Rise and decline of active chlorine in the stratosphere

Abstract

Our ground‐based millimeter‐wave measurements of chlorine monoxide (ClO) in the ozone layer above Hawaii since 1992, together with a few measurements from the same site using an earlier version of the same instrument during the 1980's, provide a unique data set for the determination of the long‐term trend of active chlorine in the middle stratosphere. The trend shows a rapid rise of 58% from 1982 to a broad maximum in 1994–1997 and a substantial decline of 1.5%/year from the maximum through late 2004. About 1/3 of the decline may be due to changes in methane. Both the rise and the decline are consistent with that expected from the rise and decline of total chlorine in the troposphere, which reached a maximum in 1992–1993, then declined sharply after implementation of international agreements to phase out chlorofluorocarbon (CFC) production starting with the Montreal Protocol.

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

“…The results found here are in agreement with and extend on previous findings (for example, Considine et al, 1997Considine et al, , 1999Anderson et al, 2000;Newchurch et al, 2003;Froidevaux et al, 2006;Solomon et al, 2006;WMO, 2006). Although the ClO trend is not statistically significant, it does imply a reduction over the past 7 years, while the HCl trend shows a clear statistically significant downward trend.…”

“…The ClO trend value obtained here is considerably less negative than the analysis performed by Solomon et al (2006), who used ground based millimetre wave measurements at Mauna Kea in Hawaii, USA, to observe ClO concentrations. They found a significant linear decline of ClO of 8 % decade −1 .…”

“…ClO on the other hand, carries most of the reactive chlorine in the stratosphere during day time. Past studies of these gases have suggested that there has been a slow down and even a decrease in the accumulation of ClO in the stratosphere using ground based measurements and satellite data sets (Considine et al, 1997(Considine et al, , 1999Anderson et al, 2000;Newchurch et al, 2003;Froidevaux et al, 2006;Solomon et al, 2006). This study intends to examine the long term evolution of HCl and ClO using satellite data sets of the Halogen Occultation Experiment (HALOE), the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), the Aura Microwave Limb Sounder (Aura-MLS), and the Odin Sub-Millimetre Radiometer (SMR).…”

Total ozone trends from 1979 to 2016 derived from five merged observational datasets – the emergence into ozone recovery

“…The main cause for the severe ozone depletion was identified as halogen-containing substances also called ozonedepleting substances (ODSs), that are sufficiently long-lived to reach the stratosphere, releasing halogens that destroy ozone (e.g., Solomon, 1999). The Montreal Protocol and its amendments which were initiated in 1986 became a binding agreement on phasing out ODSs, that ultimately initiated a decline in stratospheric halogens about 10 years later (e.g., Anderson et al, 2000;Solomon et al, 2006).…”

Comparison of SMILES ClO profiles with satellite, balloon-borne and ground-based measurements

“…A ground-based microwave instrument located on Mauna Kea, Hawaii, has been monitoring stratospheric ClO almost continuously since 1992, as one instrument of the Network for the Detection of Atmospheric Composition Change (NDACC) (e.g., Solomon et al, 2006;Nedoluha et al, 2011;Connor et al, 2013). The millimeter heterodyne receiver detects the ClO emission line at 278.632 GHz with a total bandwidth of 506 MHz.…”