Ground-based Fourier transform infrared (FTIR) O₃ retrievals from the 3040 cm⁻¹ spectral range at Xianghe, China

• Main Authors: M. Zhou, P. Wang, B. Langerock, C. Vigouroux, C. Hermans, N. Kumps, T. Wang, Y. Yang, D. Ji, L. Ran, J. Zhang, Y. Xuan, H. Chen, F. Posny, V. Duflot, J.-M. Metzger, M. De Mazière
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-10-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://amt.copernicus.org/articles/13/5379/2020/amt-13-5379-2020.pdf
• ISSN: 1867-1381; 1867-8548

<p>In this study, we present <span class="inline-formula">O₃</span> retrievals from ground-based Fourier transform infrared (FTIR) solar absorption measurements between June 2018 and December 2019 at Xianghe, China (39.75<span class="inline-formula">^∘</span>&thinsp;N, 116.96<span class="inline-formula">^∘</span>&thinsp;E). The FTIR spectrometer at Xianghe is operated with indium gallium arsenide (InGaAs) and indium antimonide (InSb) detectors, recording the spectra between 1800 and 11&thinsp;000&thinsp;cm<span class="inline-formula">⁻¹</span>. As the harmonized FTIR <span class="inline-formula">O₃</span> retrieval strategy <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx39">Vigouroux et al.</a>, <a href="#bib1.bibx39">2015</a>)</span> within the Network for the Detection of Atmospheric Composition Change (NDACC) uses the 1000&thinsp;cm<span class="inline-formula">⁻¹</span> spectral range, we apply the <span class="inline-formula">O₃</span> retrieval in the 3040&thinsp;cm<span class="inline-formula">⁻¹</span> spectral range at Xianghe.</p> <p>The retrieved <span class="inline-formula">O₃</span> profile is mainly sensitive to the vertical range between 10 and 40&thinsp;km, and the degrees of freedom for signal is <span class="inline-formula">2.4±0.3</span> (<span class="inline-formula">1<i>σ</i></span>), indicating that there are two individual pieces of information in partial columns between the surface and 20&thinsp;km and between 20 and 40&thinsp;km. According to the optimal estimation method, the systematic and random uncertainties of the FTIR <span class="inline-formula">O₃</span> total columns are about 13.6&thinsp;% and 1.4&thinsp;%, respectively. The random uncertainty is consistent with the observed daily standard deviation of the FTIR retrievals.</p> <p>To validate the FTIR <span class="inline-formula">O₃</span> total and partial columns, we apply the same <span class="inline-formula">O₃</span> retrieval strategy at Maïdo, Réunion (a.k.a. Reunion Island; 21.08<span class="inline-formula">^∘</span>&thinsp;N, 55.38<span class="inline-formula">^∘</span>&thinsp;E). The FTIR <span class="inline-formula">O₃</span> (3040&thinsp;cm<span class="inline-formula">⁻¹</span>) measurements at Xianghe and Maïdo are then compared with the nearby ozonesondes at Beijing (39.81<span class="inline-formula">^∘</span>&thinsp;N, 116.47<span class="inline-formula">^∘</span>&thinsp;E) and at Gillot (20.89<span class="inline-formula">^∘</span>&thinsp;S, 55.53<span class="inline-formula">^∘</span>&thinsp;E), respectively, as well as with co-located TROPOspheric Monitoring Instrument (TROPOMI) satellite measurements at both sites. In addition at Maïdo, we compare the FTIR <span class="inline-formula">O₃</span> (3040&thinsp;cm<span class="inline-formula">⁻¹</span>) retrievals with the standard NDACC FTIR <span class="inline-formula">O₃</span> measurements using the 1000&thinsp;cm<span class="inline-formula">⁻¹</span> spectral range. It was found that the total columns retrieved from the FTIR <span class="inline-formula">O₃</span> 3040&thinsp;cm<span class="inline-formula">⁻¹</span> measurements are underestimated by 5.5&thinsp;%–9.0&thinsp;%, which is mainly due to the systematic uncertainty in the partial column between 20 and 40&thinsp;km (about <span class="inline-formula">−10.4</span>&thinsp;%). The systematic uncertainty in the partial column between surface and 20&thinsp;km is relatively small (within 2.4&thinsp;%). By comparison with other measurements, it was found that the FTIR <span class="inline-formula">O₃</span> (3040&thinsp;cm<span class="inline-formula">⁻¹</span>) retrievals capture the seasonal and synoptic variations of the <span class="inline-formula">O₃</span> total and two partial columns very well. Therefore, the ongoing FTIR measurements at Xianghe can provide useful information on the <span class="inline-formula">O₃</span> variations and (in the future) long-term trends.</p>