Validation of ACE-FTS v2.2 measurements of HCl, HF, CCl<sub>3</sub>F and CCl<sub>2</sub>F<sub>2</sub> using space-, balloon- and ground-based instrument observations

Abstract

Abstract. 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%.

Analysis of HCl and ClO time series in the upper stratosphere using satellite data sets

“…Mismatches are thus possible in terms of time and space. This result agrees with similar analyses made by Mahieu et al (2008), who show that there is ∼10-20 % ACE-FTS bias compared to HALOE for altitudes between 20 and 55 km. Work by Froidevaux et al (2008) also show that the biases between MLS and HALOE are of a similar magnitude in the same altitude region.…”

“…Currently, HCl v2.2 VMRs are from ∼10-50 km with a vertical resolution of approximately 3-4 km. Comparisons of ACE-FTS HCl to various other satellite and ground based instrumentation show that there is a good agreement of generally better than 5-10 % above 20 km (Mahieu et al, 2008). At present, no error analysis for ACE-FTS atmospheric products has been made.…”

Satellite observations of stratospheric hydrogen fluoride and comparisons with SLIMCAT calculations

“…3.2, HALOE v19 HF has been validated against ACE-FTS v2.2, with the ACE measurements biased high by around 5-20 % between 15 and 49 km (Mahieu et al, 2008). Furthermore, HF data from the MkIV interferometer for three flights (2003)(2004)(2005) agree well with ACE-FTS, with relative differences above 19 km within ±10 %, suggesting that there is a low bias in HALOE.…”

“…The ACE v2.2 HF data product, which uses a slightly different microwindow set from v3.0/v3.5 as well as an earlier version of the PT retrieval, has previously been validated, for example, against measurements taken by HALOE and the MkIV interferometer (Mahieu et al, 2008). It was found that ACE-FTS v2.2 HF measurements are biased high compared to HALOE, with mean differences around 5-20 % between 15 and 49 km.…”

Seasonal variability of stratospheric methane: implications for constraining tropospheric methane budgets using total column observations

“…Tropospheric columns have been shown to represent the magnitude and seasonality of in situ measurements (Saad et al, 2014;Washenfelder et al, 2003;Wang et al, 2014). The tropospheric CH 4 column-averaged DMFs (X t CH 4 ) are derived by the hydrogen fluoride (HF) proxy method described in Saad et al (2014), which uses the relationship between CH 4 and HF in the stratosphere, derived from ACE-FTS satellite measurements (Bernath, 2005;De Mazière et al, 2008;Mahieu et al, 2008;Waymark et al, 2014), to calculate and remove the stratospheric contribution to X CH 4 . The X t CH 4 used in this analysis have been processed consistently with the GGG2014 TCCON products, with air-mass dependence and calibration factors calculated for and applied to X t CH 4 .…”