Latitudinal distributions and temporal changes of stratospheric HCl and HF

Abstract

Hydrogen chloride and hydrogen fluoride are important sinks in the stratosphere for free halogens. The major sources of chlorine and fluorine in the stratosphere are anthropogenic; therefore a measurement of HC1 and HF gives information about the magnitude of anthropogenic effects on stratospheric chemistry and may give some information about the stratospheric hydroxyl concentration as well. We have determined the total column amount of HCI and HF above 12 km by measuring infrared absorption spectra with a high-resolution Fourier transform spectrometer flown on a jet aircraft. The HC1 column varies from 0.7 x 10 •5 molecules-cm -'• near the equator to 2.7 x 10 •5 molecules-crn -'• at 70øN; the HF column is about a factor of 5 lower. The HCI:HF ratio is almost independent of latitude, and neither constituent shows substantial seasonal or diurnal variation. At mid-latitudes the data from 1978 to 1982 show an annual increase of 5% per year for HC1 and 12% per year for HF. INTRODUCTION One of the major chemical cycles controlling the concentration of ozone in the stratosphere is the catalytic destruction of ozone by free chlorine and chlorine monoxide I-Stolarski and Cicerone, 1974]. The principal source for free chlorine in the stratosphere is believed to be photolysis of the chlorofluoromethanes (CFM's) F-11 (CFCI3) and F-12 (CF2C12). These very stable species are released in the troposphere by man's activities and diffuse slowly to altitudes where they can be photolyzed by solar ultraviolet radiation [Molina and Rowland, 1974]. The principal sink for chlorine is the production of HC1 and its subsequent diffusion to the troposphere and rainout. HC1 also serves as a temporary reservoir for chlorine in the stratosphere, from which the chlorine can be released by reaction with hydroxyl radicals. There are other sources of stratospheric chlorine than CFM's; these include naturally produced methyl chloride and anthropogenic sources such as carbon tetrachloride and methyl chloroform. No substantial sources of fluorine in the stratosphere other than CFM's [Cicerone, 1981] have been identified. When CFM's are photolyzed, the fluorine is quickly incorporated in HF, which is relatively stable; fluorine does not directly play an important role in the chemistry of the stratosphere. Measurements of HF and of the ratio of HF to HCI provide an indication of the relative importance of CFM's and other sources of stratospheric chlorine. Further, because HF is practically inert in the stratosphere while HCI reacts with OH, variations in the profile of HF and HCI give indirect evidence of the OH chemistry [Sze, 1978; Sze and Ko, 1981]. Therefore, it is useful to obtain a data set for HF and HC1 that is measured simultaneously over as wide a range of conditions as possible. There have been a number of measurements of HC1 and HF in the stratosphere by both in-situ and remote sensing techniques. The first measurements were by collection on base impregnated filters [Lazrus et al., 1975]. The vertical profile of acidic chloride vapor, whic...

Monitoring of the integrated column of hydrogen fluoride above the Jungfraujoch Station since 1977 ? the HF/HCl column ratio

“…The trend deduced between these two points is equal to (8.5 _+ 1)% per year cumulative, or (10 _ 1)% per year linear. This value is in reasonable agreement with the linear increase of 12 %/year reported by Mankin and Coffey (1983) for HF above 12 km altitude. The mean annual column abundances of HF above ISSJ are 5.…”

“…These last authors suspect, however, the existence of a local source of hydrogen fluoride which enhances the tropospheric content of HF above that site, therefore explaining the higher values above central France. The HF/HCI ratio derived over the period 1978-1982 by Mankin and Coffey (1983) above 12 km altitude is equal to (0.2 _ 0.08), also compatible with most of the ground-derived results. The increase in the HF/HC1 ratio, from 0.15 in 1978 to 0.24 in 1985, essentialy reflects the significant increase of HF in the stratosphere.…”

“…Mankin and Coffey (1983) have provided a synthesis of results accumulated up to 1982, while more recent intercomparison investigations have been reported by Mankin and Coffey (1987) and by Zander et al (1987a). With the exception of one profile determined from in-situ sampling by filter collection (Mroz et al, 1977) and a few recent far-infrared emission measurements (Traub and Chance, 1981), most of the database regarding the content and distribution of telluric hydrogen fluoride has come from infrared solar observations near 2.45 ~tm, where lines belonging to the fundamental band of HF appear unambiguously in absorption.…”

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

“…[4] High spectral resolution infrared solar absorption spectrometry has long been recognized as a key technique for remotely measuring atmospheric HCl from the ground, airplanes, and balloons [Farmer et al, 1976;Ackerman et al, 1976;Mankin and Coffey, 1983] and subsequently from space [e.g., Raper et al, 1987;Zander et al, 1992Zander et al, , 1996Gunson et al, 1994;Russell et al, 1996] by observing the strong HCl (1 -0) band transitions located near 3 mm. Past investigations of HCl trends from long-term ground-based monitoring include the studies by Zander et al [1987], Rinsland et al [1991], Wallace and Livingston [1991], and Wallace et al [1997].…”

Chlorine in the stratosphere

“…Spectroscopic measurements by infrared solar absorption technique from the ground and aircrafts has been used by Farmer et al (1976) and Mankin and Coffey (1983), and from stratospheric balloons by Williams et al (1976a), Ackerman et al (1976), and Raper et al (1977). Eyre and Roscoe (1977) used a balloon-borne pressure modulator infrared radiometer; Chance et al (1980) used far infrared spectroscopy, while Stachnik et al (1992) used microwave emission radiometry.…”