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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
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Research article 07 Jun 2018

Research article | 07 Jun 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Lower tropospheric ozone over the North China Plain: variability and trends revealed by IASI satellite observations for 2008–2016

Gaëlle Dufour1, Maxim Eremenko1, Matthias Beekmann1, Juan Cuesta1, Gilles Foret1, Weili Lin2, Yi Liu3, Xiaobin Xu4, and Yuli Zhang3 Gaëlle Dufour et al.
  • 1Laboratoire Inter-universitaire des Systèmes Atmosphériques (LISA), UMR7583, Universités Paris-Est Créteil et Paris Diderot, CNRS, Créteil, France
  • 2Meteorological Observation Center, China Meteorological Administration, Beijing, China
  • 3Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
  • 4Key Laboratory for Atmospheric Chemistry of China Meteorological Administration, Chinese Academy of Meteorological Sciences, Beijing, China

Abstract. China, and especially the North China Plain (NCP), is a highly polluted region. Emission reductions have been applied since about 10 years, starting with SO2 emissions in 2006 and with NOx emissions in 2010. Recent studies show a decrease of NO2 tropospheric column since 2013 and attributed to the NOx emissions reduction. Quantifying how these emission reductions translates to the ozone concentrations remains. In this study, we use the lower tropospheric (LT) columns (surface-6kmasl) derived from the IASI satellite instrument to describe the variability and trend of LT ozone over the NCP for 2008–2016. Deseasonalized monthly timeseries show two distinct periods: a first period (2008–2012) with no significant trend (<−0.1%/yr) and a second period (2013–2016) with a highly significant negative trend of −1.2%/yr, leading to an overall trend of −0.77%/yr for 2008–2016. We explore the dynamical and chemical factors that could explain this overall negative trend using a multivariate regression model. The results suggest that the negative trend observed from IASI could arise from a reduction of the stratosphere-to-troposphere transport combined with reduction of regional precursor emissions, as suggested by the used CO proxy. However, no negative trend has been reported from background surface measurements in this Chinese region. As well, recent work made within the framework of the TOAR (Tropospheric Ozone Assessment Report) initiative reveals discrepancies in the sign of the trends of tropospheric ozone derived from infrared and ultraviolet satellite instruments, with no conclusive explanation found until now. We then investigate the IASI retrieval stability and robustness and compare it with surface and ozonesonde measurements and the independent IASI instrument aboard the Metop-B satellite. One issue that arises from the different comparison concerns the impact of the sampling differences between the different datasets on the different calculated trends.

Gaëlle Dufour et al.
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Gaëlle Dufour et al.
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Short summary
The analysis of IASI lower tropospheric ozone columns over the North China Plain between 2008 and 2016 reveals two distinct periods: one before 2013 without any significant trend, and on after 2013 with a significant negative trend (−1.2 %/yr). Our results suggest that the negative trend is not due to any instrumental drift and could be attributed to a reduction of the stratosphere-to-troposphere transport combined with the recent reduction of regional NOx emissions.
The analysis of IASI lower tropospheric ozone columns over the North China Plain between 2008...