Assessing the atmospheric fate of trifluoroacetaldehyde (CF3CHO) and its potential as a new source of fluoroform (HFC-23) using the AtChem2 box model

Abstract

The use of human-made refrigerants and blowing agents have a long record of restrictions because of the impacts their emissions have had on atmospheric composition and climate. One of the most recent alternatives for replacing some of the harmful and banned refrigerants and blowing agents is hydrofluoroolefins (HFOs). An example is HFO-1234ze, proposed as a replacement for HCFC-141b in the polyurethane foam industry. HFO-1234ze reacts almost exclusively with OH to produce formyl fluoride (HFCO) and trifluoroacetaldehyde (CF3CHO). However, the photodissociation of CF3CHO to fluoroform (CHF3 or HFC-23) has been shown to be a possible channel. Although the HFC-23 channel quantum yield is reported to be small (∼0.3%), this channel needs to be characterised because HFC-23 is a long-lived gas with a 100-year global warming potential (GWP-100) of 12 690. In this study, we use a suite of AtChem2 box model simulations to determine how CF3CHO is lost in the atmosphere and how much HFC-23 can be produced from its photolysis under realistic atmospheric conditions. We tested a range of scenarios with varying HFO-1234ze emission rates and HFC-23 quantum yields. We also accounted for the physical removal of CF3CHO by obtaining a range of deposition rates using the GEOS-Chem 3-D chemical transport model. We find that over one month, an upper value of 0.31 ppt of HFC-23 could be produced from HFO-1234ze through CF3CHO photolysis. Globally, the HFC-23 photolysis channel explored here could be responsible for ∼4-15% of the current HFC-23 growth rate.