Abstract
Abstract. Trends of hydrogen chloride (HCl), chlorine nitrate (ClONO2), and hydrogen fluoride (HF) total column abundances above Kiruna (Northern Sweden, 67.84° N, 20.41° E) derived from nearly 14 years (1996–2009) of measurement and model data are presented. The measurements have been performed with a Bruker 120 HR (later Bruker 125 HR) Fourier transform infrared (FTIR) spectrometer and the chemistry-transport model (CTM) used was KASIMA (KArlsruhe SImulation model of the Middle Atmosphere). The total column abundances of ClONO2 and HF calculated by KASIMA agree quite well with the FTIR measurements while KASIMA tends to underestimate the HCl columns. To calculate the long-term trends, a linear function combined with an annual cycle was fitted to the data using a least squares method. The precision of the resulting trends was estimated with the bootstrap resampling method. For HF, both model and measurements show a positive trend that seems to decrease in the last few years. This suggests a stabilisation of the HF total column abundance. Between 1996 and 2009, KASIMA simulates an increase of (+1.51±0.07) %/yr which exceeds the FTIR result of (+0.65±0.25) %/yr. The trends determined for HCl and ClONO2 are significantly negative over the time period considered here. This is expected because the emission of their precursors (chlorofluorocarbons and hydrochlorofluorocarbons) has been restricted in the Montreal Protocol in 1987 and its amendments and adjustments. The trend for ClONO2 from the FTIR measurements amounts to (−3.28±0.56) %/yr and the one for HCl to (−0.81±0.23) %/yr. KASIMA simulates a weaker decrease: For ClONO2, the result is (−0.90±0.10) %/yr and for HCl (−0.17±0.06) %/yr. Part of the difference between measurement and model data can be explained by sampling and the stronger annual cycle indicated by the measurements. There is a factor of about four between the trends of HCl and ClONO2 above Kiruna for both measurement and model data.
Highlights
Since the 1970s, anthropogenic chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons have been predicted to deplete the stratospheric ozone layer (Molina and Rowland, 1974)
Measurements of vertical columns of hydrogen chloride (HCl), ClONO2, and hydrogen fluoride (HF) with a Fourier transform infrared (FTIR) spectrometer at Kiruna (Northern Sweden, 67.84◦ N, 20.41◦ E, 419 m a.s.l.) are presented. They are compared with results from the atmospheric chemistry transport model (CTM) KASIMA (KArlsruhe SImulation model of the Middle Atmosphere) and with the longest European FTIR time series recorded on Jungfraujoch (Swiss Alps, 46.5° N, 8.0° E, 3580 m a.s.l.)
The FTIR measurements and KASIMA model calculations seem to agree on a stabilisation of the atmospheric HF content
Summary
Since the 1970s, anthropogenic chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons have been predicted to deplete the stratospheric ozone layer (Molina and Rowland, 1974). As fluorine does not play an important role in stratospheric ozone depletion, there are no direct restrictions concerning its emission like the Montreal Protocol for chlorine and bromine, for example It is contained in CFCs and HCFCs, so it is expected to be influenced by the Montreal Protocol, too. Measurements of vertical columns of HCl, ClONO2, and HF with a Fourier transform infrared (FTIR) spectrometer at Kiruna (Northern Sweden, 67.84◦ N, 20.41◦ E, 419 m a.s.l.) are presented They are compared with results from the atmospheric chemistry transport model (CTM) KASIMA (KArlsruhe SImulation model of the Middle Atmosphere) and with the longest European FTIR time series recorded on Jungfraujoch (Swiss Alps, 46.5° N, 8.0° E, 3580 m a.s.l.)
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