheric ozone pollution over India may not only affect local human health and...
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