3) columns measured by the Infrared Atmospheric Sounding Interferometer (IASI), onboard th..." /> 3 3

Decrease in tropospheric O3 levels in the Northern Hemisphere observed by IASI

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Abstract

<p><strong>Abstract.</strong> In this study, we describe the recent changes in the tropospheric ozone (O<span class="inline-formula"><sub>3</sub></span>) columns measured by the Infrared Atmospheric Sounding Interferometer (IASI), onboard the Metop satellite, during the first 9 years of operation (January 2008 to May 2017). Using appropriate multivariate regression methods, we differentiate significant linear trends from other sources of O<span class="inline-formula"><sub>3</sub></span> variations captured by IASI. The geographical patterns of the adjusted O<span class="inline-formula"><sub>3</sub></span> trends are provided and discussed on the global scale. Given the large contribution of the natural variability in comparison with that of the trend (25–85&amp;thinsp;% vs. 15–50&amp;thinsp;%, respectively) to the total O<span class="inline-formula"><sub>3</sub></span> variations, we estimate that additional years of IASI measurements are generally required to detect the estimated O<span class="inline-formula"><sub>3</sub></span> trends with high precision. Globally, additional 6 months to 6 years of measurements, depending on the regions and the seasons, are needed to detect a trend of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>|</mo><mn mathvariant="normal">5</mn><mo>|</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="15pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="d2e91589cdc40bafcf79b75df8aa10f6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-6867-2018-ie00001.svg" width="15pt" height="13pt" src="acp-18-6867-2018-ie00001.png"/></svg:svg></span></span>&amp;thinsp;DU&amp;thinsp;decade<span class="inline-formula"><sup>−1</sup></span>. An exception is interestingly found during summer at mid- and high latitudes of the Northern Hemisphere (NH; <span class="inline-formula">∼</span>&amp;thinsp;40 to <span class="inline-formula">∼</span>&amp;thinsp;75<span class="inline-formula"><sup>∘</sup></span>&amp;thinsp;N), where the large absolute fitted trend values (<span class="inline-formula">∼</span>&amp;thinsp;<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>|</mo><mn mathvariant="normal">0.5</mn><mo>|</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="198cdf2540281af9ec160aa95d892909"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-6867-2018-ie00002.svg" width="24pt" height="13pt" src="acp-18-6867-2018-ie00002.png"/></svg:svg></span></span>&amp;thinsp;DU&amp;thinsp;yr<span class="inline-formula"><sup>−1</sup></span> on average) combined with the small model residuals (<span class="inline-formula">∼</span>&amp;thinsp;10&amp;thinsp;%) allow for detection of a band-like pattern of significant negative trends. Despite no consensus in terms of tropospheric O<span class="inline-formula"><sub>3</sub></span> trends having been reached from the available independent datasets (UV or IR satellites, O<span class="inline-formula"><sub>3</sub></span> sondes, aircrafts, ground-based measurements, etc.) for the reasons that are discussed in the text, this finding is consistent with the reported decrease in O<span class="inline-formula"><sub>3</sub></span> precursor emissions in recent years, especially in Europe and USA. The influence of continental pollution on that latitudinal band is further investigated and supported by the analysis of the O<span class="inline-formula"><sub>3</sub></span>–CO relationship (in terms of correlation coefficient, regression slope and covariance) that we found to be the strongest at northern midlatitudes in summer.</p>

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APA

Wespes, C., Hurtmans, D., Clerbaux, C., Boynard, A., & Coheur, P. F. (2018). Decrease in tropospheric O3 levels in the Northern Hemisphere observed by IASI. Atmospheric Chemistry and Physics, 18(9), 6867–6885. https://doi.org/10.5194/acp-18-6867-2018

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