Trend analysis of greenhouse gases over Europe measured by a network of ground-based remote FTIR instruments

in Atmospheric Chemistry and Physics (2008), 8(22), 6719-6727

This paper describes the statistical analysis of annual trends in long term datasets of greenhouse gas measurements taken over ten or more years. The analysis technique employs a bootstrap resampling ... [more ▼]

This paper describes the statistical analysis of annual trends in long term datasets of greenhouse gas measurements taken over ten or more years. The analysis technique employs a bootstrap resampling method to determine both the long-term and intra-annual variability of the datasets, together with the uncertainties on the trend values. The method has been applied to data from a European network of ground-based solar FTIR instruments to determine the trends in the tropospheric, stratospheric and total columns of ozone, nitrous oxide, carbon monoxide, methane, ethane and HCFC-22. The suitability of the method has been demonstrated through statistical validation of the technique, and comparison with ground-based in-situ measurements and 3-D atmospheric models. [less ▲]

Validation of SCIAMACHY CH4 scientific products using ground-based FTIR measurements

Poster (2008, September)

In the framework of the past EVERGREEN project, the development of three scientific algorithms, namely WFM-DOAS (henceforward called WFMD), IMAP-DOAS (henceforward called IMAP) and IMLM, commenced in ... [more ▼]

In the framework of the past EVERGREEN project, the development of three scientific algorithms, namely WFM-DOAS (henceforward called WFMD), IMAP-DOAS (henceforward called IMAP) and IMLM, commenced in order to retrieve the total column amounts of key atmospheric trace gases, including CH4, from SCIAMACHY nadir observations in its near-infrared channels. Since then, the retrieval products of these three algorithms, have undergone serious improvements. At key phases in their development, the products have been validated by using a network of ground-based FTIR instruments. Parallel with the improved SCIAMACHY data, the FTIR groups have taken steps to optimise and harmonise their own datasets and as such the different validation efforts always used the state-of-the-art FTIR dataset. Here we present an overview of the evolution of the CH4 algorithms by re-validating the data, using the same FTIR dataset (as developed under the UFTIR project) for all algorithm versions. [less ▲]

Validation of ACE-FTS N2O measurements

in Atmospheric Chemistry and Physics (2008), 8(16), 4759-4786

The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, was launched on 12 August 2003, carrying two instruments that measure vertical profiles of atmospheric constituents using the solar ... [more ▼]

The Atmospheric Chemistry Experiment (ACE), also known as SCISAT, was launched on 12 August 2003, carrying two instruments that measure vertical profiles of atmospheric constituents using the solar occultation technique. One of these instruments, the ACE Fourier Transform Spectrometer (ACE-FTS), is measuring volume mixing ratio (VMR) profiles of nitrous oxide (N2O) from the upper troposphere to the lower mesosphere at a vertical resolution of about 3-4 km. In this study, the quality of the ACE-FTS version 2.2 N2O data is assessed through comparisons with coincident measurements made by other satellite, balloon-borne, aircraft, and ground-based instruments. These consist of vertical profile comparisons with the SMR, MLS, and MIPAS satellite instruments, multiple aircraft flights of ASUR, and single balloon flights of SPIRALE and FIRS-2, and partial column comparisons with a network of ground-based Fourier Transform InfraRed spectrometers (FTIRs). Between 6 and 30 km, the mean absolute differences for the satellite comparisons lie between -42 ppbv and +17 ppbv, with most within +/- 20 ppbv. This corresponds to relative deviations from the mean that are within +/- 15%, except for comparisons with MIPAS near 30 km, for which they are as large as 22.5%. Between 18 and 30 km, the mean absolute differences for the satellite comparisons are generally within +/- 10 ppbv. From 30 to 60 km, the mean absolute differences are within +/- 4 ppbv, and are mostly between -2 and +1 ppbv. Given the small N2O VMR in this region, the relative deviations from the mean are therefore large at these altitudes, with most suggesting a negative bias in the ACE-FTS data between 30 and 50 km. In the comparisons with the FTIRs, the mean relative differences between the ACE-FTS and FTIR partial columns (which cover a mean altitude range of 14 to 27 km) are within +/- 5.6% for eleven of the twelve contributing stations. This mean relative difference is negative at ten stations, suggesting a small negative bias in the ACE-FTS partial columns over the altitude regions compared. Excellent correlation (R=0.964) is observed between the ACE-FTS and FTIR partial columns, with a slope of 1.01 and an intercept of -0.20 on the line fitted to the data. [less ▲]

Measured and modeled trends of stratospheric Cly and Fy column amounts in the northern hemisphere

Poster (2008, July)

The german HGF virtual institute PEP (Pole-Equator-Pole) has been established in 2004 in order to investigate the variability of atmospheric trace constituents along a north-south transection. Within PEP ... [more ▼]

The german HGF virtual institute PEP (Pole-Equator-Pole) has been established in 2004 in order to investigate the variability of atmospheric trace constituents along a north-south transection. Within PEP the HGF centres AWI and FZK as well as the german Universities of Bremen, Karlsruhe and Potsdam combine their knowledge and capabilities in ground-based measurements and global and regional modelling of atmospheric trace constituents and aerosols. Here we present results of long-term measurements of the stratospheric column of HCl, ClONO2, HF, and O3 obtained at the different PEP stations in the northern hemisphere and in addtion at Jungfraujoch. All stations are affiliated to the NDACC (Network for the Detection of Atmospheric Composition Change). The measured time series are compared with long-term model calculations performed with a state of the art 2-D model of the University of Bremen and the 3-D CTM KASIMA. Please note, that the lowest altitude for the determination of the total columns is about 7 km leading to a slight underestimation w.r.t. the measurements. [less ▲]

Measured and modelled trends of stratopsheric Cly and Fy column amounts in the northern hemisphere

Poster (2007, April)

Reactive inorganic chlorine plays a crucial role in the stratospheric ozone depletion. To stabilize and enable a recovering of the stratospheric ozone layer, the Montreal protocol and its amendments and ... [more ▼]

Reactive inorganic chlorine plays a crucial role in the stratospheric ozone depletion. To stabilize and enable a recovering of the stratospheric ozone layer, the Montreal protocol and its amendments and adjustments have been progressively implemented to reduce or even stop the production and emission of important chlorinated source gases (CFCs, HCFCs, CCl4, CH3CCl3, and Halons). As these source gases are photolysed in the stratosphere into inorganic chlorine and fluorine, respectively, the turn over of the inorganic chlorine (HCl and ClONO2) and slowing down of fluorine (HF and COF2) reservoirs act as a verification of the effectiveness of these protocols. Here we present results of long-term measurements of the stratospheric column of HCl, ClONO2, and HF obtained at different stations in the northern hemisphere (Ny Alesund, Kiruna, Zugspitze, Jungfraujoch, Izana, all affiliated to the NDACC, Network for the Detection of Atmospheric Composition Change) within the PEP (Pole- Equator-Pole) network. These time series are interpreted with model calculations performed with a state of the art 2-D model and the 3-D CTM KASIMA with respect to the determination of the slowing down or turn over, respectively. In addition, trend parameters calculated using different approaches (e.g. linear trend, bootstrap-method) will be presented and intercompared. [less ▲]

Comparisons between SCIAMACHY and ground-based FTIR data for total columns of CO, CH4, CO2 and N2O

in Atmospheric Chemistry and Physics (2006), 6

Total column amounts of CO, CH4, CO2 and N2O retrieved from SCIAMACHY nadir observations in its near-infrared channels have been compared to data from a ground-based quasi-global network of Fourier ... [more ▼]

Total column amounts of CO, CH4, CO2 and N2O retrieved from SCIAMACHY nadir observations in its near-infrared channels have been compared to data from a ground-based quasi-global network of Fourier-transform infrared ( FTIR) spectrometers. The SCIAMACHY data considered here have been produced by three different retrieval algorithms, WFM-DOAS (version 0.5 for CO and CH4 and version 0.4 for CO2 and N2O), IMAP- DOAS ( version 1.1 and 0.9 (for CO)) and IMLM (version 6.3) and cover the January to December 2003 time period. Comparisons have been made for individual data, as well as for monthly averages. To maximize the number of reliable coincidences that satisfy the temporal and spatial collocation criteria, the SCIAMACHY data have been compared with a temporal 3rd order polynomial interpolation of the ground-based data. Particular attention has been given to the question whether SCIAMACHY observes correctly the seasonal and latitudinal variability of the target species. The present results indicate that the individual SCIAMACHY data obtained with the actual versions of the algorithms have been significantly improved, but that the quality requirements, for estimating emissions on regional scales, are not yet met. Nevertheless, possible directions for further algorithm upgrades have been identified which should result in more reliable data products in a near future. [less ▲]

Sulphur hexafluoride (SF6): comparison of FTIR-measurements at three sites and determination of its trend in the northern hemisphere

in Journal of Quantitative Spectroscopy & Radiative Transfer (2005), 92(3), 383-392

Fourier transform infrared spectrometry has been used to retrieve the total column abundances of SF6 at three locations in the northern hemisphere, i.e., the Ny- Angstromlesund site in Spitsbergen/Norway ... [more ▼]

Fourier transform infrared spectrometry has been used to retrieve the total column abundances of SF6 at three locations in the northern hemisphere, i.e., the Ny- Angstromlesund site in Spitsbergen/Norway at 79degreesN, the Jungfraujoch observatory in Switzerland at 47degreesN and the Kitt Peak observatory in Arizona, USA, at 32degreesN. The total column results have been converted to average tropospheric mixing ratios. The mean increases in these mixing ratios have been found to be, equal to 0.31 +/- 0.08 pptv yr(-1) at Ny Angstromlesund, 0.24 +/- 0.01 pptv yr(-1) at the Jungfraujoch and 0.28 +/- 0.09 pptv yr(-1) at Kitt Peak for the common period March 1993 to March 2002, in agreement with corresponding CMDL data (0.21 +/- 0.0002 pptv yr(-1)) at the surface. The limited accuracy of the Ny Angstromlesund and Kitt Peak data results from strong tropospheric water vapour interferences at these lower altitude sites. Observations at all three locations show that SF6 is Still accumulating in the atmosphere. Extrapolations of linear and second-order fits to the Jungfraujoch data predict tropospheric mixing ratios of SF6, respectively equal to 16.4 +/- 0.5 and. 14.7 +/- 0.6 in 2050, and 28.2 +/- 0.9 and 22.2 +/- 10.8 pptv in 2100, significantly, lower than those reported in the literature so far. (C) 2004 Elsevier Ltd. All, rights reserved. [less ▲]

The exploitation of ground-based Fourier transform infrared observations for the evaluation of tropospheric trends of greenhouse gases over Europe

in Environmental Sciences (2005), 2(2-3), 283-293

Solar absorption measurements using Fourier transform infrared (FTIR) spectrometry carry information about the atmospheric abundances of many constituents, including non-CO2 greenhouse gases. Such ... [more ▼]

Solar absorption measurements using Fourier transform infrared (FTIR) spectrometry carry information about the atmospheric abundances of many constituents, including non-CO2 greenhouse gases. Such observations have regularly been made for many years as a contribution to the Network for the Detection of Stratospheric Change (NDSC). They are the only ground-based remote sensing observations available nowadays that carry information about a number of greenhouse gases in the free troposphere. This work focuses on the discussion of the information content of FTIR long-term monitoring data of some direct and indirect greenhouse gases (CH4, N2O, O3 and CO and C2H6, respectively), at six NDSC stations in Western Europe. This European FTIR network covers the polar to subtropical regions. At several stations of the network, the observations span more than a decade. Existing spectral time series have been reanalyzed according to a common optimized retrieval strategy, in order to derive distinct tropospheric and stratospheric abundances for the above-mentioned target gases. A bootstrap resampling method has been implemented to evaluate trends of the tropospheric burdens of the target gases, including their uncertainties. In parallel, simulations of the target time series are being made with the Oslo CTM2 model: comparisons between the model results and the observations provide valuable information to improve the model and, in particular, to optimize emission estimates that are used as inputs to the model simulations. The work is being performed within the EC project UFTIR. The paper focuses on N2O for which the first trend results have been obtained. [less ▲]

Long-term trends of inorganic chlorine from ground-based infrared solar spectra: Past increases and evidence for stabilization

in Journal of Geophysical Research (2003), 108(D8), 4252

Long-term time series of hydrogen chloride (HCl) and chlorine nitrate (ClONO2) total column abundances has been retrieved from high spectral resolution ground-based solar absorption spectra recorded with ... [more ▼]

Long-term time series of hydrogen chloride (HCl) and chlorine nitrate (ClONO2) total column abundances has been retrieved from high spectral resolution ground-based solar absorption spectra recorded with infrared Fourier transform spectrometers at nine NDSC (Network for the Detection of Stratospheric Change) sites in both Northern and Southern Hemispheres. The data sets span up to 24 years and most extend until the end of 2001. The time series of Cly (defined here as the sum of the HCl and ClONO2 columns) from the three locations with the longest time-span records show rapid increases until the early 1990s superimposed on marked day-to-day, seasonal and inter-annual variability. Subsequently, the buildup in Cly slows and reaches a broad plateau after 1996, also characterized by variability. A similar time evolution is also found in the total chlorine concentration at 55 km altitude derived from Halogen Occultation Experiment (HALOE) global observations since 1991. The stabilization of inorganic chlorine observed in both the total columns and at 55 km altitude indicates that the near-global 1993 organic chlorine (CCly) peak at the Earth’s surface has now propagated over a broad altitude range in the upper atmosphere, though the time lag is difficult to quantify precisely from the current data sets, due to variability. We compare the three longest measured time series with two-dimensional model calculations extending from 1977 to 2010, based on a halocarbon scenario that assumes past measured trends and a realistic extrapolation into the future. The model predicts broad Cly maxima consistent with the long-term observations, followed by a slow Cly decline reaching 12–14% relative to the peak by 2010. The data reported here confirm the effectiveness of the Montreal Protocol and its Amendments and Adjustments in progressively phasing out the major man-related perturbations of the stratospheric ozone layer, in particular, the anthropogenic chlorine-bearing source gases. [less ▲]

On the use of HF as a reference for the comparison of stratospheric observations and models

in Journal of Geophysical Research (1997), 102(11D), 12901-12919

Hydrogen fluoride (HF) is often used as a simple reference for other column observations of chemically active stratospheric species. However, seasonal and shorter timescale variations in column HF make ... [more ▼]

Hydrogen fluoride (HF) is often used as a simple reference for other column observations of chemically active stratospheric species. However, seasonal and shorter timescale variations in column HF make its use as a reference more complicated. In this paper we characterize the expected magnitude of these variations in HF, and variations of ratio quantities involving HF, using a two-dimensional (2-D) photochemical model and two versions of a three-dimensional (3-D) transport model. The 2-D model predicts that the column ratios HNO3/HF and HCl/HF increase from midlatitudes to the tropics, although this is very sensitive to HCl and HNO3 abundances in the tropical upper troposphere. Seasonal variations in vertical motion modifys the predicted ratios; for example, wintertime descent at high latitudes decreases HCl/HF. The ratio HNO3/HF at high latitudes is strongly modified by seasonal variations in the chemical partitioning of the odd nitrogen (NOy) species. We compare these model predictions with ground-based Fourier transform infrared spectroscopy (FTIR) observations of HF along with HCl, ClONO2 and HNO3 obtained at eight northern hemisphere sites between October 1994 and July 1995. We investigate quantitatively how HF can be used as a tracer to follow the evolution of observations at a single station and to intercompare results from different stations or with photochemical models. The magnitude of the 3-D model HF column agrees well with the observations, except on some occasions at high latitudes, giving indirect support for the important role of COF2 in the stratospheric inorganic fluorine budget. The observed day-to-day variability in the column ratios HCl/HF and HNO3/HF is much larger at high latitudes. This variability is reproduced in the 3-D models and is due to horizontal motion. Short timescale vertical displacement of the species profiles is estimated to have a small effect on the column ratios. In particular, we analyze the usefulness of the observed column ratio (ClONO2 + HCl)/HF as an indicator for chlorine activation. Current measurement uncertainties limit the degree of activation which can be unambiguously detected using this observed quantity, but we can determine that chlorine-activated air was observed above Aberdeen (58 degrees N) on 6 days in late January 1995. [less ▲]