Performance assessment of the IASI-O3 KOPRA product for observing midlatitude tropospheric ozone evolution for 15 years: validation with ozone sondes and consistency of the three IASI instruments

Abstract. The Infrared Atmospheric Sounding Interferometer (IASI) has been monitoring the atmosphere for operational meteorology and atmospheric composition studies since 2007 with a succession of three instruments aboard the Metop-A (2006–2021), Metop-B (2012-) and Metop-C (2018-) missions. One of the key species monitored is ozone (O₃). This study assesses the quality of the regional IASI-O3 KOPRA product, version v3.0, and the consistency of the three IASI instruments, IASI-A, IASI-B, and IASI-C for timeseries and trend analyses. The IASI-O3 KOPRA products for IASI-A, IASI-B and IASI-C. IASI-B show a very good agreement and consistency, better than 1 %, for the tropospheric ozone column (TrOC) and several partial columns (surface-450 hPa, surface-300 hPa) over the three domains, Europe, North America, and East Asia of this study. For the quality assessment and trend analyses, we combine the ozone products derived from IASI-A (2008–2018) and IASI-B (2019–2022) without any bias correction. The comparison with homogenized ozone sondes for six northern midlatitude stations reveals a small negative bias of about 3–6 % of the IASI-O3 KOPRA products in the troposphere for both profiles and columns with rather good correlation between 0.7 and 0.9 and an error estimate about 15–17 % (compared to sondes smoothed with averaging kernels (AKs)). The ozone variability is also well reproduced for all the partial columns with a slight underestimation of about 10 % for the TrOC. Based on the comparison with the ozone sondes, we identified a temporal drift (of about -0.06 ± 0.02 DU/yr in average), while more pronounced in summer, for three different ozone columns (TrOC, surface-450 hPa, surface-300 hPa). However, a significant variability of the estimated drifts depending on the sample of ozone sonde sites is remarked, that does not allow its use for correcting the IASI ozone product timeseries over broad domains. Whereas the upper tropospheric ozone trends are mainly positive or undefined, the lower tropospheric ozone trends are mainly systematically negative. The regions the most affected by negative trends are the Mediterranean, Western North America, Eastern North America and East Asia. Compensations between lower and upper tropospheric trends prevent the identification of any specific long-term behaviour for TrOCs over the three domains. The negative tropospheric ozone column anomalies in the 2020–2022 (post-COVID19) time period observed in our northern hemisphere mid-latitude domains slightly impact the estimated trends but do not change the conclusions stressed before.