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International audience

Ammonia NH3 is now widely recognized as a major primary pollutant, deteriorating water, soil and air quality. While the importance of monitoring and regulating atmospheric NH3 emissions has been underlined for decades by experts in the field and endorsed or ratified by a multitude of international organizations, it is only recently that the issue is making its way onto the political agendas. In the past decade, it was discovered that high-resolution infrared satellites observations can measure atmospheric NH3, leading to major progress in our understanding of this atmospheric compound and its sources, and to new possibilities for benchmarking or enforcing regulations.Currently, several polar-orbiting instruments are in orbit that measure NH3 global distributions twice a day. In this talk, we present the first observations of NH3 from the Geostationary Interferometric Infrared Sounder (GIIRS) onboard the Chinese FY- 4A satellite. GIIRS measures almost all of Asia ten times per day. As its spectral range includes a large portion of the thermal infrared, the instrument allows studying for the first time the diurnal and nocturnal variations of atmospheric NH3. We analyze the daily cycle of NH3 in detail over two small regions in Pakistan and China, and how it varies across different seasons.In keeping with the temporal theme, we present in the second part of this talk, long term global trends of NH3 derived using the 2008-2018 reanalyzed IASI-NH3 dataset. Trends are presented and analyzed from the regional to the national and global scale.

International audience

In this study, we present a global fingerprint of recent changes in mid-upper stratospheric (MUSt;>25hPa) and in lower stratospheric (LSt, 150-25 hPa) ozone (O3), as well as in the correspondinglongwave radiative effects (LWRE), derived from the first 13 years of the IASI/Metop-A and -B satellitemeasurements (January 2008 – December 2020). IASI provides a unique twice daily global dataset ofvertically-resolved O3 profiles and of associated instantaneous radiative kernels (IRKs), which representthe sensitivity of the outgoing longwave radiation (OLR) flux with respect to the O3 vertical profile,allowing to monitor changes in both O3 and its corresponding LWRE in these two regions of thestratosphere. The retrievals are performed using the FORLI software, a fast radiative transfer modelbased on the optimal estimation method, set up for near real-time and large scale processing of IASIdata.We describe the O3 response to global atmospheric change and, in particular, to the decline instratospheric halogen species, which requires first identifying and quantifying natural cycles that mayproduce trend-like segments in the O3 time series. The disentanglement between the O3 response to itsnatural drivers and to the anthropogenic influence is performed by applying multivariate regressions,which account for the main geophysical drivers of O3 variation and a linear trend term, on time series ofspatially gridded daily mean O3. The results of this study confirm the effectiveness of the Montrealprotocol and its amendments. They show the first detection of a significant recovery of O3 concurrentlyin the LSt, in the MUSt and in the total column in the southern hemisphere (S.H.) from one singlesatellite dataset. The results also show a contrasting significant O3 decline in the LSt in the northernhemisphere (N.H.). A speeding up in both the O3 healing of the S.H. and in the LSt O3 decline of theN.H is also demonstrated. Finally, we show how these changes in O3 levels translate to changes in O3LWRE.

In this paper, we present the global fingerprint of recent changes in middle-upper stratosphere (MUSt; 25 hPa) ozone (O3) in comparison with lower stratosphere (LSt; 150-25 hPa) O3 derived from the first 10 years of the IASI/Metop-A satellite measurements (January 2008-December 2017). The IASI instrument provides vertically resolved O3 profiles with very high spatial and temporal (twice daily) samplings, allowing O3 changes to be monitored in these two regions of the stratosphere. By applying multivariate regression models with adapted geophysical proxies on daily mean O3 time series, we discriminate anthropogenic trends from various modes of natural variability, such as the El Niño-Southern Oscillation (ENSO). The representativeness of the O3 response to its natural drivers is first examined. One important finding relies on a pronounced contrast between a positive LSt O3 response to ENSO in the extratropics and a negative one in the tropics, with a delay of 3 months, which supports a stratospheric pathway for the ENSO influence on lower stratospheric and tropospheric O3. In terms of trends, we find an unequivocal O3 recovery from the available period of measurements in winter-spring at middle to high latitudes for the two stratospheric layers sounded by IASI ( 35 N-S in the MUSt and 45 S in the LSt) as well as in the total columns at southern latitudes (45 S) where the increase reaches its maximum. These results confirm the effectiveness of the Montreal Protocol and its amendments and represent the first detection of a significant recovery of O3 concurrently in the lower, in the middle-upper stratosphere and in the total column from one single satellite dataset. A significant decline in O3 at northern mid-latitudes in the LSt is also detected, especially in winter-spring of the Northern Hemisphere. Given counteracting trends in the LSt and MUSt at these latitudes, the decline is not categorical in total O3. When freezing the regression coefficients determined for each natural driver over the whole IASI period but adjusting a trend, we calculate a significant speeding up in the O3 response to the decline of O3-depleting substances (ODSs) in the total column, in the LSt and, to a lesser extent, in the MUSt, at high southern latitudes over the year. Results also show a small significant acceleration of the O3 decline at northern mid-latitudes in the LSt and in the total column over the last few years. That, specifically, needs urgent investigation to identify its exact origin and apprehend its impact on climate change. Additional years of IASI measurements would, however, be required to confirm the O3 change rates observed in the stratospheric layers over the last few years., SCOPUS: ar.j, info:eu-repo/semantics/published

International audience; The Earth’s Outgoing Longwave Radiation (OLR) is a key component in the study of climate feedbacks and processes. As part of the Earth’s radiation budget, it reflects how the Earth-atmosphere system compensates the incoming solar radiation at the top of the atmosphere. It can be retrieved from the radiance intensities measured by satellite sounders and integrated over all the zenith angles of observation. Since satellite instruments generally acquire the radiance at a limited number of viewing angle directions and because the radiance field is not isotropic, the conversion is however not straightforward. This problem is usually overcome by the use of empirical angular distribution models (ADMs) developed for different scene types that directly link the directional radiance measurement to the corresponding OLR. OLR estimates from dedicated broadband instruments are available since the mid-1970s; however, such instruments only provide an integrated OLR estimate over a broad spectral range. They are therefore not well suited for tracking separately the impact of the different parameters affecting the OLR (including greenhouse gases), making it difficult to track down deficiencies in climate models. Currently, several hyperspectral instruments in space acquire radiances in the thermal infrared region, and in principle, these should allow to better constrain the OLR. However, as these instruments were not specifically designed to measure the OLR, there are several challenges to overcome. Here we propose a new retrieval algorithm for the estimation of the spectrally resolved OLR from measurements made by the IASI sounder on board the Metop satellites. It is based on a set of spectrally resolved ADMs developed from synthetic spectra for a large selection of scene types associated with different states of the atmosphere and the surface. Atmospheric and surface parameters are derived from the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis dataset and selected using a dissimilarity-based subset selection algorithm. These spectral ADMs are then used to convert the measured IASI radiances into spectral OLR. We then analyze how the integrated IASI OLR compare with the CERES and integrated AIRS OLR. We present time series of OLR over the 10 years of IASI for selected spectral channels. Trends are analyzed in the spectral ranges of major climate gases (e.g. CO2, CH4), which provides robust constraints on the climatic impact of their continued rise. We also show the existence of strong trends for weaker absorbers (such as CFCs).

International audience; Carbon monoxide (CO) is an important trace gas for understanding air quality and atmospheric composition. It isa good tracer of pollution plumes and atmospheric dynamics.With three IASI instruments flying on the Metop-A, Metop-B and Metop-C satellites, any location onEarth is now observed at least six times per day in the infrared spectral range. All cloud free observations areanalysed in near real time mode.IASI CO concentrations are retrieved from the radiance data using the Fast Operational Retrievals on Lay-ers for IASI (FORLI) algorithm, based on the Optimal Estimation theory. The operational production is performedat EUMETSAT and the products are distributed in NRT via EUMETCast under the AC SAF auspices.We present here an analysis of 11 years of global distributions of CO. Comparison with MOPITT CO data(v7T/v8T, record starting in 2000) will be shown. IASI and MOPITT data are jointly assimilated in the CopernicusAtmospheric Monitoring Service (CAMS) to generate CO pollution forecasts. We will also focus on the pollutionevent that occurred in Europe in October 2017, where dust from Sahara and smoke from Portugal/Spain wildfireswere transported by hurricane Ophelia across Europe. 3D observations by ground-based, aircraft, and satellitedata compared with CAMS atmospheric composition analyses will be presented.

International audience; Formic acid (HCOOH) and acetic acid (CH3COOH) are ubiquitous atmospheric trace gases and the most abundantcarboxylic acids in the global troposphere. They have a substantial impact on the atmospheric aqueous-phasechemistry and are major sources of cloud and precipitation acidity. Together, they account for > 60% of the rain-water acidity in remote regions (e.g., over tropical and boreal forests). Sources of formic and acetic acids includedirect emissions (e.g., from biomass burning, fossil fuel, plants) and secondary production from sunlight-induceddegradation of a suite of other volatile organic compounds. However, several investigations have pointed to largeinconsistencies between measurements and model simulations, suggesting key gaps in our understanding of theirsources and the likely existence of so far unidentified sources.Here we use a neural network-based approach to retrieve total columns of formic and acetic acids from theIASI (Infrared Atmospheric Sounding Interferometer) satellite observations, and to produce daily global andregional pictures of both species. With this dataset we characterize their respective spatial distributions, seasonalvariability as well as their transport patterns from emission sources. We focus on their emission regions to studythe variability and evolution of the HCOOH-to-CH3COOH ratios. Their respective enhancement ratios withrespect to CO total columns from IASI are also investigated in fire plumes. This study contributes to improvingour understanding of the emission sources of these dominant carboxylic acids.

In this paper, we present the global fingerprint of recent changes in the mid-upper stratospheric (MUSt; > 25 hPa) ozone (O3) in comparison with the lower stratospheric (LSt, 150–25 hPa) O3 derived from the first 10 years of the IASI/Metop-A satellite measurements (January 2008–December 2017). The IASI instrument provides vertically-resolved O3 profiles with very high spatial and temporal (twice daily) samplings, allowing to monitor O3 changes in these two regions of the stratosphere. By applying multivariate regression models with adapted geophysical proxies on daily mean O3 time series, we discriminate anthropogenic trends from various modes of natural variability, such as the El Niño/Southern Oscillation – ENSO. The representativeness of the O3 response to its natural drivers is first examined. One important finding relies on a pronounced contrast between a positive LSt O3 response to ENSO in the extra-tropics and a negative one in the tropics, with a delay of 3 months, which supports a stratospheric pathway for the ENSO influence on lower stratospheric and tropospheric O3. In terms of trends, we find an unequivocal O3 recovery from the available period of measurements in winter/spring at mid-high latitudes for the two stratospheric layers sounded by IASI (>∼35° N/S in the MUSt and >∼45° S in the LSt) as well as in the total columns at southern latitudes (>∼45° S) where the increase reaches its maximum. These results confirm the effectiveness of the Montreal protocol and its amendments, and represent the first detection of a significant recovery of O3 concurrently in the lower, in the mid-upper stratosphere and in the total column from one single satellite dataset. A significant decline in O3 at northern mid-latitudes in the LSt is also detected, especially in winter/spring of the northern hemisphere. Given counteracting trends in LSt and MUSt at these latitudes, the decline is not categorical in total O3. When freezing the regression coefficients determined for each natural driver over the whole IASI period but adjusting a trend, we calculate a significant speeding up in the O3 response to the decline of O3 depleting substances (ODS) in the total column, in the LSt and, in a lesser extent, in the MUSt, at high southern latitudes over the year. A significant acceleration of the O3 decline at northern mid-latitudes in the LSt and in the total column is also highlighted over the last years. That, specifically, needs urgent investigation for identifying its exact origin and apprehending its impact on climate change.