Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
}
TY - JOUR
T1 - Recent Northern Hemisphere stratospheric HCl increase due to atmospheric circulation changes
AU - Mahieu, E.
AU - Chipperfield, M. P.
AU - Notholt, J.
AU - Reddmann, T.
AU - Anderson, J.
AU - Bernath, P. F.
AU - Blumenstock, T.
AU - Coffey, M. T.
AU - Dhomse, S. S.
AU - Feng, W.
AU - Franco, B.
AU - Froidevaux, L.
AU - Griffith, D. W. T.
AU - Hannigan, J. W.
AU - Hase, F.
AU - Hossaini, R.
AU - Jones, N. B.
AU - Morino, I.
AU - Murata, I.
AU - Nakajima, H.
AU - Palm, M.
AU - Paton-Walsh, C.
AU - Russell, J. M.
AU - Schneider, M.
AU - Servais, C.
AU - Smale, D.
AU - Walker, K. A.
PY - 2014/11/6
Y1 - 2014/11/6
N2 - The abundance of chlorine in the Earth's atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale(1), before they reach the stratosphere where they release chlorine atoms that cause ozone depletion(2). The large ozone loss over Antarctica(3) was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine-and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year(4), in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 1996(5), then a decrease of close to one per cent per year(6,7), in agreement with the surface observations of the chlorine source gases and model calculations(7). Here we present ground-based and satellite data that show a recent and significant increase, at the 2 sigma level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slow down in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. 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.
AB - The abundance of chlorine in the Earth's atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale(1), before they reach the stratosphere where they release chlorine atoms that cause ozone depletion(2). The large ozone loss over Antarctica(3) was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine-and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year(4), in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 1996(5), then a decrease of close to one per cent per year(6,7), in agreement with the surface observations of the chlorine source gases and model calculations(7). Here we present ground-based and satellite data that show a recent and significant increase, at the 2 sigma level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slow down in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. 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.
KW - INORGANIC CHLORINE
KW - OZONE
KW - EVOLUTION
KW - SYSTEM
KW - AIR
KW - AGE
U2 - 10.1038/nature13857
DO - 10.1038/nature13857
M3 - Journal article
VL - 515
SP - 104
EP - 107
JO - Nature
JF - Nature
SN - 0028-0836
IS - 7525
ER -