Present and future sources and emissions of halocarbons: Toward new constraints

Accurate chlorocarbon and bromocarbon mixing ratio projections are necessary to make accurate estimates of future stratospheric ozone depletion. As global production of ozone depleting substances (ODSs) continues to decline in response to the Montreal Protocol, the quantity of ODSs in existing products and equipment, referred to as “banks,” has the potential to make an important contribution to future ODS emissions and the associated ozone depletion. Recently, large discrepancies between two approaches to estimating bank sizes have been reported for several ODSs (World Meteorological Organization (WMO), 2003; Intergovernmental Panel on Climate Change/Technology and Economic Assessment Panel (IPCC/TEAP), 2005). We analyze these bank differences for CFC‐11 and CFC‐12 and find that they are significant in terms of the amount of projected future ozone depletion, a finding that is also relevant to assessing the potential environmental benefits of recovering and destroying banked CFCs. We consider observed trends in atmospheric abundances and past production estimates of these chemicals to gain insight into the bank sizes and their roles as emission sources for the CFCs. If it is assumed that the rates of release from the banks have not increased over the last few years, a lower limit for the CFC‐12 bank size in 2002 is approximately 500 kt, consistent with the recent bottom‐up estimate of IPCC/TEAP (2005). The larger estimated CFC‐11 and CFC‐12 banks (IPCC/TEAP, 2005), if accurate, would lead to greater future emissions and, hence, to greater stratospheric chlorine abundances that can affect future ozone as compared to the smaller WMO (2003) banks.