Trends of HCl, ClONO<sub>2</sub>, and HF column abundances from ground-based FTIR measurements in Kiruna (Sweden) in comparison with KASIMA model calculations

Abstract

Abstract. Trends of hydrogen chloride (HCl), chlorine nitrate (ClONO 2 ), and hydrogen fluoride (HF) total column abundances above Kiruna (Northern Sweden, 67.84 • N, 20.41 • E) derived from nearly 14 years (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009) 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 ClONO 2 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 ClONO 2 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 Correspondence to: R. Kohlhepp (regina.kohlhepp@kit.edu) decrease: For ClONO 2 , 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 ClONO 2 above Kiruna for both measurement and model data.

Quality assessment of ozone total column amounts as monitored by ground-based solar absorption spectrometry in the near infrared (> 3000 cm<sup>−1</sup>)

“…The smoothing error profile is also shown for each spectral region. The multi-annual evolution of the relative differences and of the ozone total column amounts has been estimated by using a bootstrap re-sampling method Kohlhepp et al, 2011), which fits the following function to the corresponding time series:…”

Chlorine nitrate in the atmosphere

“…Later the research interest moved towards identification of multi-year regularities and time series (e.g., Rinsland et al, 1996b;Blumenstock et al, 2000;Reisinger et al, 1995;Notholt et al, 1997;Rinsland et al, 2003Rinsland et al, , 2010Kohlhepp et al, 2011Kohlhepp et al, , 2012. Meanwhile worldwide monitoring of stratospheric ClONO 2 is performed by the Network for Detection of Atmospheric Composi- tion Change (NDACC; De Maziére et al, 2018), using high-resolution Fourier transform infrared solar absorption spectroscopy.…”

“…The measurement site was Jungfraujoch in the Swiss Alps, and its high elevation was advantageous for the measurements because the measured light does not pass through the humid boundary layer, yielding a much clearer spectral signature of ClONO 2 . Today this gas is routinely measured for monitoring purposes from stations cooperating in the framework of the Network for Detection of Atmospheric Composition Change (NDACC) (e.g., Reisinger et al, 1995;Rinsland et al, 2003;Kohlhepp et al, 2011;De Maziére et al, 2018).…”

Chlorine in the stratosphere

“…Zander and Demoulin (1988) for the first time identified ClO-NO 2 in ground-based infrared spectra taken from the Jungfraujoch station in the Swiss Alps. Today, within the NDACC activities, this species is monitored on a regular basis from FTIR measurement stations already mentioned in the context of HCl monitoring (see above) (e.g., Reisinger et al, 1995;Rinsland et al, 2003;Kohlhepp et al, 2011). As with HCl, one of the main scientific questions is how the time series reflect the decrease of CFCs after the Montreal Protocol.…”