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See detailAnalysis of historical grating spectra: Jungfraujoch atmospheric database extended back to 1977
Demoulin, Philippe ULg; Roland, Ginette; Bader, Whitney ULg et al

Conference (2011, November 10)

Historical solar spectra recorded at the Jungfraujoch station with a high-resolution grating spectrometer have been re-analyzed to derive total columns of a series of atmospheric gases. This instrument ... [more ▼]

Historical solar spectra recorded at the Jungfraujoch station with a high-resolution grating spectrometer have been re-analyzed to derive total columns of a series of atmospheric gases. This instrument, built and operated by the University of Liège (Belgium), was used in the Sixties and Seventies to record two solar spectrum atlases extending from the near-UV to the near-IR. From 1977 to 1989, it was also regularly used to record narrow spectral intervals in the mid-infrared, encompassing absorption lines of gases of atmospheric interest, e.g. CH4, HF, HCl, H2O, N2O, NO2, C2H6, O3 and CO. More than 10 thousand spectra were recorded during this period. The total columns derived from these grating spectra have been combined with the FTIR columns derived at the Jungfraujoch since the mid-1980s, in order to derive the temporal evolution of various target gases for the period 1977-2011. [less ▲]

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See detailChanges in atmospheric composition discerned from long-term NDACC measurements: trends in direct greenhouse gases derived from infrared solar absorption spectra recorded at the Jungfraujoch station
Mahieu, Emmanuel ULg; Duchatelet, Pierre ULg; Zander, Rodolphe ULg et al

Poster (2011, October 25)

The University of Liège (ULg) is operating -under clear sky conditions- two state-of-the-art Fourier Transform Infrared (FTIR) spectrometers at the high-altitude research station of the Jungfraujoch ... [more ▼]

The University of Liège (ULg) is operating -under clear sky conditions- two state-of-the-art Fourier Transform Infrared (FTIR) spectrometers at the high-altitude research station of the Jungfraujoch (Swiss Alps, 46.5ºN, 3580m asl), within the framework of the Network for the Detection of Atmospheric Composition Changes (NDACC). Routine FTIR operation started in 1984. Since then, it has been continued without disruption, allowing collecting more than 45000 high-resolution broadband IR solar absorption spectra, between 2 and 16 µm, using either HgCdTe or InSb detectors as well as a suite of optical filters. Typically, the spectral resolutions achieved lie in the 0.003 to 0.009 cm-1 interval while signal-to-noise ratios of 1000 and more are reached. Numerous narrow-band IR spectra essentially recorded from 1976 to 1989 with grating instruments are also available. Their analyses with modern tools have recently started [Bader et al., 2011] and will be pursued to consistently extend our datasets back in the 1970s. Geophysical parameters are deduced from the ULg observational database either with the SFIT-1, SFIT-2 or PROFFIT-9 algorithm, allowing producing total column time series of the target gases. In addition, information on their vertical distributions with altitude can generally be derived when using SFIT-2 or PROFFIT-9 which both implement the Optimal Estimation Method of Rodgers [1990]. Presently, more than two dozen atmospheric species are systematically retrieved from the Jungfraujoch observations, allowing the monitoring of key constituents of the Earth's atmosphere which play important roles in stratospheric ozone depletion and/or in global warming. This communication will focus on the direct and major greenhouse gases available from our database, namely water vapor, CO2, CH4, N2O, tropospheric ozone, CFC-11, CFC-12, HCFC-22, CCl4, SF6, as well as CF4 which has recently been added to our targets list [Duchatelet et al., 2011]. Trends and associated uncertainties characterizing the available -and often multi-decadal- time series have been derived or updated with a statistical bootstrap resampling tool [Gardiner et al., 2008], they will be presented and critically compared with data available from the literature. [less ▲]

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See detailCarbon monoxide (CO) and ethane (C2H6) trends from ground-based solar FTIR measurements at six European stations, comparison and sensitivity analysis with the EMEP model
Angelbratt, J.; Mellqvist, J.; Simpson, D. et al

in Atmospheric Chemistry and Physics (2011), 11(17), 9253--9269

Trends in the CO and C2H6 partial columns ~0–15 km) have been estimated from four European ground-based solar FTIR (Fourier Transform InfraRed) stations for the 1996–2006 time period. The CO trends from ... [more ▼]

Trends in the CO and C2H6 partial columns ~0–15 km) have been estimated from four European ground-based solar FTIR (Fourier Transform InfraRed) stations for the 1996–2006 time period. The CO trends from the four stations Jungfraujoch, Zugspitze, Harestua and Kiruna have been estimated to −0.45 ± 0.16% yr−1, −1.00 ± 0.24% yr−1, −0.62 ± 0.19 % yr−1 and −0.61 ± 0.16% yr−1, respectively. The corresponding trends for C2H6 are −1.51 ± 0.23% yr−1, −2.11 ± 0.30% yr−1, −1.09 ± 0.25% yr−1 and −1.14 ± 0.18% yr−1. All trends are presented with their 2-σ confidence intervals. To find possible reasons for the CO trends, the global-scale EMEP MSC-W chemical transport model has been used in a series of sensitivity scenarios. It is shown that the trends are consistent with the combination of a 20% decrease in the anthropogenic CO emissions seen in Europe and North America during the 1996–2006 period and a 20% increase in the anthropogenic CO emissions in East Asia, during the same time period. The possible impacts of CH4 and biogenic volatile organic compounds (BVOCs) are also considered. The European and global-scale EMEP models have been evaluated against the measured CO and C2H6 partial columns from Jungfraujoch, Zugspitze, Bremen, Harestua, Kiruna and Ny-Ålesund. The European model reproduces, on average the measurements at the different sites fairly well and within 10–22% deviation for CO and 14–31% deviation for C2H6. Their seasonal amplitude is captured within 6–35% and 9–124% for CO and C2H6, respectively. However, 61–98% of the CO and C2H6 partial columns in the European model are shown to arise from the boundary conditions, making the global-scale model a more suitable alternative when modeling these two species. In the evaluation of the global model the average partial columns for 2006 are shown to be within 1–9% and 37–50% of the measurements for CO and C2H6, respectively. The global model sensitivity for assumptions made in this paper is also analyzed. [less ▲]

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See detailA new method to detect long term trends of methane (CH4) and nitrous oxide (N2O) total columns measured within the NDACC ground-based high resolution solar FTIR network
Angelbratt, J.; Mellqvist, J.; Blumenstock, T. et al

in Atmospheric Chemistry and Physics (2011), 11(13), 6167--6183

Total columns measured with the ground-based solar FTIR technique are highly variable in time due to atmospheric chemistry and dynamics in the atmosphere above the measurement station. In this paper, a ... [more ▼]

Total columns measured with the ground-based solar FTIR technique are highly variable in time due to atmospheric chemistry and dynamics in the atmosphere above the measurement station. In this paper, a multiple regression model with anomalies of air pressure, total columns of hydrogen fluoride (HF) and carbon monoxide (CO) and tropopause height are used to reduce the variability in the methane (CH4) and nitrous oxide (N2O) total columns to estimate reliable linear trends with as small uncertainties as possible. The method is developed at the Harestua station (60 N, 11 E, 600m a.s.l.) and used on three other European FTIR stations, i.e. Jungfraujoch (47 N, 8 E, 3600m a.s.l.), Zugspitze (47 N, 11 E, 3000m a.s.l.), and Kiruna (68 N, 20 E, 400m a.s.l.). Linear CH4 trends between 0.13±0.01-0.25±0.02%yr-1 were estimated for all stations in the 1996-2009 period. A piecewise model with three separate linear trends, connected at change points, was used to estimate the short term fluctuations in the CH4 total columns. This model shows a growth in 1996–1999 followed by a period of steady state until 2007. From 2007 until 2009 the atmospheric CH4 amount increases between 0.57±0.22–1.15±0.17%yr-1. Linear N2O trends between 0.19±0.01–0.40±0.02%yr-1 were estimated for all stations in the 1996-2007 period, here with the strongest trend at Harestua and Kiruna and the lowest at the Alp stations. From the N2O total columns crude tropospheric and stratospheric partial columns were derived, indicating that the observed difference in the N2O trends between the FTIR sites is of stratospheric origin. This agrees well with the N2O measurements by the SMR instrument onboard the Odin satellite showing the highest trends at Harestua, 0.98±0.28%yr-1, and considerably smaller trends at lower latitudes, 0.27±0.25%yr-1. The multiple regression model was compared with two other trend methods, the ordinary linear regression and a Bootstrap algorithm. The multiple regression model estimated CH4 and N2O trends that differed up to 31% compared to the other two methods and had uncertainties that were up to 300% lower. Since the multiple regression method were carefully validated this stresses the importance to account for variability in the total columns when estimating trend from solar FTIR data. [less ▲]

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See detailFluorine in the atmosphere: Inorganic fluorine budget and long-term trends based on FTIR measurements at Jungfraujoch
Duchatelet, Pierre ULg

Doctoral thesis (2011)

High resolution solar spectra are routinely recorded since more than two decades by the University of Liège at the International Scientific Station of the Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580 m ... [more ▼]

High resolution solar spectra are routinely recorded since more than two decades by the University of Liège at the International Scientific Station of the Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580 m asl) with Fourier Transform Infrared (FTIR) spectrometers. Over the last years, major improvements have been implemented in the algorithms used to retrieve the abundances of atmospheric constituents accessible to the FTIR technique. Now, in addition to total column, information on the vertical distribution of the target gas is often available, allowing producing partial column data sets. We take advantage of these improvements to generate and characterize long-term total and partial columns time series of some important inorganic fluorinated trace gases deduced from FTIR measurements performed at Jungfraujoch. First, our investigations on hydrogen fluoride (HF) indicate that the adoption of a Galatry line shape model for this species significantly improves the fitting quality of the retrievals. The sensitivity of our FTIR measurements to HF inversions in three distinct regions that range from the low to the high stratosphere is confirmed thanks to products derived from two satellites and from two numerical models. We further demonstrate that the HF seasonal variations that occur in the low stratosphere are mainly responsible for the seasonal cycle observed in our HF total column time series. We have also developed an original multi-spectrum multi-window retrieval strategy allowing to derive, for the first time, some information on the vertical distribution of carbonyl fluoride (COF2) from ground-based FTIR measurements. After comparison with model data, our COF2 and HF FTIR datasets are combined to assess the atmospheric inorganic fluorine burden Fy. A trend analysis of our HF, COF2 and Fy time series is then performed for four different time periods spanning the 1985-2010 time interval. While we observe a recent stabilization for HF, corresponding COF2 data show a significant rise, after a period of significant reduction in its accumulation rate. This is probably ascribable to the combination of the decrease of its main source gas CFC-12 with the increase of the substitute product HCFC-22. However, this increase in the COF2 rate of change does not significantly impact the Fy trend, which is essentially driven by the change in HF. In addition, we show that the partitioning between the two major fluorine reservoirs HF and COF2 has not changed since the beginning of this century. Together, they account for around 95% of total inorganic fluorine in the atmosphere. Finally, we study the long-term evolution of carbon tetrafluoride (CF4), for the first time from ground-based FTIR measurements. The trend analysis of our time series indicates a slowing, initiated during the nineties, in the CF4 growth rate despite the fact that the absolute loading of this compound is still increasing. Our linear accumulation rates are consistent with those deduced from space or surface measurements. [less ▲]

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See detailAdvanced exploitation of Ground-Based measurements for Atmospheric Chemistry and Climate Applications "AGACC"
De Mazière, Martine; De Backer, Hugo; Carleer, Michel et al

Report (2011)

We live in an era in which human activities are causing significant changes to the atmospheric environment which result in local to global consequences on the ecosystems. Changes in the atmospheric ... [more ▼]

We live in an era in which human activities are causing significant changes to the atmospheric environment which result in local to global consequences on the ecosystems. Changes in the atmospheric composition impact our climate via chemical and dynamical feedback mechanisms; in many instances they also affect air quality, and the health of the biosphere. Monitoring and understanding those changes and their consequences is fundamental to establish adequate actions for adaptation to and mitigation of the environmental changes. Furthermore, after implementation of regulatory measures like the Montreal Protocol, it is necessary to verify whether the measures are effective. This can only be achieved if we have adequate detection methods and a reliable long record of a series of key geophysical parameters. Thus the AGACC project contributes to the provision of basic new knowledge regarding the atmospheric composition and its changes, based on advanced groundbased monitoring, in combination with satellite and numerical modelling data. Its results are integrated in ongoing international research programmes. The general objective of AGACC has been to improve and extend the groundbased detection capabilities for a number of climate-related target species and, based hereupon, analyse past and present observations to derive new information about the atmospheric composition, its variability and long-term changes. Despite the advent of a growing and more performant fleet of Earth Observation satellites, ground-based observations are still indispensable to (1) guarantee long-term continuity, homogeneity and high quality of the data, and (2) to underpin the satellite data for calibration and (long-term) validation. A first target gas is atmospheric water vapour. It is the key trace gas controlling weather and climate. It is also the most important greenhouse gas in the Earth’s atmosphere. Its amount and vertical distribution are changing, but how and why? Especially in the upper troposphere - lower stratosphere, the radiative effects of changes in the water vapour are significant and should be quantified. The measurement of water vapour is a hot topic since several years. It is a challenge, because water vapour exhibits a large gradient in its concentration when going from the ground to the stratosphere, and because it is highly variable in time and space. For example, we have found that the time scale of the variations of the total water vapour amount at Jungfraujoch is in the order of minutes. In AGACC, we have therefore investigated various experimental techniques to measure the concentration of water vapour in the atmosphere, focusing on the total column as well as on the vertical distribution in the troposphere up to the lower stratosphere. The retrieval of water vapour vertical profiles and total columns from ground-based FTIR data has been initiated at three very different stations where correlative data for verification are available, namely Ukkel (± sea level, mid-latitude), Ile de La Réunion (± sea level, tropical) and Jungfraujoch (high altitude, mid-latitude), with promising results. In particular, at Jungfraujoch, it has been demonstrated that the precision of the FTIR integrated water vapour (IWV) measurements is of order 2%. The capability to retrieve individual isotopologues of water vapour, and to monitor their daily and diurnal variations, has also been demonstrated. This could open new ways to study in the future the role of water vapour in the radiative balance, the global circulation, precipitation etc. We also started joint exploitation of ground-based FTIR and satellite IASI data for water vapour and its isotopologues, in order to exploit fully the potential of the existing instrumentation. A correction method for the radiosoundings at Ukkel has been successfully implemented, resulting in a homogeneous and reliable time series from 1990 to 2008 from which trends in upper troposphere humidity (UTH) and tropopause characteristics have been derived. One observes a rising UTH until September 2001, followed by a decline, accompanied by a descent and heating of the tropopause up to the turning point and an ascent and cooling afterwards. The changes after September 2001 in the upper troposphere can be explained by surface heating and convective uplift. At Jungfraujoch, one does not observe any significant trend in the total water vapour abundance above the station over the 1988-2010 time period, although significant positive summer and negative winter trends have been detected. We have made a quantitative statistical comparison between ground-based FTIR, CIMEL, GPS and integrated (corrected) radio sounding measurements of the IWV at Ukkel. This work is important to better characterize the different sensors in order to exploit together different observations made by different instruments. A second target species is atmospheric aerosol. There is a very large variety of aerosol both from natural or anthropogenic origin. One of the reasons why they are so important is that they affect the optical properties of the atmosphere. In particular, it has been demonstrated in previous studies that the aerosols have a large impact on the quantity of harmful UV-B radiation received at the Earth’s surface. The latest IPCC Report also stressed that the radiative forcing caused by atmospheric aerosols is one of the largest uncertainties in determining the total radiative forcing in the atmosphere. Better monitoring capabilities of aerosol properties can therefore improve our understanding and forecasting of the atmospheric processes and evolution, and in particular of UV-B and climate changes. Several measurement techniques are now operational in the AGACC consortium for the ground-based monitoring of aerosol properties. These are the Brewer spectrometer and CIMEL observations at Ukkel, the latter contributing also to the AERONET network since July 2006, and the newly developed MAXDOAS observations. Unlike CIMEL and Brewer measurements, that provide the total Aerosol Optical Depth, it has been demonstrated that the MAXDOAS measurements also provide additional information about the vertical distribution of the aerosol extinction in the lowest kilometres of the troposphere. A better understanding of the ultimate capabilities of MAXDOAS aerosol remote sensing has been gained through participation to the international CINDI campaign (Cabauw Intercomparison Campaign of Nitrogen Dioxide measuring Instruments ) in summer 2009. The combination of Brewer, CIMEL and MAXDOAS instruments gives us a remote-sensing dataset that will enable a more comprehensive characterization of the tropospheric aerosol optical properties. The usefulness of these aerosol observations has already been demonstrated in the improvement of the UVindex predictions for the general public. Another application is their use as input data in the retrieval of vertical profiles of tropospheric pollutants from MAXDOAS measurements, like tropospheric NO2 and formaldehyde. Third we have focused on a few climate-related trace gases. Changing greenhouse gas and aerosol concentrations directly affect the radiative budget of the atmosphere, and therefore climate. But many species known as pollutants like carbon monoxide (CO), nitrogen oxides (NOx) and hydrocarbons, - often related to fossil fuel or biomass burning -, also affect climate through their role in chemical reactions that produce tropospheric ozone, which is a well-known greenhouse gas, or that modify the lifetime of gases like methane, or the oxidation capacity of the atmosphere. Therefore in AGACC, we have focused on the measurement of a number of trace gases that are subject to changing concentrations, that directly or indirectly affect climate, and that are either difficult to monitor or that have not yet been measured from the ground. We have included attempts to observe distinctly some isotopologues, because the isotopic ratios observed in an airmass provide information on its history, and because the FTIR solar absorption measurements provide a rather unique capability hereto. The investigated species are the isotopologues of CH4 and CO, and hydrogen cyanide (HCN), as examples of biomass burning tracers, some hydrocarbons like formaldehyde (HCHO), ethylene (C2H4) and acetylene (C2H2), and HCFC-142b, a replacement product for CFCs and a greenhouse gas. In many cases, retrieval strategies had to be adapted when going from one site to another with different atmospheric conditions, especially when the local humidity and abundances are very different as is the case between Jungfraujoch (dry, high altitude, mid-latitude) and Ile de La Réunion (humid, low altitude, low latitude). Still we have been able to show the feasibility of retrieving particular trace gas information even under difficult conditions. Many of our results have been compared to correlative data, to validate the approach and to gain complementary information. It is also important to note that the retrieval strategies developed in AGACC have regularly been presented to the global Network for the Detection of Atmospheric Composition Change (NDACC) UV-Vis and Infrared communities and have often been adopted by others or even proposed for adoption as a standard in the community (e.g., for hydrogen cyanide (HCN)). In particular: We have been able to study the seasonal variations of HCN at the Jungfraujoch and at Ile de La Réunion, and to show the dominant impact of biomass burning. Formaldehyde was studied in much detail at Ukkel, Jungfraujoch and Ile de la Réunion. The challenge for detection at Jungfraujoch is the small abundance (about 10 times smaller than at Ukkel and Ile de La Réunion); a particular observation strategy was developed successfully, resulting in a time series that already shows the day-to-day and seasonal variations. At Ile de La Réunion, comparisons of FTIR, MAXDOAS, satellite and model data have (1) shown the good agreement between the various data sets, but also, (2), the variability of HCHO (diurnal, seasonal, day-to-day), and (3), thanks to the complementarities of the various data sets, they have enabled us to learn more about the long-range transport of Non-methane Volatile Organic Compounds (NMVOCS, precursors of HCHO) and deficiencies in the models. It was shown that fast, direct transport of NMVOCS from Madagascar has a significant impact on the HCHO abundance and its variability at Ile de La Réunion, and that this is underestimated in the model. Significant progress was made as to the detection of 13CH4 and CH3D from ground-based FTIR observations, both at Jungfraujoch and Ile de La Réunion. To our knowledge, it is the first time that a d13C data set is derived from ground-based FTIR observations. More work is needed to improve the CH3D retrieval at Ile de La Réunion, and to interpret the results, in combination with models. Also for the first time, 12CO and 13CO have been retrieved individually at Jungfraujoch. The d13C time series shows significant seasonal and interannual changes. As to the hydrocarbon ethylene, it is shown that it can be detected at Jungfraujoch only in spectra at low solar elevation, given its small atmospheric abundance. Regarding acetylene, the observed time series at Jungfraujoch and Ile de La Réunion show clear seasonal variations and enhancements due to the impact of biomass burning events, correlated with enhancements in CO, C2H6 and HCN. It is not clear yet whether we can reliably retrieve the concentration of HCFC- 142b, a replacement product that is increasing strongly in the troposphere. New line parameters for the interfering species HFC-134a are required to confirm/infirm the preliminary results. This highlights again the importance of the laboratory work for providing such parameters. Improved line parameters have been obtained for water vapour and its isotopologues, ethylene and formic acid. These AGACC results have been integrated in the international spectroscopic databases. We also showed that line intensities available around 2096 cm–1 for the 13C16O isotopologue of carbon monoxide in the HITRAN database seem to be accurate to 2%. We failed to improve line intensities for the 13.6 μm region of acetylene. The new data sets that have been derived in AGACC from FTIR and MAXDOAS observations have been archived in the NDACC data centre, where they are available for users (generally modelers and satellite teams). In addition, they are stored locally and are available to users upon request. AGACC results have been reported to the international scientific community, via the literature, via integration in geophysical or spectroscopic databases, and via participation to international research initiatives like the Atmospheric Water Vapour in the Climate System (WAVACS) Cost Action, the International Space Science Institute (ISSI) Working Group on Atmospheric Water Vapour, the International Union of Pure and Applied Chemistry (IUPAC) project, the International CINDI campaign, etc. The results have already found important scientific applications. A few examples are worth mentioning: the re-evaluation of methane emissions in the tropics from SCIAMACHY based on the new H2O spectroscopy, and the improved retrievals of HCOOH from the satellite experiments ACE-FTS and IASI, and from the ground. In the longer-term, the AGACC results will no doubt benefit the research in atmospheric sciences –in particular in the monitoring of its composition changes–, which is the fundamental basis of environmental assessment reports for supporting policy makers. [less ▲]

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See detailExtension of the long-term total column time series of atmospheric methane above the Jungfraujoch station: analysis of grating infrared spectra between 1976 and 1989
Bader, Whitney ULg; Lejeune, Bernard ULg; Demoulin, Philippe ULg et al

in Geophysical Research Abstracts (2011), 13

Methane (CH4) is one of the most abundant greenhouse gases in the Earth’s atmosphere, with current mean volume mixing ratio close to 1800 ppb. Since methane has a global warming potential of 25 (100-yr ... [more ▼]

Methane (CH4) is one of the most abundant greenhouse gases in the Earth’s atmosphere, with current mean volume mixing ratio close to 1800 ppb. Since methane has a global warming potential of 25 (100-yr horizon) and an atmospheric lifetime of 12 years, the Kyoto Protocol has included it among the species to be regulated to limit global warming. Anthropogenic sources of methane are mainly energy production (coal and leaks) and agriculture while main natural sources are swamps and biomass waste. The main sink of methane is oxidation in the troposphere, primarily by reaction with the hydroxyl radical. Methane trends have exhibited significant changes during the last twenty-five years. For instance, long-term monitoring of its vertical total column above the high-altitude station of the Jungfraujoch (46.5°N, 8°E, 3580 m asl) has indeed allowed to derive column changes ranging from +0.72% in 1987-1988 to +0.14% in 1999-2000 (Zander et al., 2002), relative to 1988 and 2000, respectively. More recently and for the same site, Duchatelet et al. (2010) have even reported a significant slowdown of -0.02%/yr between years 2000 and 2005. This study also showed that since then, CH4 is on the rise again, at a rate close to +0.30%/yr. While the numbers reported here above have been derived from the Fourier Transform Infrared (FTIR) data set starting in 1984, earlier pioneering observations have been collected at the Jungfraujoch since 1950, using grating spectrometers. During the 1958-1975 period, the main objectives has been the study of the solar photosphere in the visible and the near infrared and the publication of high-resolution solar atlases. From 1976 to 1989, narrow-band IR solar absorption observations achieving a spectral resolution of about 0.02 cm-1 have been recorded with the high-performance double-pass grating spectrometer. Analysis of these historical spectra provides a unique opportunity to extend the Jungfraujoch’s total column time series of important atmospheric gases, including methane, by nearly 10 years. The aim of this contribution is to present the inversion strategy adopted to derive CH4 from the grating spectra, using the SFIT-2 algorithm (v3.91) We will evaluate the impact of resolution, spectroscopic parameters (from the EU HYMN project -see www.knmi.nl/samen/hymn-, and from HITRAN 2004), atmospheric pressure and temperature profiles on the error budget. The 1976-1989 total column time series produced will be presented and critically discussed. In particular, we will identify and correct for possible biases between double-pass grating spectrometer measurements and more recent FTIR total columns. The harmonized and consolidated time series will be investigated to characterize the long-term trend of methane for the 1976-2010 time period. Comparisons with synthetic data produced by the CHASER 3-dimensional chemical transport model will also be presented and analyzed. [less ▲]

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See detailTrend evolution and seasonal variation of tropospheric and stratospheric carbonyl sulfide (OCS) above Jungfraujoch
Lejeune, Bernard ULg; Mahieu, Emmanuel ULg; Duchatelet, Pierre ULg et al

in Geophysical Research Abstracts (2011), 13

Carbonyl sulfide (OCS) is the most abundant sulfur-containing trace gas in the atmosphere and accounts for a substantial portion of the sulfur in the stratospheric aerosol layer which influences the ... [more ▼]

Carbonyl sulfide (OCS) is the most abundant sulfur-containing trace gas in the atmosphere and accounts for a substantial portion of the sulfur in the stratospheric aerosol layer which influences the Earth’s radiation budget and stratospheric ozone chemistry. The major identified OCS sources are oceans and anthropogenic emissions, while atmospheric loss and uptake by vegetation and soils constitute the main OCS sinks. The uptake by vegetation strongly influences the distribution and seasonality of OCS throughout most of the Northern Hemisphere, just like for CO2. Montzka et al. (2007) pointed that atmospheric OCS measurements have the potential to constrain the biomass Gross Primary Production (GPP). Unfortunately, there remain large uncertainties on some components strengths of the atmospheric OCS budget. A recent work by Suntharalingam et al. (2008) showed that uptake by plants has been strongly underestimated in actual balanced budgets, suggesting that additional significant OCS sources have still to be identified. In order to improve our understanding of the different processes governing seasonal and inter-annual OCS variability, a new approach has been developed and optimized, using the SFIT-2 algorithm, to retrieve atmospheric abundance of OCS from high-resolution ground-based infrared solar spectra. Our observations are recorded on a regular basis with Fourier Transform Infrared spectrometers (FTIRs), under clear-sky conditions, at the NDACC site (Network for the Detection of Atmospheric Composition Change, http://www.ndacc.org) of the International Scientific Station of the Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580m asl). Information content analysis of the retrieved OCS products shows us that we are able to distinguish between tropospheric and stratospheric partial column contributions for this species. Thanks to our unique observational database, we have produced an updated OCS long-term trend from 1995 to 2010, representative for both the troposphere and stratosphere at northern mid-latitudes. In this contribution, we will present and critically discuss the recent OCS trend evolution, in particular the end of the slow decline of its abundance observed in 2002 and the maximum reached in 2008. In addition to the OCS inter-annual variations, we will analyze the OCS seasonal cycle during the 15 last years. We will also compare our results with simulations of seasonal OCS variations issued from a 3D global atmospheric chemical transport model (CTM), in order to try to quantify the individual contribution of the various processes playing a role in the Jungfraujoch OCS variability and influencing its atmospheric abundance. [less ▲]

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See detailFirst retrievals of carbon tetrafluoride (CF4) from ground-based FTIR measurements: production and analysis of the two-decadal time series above the Jungfraujoch
Duchatelet, Pierre ULg; Zander, Rodolphe ULg; Mahieu, Emmanuel ULg et al

in Geophysical Research Abstracts (2011)

Carbon tetrafluoride (CF4 or PFC-14) is a potent greenhouse gas that is almost 7400 times more effective (100-yr horizon) than CO2 on a per molecule basis (IPCC, 2007). This high global warming potential ... [more ▼]

Carbon tetrafluoride (CF4 or PFC-14) is a potent greenhouse gas that is almost 7400 times more effective (100-yr horizon) than CO2 on a per molecule basis (IPCC, 2007). This high global warming potential, coming from its medium absorbance combined with a very long atmospheric lifetime (>50000 years; Ravishankara et al., 1993), makes CF4 a key species among the various greenhouse gases targeted by the Kyoto Protocol. In the Northern hemisphere, current atmospheric CF4 concentrations are close to 78 pptv, with a large fraction (around 35 pptv, Mühle et al., 2010) coming from natural processes like lithospheric emissions (Harnisch and Eisenhauer, 1998). In addition, CF4 has been used increasingly since the eighties in electronic and semiconductors industry. The primary aluminum production processes have also been clearly identified as an important anthropogenic source of CF4 emissions. The partitioning between these two main sources is however problematic, principally due to lacking or incomplete CF4 emission factors from inventories performed in industrial fields (e.g. International Aluminum Institute, 2009). Recent in situ ground level measurements of CF4 in the Northern hemisphere (Khalil et al., 2003; Mühle et al., 2010) or remotely from space (Rinsland et al., 2006) have indicated a significant slowdown in the increase rate of atmospheric CF4. This probably results from measures adopted by the aluminum industry aiming at the reduction of the frequency and duration of “anode effects” and therefore of related PFCs emissions (International Aluminum Institute, 2009). The present contribution reports on the long-term evolution (1990-2010) of the atmospheric carbon tetrafluoride total vertical abundance derived from ground-based Fourier transform infrared (FTIR) solar spectroscopy observations around 1285 cm-1 at the Jungfraujoch (46.5°N, 8.0°E, 3580m asl) and compares our findings with results available in the literature. To our knowledge, no equivalent time series (i.e. based on ground-based FTIR technique) has been published to date. [less ▲]

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See detailFirst retrievals of methyl chloride from ground-based high-resolution FTIR solar observations
Mahieu, Emmanuel ULg; Harrison, Jeremy; Bernath, Peter F. et al

in Geophysical Research Abstracts (2011), 13

Methyl chloride (CH3Cl) is one of the most abundant chlorine-bearing gas in the Earth’s troposphere and a significant contributor to the organic chlorine budget. Measurements by in situ networks indicate ... [more ▼]

Methyl chloride (CH3Cl) is one of the most abundant chlorine-bearing gas in the Earth’s troposphere and a significant contributor to the organic chlorine budget. Measurements by in situ networks indicate a mean volume mixing ratio of 550 pptv, with a significant seasonal cycle of about 80 pptv, peak to peak. This species also exhibits inter-annual variability, but no long-term trend. Major sources are from tropical and sub-tropical plants and dead leaves, the oceans and biomass burning. Some industrial processes and waste incineration further add to the emissions. Oxidation by the hydroxyl radical is by far the largest CH3Cl sink, followed by soil uptake. Although balanced, its atmospheric budget is still affected by large uncertainties and contributions from unidentified sources and sinks cannot be ruled out. Methyl chloride has an atmospheric lifetime of 1 year, a global warming potential of 13 (100-yr horizon) and an ozone depleting potential of 0.02. The retrieval of methyl chloride from ground-based infrared (IR) spectra is very challenging. Indeed, numerous interferences by strong water vapor and methane lines complicate the detection of small CH3Cl absorptions, close to 1%, near 3 microns. In addition, and although weak, ethane features contribute to the difficulty, in particular since a significant number of ethane branches were absent until very recently from official HITRAN compilations. Therefore, the scientific literature does not report thus far about any investigations of CH3Cl from ground-based remote sensing observations. In this contribution, we will present first CH3Cl total column retrievals, using the SFIT-2 algorithm (v3.94) and high-resolution Fourier Transform Infrared (FTIR) solar absorption observations recorded with a Bruker 120HR instrument, at the high altitude station of the Jungfraujoch (46.5°N, 8°E, 3580 m asl), within the framework of the Network for the Detection of Atmospheric Composition Change (NDACC, visit http://www.ndacc.org). In our retrievals, we use new ethane absorption cross sections recorded at the Molecular Spectroscopy Facility of the Rutherford Appleton Laboratory (Harrison et al., 2010). They were calibrated in intensity by using reference low-resolution spectra from the Pacific Northwest National Laboratory (PNNL) IR database. These new cross sections were recently released as a HITRAN update (see http://www.hitran.com). Pseudoline parameters fitted to these ethane spectra have been combined with HITRAN 2004 line parameters (including all the 2006 updates) for all other species encompassed in the selected microwindows, including our target CH3Cl. We will evaluate the improvement brought by the new ethane line parameters on the fitting residuals, and characterize the quality, the precision and the reliability of the retrieved product. If successful, a long-term CH3Cl total column time series will be produced using the Jungfraujoch observational database, and we will perform preliminary investigations of the seasonal and inter-annual variations of methyl chloride total columns at northern mid-latitudes. [less ▲]

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See detailThe evolution of the inorganic fluorine budget since the mid-1980s based on FTIR measurements at northern mid-latitudes
Duchatelet, Pierre ULg; Feng, Wuhu; Chipperfield, Martyn et al

in Geophysical Research Abstracts (2011)

Fluorine enters the stratosphere principally in the form of CFCs (chlorofluorocarbons, mainly CFC-12 and CFC-11), HCFCs (hydrochlorofluorocarbons, mainly HCFC-22) and HFCs (hydrofluorocarbons, mainly HFC ... [more ▼]

Fluorine enters the stratosphere principally in the form of CFCs (chlorofluorocarbons, mainly CFC-12 and CFC-11), HCFCs (hydrochlorofluorocarbons, mainly HCFC-22) and HFCs (hydrofluorocarbons, mainly HFC-134a) which have been (or are still) widely emitted at ground level by human activities. In the lower stratosphere, the photolysis of these halogenated source gases leads to the formation of the two fluorine reservoirs COClF and COF2. The subsequent photolysis of these two compounds frees F atoms, which principally react with CH4 and H2O to form the extremely stable HF gas, by far the dominant fluorine reservoir in the middle and upper stratosphere. Despite the fact that fluorine does not significantly contribute in stratospheric ozone depletion, measurements of the concentrations of individual F-containing species in different altitude ranges of the atmosphere are important as they reflect the amounts of anthropogenic gases transported into the middle atmosphere as well as their decomposition. Such measurements also provide insight into the partitioning between major fluorine source gases (which are potent greenhouse gases) and reservoirs and allows a global inventory of organic (CFy), inorganic (Fy) and total (FTOT) fluorine burdens to be monitored as a function of time. Indeed, regular updates of such inventories are important as the partitioning between F-containing gases in the stratosphere is continually evolving as emissions of anthropogenic gases from the surface change, principally as a consequence of the progressive ban on the production of CFCs and HCFCs adopted by the Montreal Protocol and its subsequent Amendments and Adjustments. To complement recent studies regarding fluorine species (Duchatelet et al., 2009, 2010, 2011; Mahieu et al., 2011), this communication presents the time series of the inorganic fluorine budget Fy over the last twenty-five years, based on HF and COF2 total column amounts derived from high resolution Fourier transform infrared (FTIR) solar spectra recorded at Jungfraujoch (46.5°N, 8.0°E, 3580m asl). A trend analysis of our HF, COF2 and Fy time series is performed and discussed in the context of past and current emissions of halogenated source gases. Comparisons with model and space data are also included. [less ▲]

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See detailTrend and lifetime of sulfur hexafluoride at mid-latitudes deduced from ACE-FTS occultation measurements
Mahieu, Emmanuel ULg; Duchatelet, Pierre ULg; Zander, Rodolphe ULg et al

in Geophysical Research Abstracts (2011), 13

Sulfur hexafluoride (SF6) is one of the strongest greenhouse gases on a per molecule basis, with a global warming potential of 22800 (100-yr horizon). This is an extremely stable gas in the atmosphere ... [more ▼]

Sulfur hexafluoride (SF6) is one of the strongest greenhouse gases on a per molecule basis, with a global warming potential of 22800 (100-yr horizon). This is an extremely stable gas in the atmosphere, which results in a very long lifetime, with large uncertainties. The value adopted by IPCC is 3200 years, but some studies suggest shorter lifetimes, as low as 800 years. Surface concentrations are now about 7 ppt, with reported trends indicating a steady and strong increase of 0.3 ppt/yr. Most emissions are of anthropogenic origin, related to its use as an insulator in high-voltage electrical installations. Secondary contributions result from magnesium and aluminum production as well as from the manufacturing of semiconductors (see e.g. Levin et al., 2010; Rigby et al., 2010 and references therein). In this contribution, we use occultation measurements performed by the ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument, launched in August 2003 onboard the Canadian SCISAT satellite (Bernath et al., 2005). ACE-FTS is still in operation to date, with no significant degradation in its performance. This spectrometer achieves a spectral resolution of 0.02 cm-1 in the broad 750-4400 cm-1 range which covers the unresolved nu-3 band Q branch of SF6 centered at 947.9 cm-1. Signal-to-noise ratios of 200-300 are typically obtained in the spectral region of interest. Version 3 retrievals performed by University of Waterloo give volume mixing ratio profiles of SF6 in the 11-32 km altitude range. We consider all available sunrise and sunset occultation measurements obtained at midlatitudes in both hemispheres to derive the trend of SF6 in the lower stratosphere, from late February 2004 onwards. Consistency between both hemispheres will be investigated. In addition, concurrent N2O measurements are used to evaluate the atmospheric lifetime of SF6, following a method used previously for other long-lived gases (e.g. Zander et al, 1996). Comparisons with trends derived from in situ surface measurements or from ground-based remote-sensing observations (e.g. at the Jungfraujoch station, 46.5ºN) are also included. [less ▲]

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See detailOzone-Depleting Substances (ODSs) and Related Chemicals (Chapter 1)
Montzka, S. A.; Reimann, S.; Engel, A. et al

in Nohende Ajavon, Ayité-Lô; Newmann, Paul A.; Pyle, John A. (Eds.) et al Scientific Assessment of Ozone Depletion: 2010 (2011)

The amended and adjusted Montreal Protocol continues to be successful at reducing emissions and atmospheric abundances of most controlled ozone-depleting substances (ODSs).

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See detailFormic acid above the Jungfraujoch during 1985–2007: observed variability, seasonality, but no long-term background evolution
Zander, Rodolphe ULg; Duchatelet, Pierre ULg; Mahieu, Emmanuel ULg et al

in Atmospheric Chemistry and Physics (2010), 10(20), 10047--10065

This paper reports on daytime total vertical column abundances of formic acid (HCOOH) above the Northern mid-latitude, high altitude Jungfraujoch station (Switzerland; 46.5° N, 8.0° E, 3580 m alt.). The ... [more ▼]

This paper reports on daytime total vertical column abundances of formic acid (HCOOH) above the Northern mid-latitude, high altitude Jungfraujoch station (Switzerland; 46.5° N, 8.0° E, 3580 m alt.). The columns were derived from the analysis of infrared solar observations regularly performed with high spectral resolution Fourier transform spectrometers during over 1500 days between September 1985 and September 2007. The investigation was based on the spectrometric fitting of five spectral intervals, one encompassing the HCOOH ν6 band Q branch at 1105 cm−1, and four additional ones allowing to optimally account for critical temperature-sensitive or time-evolving interferences by other atmospheric gases, in particular HDO, CCl2F2 and CHClF2. The main results derived from the 22 years long database indicate that the free tropospheric burden of HCOOH above the Jungfraujoch undergoes important short-term daytime variability, diurnal and seasonal modulations, inter-annual anomalies, but no significant long-term background change. A major progress in the remote determination of the atmospheric HCOOH columns reported here has resulted from the adoption of new, improved absolute spectral line intensities for the infrared ν6 band of trans-formic acid, resulting in retrieved free tropospheric loadings being about a factor two smaller than if derived with previous spectroscopic parameters. Implications of this significant change with regard to earlier remote measurements of atmospheric formic acid and comparison with relevant Northern mid-latitude findings, both in situ and remote, will be assessed critically. Sparse HCOOH model predictions will also be evoked and assessed with respect to findings reported here. [less ▲]

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See detailUpdating hydrogen fluoride (HF) FTIR time series above Jungfraujoch: comparison of two retrieval algorithms and impact of line shape models
Duchatelet, Pierre ULg; Demoulin, Philippe ULg; Hase, Frank et al

Poster (2010, May)

Fluorine enters the stratosphere mainly in the form of chlorofluorocarbons (CFCs; principally CFC-11 and CFC-12) and tetrafluoromethane (CF4), which have been widely emitted at ground level by human ... [more ▼]

Fluorine enters the stratosphere mainly in the form of chlorofluorocarbons (CFCs; principally CFC-11 and CFC-12) and tetrafluoromethane (CF4), which have been widely emitted at ground level by human activities over the past few decades. In the lower stratosphere, the photolysis of the long-lived CFC-11 (CCl3F) and CFC-12 (CCl2F2), whose emissions from the ground have been progressively phased out by the Montreal Protocol and its successive Amendments and Adjustments, leads to the formation of the two reservoirs: COClF and COF2. Subsequent photolysis of these two compounds then liberates F atoms, which could quickly react with CH4, H2O or H2 to form the extreme stable hydrogen fluoride (HF) gas. The formation of HF by these reactions is significant, as they make HF the largest fluorine reservoir in the middle and upper stratosphere. Despite the fact that fluorine does not directly participate in ozone depletion, measurements of the concentration of individual F-containing species at different altitude of the atmosphere are important as they reflect the amounts of anthropogenic gases – which also often bear ozone-threatening Cl atoms - transported into the middle atmosphere as well as their decomposition. Since the first detection of hydrogen fluoride in the Earth’s atmosphere by Zander (1975), several studies dealing with HF total column amounts derived from ground-based Fourier transform infrared (FTIR) observations at several latitudes in both hemispheres have been published. In addition, these last years have seen the emergence of more sophisticated retrieval algorithms (e.g. SFIT-2, PROFFIT) allowing to inverse total or partial columns as well as vertical distribution of the target gas from ground-based FTIR spectra. In this contribution, we propose to compare HF total columns derived from FTIR high-resolution ground-based observations performed at the Jungfraujoch (46.5°N, 8.0°E, 3580 m asl) by using two different retrieval codes: SFIT-2 v.3.91 and PROFFIT v.9.5. The impact of spectroscopic parameters (Voigt line shape model versus Galatry model line shape) on HF retrievals is also analyzed. References: Zander, R.: Présence de HF dans la stratosphère supérieure, C.R. Acad. Sci. Paris. Série B., 281, 213-214, 1975. [less ▲]

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See detailOptimized approach to retrieve information on the tropospheric and stratospheric carbonyl sulfide (OCS) vertical distributions above Jungfraujoch from high-resolution FTIR solar spectra
Lejeune, Bernard ULg; Mahieu, Emmanuel ULg; Servais, Christian ULg et al

in Geophysical Research Abstracts (2010), 12(EGU2010-3513),

Carbonyl sulfide (OCS), which is produced in the troposphere from both biogenic and anthropogenic sources, is the most abundant gaseous sulfur species in the unpolluted atmosphere. Due to its low chemical ... [more ▼]

Carbonyl sulfide (OCS), which is produced in the troposphere from both biogenic and anthropogenic sources, is the most abundant gaseous sulfur species in the unpolluted atmosphere. Due to its low chemical reactivity and water solubility, a significant fraction of OCS is able to reach the stratosphere where it is converted to SO2 and ultimately to H2SO4 aerosols (Junge layer). These aerosols have the potential to amplify stratospheric ozone destruction on a global scale and may influence Earth’s radiation budget and climate through increasing solar scattering. The transport of OCS from troposphere to stratosphere is thought to be the primary mechanism by which the Junge layer is sustained during nonvolcanic periods. Because of this, long-term trends in atmospheric OCS concentration, not only in the troposphere but also in the stratosphere, are of great interest. A new approach has been developed and optimized to retrieve atmospheric abundance of OCS from high-resolution ground-based infrared solar spectra by using the SFIT-2 (v3.91) algorithm, including a new model for solar lines simulation (solar lines often produce significant interferences in the OCS microwindows). The strongest lines of the nu3 fundamental band of OCS at 2062 cm-1 have been systematically evaluated with objective criteria to select a new set of microwindows, assuming the HITRAN 2004 spectroscopic parameters with an increase in the OCS line intensities of the nu3band main isotopologue 16O12C32S by 15.79% as compared to HITRAN 2000 (Rothman et al., 2008, and references therein). Two regularization schemes have further been compared (deducted from ATMOS and ACE-FTS measurements or based on a Tikhonov approach), in order to select the one which optimizes the information content while minimizing the error budget. The selected approach has allowed us to determine updated OCS long-term trend from 1988 to 2009 in both the troposphere and the stratosphere, using spectra recorded on a regular basis with Fourier Transform Infrared spectrometers (FTIRs), under clear-sky conditions, at the NDACC site (Network for the Detection of Atmospheric Composition Change, visit http://www.ndacc.org) of the International Scientific Station of the Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580m asl). Trends and seasonal cycles deduced from our results will be compared to values published in the literature and critically discussed. In particular, we will confirm the recent change in the OCS total column trend, which has become positive since 2002 before undergoing a slowing down over the last years. [less ▲]

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See detailTrends of CO2, CH4 and N2O over 1985-2010 from high-resolution FTIR solar observations at the Jungfraujoch station
Duchatelet, Pierre ULg; Mahieu, Emmanuel ULg; Zander, Rodolphe ULg et al

in Geophysical Research Abstracts (2010), 12(EGU2010-15418-2),

Two state-of-the-art Fourier Transform Infrared (FTIR) spectrometers are operated at the Jungfraujoch station (46.5ºN, 8.0ºE, 3580m asl) within the framework of the Network for the Detection of ... [more ▼]

Two state-of-the-art Fourier Transform Infrared (FTIR) spectrometers are operated at the Jungfraujoch station (46.5ºN, 8.0ºE, 3580m asl) within the framework of the Network for the Detection of Atmospheric Composition Change (NDACC, visit http://www.ndacc.org). The earliest FTIR observations have been obtained there in 1984. Since then, regular recordings of high-resolution solar absorption spectra have been performed at that site, under clear-sky conditions, allowing to collect almost 29000 observations relevant to the present communication. We present time series of three greenhouse gases targeted by the Kyoto Protocol: CO2, CH4 (and its isotopologue 13CH4) and N2O. These data sets have been obtained with the SFIT-2 algorithm which implements the Optimal Estimation Method of Rodgers (1990). This allows retrieving total columns of the target gases as well as information on their distribution with altitude. For the methane isotopologues and N2O, a Tikhonov L1 regularization scheme has been applied, as part of an harmonization effort carried out within the European HYMN project (see also Dils et al, 2010; Foster et al., 2010). Trends –and their associated uncertainties– characterizing these long series as well as the seasonal modulations have been determined with a statistical tool using bootstrap resampling (Gardiner et al., 2008). Trend values will be presented and critically discussed; in particular, we will investigate if significant changes in the rate of accumulations of these four atmospheric gases occurred over the last 25 years. Numerous additional greenhouse gases are accessible to the FTIR technique. Examples of such trend studies are reported at the EGU General Assembly by Mahieu et al. (2010) and Rinsland et al. (2010). [less ▲]

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See detailHydrogen fluoride total and partial column time series above the Jungfraujoch from long-term FTIR measurements: Impact of the line-shape model, characterization of the error budget and seasonal cycle, and comparison with satellite and model data
Duchatelet, Pierre ULg; Demoulin, Philippe ULg; Hase, Frank et al

in Journal of Geophysical Research. Atmospheres (2010), 115

Time series of hydrogen fluoride (HF) total columns have been derived from ground-based Fourier transform infrared (FTIR) solar spectra recorded between March 1984 and December 2009 at the International ... [more ▼]

Time series of hydrogen fluoride (HF) total columns have been derived from ground-based Fourier transform infrared (FTIR) solar spectra recorded between March 1984 and December 2009 at the International Scientific Station of the Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580 m asl) with two high resolution spectrometers (one home-made and one Bruker 120-HR). Solar spectra have been inverted with the PROFFIT 9.5 algorithm, using the optimal estimation method. An inter-comparison of HF total columns retrieved with PROFFIT and SFIT-2 – the other reference algorithm in the FTIR community - is performed for the first time. The effect of a Galatry line shape model on HF retrieved total columns and vertical profiles, on the residuals of the fits and on the error budget is also quantified. Information content analysis indicates that, in addition to HF total vertical abundance, three independent stratospheric HF partial columns can be derived from our Bruker spectra. A complete error budget has been established and indicates that the main source of systematic error is linked to HF spectroscopy and that the random error affecting our HF total columns does not exceed 2.5%. Ground-based middle and upper stratospheric HF amounts have been compared to satellite data collected by the HALOE or ACE-FTS instruments. Comparisons of our FTIR HF total and partial columns with runs performed by two 3D numerical models (SLIMCAT and KASIMA) are also included. Finally, FTIR and model HF total and partial columns time series have been analyzed to derive the main characteristics of their seasonal cycles. [less ▲]

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