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See detailFirst Ground-based DOAS Measurements of NO2 at Kinshasa and Comparisons with Satellite Observations
Yombo Phaka, Rodriguez ULiege; Merlaud, Alexis; Pinardi, Gaia et al

in Journal of Atmospheric and Oceanic Technology (2021)

We present the first ground-based remote sensing measurements of NO2 made in Kinshasa. They were performed from 2017 to 2019. The motivation of making observations on air pollution in Kinshasa comes from ... [more ▼]

We present the first ground-based remote sensing measurements of NO2 made in Kinshasa. They were performed from 2017 to 2019. The motivation of making observations on air pollution in Kinshasa comes from its geographical location, its demography, its climatic conditions and the different sources of NO2 existing in its surroundings. A method for recovering the vertical density of the NO2 tropospheric column (VCD) based on the Differential Optical Absorption Spectroscopy (DOAS) applied to observations at the zenith and 35° elevation angle is described. The mean value of VCDtropo observed in Kinshasa is 3 E15 molecules cm -2 . We further present first comparisons with the OMI and TROPOMI satellite observations. When comparing OMI data with our observations and using a linear regression analysis, we find a slope of 0.34 and a correlation coefficient of 0.50 for 51 days of coincidences over 2017-2019. Similar comparisons with TROPOMI for 44 days show a slope of 0.41 and a correlation coefficient of 0.72. This study opens up perspectives for further air quality related studies in Kinshasa and central Africa. [less ▲]

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See detailUbiquitous atmospheric production of organic acids mediated by cloud droplets
Franco, B.; Blumenstock, T.; Cho, C. et al

in Nature (2021), 593(7858), 233--237

Atmospheric acidity is increasingly determined by carbon dioxide and organic acids. Among the latter, formic acid facilitates the nucleation of cloud droplets4 and contributes to the acidity of clouds and ... [more ▼]

Atmospheric acidity is increasingly determined by carbon dioxide and organic acids. Among the latter, formic acid facilitates the nucleation of cloud droplets4 and contributes to the acidity of clouds and rainwater. At present, chemistry–climate models greatly underestimate the atmospheric burden of formic acid, because key processes related to its sources and sinks remain poorly understood. Here we present atmospheric chamber experiments that show that formaldehyde is efficiently converted to gaseous formic acid via a multiphase pathway that involves its hydrated form, methanediol. In warm cloud droplets, methanediol undergoes fast outgassing but slow dehydration. Using a chemistry–climate model, we estimate that the gas-phase oxidation of methanediol produces up to four times more formic acid than all other known chemical sources combined. Our findings reconcile model predictions and measurements of formic acid abundance. The additional formic acid burden increases atmospheric acidity by reducing the pH of clouds and rainwater by up to 0.3. The diol mechanism presented here probably applies to other aldehydes and may help to explain the high atmospheric levels of other organic acids that affect aerosol growth and cloud evolution. [less ▲]

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See detailMAX-DOAS measurements of NO2 and H2CO in the city of Kinshasa from 2019 2020
Yombo Phaka, Rodriguez ULiege; Merlaud, Alexis; Pinardi, Gaia et al

Conference (2021, April 20)

The first MAX-DOAS measurements of NO2 and H2CO were presented in this study. A preliminary comparison with TROPOMI is also presented

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See detailPreliminary study of long-term trends of N2O as a proxy of the Brewer-Dobson Circulation
Minganti, Daniele ULiege; Chabrillat, Simon; Errera, Quentin et al

Scientific conference (2021, February 26)

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See detailCOVID-19 Crisis Reduces Free Tropospheric Ozone Across the Northern Hemisphere
Steinbrecht, Wolfgang; Kubistin, Dagmar; Plass-Dülmer, Christian et al

in Geophysical Research Letters (2021), 48(5), 2020091987

Abstract Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude ... [more ▼]

Abstract Throughout spring and summer 2020, ozone stations in the northern extratropics recorded unusually low ozone in the free troposphere. From April to August, and from 1 to 8 kilometers altitude, ozone was on average 7% (≈4 nmol/mol) below the 2000–2020 climatological mean. Such low ozone, over several months, and at so many stations, has not been observed in any previous year since at least 2000. Atmospheric composition analyses from the Copernicus Atmosphere Monitoring Service and simulations from the NASA GMI model indicate that the large 2020 springtime ozone depletion in the Arctic stratosphere contributed less than one-quarter of the observed tropospheric anomaly. The observed anomaly is consistent with recent chemistry-climate model simulations, which assume emissions reductions similar to those caused by the COVID-19 crisis. COVID-19 related emissions reductions appear to be the major cause for the observed reduced free tropospheric ozone in 2020. [less ▲]

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See detailClimatological impact of the Brewer–Dobson circulation on the N2O budget in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses
Minganti, Daniele ULiege; Chabrillat, Simon; Christophe, Yves et al

in Atmospheric Chemistry and Physics (2020), 20(21), 1260912631

The Brewer–Dobson circulation (BDC) is a stratospheric circulation characterized by upwelling of tropospheric air in the tropics, poleward flow in the stratosphere, and downwelling at mid and high ... [more ▼]

The Brewer–Dobson circulation (BDC) is a stratospheric circulation characterized by upwelling of tropospheric air in the tropics, poleward flow in the stratosphere, and downwelling at mid and high latitudes, with important implications for chemical tracer distributions, stratospheric heat and momentum budgets, and mass exchange with the troposphere. As the photochemical losses of nitrous oxide (N2O) are well known, model differences in its rate of change are due to transport processes that can be separated into the mean residual advection and the isentropic mixing terms in the transformed Eulerian mean (TEM) framework. Here, the climatological impact of the stratospheric BDC on the long-lived tracer N2O is evaluated through a comparison of its TEM budget in the Whole Atmosphere Community Climate Model (WACCM), in a chemical reanalysis of the Aura Microwave Limb Sounder version 2 (BRAM2) and in a chemistry transport model (CTM) driven by four modern reanalyses: the European Centre for Medium-Range Weather Forecasts Interim reanalysis (ERA-Interim; Dee et al., 2011), the Japanese 55-year Reanalysis (JRA-55; Kobayashi et al., 2015), and the Modern-Era Retrospective analysis for Research and Applications version 1 (MERRA; Rienecker et al., 2011) and version 2 (MERRA-2; Gelaro et al., 2017). The effects of stratospheric transport on the N2O rate of change, as depicted in this study, have not been compared before across this variety of datasets and have never been investigated in a modern chemical reanalysis. We focus on the seasonal means and climatological annual cycles of the two main contributions to the N2O TEM budget: the vertical residual advection and the horizontal mixing terms. The N2O mixing ratio in the CTM experiments has a spread of approximately ∼20 % in the middle stratosphere, reflecting the large diversity in the mean age of air obtained with the same CTM experiments in a previous study. In all datasets, the TEM budget is closed well; the agreement between the vertical advection terms is qualitatively very good in the Northern Hemisphere, and it is good in the Southern Hemisphere except above the Antarctic region. The datasets do not agree as well with respect to the horizontal mixing term, especially in the Northern Hemisphere where horizontal mixing has a smaller contribution in WACCM than in the reanalyses. WACCM is investigated through three model realizations and a sensitivity test using the previous version of the gravity wave parameterization. The internal variability of the horizontal mixing in WACCM is large in the polar regions and is comparable to the differences between the dynamical reanalyses. The sensitivity test has a relatively small impact on the horizontal mixing term, but it significantly changes the vertical advection term and produces a less realistic N2O annual cycle above the Antarctic. In this region, all reanalyses show a large wintertime N2O decrease, which is mainly due to horizontal mixing. This is not seen with WACCM, where the horizontal mixing term barely contributes to the TEM budget. While we must use caution in the interpretation of the differences in this region (where the reanalyses show large residuals of the TEM budget), they could be due to the fact that the polar jet is stronger and is not tilted equatorward in WACCM compared with the reanalyses. We also compare the interannual variability in the horizontal mixing and the vertical advection terms between the different datasets. As expected, the horizontal mixing term presents a large variability during austral fall and boreal winter in the polar regions. In the tropics, the interannual variability of the vertical advection term is much smaller in WACCM and JRA-55 than in the other experiments. The large residual in the reanalyses and the disagreement between WACCM and the reanalyses in the Antarctic region highlight the need for further investigations on the modeling of transport in this region of the stratosphere. [less ▲]

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See detailDetection and attribution of wildfire pollution in the Arctic and northern midlatitudes using a network of Fourier-transform infrared spectrometers and GEOS-Chem
Lutsch, E.; Strong, K.; Jones, D. B. A. et al

in Atmospheric Chemistry and Physics (2020), 20(21), 12813--12851

Abstract. We present a multiyear time series of column abundances of carbon monoxide (CO), hydrogen cyanide (HCN), and ethane (C2H6) measured using Fourier transform infrared (FTIR) spectrometers at 10 ... [more ▼]

Abstract. We present a multiyear time series of column abundances of carbon monoxide (CO), hydrogen cyanide (HCN), and ethane (C2H6) measured using Fourier transform infrared (FTIR) spectrometers at 10 sites affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC). Six are high-latitude sites: Eureka, Ny-Ålesund, Thule, Kiruna, Poker Flat, and St. Petersburg, and four are midlatitude sites: Zugspitze, Jungfraujoch, Toronto, and Rikubetsu. For each site, the interannual trends and seasonal variabilities of the CO time series are accounted for, allowing background column amounts to be determined. Enhancements above the seasonal background were used to identify possible wildfire pollution events. Since the abundance of each trace gas emitted in a wildfire event is specific to the type of vegetation burned and the burning phase, correlations of CO to the long-lived wildfire tracers HCN and C2H6 allow for further confirmation of the detection of wildfire pollution. A GEOS-Chem tagged CO simulation with Global Fire Assimilation System (GFASv1.2) biomass burning emissions was used to determine the source attribution of CO concentrations at each site from 2003 to 2018. For each detected wildfire pollution event, FLEXPART back-trajectory simulations were performed to determine the transport times of the smoke plume. Accounting for the loss of each species during transport, the enhancement ratios of HCN and C2H6 with respect to CO were converted to emission ratios. We report mean emission ratios with respect to CO for HCN and C2H6 of 0.0047 and 0.0092, respectively, with a standard deviation of 0.0014 and 0.0046, respectively, determined from 23 boreal North American wildfire events. Similarly, we report mean emission ratios for HCN and C2H6 of 0.0049 and 0.0100, respectively, with a standard deviation of 0.0025 and 0.0042, respectively, determined from 39 boreal Asian wildfire events. The agreement of our emission ratios with literature values illustrates the capability of ground-based FTIR measurements to quantify biomass burning emissions. We provide a comprehensive dataset that quantifies HCN and C2H6 emission ratios from 62 wildfire pollution events. Our dataset provides novel emission ratio estimates, which are sparsely available in the published literature, particularly for boreal Asian sources. [less ▲]

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See detailNDACC Infrared working group report 2020
Mahieu, Emmanuel ULiege; Hannigan, J. W.

Conference (2020, November 05)

Working group report to the Steering Committee of the NDACC network, including among others the impact of the covid-19 pandemic on the onsite operations and on the atmosphere.

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See detailObserved and simulated atmospheric inorganic fluorine: short term and long term trends related to circulation changes
Prignon, Maxime ULiege; Bernath, P. F.; Chabrillat, S. et al

Conference (2020, October 15)

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See detailTrends of atmospheric water vapour in Switzerland from ground-based radiometry, FTIR and GNSS data
Bernet, L.; Brockmann, E.; von Clarmann, T. et al

in Atmospheric Chemistry and Physics (2020), 20(19), 11223--11244

Vertically integrated water vapour (IWV) is expected to increase globally in a warming climate. To determine whether IWV increases as expected on a regional scale, we present IWV trends in Switzerland ... [more ▼]

Vertically integrated water vapour (IWV) is expected to increase globally in a warming climate. To determine whether IWV increases as expected on a regional scale, we present IWV trends in Switzerland from ground-based remote sensing techniques and reanalysis models, considering data for the time period 1995 to 2018. We estimate IWV trends from a ground-based microwave radiometer in Bern, from a Fourier transform infrared (FTIR) spectrometer at Jungfraujoch, from reanalysis data (ERA5 and MERRA-2) and from Swiss ground-based Global Navigation Satellite System (GNSS) stations. Using a straightforward trend method, we account for jumps in the GNSS data, which are highly sensitive to instrumental changes. We found that IWV generally increased by 2 % per decade to 5 % per decade,with deviating trends at some GNSS stations. Trends were significantly positive at 17 % of all GNSS stations, which of-ten lie at higher altitudes (between 850 and 1650 m above sea level). Our results further show that IWV in Bern scales to air temperature as expected (except in winter), but the IWV–temperature relation based on reanalysis data in the whole of Switzerland is not clear everywhere. In addition to our positive IWV trends, we found that the radiometer in Bern agrees within 5 % with GNSS and reanalyses. At the Jungfraujoch high-altitude station, we found a mean difference of 0.26 mm (15 %) between the FTIR and coincident GNSS data, improving to 4 % after an antenna update in 2016. In general,we showed that ground-based GNSS data are highly valuable for climate monitoring, given that the data have been homogeneously reprocessed and that instrumental changes are accounted for. We found a response of IWV to rising temperature in Switzerland, which is relevant for projected changes in local cloud and precipitation processes [less ▲]

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See detailObserved Hemispheric Asymmetry in Stratospheric Transport Trends From 1994 to 2018
Strahan, Susan E.; Smale, Dan; Douglass, Anne R. et al

in Geophysical Research Letters (2020), 47(17), 2020088567

Abstract Total columns of the trace gases nitric acid (HNO3) and hydrogen chloride (HCl) are sensitive to variations in the lower stratospheric age of air, a quantity that describes transport time scales ... [more ▼]

Abstract Total columns of the trace gases nitric acid (HNO3) and hydrogen chloride (HCl) are sensitive to variations in the lower stratospheric age of air, a quantity that describes transport time scales in the stratosphere. Analyses of HNO3 and HCl columns from the Network for the Detection of Atmospheric Composition Change panning 77°S to 79°N have detected changes in the extratropical stratospheric transport circulation from 1994 to 2018. The HNO3 and HCl analyses combined with the age of air from a simulation using the MERRA2 reanalysis show that the Southern Hemisphere lower stratosphere has become 1 month/decade younger relative to the Northern Hemisphere, largely driven by the Southern Hemisphere transport circulation. The analyses reveal multiyear anomalies with a 5- to 7-year period driven by interactions between the circulation and the quasi-biennial oscillation in tropical winds. This hitherto unrecognized variability is large relative to hemispheric transport trends and may bias ozone trend regressions. [less ▲]

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See detailA statistical analysis of time trends in atmospheric ethane
Friedrich, Marina; Beutner, Eric; Reuvers, Hanno et al

in Climatic Change (2020)

Ethane is the most abundant non-methane hydrocarbon in the Earth’s atmosphere and an important precursor of tropospheric ozone through various chemical pathways. Ethane is also an indirect greenhouse gas ... [more ▼]

Ethane is the most abundant non-methane hydrocarbon in the Earth’s atmosphere and an important precursor of tropospheric ozone through various chemical pathways. Ethane is also an indirect greenhouse gas (global warming potential), influencing the atmospheric lifetime of methane through the consumption of the hydroxyl radical (OH). Understanding the development of trends and identifying trend reversals in atmospheric ethane is thereforecrucial. Our dataset consists of four series of daily ethane columns. As with many otherdecadal time series, our data are characterized by autocorrelation, heteroskedasticity, and seasonal effects. Additionally, missing observations due to instrument failure or unfavorable measurement conditions are common in such series. The goal of this paper is therefore to analyze trends in atmospheric ethane with statistical tools that correctly address these data features. We present selected methods designed for the analysis of time trends and trend reversals. We consider bootstrap inference on broken linear trends and smoothly varying nonlinear trends. In particular, for the broken trend model, we propose a bootstrap method for inference on the break location and the corresponding changes in slope. For the smooth trend model, we construct simultaneous confidence bands around the non parametrically estimated trend. Our autoregressive wild bootstrap approach, combined with a seasonal filter, is able to handle all issues mentioned above (we provide R code for all proposed methods on https://www.stephansmeekes.nl/code.). [less ▲]

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See detailDOAS Measurements of NO2 at Kinshasa and Comparisons with Satellite Observations
Yombo Phaka, Rodriguez ULiege; Merlaud, A; Pinardi, G et al

Conference (2020, July 14)

Recent studies show that air pollution also affects Africa. Air quality is worsening in large cities with growing populations. Satellite observations over some Central African cities seem to confirm this ... [more ▼]

Recent studies show that air pollution also affects Africa. Air quality is worsening in large cities with growing populations. Satellite observations over some Central African cities seem to confirm this pollution for species such as NO2, HCHO and aerosols. The sources of pollution are generally different from those found in Europe for example. In Central Africa, particularly in the Congo Basin, the main sources of NO2 and HCHO emissions are forest fires and the use of embers in cooking. Kinshasa, the capital of the Democratic Republic of Congo, a large megalopolis of about 11 million inhabitants, like several other large cities in Africa, lack ground-based atmospheric measurement systems. To improve this situation, the researchers of the University of Kinshasa (Unikin) in collaboration with the UV-Vis group of the Belgian Institute for Space Aeronomy (IASB) have set up a first installation of a simple atmospheric observation equipment. This equipment was installed on the roof of the Faculty of Sciences of Unikin ( -4.42°S, 15.31°E) in May 2017 and has operated until November 2019. The instrument is based on a compact AVANTES spectrometer covering the spectral range 290 - 450 nm with 0.7 nm resolution. The spectrometer is a Czerny-Turner type with an entry slit of 50 µm wide, and an array of 1200 l/mm. A 10 m long and 600 µm thick diameter optical fiber is connected to the spectrometer to receive the incident light beam from the sky. Measurements were mainly made by looking in a fixed direction. In November 2019, a Multi-Axis DOAS instrument (MAX-DOAS) has been installed to replace the first instrument. The measurements clearly show the signature of polluting species such as NO2 and HCHO in Kinshasa’s atmosphere. In this study, we therefore show all the different steps of the algorithm we used to obtain the vertical columns from the observations of the instrument installed in Kinshasa. We present a first comparison of these ground-based observations of NO2 in Kinshasa with those from the OMI and TROPOMI satellites for clear days between May and November 2017. [less ▲]

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See detailTROPOMI--Sentinel-5 Precursor formaldehyde validation using an extensive network of ground-based Fourier-transform infrared stations
Vigouroux, C.; Langerock, B.; Bauer Aquino, C. A. et al

in Atmospheric Measurement Techniques (2020), 13(7), 3751--3767

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See detailFourier transform infrared time series of tropospheric HCN in eastern China: seasonality interannual variability, and source attribution
Sun, Y.; Liu, C.; Zhang, L. et al

in Atmospheric Chemistry and Physics (2020), 20(9), 5437--5456

We analyzed seasonality and interannual variability of tropospheric hydrogen cyanide (HCN) columns in densely populated eastern China for the first time. The results were derived from solar absorption ... [more ▼]

We analyzed seasonality and interannual variability of tropospheric hydrogen cyanide (HCN) columns in densely populated eastern China for the first time. The results were derived from solar absorption spectra recorded with a ground-based high-spectral-resolution Fourier transform infrared (FTIR) spectrometer in Hefei (31°54′ N, 117°10′ E) between 2015 and 2018. The tropospheric HCN columns over Hefei, China, showed significant seasonal variations with three monthly mean peaks throughout the year. The magnitude of the tropospheric HCN column peaked in May, September, and December. The tropospheric HCN column reached a maximum monthly mean of (9.8±0.78)E15 molecules cm−2 in May and a minimum monthly mean of (7.16±0.75)E15 molecules cm−2 in November. In most cases, the tropospheric HCN columns in Hefei (32°N) are higher than the FTIR observations in Ny-Ålesund (79°N), Kiruna (68°N), Bremen (53°N), Jungfraujoch (47°N), Toronto (44°N), Rikubetsu (43°N), Izana (28°N), Mauna Loa (20°N), La Reunion Maido (21°S), Lauder (45°S), and Arrival Heights (78°S) that are affiliated with the Network for Detection of Atmospheric Composition Change (NDACC). Enhancements of tropospheric HCN column were observed between September 2015 and July 2016 compared to the same period of measurements in other years. The magnitude of the enhancement ranges from 5 % to 46 % with an average of 22 %. Enhancement of tropospheric HCN (ΔHCN) is correlated with the concurrent enhancement of tropospheric CO (ΔCO), indicating that enhancements of tropospheric CO and HCN were due to the same sources. The GEOS-Chem tagged CO simulation, the global fire maps, and the potential source contribution function (PSCF) values calculated using back trajectories revealed that the seasonal maxima in May are largely due to the influence of biomass burning in Southeast Asia (SEAS) (41±13.1 %), Europe and boreal Asia (EUBA) (21±9.3 %), and Africa (AF) (22±4.7 %). The seasonal maxima in September are largely due to the influence of biomass burnings in EUBA (38±11.3 %), AF (26±6.7 %), SEAS (14±3.3 %), and North America (NA) (13.8±8.4 %). For the seasonal maxima in December, dominant contributions are from AF (36±7.1 %), EUBA (21±5.2 %), and NA (18.7±5.2 %). The tropospheric HCN enhancement between September 2015 and July 2016 at Hefei (32°N) was attributed to an elevated influence of biomass burnings in SEAS, EUBA, and Oceania (OCE) in this period. In particular, an elevated number of fires in OCE in the second half of 2015 dominated the tropospheric HCN enhancement between September and December 2015. An elevated number of fires in SEAS in the first half of 2016 dominated the tropospheric HCN enhancement between January and July 2016. [less ▲]

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See detailN2O-based climatology of the Brewer Dobson Circulation in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses
Minganti, Daniele ULiege; Chabrillat, Simon; Christophe, Yves et al

Conference (2020, May 05)

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See detailDOAS measurements of NO2 and H2CO at Kinshasa and Comparisons with Satellites Observations
Yombo Phaka, Rodriguez ULiege; Merlaud, Alexis; Pinardi, Gaia et al

Poster (2020, April 04)

Africa experiences a fast urban inhabitants growth, caused by the largest population boom in the world, combined with rural exodus. Many cities are heavily affected by air pollution. It is therefore ... [more ▼]

Africa experiences a fast urban inhabitants growth, caused by the largest population boom in the world, combined with rural exodus. Many cities are heavily affected by air pollution. It is therefore essential to monitor the concentrations of the various polluting species such as NO2, HCHO, O3 and aerosols, which have a direct impact on the population health. The sources of pollutant in Africa are different from those found in Europe. For example, forest fires and household cooking largely contribute to the NO2 and HCHO burdens in Central Africa. However, many large African cities, such as the City of Kinshasa, capital of the Democratic Republic of Congo, do not have atmospheric measurement instruments. In order to tackle the lack of measurements in Kinshasa, the Royal Belgian Institute of Space Aeronomy (BIRA-IASB) has, in collaboration with the University of Kinshasa (UniKin), installed an optical remote sensing instrument on the UniKin site (-4.42°S, 15.31°E). Installed in May 2017, the instrument has been in operation until today and provides data to measure the column amounts of several polluting species in the atmosphere of Kinshasa. The instrument is based on a compact AVANTES spectrometer covering the spectral range 290 - 450 nm with 0.7 nm resolution. The spectrometer is a Czerny-Turner type with an entry slit of 50 μm wide, and an array of 1200 l/mm. A 10 m long and 600 μm diameter optical fiber is connected to the spectrometer to receive the incident light beam from the sky. Measurements were mainly made by looking in a fixed direction until November 2019. Since then, a Multi-Axis geometry (MAX-DOAS) has been implemented. The measurements provided by this DOAS instrument allowed us to start studying the atmosphere of Kinshasa using the QDOAS software, which allows us to find the oblique columns of different observed species. This poster will present the instrument, the database and the procedure used to convert these oblique columns into vertical columns, using the air mass factors calculated with the radiative transfer model. We also present our first MAX-DOAS results, analyzed using the retrieval tools of the ESA FRM4DOAS project. The study of current results clearly shows the signature of polluting species such as NO2, HCHO in the atmosphere of Kinshasa. We also use simulations by the GEOS-Chem chemistry transport model to evaluate the magnitude of the emissions needed to explain the observed column amounts. These observations made in Kinshasa could contribute to the validation of satellite products and the refinement of models. We present a first comparison of Kinshasa's ground-based observations with those of the OMI and TROPOMI satellites [less ▲]

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See detailSpaceborne Measurements of Formic and Acetic Acid: A Global View of the Regional Sources
Franco, B; Clarisse, L; Stavrakou, T et al

in Geophysical Research Letters (2020), 47

Formic (HCOOH) and acetic acid (CH3COOH) are the most abundant carboxylic acids in the Earth’s atmosphere and key compounds to aqueous-phase chemistry. Here we present the first distributions of CH3COOH ... [more ▼]

Formic (HCOOH) and acetic acid (CH3COOH) are the most abundant carboxylic acids in the Earth’s atmosphere and key compounds to aqueous-phase chemistry. Here we present the first distributions of CH3COOH retrieved from the 2007–2018 satellite observations of the nadir-looking Infrared Atmospheric Sounding Interferometer (IASI), using a neural network-based retrieval approach. A joint analysis with the IASI HCOOH product reveals that the two species exhibit similar distributions, seasonality and atmospheric burden, pointing to major common sources. We show that their abundance is highly correlated to isoprene and monoterpenes emissions, as well as to biomass burning. Over Africa, evidence is provided that residual smoldering combustion might be a major driver of the HCOOH and CH3COOH seasonality. Earlier seasonal enhancement of HCOOH at Northern Hemisphere middle and high latitudes, and late seasonal secondary peaks of CH3COOH in the tropics, suggest that sources and production pathways specific to each species are also at play. [less ▲]

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See detailQuantification of Stratospheric Ozone Recovery Due to Anthropogenic Halogens
Salawitch, R. J.; Tribett, W.; Wales, P. et al

Conference (2020, January 14)

Human release of CFCs and other ozone depleting substances (ODS) has led to a slow, steady erosion of the thickness of the global ozone layer over the past several decades. The ozone layer has begun to ... [more ▼]

Human release of CFCs and other ozone depleting substances (ODS) has led to a slow, steady erosion of the thickness of the global ozone layer over the past several decades. The ozone layer has begun to recover due to actions taken under the Montreal Protocol, which has led to a decrease in the atmospheric abundance of ozone depleting substances. Yet, unreported emissions of CFC-11 have led to a slower than expected decline, and there has been a rise in the atmospheric abundance of chlorinated very short lived (VSL) compounds not regulated under the Montreal Protocol. In this presentation, we examine time series of ozone and halogens from a variety of observational platforms to quantify the attribution of the change in stratospheric ozone that is due to halogens. Our focus is on the extra-polar region: i.e., the state of the ozone layer between 55S and 55N where the vast majority of the world’s population resides. We will quantify the effect of continued release of CFC-11 and the presence of chlorinated VSL species on the recovery of the ozone layer. Additionally, we will use atmospheric observations to evaluate several proposed formulations for defining the quantity known as “Equivalent Effective Stratospheric Chlorine” (EESC) and assess the impact of these formulations on the projected recovery of the ozone layer. [less ▲]

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