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

Abstract

[1] Long-term time series of hydrogen chloride (HCl) and chlorine nitrate (ClONO 2 ) total column abundances has been retrieved from high spectral resolution ground-based solar absorption spectra recorded with infrared Fourier transform spectrometers at nine NDSC (Network for the Detection of Stratospheric Change) sites in both Northern and Southern Hemispheres. The data sets span up to 24 years and most extend until the end of 2001. The time series of Cl y (defined here as the sum of the HCl and ClONO 2 columns) from the three locations with the longest time-span records show rapid increases until the early 1990s superimposed on marked day-to-day, seasonal and inter-annual variability. Subsequently, the buildup in Cl y slows and reaches a broad plateau after 1996, also characterized by variability. A similar time evolution is also found in the total chlorine concentration at 55 km altitude derived from Halogen Occultation Experiment (HALOE) global observations since 1991. The stabilization of inorganic chlorine observed in both the total columns and at 55 km altitude indicates that the near-global 1993 organic chlorine (CCl y ) peak at the Earth's surface has now propagated over a broad altitude range in the upper atmosphere, though the time lag is difficult to quantify precisely from the current data sets, due to variability. We compare the three longest measured time series with two-dimensional model calculations extending from 1977 to 2010, based on a halocarbon scenario that assumes past measured trends and a realistic extrapolation into the future. The model predicts broad Cl y maxima consistent with the long-term observations, followed by a slow Cl y decline reaching 12-14% relative to the peak by 2010. The data reported here confirm the effectiveness of the Montreal Protocol and its Amendments and Adjustments in progressively phasing out the major man-related perturbations of the stratospheric ozone layer, in particular, the anthropogenic chlorinebearing source gases. Citation: Rinsland, C. P., et al., Long-term trends of inorganic chlorine from ground-based infrared solar spectra: Past increases and evidence for stabilization,

The Network for the Detection of Atmospheric Composition Change (NDACC): History, status and perspectives

“…For example, extended NDACC FTIR data sets, combined with HALOE observations from UARS gave evidence for a stabilization of stratospheric chlorine around the mid-1990s (Rinsland et al, 2003). Subsequently, NDACC showed there to be a decrease in atmospheric HCl and ClONO 2 at rates ~ 1%/year in both hemispheres, between 80°N and 78°S (Kohlhepp, et al, 2012).…”

Interannual variation patterns of total ozone and lower stratospheric temperature in observations and model simulations

“…Recently, chlorine levels seem to have begun decreasing in the stratosphere (WMO, 2003;Rinsland et al, 2003). It is now being discussed whether ozone also might show signs of a beginning recovery (Newchurch et al, 2003;Steinbrecht et al, 2004;Reinsel et al, 2005).…”

Analysis of HCl and ClO time series in the upper stratosphere using satellite data sets

“…However, due to the 1987 Montreal protocol agreement (and the subsequent adjustments), ozone depleting substance (ODS) emissions have slowly been phased out. It has been estimated that the total inorganic loading of tropospheric Cl peaked in 1993 (Rinsland et al, 2003) and has decreased by ∼5 % through early 2002 (O' Doherty et al, 2004). As it is estimated that it takes 3-6 years for air to be transported into the middle and upper stratosphere (Stiller et al, 2008), then peak stratospheric values are suggested to be somewhere between and 1999(WMO, 2006.…”