Validation of ACE-FTS v2.2 measurements of HCl, HF, CCl3F and CCl2F2 using space-, balloon- and ground-based instrument observations

in Atmospheric Chemistry and Physics (2008), 8

Hydrogen chloride (HCl) and hydrogen fluoride (HF) are respectively the main chlorine and fluorine reservoirs in the Earth's stratosphere. Their buildup resulted from the intensive use of man-made ... [more ▼]

Hydrogen chloride (HCl) and hydrogen fluoride (HF) are respectively the main chlorine and fluorine reservoirs in the Earth's stratosphere. Their buildup resulted from the intensive use of man-made halogenated source gases, in particular CFC-11 (CCl3F) and CFC-12 (CCl2F2), during the second half of the 20th century. It is important to continue monitoring the evolution of these source gases and reservoirs, in support of the Montreal Protocol and also indirectly of the Kyoto Protocol. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) is a space-based instrument that has been performing regular solar occultation measurements of over 30 atmospheric gases since early 2004. In this validation paper, the HCl, HF, CFC-11 and CFC-12 version 2.2 profile data products retrieved from ACE-FTS measurements are evaluated. Volume mixing ratio profiles have been compared to observations made from space by MLS and HALOE, and from stratospheric balloons by SPIRALE, FIRS-2 and Mark-IV. Partial columns derived from the ACE-FTS data were also compared to column measurements from ground-based Fourier transform instruments operated at 12 sites. ACE-FTS data recorded from March 2004 to August 2007 have been used for the comparisons. These data are representative of a variety of atmospheric and chemical situations, with sounded air masses extending from the winter vortex to summer sub-tropical conditions. Typically, the ACE-FTS products are available in the 10-50 km altitude range for HCl and HF, and in the 7-20 and 7-25 km ranges for CFC-11 and -12, respectively. For both reservoirs, comparison results indicate an agreement generally better than 5-10% above 20 km altitude, when accounting for the known offset affecting HALOE measurements of HCl and HF. Larger positive differences are however found for comparisons with single profiles from FIRS-2 and SPIRALE. For CFCs, the few coincident measurements available suggest that the differences probably remain within +/-20%. [less ▲]

Determination of COF2 vertical distributions above Jungfraujoch by FTIR and multi-spectra fitting

Poster (2007, April)

The major sources of fluorine in the stratosphere are CFC-11 and CFC-12. Photolysis of these compounds leads to release of chlorine atoms, while the fluorine is, in a first step, present in the form of ... [more ▼]

The major sources of fluorine in the stratosphere are CFC-11 and CFC-12. Photolysis of these compounds leads to release of chlorine atoms, while the fluorine is, in a first step, present in the form of carbonyl compounds like COClF and COF2. Their further photolysis liberates fluorine atoms, which are quickly converted to HF. Given its long life time, COF2 is the second stratospheric fluorine reservoir. The first COF2 vertical distributions were derived from occultation measurements performed by the ATMOS instrument during the SPACELAB-3 Space Shuttle mission in 1985. The Canadian FTIR spectrometer ACE-FTS, onboard the SCISAT-1 satellite, is the first instrument since the last ATMOS flight in 1994, to record COF2 vertical profiles from space. All these observations show that, at mean latitudes, COF2 concentration is maximum between 30 and 35 km. Several COF2 IR absorption lines located either in the so-called InSb (1-5 µm) and MCT (2-16 µm) spectral ranges can be used to determine its total column from ground-based FTIR observations. In this context, several studies concerning the evolution of COF2 total column above various stations were published during the nineties. At this time, no study concerning the inversion of COF2 vertical distributions from ground-based FTIR spectra has been published. This report deals with the feasibility of such inversions, using, simultaneously, via the SFIT-2 v3.91 algorithm, a multi-microwindows and a multi-spectra fitting procedure. The multi-spectra method consists of combining several FTIR observations, recorded during the same day, to increase the information content. A selection of microwindows in InSb and MCT ranges, a complete discussion about the data characterization (e.g. information content) and typical examples of COF2 retrieved profiles from high resolution solar spectra recorded with the University of Liège Jungfraujoch FTS will be revealed. [less ▲]

Validation of MIPAS HNO3 operational data

in Atmospheric Chemistry and Physics (2007), 7(18), 4905-4934

Nitric acid (HNO3) is one of the key products that are operationally retrieved by the European Space Agency (ESA) from the emission spectra measured by the Michelson Interferometer for Passive Atmospheric ... [more ▼]

Nitric acid (HNO3) is one of the key products that are operationally retrieved by the European Space Agency (ESA) from the emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT. The product version 4.61/4.62 for the observation period between July 2002 and March 2004 is validated by comparisons with a number of independent observations from ground-based stations, aircraft/balloon campaigns, and satellites. Individual HNO3 profiles of the ESA MIPAS level-2 product show good agreement with those of MIPAS-B and MIPAS-STR (the balloon and aircraft version of MIPAS, respectively), and the balloon-borne infrared spectrometers MkIV and SPIRALE, mostly matching the reference data within the combined instrument error bars. In most cases differences between the correlative measurement pairs are less than 1 ppbv (5-10%) throughout the entire altitude range up to about 38 km (similar to 6 hPa), and below 0.5 ppbv (15-20% or more) above 30 km (similar to 17 hPa). However, differences up to 4 ppbv compared to MkIV have been found at high latitudes in December 2002 in the presence of polar stratospheric clouds. The degree of consistency is further largely affected by the temporal and spatial coincidence, and differences of 2 ppbv may be observed between 22 and 26 km (similar to 50 and 30 hPa) at high latitudes near the vortex boundary, due to large horizontal inhomogeneity of HNO3. Similar features are also observed in the mean differences of the MIPAS ESA HNO3 VMRs with respect to the ground-based FTIR measurements at five stations, aircraft-based SAFIRE-A and ASUR, and the balloon campaign IBEX. The mean relative differences between the MIPAS and FTIR HNO3 partial columns are within +/- 2%, comparable to the MIPAS systematic error of similar to 2%. For the vertical profiles, the biases between the MIPAS and FTIR data are generally below 10% in the altitudes of 10 to 30 km. The MIPAS and SAFIRE HNO3 data generally match within their total error bars for the mid and high latitude flights, despite the larger atmospheric inhomogeneities that characterize the measurement scenario at higher latitudes. The MIPAS and ASUR comparison reveals generally good agreements better than 10-13% at 20-34 km. The MIPAS and IBEX measurements agree reasonably well (mean relative differences within +/- 15%) between 17 and 32 km. Statistical comparisons of the MIPAS profiles correlated with those of Odin/SMR, ILAS-II, and ACE-FTS generally show good consistency. The mean differences averaged over individual latitude bands or all bands are within the combined instrument errors, and generally within 1, 0.5, and 0.3 ppbv between 10 and 40 km (similar to 260 and 4.5 hPa) for Odin/SMR, ILAS-II, and ACE-FTS, respectively. The standard deviations of the differences are between 1 to 2 ppbv. The standard deviations for the satellite comparisons and for almost all other comparisons are generally larger than the estimated measurement uncertainty. This is associated with the temporal and spatial coincidence error and the horizontal smoothing error which are not taken into account in our error budget. Both errors become large when the spatial variability of the target molecule is high. [less ▲]