Global modeling of trifluoroacetic acid surface concentration and deposition from the gas phase oxidation of a wide range of precursor hydrofluoroolefins

Oxidation of third and fourth generation refrigerants are likely to be sources of trifluoroacetic acid (TFA) in the lower atmosphere which can be deposited in precipitation and accumulate in both water bodies resulting in potential aquatic risks and to land surfaces posing potential ecosystem damage. The formation and distribution of atmospheric TFA from the gas-phase oxidation of fifteen hydrofluoroolefins (HFOs)were studied. The subsequent deposition of TFA, and the environmental impact of regional emissions of HFOs using a three-dimensional chemical transport model, STOCHEM-CRI was performed. Globally, a significant amount of TFA (125 Gg yr-1) is produced from the oxidation of a range of HFOs (total mass emitted 0.15 Tg yr-1) with the most significant contributors being HFO-1234zeZ (11.07 Gg yr-1, 8.9%), HFO-1234zeE (11.04 Gg yr-1, 8.8%), and HFO-1243zf (11.79 Gg yr-1, 9.5%). The tropospheric global burden and lifetime of TFA are found to be 1.26 Gg and 3.8 days, respectively. Atmospheric TFA were found be most abundant in the northern mid-latitude with up to 4 ppt in Europe, 1 ppt in Asia and 1 ppt in North America during the northern hemispheric summer. North America, Europe, and Asia are found to be the main hot spots for the annual global deposition of TFA with maximum deposition up to 200 tonnes yr-1, 300 tonnes yr-1, and 200 tonnes yr-1, respectively. 35% TFA deposition from HFO-1234yf, 48% from HFO-1216 (short-lived) and 13% from HFO-1336mzzmE (long-lived) emissions were found for North America, Europe and Asia emission scenarios. A metric called the TFA Deposition Potential (TDP) is proposed which provides a relative insight into the extent to which different HFOs contribute towards peak environmental TFA deposition, relative to that from the oxidation of HFO-1234yf.