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See detailInvestigation of the consistency of the recent CH4 increase derived from NDACC-FTIR, ACE-FTS and GEOS-Chem
Bader, Whitney ULg; Conway, Stephanie; Strong, Kim et al

Conference (2015, May 21)

We present an update on the status of the recent methane increase study based on six FTIR ground-based sites, ACE-FTS satellite occultations and GEOS-Chem simulation.

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See detailAcetylene (C2H2) and hydrogen cyanide (HCN) from IASI satellite observations: global distributions, validation, and comparison with model
Duflot, V.; Wespes, C.; Clarisse, L. et al

in Atmospheric Chemistry & Physics Discussions (2015), 15(10), 14357--14401

We present global distributions of C2H2 and HCN total columns derived from the Infrared Atmospheric Sounding Interferometer (IASI). These distributions are obtained with a fast method allowing to retrieve ... [more ▼]

We present global distributions of C2H2 and HCN total columns derived from the Infrared Atmospheric Sounding Interferometer (IASI). These distributions are obtained with a fast method allowing to retrieve C2H2 abundance globally with a 5% precision and HCN abundance in the tropical (subtropical) belt with a 10% (30%) precision. IASI data are compared for validation purposes with ground-based Fourier Transform Infrared (FTIR) spectrometer measurements at four selected stations. We show that there is an overall agreement between the ground-based and space measurements. Global C2H2 and subtropical HCN abundances retrieved from IASI spectra show the expected seasonality linked to variations in the anthropogenic emissions and seasonal biomass burning activity, as well as exceptional events, and are in good agreement with previous spaceborne studies. IASI measurements are also compared to the distributions from the Model for Ozone and Related Chemical Tracers, version 4 (MOZART- 4). Seasonal cycles observed from satellite data are reasonably well reproduced by the model. However, the model seems to overestimate (underestimate) anthropogenic (biomass burning) emissions and a negative global mean bias of 1% (16 %) of the model relative to the satellite observations was found for C2H2 (HCN). [less ▲]

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See detailRecent results derived from regular ground-based FTIR observations at the Jungfraujoch and other NDACC stations
Mahieu, Emmanuel ULg; Bader, Whitney ULg; Franco, Bruno ULg

Scientific conference (2015, May 20)

We present an overview of the recent results derived from the observational program for the long-term monitoring of the Earth's atmosphere from the Jungfraujoch station, including comparison with data ... [more ▼]

We present an overview of the recent results derived from the observational program for the long-term monitoring of the Earth's atmosphere from the Jungfraujoch station, including comparison with data from the ACE-FTS satellite instrument and other NDACC stations. [less ▲]

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See detailUse of GEOS-Chem for the interpretation of long-term FTIR measurements at the Jungfraujoch and other NDACC sites
Mahieu, Emmanuel ULg; Bovy, Benoît ULg; Bader, Whitney ULg et al

Poster (2015, May 04)

We present recent and ongoing investigations using 3D CTM GEOS-Chem model simulations for the interpretation of long-term FTIR measurements performed at selected NDACC sites.

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See detailValidation of SCIAMACHY HDO/H2O measurements using the TCCON and NDACC-MUSICA networks
Scheepmaker, R. A.; Frankenberg, C.; Deutscher, N. M. et al

in Atmospheric Measurement Techniques (2015), 8(4), 1799-1818

Measurements of the atmospheric HDO/H2O ratio help us to better understand the hydrological cycle and improve models to correctly simulate tropospheric humidity and therefore climate change. We present an ... [more ▼]

Measurements of the atmospheric HDO/H2O ratio help us to better understand the hydrological cycle and improve models to correctly simulate tropospheric humidity and therefore climate change. We present an updated version of the column-averaged HDO/H2O ratio data set from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY). The data set is extended with 2 additional years, now covering 2003–2007, and is validated against co-located ground-based total column δD measurements from Fourier transform spectrometers (FTS) of the Total Carbon Column Observing Network (TCCON) and the Network for the Detection of Atmospheric Composition Change (NDACC, produced within the framework of the MUSICA project). Even though the time overlap among the available data is not yet ideal, we determined a mean negative bias in SCIAMACHY δD of −35 ± 30‰ compared to TCCON and −69 ± 15‰ compared to MUSICA (the uncertainty indicating the station-to-station standard deviation). The bias shows a latitudinal dependency, being largest (∼ −60 to −80‰) at the highest latitudes and smallest (∼ −20 to −30‰) at the lowest latitudes. We have tested the impact of an offset correction to the SCIAMACHY HDO and H2O columns. This correction leads to a humidity- and latitude-dependent shift in δD and an improvement of the bias by 27‰, although it does not lead to an improved correlation with the FTS measurements nor to a strong reduction of the latitudinal dependency of the bias. The correction might be an improvement for dry, high-altitude areas, such as the Tibetan Plateau and the Andes region. For these areas, however, validation is currently impossible due to a lack of ground stations. The mean standard deviation of single-sounding SCIAMACHY–FTS differences is ∼ 115‰, which is reduced by a factor ∼ 2 when we consider monthly means. When we relax the strict matching of individual measurements and focus on the mean seasonalities using all available FTS data, we find that the correlation coefficients between SCIAMACHY and the FTS networks improve from 0.2 to 0.7–0.8. Certain ground stations show a clear asymmetry in δD during the transition from the dry to the wet season and back, which is also detected by SCIAMACHY. This asymmetry points to a transition in the source region temperature or location of the water vapour and shows the added information that HDO/H2O measurements provide when used in combination with variations in humidity. [less ▲]

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See detailRetrievals of formaldehyde from ground-based FTIR and MAX-DOAS observations at the Jungfraujoch station and comparisons with GEOS-Chem and IMAGES model simulations
Franco, Bruno ULg; Hendrick, François; Van Roozendael, Michel et al

in Atmospheric Measurement Techniques (2015), 8

As an ubiquitous product of the oxidation of many volatile organic compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation ... [more ▼]

As an ubiquitous product of the oxidation of many volatile organic compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation pathways leading to the formation of tropospheric ozone and secondary organic aerosols. In this study, HCHO profiles have been successfully retrieved from ground-based Fourier transform infrared (FTIR) solar spectra and UV-visible Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) scans recorded during the July 2010–December 2012 time period at the Jungfraujoch station (Swiss Alps, 46.5° N, 8.0° E, 3580m a.s.l.). Analysis of the retrieved products has revealed different vertical sensitivity between both remote sensing techniques. Furthermore, HCHO amounts simulated by two state-of-the-art chemical transport models (CTMs), GEOSChem and IMAGES v2, have been compared to FTIR total columns and MAX-DOAS 3.6–8 km partial columns, accounting for the respective vertical resolution of each ground-based instrument. Using the CTM outputs as the intermediate, FTIR and MAX-DOAS retrievals have shown consistent seasonal modulations of HCHO throughout the investigated period, characterized by summertime maximum and wintertime minimum. Such comparisons have also highlighted that FTIR and MAX-DOAS provide complementary products for the HCHO retrieval above the Jungfraujoch station. Finally, tests have revealed that the updated IR parameters from the HITRAN 2012 database have a cumulative effect and significantly decrease the retrieved HCHO columns with respect to the use of the HITRAN 2008 compilation. [less ▲]

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See detailHalogenated source gases measured by FTIR at the Jungfraujoch station: updated trends and new target species
Mahieu, Emmanuel ULg; Bader, Whitney ULg; Bovy, Benoît ULg et al

in Geophysical Research Abstracts (2015, April 13), 17

In this contribution, we present decadal time series of halogenated source gases monitored at the high altitude station of the Jungfraujoch (46.5°N, 8°E, 3580 m asl) with Fourier Transform Infared (FTIR ... [more ▼]

In this contribution, we present decadal time series of halogenated source gases monitored at the high altitude station of the Jungfraujoch (46.5°N, 8°E, 3580 m asl) with Fourier Transform Infared (FTIR) spectrometers, within the framework of the Network for the Detection of Atmospheric Composition Change. Total column trends presented in previous studies for CFC-11, -12 and HCFC-22, CCl4, HCFC-142b, CF4 and SF6 will be updated using the latest available Jungfraujoch solar observations. Investigations dealing with the definition of approaches to retrieve additional halogenated source gases from FTIR spectra will also be evoked. Our trend results will be critically discussed and compared with measurements performed in the northern hemisphere by the in situ networks. [less ▲]

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See detailRecent increase of ethane detected in the remote atmosphere of the Northern Hemisphere
Franco, Bruno ULg; Bader, Whitney ULg; Bovy, Benoît ULg et al

Conference (2015, April 13)

Ethane (C2H6) has a large impact on tropospheric composition and air quality because of its involvement in the global VOC (volatile organic compound) – HOx – NOx chemistry responsible for generating and ... [more ▼]

Ethane (C2H6) has a large impact on tropospheric composition and air quality because of its involvement in the global VOC (volatile organic compound) – HOx – NOx chemistry responsible for generating and destroying tropospheric ozone. By acting as a major sink for tropospheric OH radicals, the abundance of C2H6 influences the atmospheric content of carbon monoxide and impacts the lifetime of methane. Moreover, it is an important source of PAN, a thermally unstable reservoir for NOx radicals. On a global scale, the main sources of C2H6 are leakage from the production, transport of natural gas loss, biofuel consumption and biomass burning, mainly located in the Northern Hemisphere. Due to its relatively long lifetime of approximately two months, C2H6 is a sensitive indicator of tropospheric pollution and transport. Using an optimized retrieval strategy (see Franco et al., 2014), we present here a 20-year long-term time series of C2H6 column abundance retrieved from ground-based Fourier Transform InfraRed (FTIR) solar spectra recorded from 1994 onwards at the high-altitude station of Jungfraujoch (Swiss Alps, 46.5° N, 3580 m a.s.l.), part of the Network for the Detection of Atmospheric Composition Change (NDACC, see http://www.ndacc.org). After a regular 1994 – 2008 decrease of the C2H6 amounts, which is very consistent with prior major studies (e.g., Aydin et al., 2011; Simpson et al., 2012) and our understanding of global C2H6 emissions, trend analysis using a bootstrap resampling tool reveals a C2H6 upturn and a statistically-significant sharp burden increase from 2009 onwards (Franco et al., 2014). We hypothesize that this observed recent increase in C2H6 could affect the whole Northern Hemisphere and may be related to the recent massive growth in the exploitation of shale gas and tight oil reservoirs. This hypothesis is supported by measurements derived from solar occultation observations performed since 2004 by the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) instrument and at other NDACC sites, namely Toronto (44° N) and Thule (77° N). Indeed, the recent rates of changes characterizing these data sets are consistent in magnitude and sign with the one derived from the FTIR measurements at Jungfraujoch. In contrast, the ethane time series form Lauder (45° S) shows a monotonic decrease over the last two decades. Investigating both the cause and impact on air quality of the C2H6 upturn should be a high priority for the atmospheric chemistry community. [less ▲]

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See detailRetrieval of ammonia from ground-based FTIR measurements and its use for validation of satellite observations by IASI
Dammers, E; Palm, M; Warneke, T et al

in Geophysical Research Abstracts (2015, April 13), 17

Atmospheric Ammonia (NH3) has a major impact on human health and ecosystem services and plays a major role in the formation of aerosols [Erisman et al.,2013; Paulot and Jacob 2014]. NH3 concentrations are ... [more ▼]

Atmospheric Ammonia (NH3) has a major impact on human health and ecosystem services and plays a major role in the formation of aerosols [Erisman et al.,2013; Paulot and Jacob 2014]. NH3 concentrations are highly variable in space and time with overall short lifetime due to deposition and aerosol formation. The global atmospheric budget of nitrogen and in turn NH3 is still uncertain which asks for more ground-based and satellite observations around the world. Recent papers have described the possibility to measure NH3 with satellite infrared sounders which open up the way for calculations of global and regional nitrogen budgets [Clarisse et al 2009,Van Damme et al 2014a]. Validation of the satellite observations is essential to determine the uncertainty in the signal and its potential use. So far available surface layer observations of atmospheric NH3 concentrations have been used for comparisons with total columns retrieved from satellite observations [Van Damme 2014b]. We developed a retrieval for NH3 column density concentrations (molecules NH3/cm2) by fitting a set of spectral windows to ground-based solar absorption Fourier transform infrared (FTIR) measurements with the spectral fitting program SFIT4 [Hase et al., 2004]. The retrieval is then applied to FTIR measurements from a set of spectrometer sites from the Network for detection of Atmospheric Composition Change (NDACC) to retrieve NH3 columns for the sites located in Bremen, Germany; Lauder, New Zealand; Jungfraujoch, Switzerland; and the island of Reunion, France. Using eight years (2005-2013) of retrieved NH3 columns clear seasonal cycles are observed for each of the stations. Maximum concentrations can be related to NH3 emission sources, specific for the regions. A comparison between the retrieved NH3 columns and observations from the recent IASI- NH3 product [Van Damme et al, 2014a] using strict spatial and temporal criteria for the selection of observations showed a good correlation (R=0.82; slope=0.63). The IASI- NH3 columns for the Bremen and Lauder area show similar temporal cycles when compared to the FTIR observations. [less ▲]

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See detailImproved spectral fitting of nitrogen dioxide from OMI in the 405-465 nm window
van Geffen, J H G M; Boersma, K F; Van Roozendael, M et al

in Atmospheric Measurement Techniques (2015), 8

An improved nitrogen dioxide (NO2) slant column density retrieval for the Ozone Monitoring Instrument (OMI) in the 405–465 nm spectral region is presented. Since the launch of OMI on board NASA’s EOS-Aura ... [more ▼]

An improved nitrogen dioxide (NO2) slant column density retrieval for the Ozone Monitoring Instrument (OMI) in the 405–465 nm spectral region is presented. Since the launch of OMI on board NASA’s EOS-Aura satellite in 2004, differential optical absorption spectroscopy (DOAS) retrievals of NO2 slant column densities have been the starting point for the KNMI DOMINO and NASA SP NO2 vertical column data as well as the OMI NO2 data of some other institutes. However, recent intercomparisons between NO2 retrievals from OMI and other UV/Vis and limb spectrometers, as well as ground-based measurements, suggest that OMI stratospheric NO2 is biased high. This study revises and, for the first time, fully documents the OMI NO2 retrieval in detail. The representation of the OMI slit function to convolve high-resolution reference spectra onto the relevant spectral grid is improved. The window used for the wavelength calibration is optimised, leading to much-reduced fitting errors. Ozone and water vapour spectra used in the fit are updated, reflecting the recently improved knowledge of their absorption cross section in the literature. The improved spectral fit also accounts for absorption by the O2–O2 collision complex and by liquid water over clearwater areas. The main changes in the improved spectral fitting result from the updates related to the wavelength calibration: the RMS error of the fit is reduced by 23% and the NO2 slant column by 0.85 1015 molec cm-2, independent of latitude, solar zenith angle and NO2 value. Including O2–O2 and liquid water absorption and updating the O3 and water vapour cross-section spectra further reduces NO2 slant columns on average by 0.35 1015 molec cm-2, accompanied by a further 9% reduction in the RMS error of the fit. The improved OMI NO2 slant columns are consistent with independent NO2 retrievals from other instruments to within a range that can be explained by photochemically driven diurnal increases in stratospheric NO2 and by small differences in fitting window and approach. The revisions indicate that current OMI NO2 slant columns suffered mostly from an additive positive offset, which is removed by the improved wavelength calibration and representation of the OMI slit function. It is therefore anticipated that the improved NO2 slant columns are most important to retrievals of spatially homogeneous stratospheric NO2 rather than to heterogeneous tropospheric NO2. [less ▲]

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See detailRetrieval of ethane from ground-based FTIR solar spectra using improved spectroscopy: recent burden increase above Jungfraujoch
Franco, Bruno ULg; Bader, Whitney ULg; Toon, G. C. et al

in Journal of Quantitative Spectroscopy & Radiative Transfer (2015), 160(C), 36-49

An improved spectroscopy is used to implement and optimize the retrieval strategy of ethane (C2H6) from ground-based Fourier Transform Infrared (FTIR) solar spectra recorded at the high-altitude station ... [more ▼]

An improved spectroscopy is used to implement and optimize the retrieval strategy of ethane (C2H6) from ground-based Fourier Transform Infrared (FTIR) solar spectra recorded at the high-altitude station of Jungfraujoch (Swiss Alps, 46.5° N, 8.0° E, 3580m a.s.l.). The improved spectroscopic parameters include C2H6 pseudo-lines in the 2720-3100 cm-1 range and updated line parameters for methyl chloride and ozone. These improved spectroscopic parameters allow for substantial reduction of the fitting residuals as well as enhanced information content. They also contribute to limiting oscillations responsible for ungeophysical negative mixing ratio profiles. This strategy has been successfully applied to the Jungfraujoch solar spectra available from 1994 onwards. The resulting time series is compared with C2H6 total columns simulated by the state-of-the-art chemical transport model GEOS-Chem. Despite very consistent seasonal cycles between both data sets, a negative systematic bias relative to the FTIR observations suggests that C2H6 emissions are underestimated in the current inventories implemented in GEOS-Chem. Finally, C2H6 trends are derived from the FTIR time series, revealing a statistically-significant sharp increase of the C2H6 burden in the remote atmosphere above Jungfraujoch since 2009. Evaluating cause of this change in the C2H6 burden, which may be related to the recent massive growth of shale gas exploitation in North America, is of primary importance for atmospheric composition and air quality in the Northern Hemisphere. [less ▲]

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See detailUsing XCO2 retrievals for assessing the long-term consistency of NDACC/FTIR data sets
Barthlott, S; Schneider, M; Hase, F et al

in Atmospheric Measurement Techniques (2015), 8

Within the NDACC (Network for the Detection of Atmospheric Composition Change), more than 20 FTIR (Fourier-transform infrared) spectrometers, spread worldwide, provide long-term data records of many ... [more ▼]

Within the NDACC (Network for the Detection of Atmospheric Composition Change), more than 20 FTIR (Fourier-transform infrared) spectrometers, spread worldwide, provide long-term data records of many atmospheric trace gases. We present a method that uses measured and modelled XCO2 for assessing the consistency of these NDACC data records. Our XCO2 retrieval setup is kept simple so that it can easily be adopted for any NDACC/FTIR-like measurement made since the late 1950s. By a comparison to coincident TCCON (Total Carbon Column Observing Network) measurements, we empirically demonstrate the useful quality of this suggested NDACC XCO2 product (empirically obtained scatter between TCCON and NDACC is about 4‰ for daily mean as well as monthly mean comparisons, and the bias is 25 ‰). Our XCO2 model is a simple regression model fitted to CarbonTracker results and the Mauna Loa CO2 in situ records. A comparison to TCCON data suggests an uncertainty of the model for monthly mean data of below 3 ‰. We apply the method to the NDACC/FTIR spectra that are used within the project MUSICA (multi-platform remote sensing of isotopologues for investigating the cycle of atmospheric water) and demonstrate that there is a good consistency for these globally representative set of spectra measured since 1996: the scatter between the modelled and measured XCO2 on a yearly time scale is only 3 ‰. [less ▲]

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See detailPast changes in the vertical distribution of ozone – Part 3: Analysis and interpretation of trends
Harris, N. R. P.; Hassler, B.; Tummon, F. et al

in Atmospheric Chemistry & Physics Discussions (2015), 15(6), 8565--8608

Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised datasets. The amount of ozone-depleting compounds in the stratosphere (as measured by ... [more ▼]

Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised datasets. The amount of ozone-depleting compounds in the stratosphere (as measured by Equivalent Effective Stratospheric Chlorine – EESC) maximised in the second half of the 1990s. We therefore examine the trends in the periods before and after that peak to see if any change in trend is discernible in the ozone record. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10% per decade at mid-latitudes and closer to −5% per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt. Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the two main satellite instruments (SBUV and SAGE II) and the ground-based Umkehr and ozonesonde stations have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2% per decade in mid-latitudes and ~ 3% per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different datasets. The averaged upward trends are significant if the trends derived from various datasets are assumed to be independent, but are generally not significant if the trends are not independent. This arises because many of the underlying measurement records are used in more than one merged dataset. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties. [less ▲]

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See detailTrends of ozone total columns and vertical distribution from FTIR observations at eight NDACC stations around the globe
Vigouroux, C; Blumenstock, T; Coffey, M et al

in Atmospheric Chemistry and Physics (2015), 15

Ground-based Fourier transform infrared (FTIR) measurements of solar absorption spectra can provide ozone total columns with a precision of 2 % but also independent partial column amounts in about four ... [more ▼]

Ground-based Fourier transform infrared (FTIR) measurements of solar absorption spectra can provide ozone total columns with a precision of 2 % but also independent partial column amounts in about four vertical layers, one in the troposphere and three in the stratosphere up to about 45 km, with a precision of 5–6 %. We use eight of the Network for the Detection of Atmospheric Composition Change (NDACC) stations having a long-term time series of FTIR ozone measurements to study the total and vertical ozone trends and variability, namely, Ny-Ålesund (79ºN), Thule (77ºN), Kiruna (68ºN), Harestua (60ºN), Jungfraujoch (47ºN), Izaña (28ºN), Wollongong (34ºS) and Lauder (45ºS). The length of the FTIR time series varies by station but is typically from about 1995 to present. We applied to the monthly means of the ozone total and four partial columns a stepwise multiple regression model including the following proxies: solar cycle, quasi-biennial oscillation (QBO), El Niño–Southern Oscillation (ENSO), Arctic and Antarctic Oscillation (AO/AAO), tropopause pressure (TP), equivalent latitude (EL), Eliassen–Palm flux (EPF), and volume of polar stratospheric clouds (VPSC). At the Arctic stations, the trends are found mostly negative in the troposphere and lower stratosphere, very mixed in the middle stratosphere, positive in the upper stratosphere due to a large increase in the 1995–2003 period, and non-significant when considering the total columns. The trends for mid-latitude and subtropical stations are all non-significant, except at Lauder in the troposphere and upper stratosphere and at Wollongong for the total columns and the lower and middle stratospheric columns where they are found positive. At Jungfraujoch, the upper stratospheric trend is close to significance (+0.9 ± 1.0 %/decade). Therefore, some signs of the onset of ozone mid-latitude recovery are observed only in the Southern Hemisphere, while a few more years seem to be needed to observe it at the northern mid-latitude station. [less ▲]

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See detailUpdate on Ozone-Depleting Substances (ODSs) and Other Gases of Interest to the Montreal Protocol
Carpenter, L. J.; Reimann, S.; Burkholder, J. B. et al

in Nohende Ajavon, Ayité-Lô; Newman, Paul. A.; Pyle, John A. (Eds.) et al Scientific Assessment of Ozone Depletion: 2014 (2014)

The amended and adjusted Montreal Protocol has continued to reduce emissions and atmospheric abundances of most controlled ozone-depleting substances. By 2012, the total combined abundance of ... [more ▼]

The amended and adjusted Montreal Protocol has continued to reduce emissions and atmospheric abundances of most controlled ozone-depleting substances. By 2012, the total combined abundance of anthropogenic ODSs in the troposphere (measured as Equivalent Chlorine) had decreased by nearly 10% from its peak value in 1994. [less ▲]

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See detailLong-term evolution and seasonal modulation of methanol above Jungfraujoch (46.5°N, 8.0°E): Optimisation of the retrieval strategy, comparison with model and independant observations
Bader, Whitney ULg; Stavrakou, T; Muller, J-F et al

in Atmospheric Measurement Techniques (2014), 7

Methanol (CH3OH) is the second most abundant organic compound in the Earth's atmosphere after methane. In this work, we present the first long-term time series of methanol total, lower tropospheric and ... [more ▼]

Methanol (CH3OH) is the second most abundant organic compound in the Earth's atmosphere after methane. In this work, we present the first long-term time series of methanol total, lower tropospheric and upper tropospheric-lower stratospheric partial columns derived from the analysis of high resolution Fourier transform infrared solar spectra recorded at the Jungfraujoch station (46.5° N, 3580 m a.s.l.). The retrieval of methanol is very challenging due to strong absorptions of ozone in the region of the selected υ8 band of CH3OH. Two wide spectral intervals have been defined and adjusted in order to maximize the information content. Methanol does not exhibit a significant trend over the 1995–2012 time period, but a strong seasonal modulation characterized by maximum values and variability in June–July, minimum columns in winter and a peak-to-peak amplitude of 130%. In situ measurements performed at the Jungfraujoch and ACE-FTS occultations give similar results for the methanol seasonal variation. The total and lower tropospheric columns are also compared with IMAGESv2 model simulations. There is no systematic bias between the observations and IMAGESv2 but the model underestimates the peak-to-peak amplitude of the seasonal modulations. [less ▲]

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See detailRetrievals of formaldehyde from ground-based FTIR and MAX-DOAS observations at the Jungfraujoch station and comparisons with GEOS-Chem and IMAGES model simulations
Franco, Bruno ULg; Hendrick, François; Van Roozendael, Michel et al

Conference (2014, November 07)

As a ubiquitous product of the oxidation of many Volatile Organic Compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation ... [more ▼]

As a ubiquitous product of the oxidation of many Volatile Organic Compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation pathways leading to the formation of tropospheric ozone and secondary organic aerosols. We have successfully retrieved HCHO columns from ground-based Fourier Transform Infrared (FTIR) solar spectra and UV-Visible Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) scans recorded during the July 2010 – December 2012 time period at the Jungfraujoch station (Swiss Alps, 46.5 °N, 8.0 °E, 3580 m a.s.l.). Characterization of the retrieved products has revealed different vertical sensitivity between both remote sensing techniques. Furthermore, HCHO amounts simulated by two state-of-the-art Chemical Transport Models (CTMs), GEOS-Chem and IMAGESv2, have been compared to FTIR total columns and MAX-DOAS 3.6 – 8 km partial columns, accounting for the respective vertical resolution of each ground-based instrument. Using the CTMs outputs as intermediate, FTIR and MAX-DOAS retrievals have shown consistent seasonal modulations of HCHO throughout the investigated period, characterized by summertime maximum and wintertime minimum. Such comparisons have also highlighted that FTIR and MAX-DOAS provide complementary products for HCHO above the Jungfraujoch station. [less ▲]

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See detailRecent Northern Hemisphere stratospheric HCl increase due to atmospheric circulation changes
Mahieu, Emmanuel ULg; Chipperfield, M. P.; Notholt, J. et al

in Nature (2014), 515(7525), 104--107

The abundance of chlorine in the Earth’s atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the ... [more ▼]

The abundance of chlorine in the Earth’s atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale[1], before they reach the stratosphere where they release chlorine atoms that cause ozone depletion[2]. The large ozone loss over Antarctica[3] was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine- and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year[4], in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 1996[5], then a decrease of close to one per cent per year[6,7], in agreement with the surface observations of the chlorine source gases and model calculations[7]. Here we present ground-based and satellite data that show a recent and significant increase, at the 2σ level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slowdown in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. This short-term dynamical variability will also affect other stratospheric tracers and needs to be accounted for when studying the evolution of the stratospheric ozone layer. [less ▲]

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See detailIncrease in northern hemisphere stratospheric hydrogen chloride over recent years
Mahieu, Emmanuel ULg; Chipperfield, MP; Notholt, J et al

Poster (2014, October 07)

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