US EPA

3690637 

Technical Report 

68A | Air Pollution & Control 

2014 

NTIS\PB2015-103631_a 

GRA and I 

GRA and I 

Actions taken under the Montreal Protocol have led to decreases in the atmosphericabundance of controlled ozone-depleting substances (ODSs), and are enabling thereturn of the ozone layer toward 1980 levels.? The sum of the measured tropospheric abundances of substances controlled under theMontreal Protocol continues to decrease. Most of the major controlled ODSs are decreasinglargely as projected, and hydro chlorofluorocarbons (HCFCs) and halon-1301 are still increasing.Unknown or unreported sources of carbon tetrachloride are needed to explain its abundance.? Measured stratospheric abundances of chlorine- and bromine-containing substancesoriginating from the degradation of ODSs are decreasing. By 2012, combined chlorine andbromine levels (as estimated by Equivalent Effective Stratospheric Chlorine, EESC) had declinedby about 10?15% from the peak values of ten to fifteen years ago. Decreases in atmosphericabundances of methyl chloroform (CH3CCl3), methyl bromide (CH3Br), and chlorofluorocarbons(CFCs) contributed approximately equally to these reductions.