Ongoing Decline in the Atmospheric COS Seasonal Cycle Amplitude over Western Europe: Implications for Surface Fluxes

Abstract

Atmospheric carbonyl sulfide (COS) was monitored at the GIF site (France) from August 2014 to November 2021. A significant decreasing trend in the seasonal cycle amplitude (SCA) of the COS was observed for the first time in the Northern Hemisphere (−27 ppt over 6 years). The lowest SCA was recorded in 2021 (80 ppt vs. 107 ppt in 2015). The trend in the SCA results revealed a steeper decline in the spring maximum than in that of the autumn minimum (−49 ppt vs. −10 ppt over 6 years, respectively). These negative trends were qualitatively consistent with those in the tropospheric COS put forward by the NDACC network of ground-based FTIR instruments, which were attributed to a slowing in the rate of COS anthropogenic emissions. Simulations using the ORCHIDEE land-surface model showed that a decrease in COS lowers the uptake of this gas by plants. Our observations suggest the existence of a causal relationship between the decline in the SCA and that in the tropospheric COS, implying that the temporal variations in the COS SCA over Western Europe are essentially driven by plant uptake. However, the transport by the LMDz 3-D model of surface fluxes for each component of the COS budget failed to reproduce this feature at GIF, pointing to a likely misrepresentation of the marine and anthropogenic fluxes in the footprint of this station.

Intercomparison of Atmospheric Carbonyl Sulfide (TransCom‐COS; Part One): Evaluating the Impact of Transport and Emissions on Tropospheric Variability Using Ground‐Based and Aircraft Data

“…anthropogenic) were not always available. Moreover, the COS mixing ratios derived from the atmospheric inversion of Ma et al (2021) that was used to rescale the biosphere fluxes were climatological, which is not realistic in regards to the current decreasing trend of COS mole fraction since 2014 and its implication on biosphere fluxes (Belviso et al, 2022). Finally, the sparse and uneven cover of the observations limits the evaluation of the COS fluxes to the footprint area of these stations.…”

“…The trend was not analyzed because some interannual fluxes (e.g., anthropogenic) were not always available. Moreover, the COS mixing ratios derived from the atmospheric inversion of Ma et al (2021) that was used to rescale the biosphere fluxes were climatological, which is not realistic in regards to the current decreasing trend of COS mole fraction since 2014 and its implication on biosphere fluxes (Belviso et al, 2022).…”

“…Most measurements have been performed in the afternoon between 11 and 17h local time when the boundary layer is well mixed, thereby optimizing the comparability with model simulations.Only COS measurements with a difference between the paired flasks of less than 6.3 ppt are considered. These data are an extension of the measurements first published inMontzka et al, 2007. In addition, we used the French sampling site, GIF (48.7°N -2.1°'E), located about 20 km to the south west of Paris where ground level COS has been monitored on an hourly basis since August 2014(Belviso et al, 2022).…”

The Z-2018 emissions inventory of COS in Europe: A semiquantitative multi-data-streams evaluation

“…Neither COS nor CS 2 atmospheric emissions are taken into account by the European Environment Agency (https://industry.eea.europa.eu/pollutants/pollutant Belviso et al (2016) and Belviso et al (2020) for a description of GC COS measurements, their calibration and comparability with other atmospheric COS datasets. The GIF time series is presently made of 46,860 hourly data points available in Belviso et al (2022a).…”

“…Since about 2016, almost all NOAA and NDACC stations show a decrease of COS in the free troposphere (https://gml.noaa.gov/hats/gases/OCS. html; Hannigan et al, 2022;Belviso et al, 2022a), a slowing of COS anthropogenic emissions likely being the cause of this tropospheric negative trend (Hannigan et al, 2022). However, an increasing uptake of COS by plants cannot be ruled out until a revised version of the 1980-2012 anthropogenic emissions budget of Zumkehr et al (2018), hereafter named Z-2018, is made available for the 2013-2020 period.…”