Are Ozone Concentrations at risk in Northern Hemisphere?

Stratospheric hydrogen chloride (HCl) is the main stratospheric chlorine reservoir and, thus, an indicator of ozone-destroying substances (ODSs). An international reseach team including scientists of the Karlsruhe Institute of Technology (KIT) observed an annual increase by up to three percent in the HCl content over the northern hemisphere since 2007 in contrast with the ongoing monotonic decrease of near-surface source gases.

However, by using model simulations, the authors attribute this trend anomaly to a slowdown in the Northern Hemisphere atmospheric circulation, not to higher emissions of the precursor substances of the ODSs banned in the Montreal Protocol. This short-term dynamical variability will also affect other stratospheric tracers and needs to be accounted for when studying the evolution of the stratospheric ozone layer in the coming years.

This study was carried out by combining ground-based Fourier Transform Spectrometer observations and satellite data. Among other ground-based FTS stations contributing to the NDACC (Network for the Detection of Atmospheric Composition Change), Izaña Observatory’s FTS was one of the observation sites used to confirm the rise of stratospheric HCL in Northern Hemisphere since 2007. Figure 1 shows the time series of the HCl total column amounts measured at Izaña Observatory since 1999, where the decrease/increase periods have been highlighted.

Figure 1. Time series of the HCl total column amounts measured by ground-based FTS at Izaña Observatory since 1999.

The results of this study have recently been published in the prestigious journal of science “Nature” with the title of “Recent northern hemisphere hydrogen chloride increase due to atmospheric circulation change”. For more details, please refer to:

Recent northern hemisphere hydrogen chloride increase due to atmospheric circulation change, E. Mahieu, M.P. Chipperfield, J. Notholt, T. Reddmann, J. Anderson, P.F. Bernath, T. Blumenstock, M.T. Coffey, S. Dhomse, W. Feng, B. Franco, L. Froidevaux, D.W.T. Griffith, J. Hannigan, F. Hase, R. Hossaini, N.B. Jones, I. Morino, I. Murata, H. Nakajima, M. Palm, C. Paton-Walsh, J.M. Russell III, M. Schneider, C. Servais, D. Smale, K.A. Walker. DOI: 10.1038/nature13857,

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