Evaluation of tropospheric and stratospheric ozone trends over Western Europe from ground-based FTIR network observations

Abstract

Abstract. Within the European project UFTIR (Time series of Upper Free Troposphere observations from an European ground-based FTIR network), six ground-based stations in Western Europe, from 79° N to 28° N, all equipped with Fourier Transform infrared (FTIR) instruments and part of the Network for the Detection of Atmospheric Composition Change (NDACC), have joined their efforts to evaluate the trends of several direct and indirect greenhouse gases over the period 1995–2004. The retrievals of CO, CH4, C2H6, N2O, CHClF2, and O3 have been optimized. Using the optimal estimation method, some vertical information can be obtained in addition to total column amounts. A bootstrap resampling method has been implemented to determine annual partial and total column trends for the target gases. The present work focuses on the ozone results. The retrieved time series of partial and total ozone columns are validated with ground-based correlative data (Brewer, Dobson, UV-Vis, ozonesondes, and Lidar). The observed total column ozone trends are in agreement with previous studies: 1) no total column ozone trend is seen at the lowest latitude station Izaña (28° N); 2) slightly positive total column trends are seen at the two mid-latitude stations Zugspitze and Jungfraujoch (47° N), only one of them being significant; 3) the highest latitude stations Harestua (60° N), Kiruna (68° N) and Ny-Ålesund (79° N) show significant positive total column trends. Following the vertical information contained in the ozone FTIR retrievals, we provide partial columns trends for the layers: ground-10 km, 10–18 km, 18–27 km, and 27–42 km, which helps to distinguish the contributions from dynamical and chemical changes on the total column ozone trends. We obtain no statistically significant trends in the ground-10 km layer for five out of the six ground-based stations. We find significant positive trends for the lowermost stratosphere at the two mid-latitude stations, and at Ny-Ålesund. We find smaller, but significant trends for the 18–27 km layer at Kiruna, Harestua, Jungfraujoch, and Izaña. The results for the upper layer are quite contrasted: we find significant positive trends at Kiruna, Harestua, and Jungfraujoch, and significant negative trends at Zugspitze and Izaña. These ozone partial columns trends are discussed and compared with previous studies.

Analysis of stratospheric NO<sub>2</sub> trends above Jungfraujoch using ground-based UV-visible, FTIR, and satellite nadir observations

“…8): +0.6 ± 0.6 % decade −1 (Dobson) and +0.3 ± 0.6 % decade −1 (satellite) for 1990-2009 and +1.6 ± 0.8 % decade −1 (Dobson) and +1.1 ± 0.8 % decade −1 (satellite) for 1996-2009. It should be noted that the two latter values are also reasonably consistent with the O 3 trend of +0.6 ± 0.9 % decade −1 estimated from FTIR observations at Jungfraujoch during the 1996-2009 period (Vigouroux et al, 2008;WMO, 2011b). Given the Reaction (R1), these slight increases in ozone could at least partly contribute to the observed negative trend in NO 2 , even if not statistically significant at the 95 % confidence level.…”

Continuous quality assessment of atmospheric water vapour measurement techniques: FTIR, Cimel, MFRSR, GPS, and Vaisala RS92

“…There are about 25 groundbased FTIR experiments performed within NDACC, mostly in northern mid-latitudes and in polar regions. For several decades, the NDACC FTIR experiments have been essential for studying stratospheric ozone chemistry by providing a long-term dataset of different ozone relevant trace gases (e.g., Rinsland et al, 2003;Vigouroux et al, 2008). Due to its versatility, a ground-based FTIR instrument is a key experiment of an NDACC station.…”

Ground-based FTIR water vapour profile analyses

“…Over the last decades, the NDACC FTIR experiments contributed to the study of stratospheric ozone chemistry by providing a long-term dataset of different ozone relevant trace gases (e.g. Rinsland et al, 2003;Vigouroux et al, 2008). During the last years, the NDACC-FTIR community has increased its efforts of monitoring the tropospheric distribution of greenhouse gases, including water vapour.…”