A new production-based model for estimating emissions and banks of ODSs: Application to HCFC-141b

Abstract. The Montreal Protocol on Substances that Deplete the Ozone Layer is a global agreement to protect the stratospheric ozone layer. It requires the phase out of the production of long-lived ozone-depleting substances (ODSs) that are intended for use in emissive applications. The Protocol does not, however, limit the release to the atmosphere of ODSs that currently exist in applications and equipment. Accounting for emissions from these “banked” ODSs (e.g., in insulating foams) is important for monitoring the success of and compliance with the Protocol, for understanding where further mitigation of ODS emissions might be effective, and for estimating future ozone depletion. Here, we present a new bottom-up model for 1,1-dichloro-1-fluoroethane (HCFC-141b), a chemical used primarily in foam insulation and whose production is currently being phased out. Using this refined model, we calculate global emissions that are similar to those derived from atmospheric measurements for the period from 1990 to 2017. After 2017, our modelled emissions are increasingly lower than the observationally based estimates through the end of the comparison in 2021. This discrepancy suggests either a growing additional source of emissions that is inconsistent with reported production or a model deficiency that did not exist or was not apparent before 2017. Our calculations also show that the easily accessible bank will be much smaller in the future than the total bank estimated in other recent work, with important implications for the feasibility of recovering and destroying banks before the release of HCFC-141b to the atmosphere.