CF₃ chemistry: Potential implications for stratospheric ozone

Abstract

Previous evaluations of the impact of fluorine chemistry on stratospheric ozone have concluded that the role of fluorine compounds in catalytic ozone removal is negligible. However, recent investigations of the degradation pathways for compounds containing CF3 groups indicates that if the reaction of CF3O with O3 is sufficiently fast, there may be an ozone impact. Some recent measurements indicate that the reaction rate constant of CF3O+O3 is sufficiently low that the ozone impact is likely to be small. However, it is not possible a‐priori to rule out significant ozone removal without additional kinetic data on other reactions. We present calculations to illustrate how different key reactions affect the calculated stratospheric concentrations of the CF3X species (CF3, CF3O, CF3O2, CF3OH, CF3OOH, CF3ONO2, CF3O2NO2, CF3OOCl) and their ability to remove stratospheric ozone. We utilize our results to suggest kinetic measurements that could substantially reduce the uncertainties in CF3 chemistry relevant to the determination of ozone depletion potential of CF3‐bearing compounds.

The SF5Ox Radicals, x=0–3

“…This is similar to the known atmospheric fate of the radical CF 3 , which is converted rapidly into CF 3 OO in the presence of O 2 . [23] The SF 5 O radical: Merill and Cady postulated that the SF 5 O radical results from irradiation of bis(pentafluorosulfur) peroxide, F 5 SOOSF 5 . [24] Czarnowski and Schumacher [25,26] also suggested the formation of SF 5 O from the thermal decomposition of the peroxide.…”

Thermal decomposition of trifluoromethoxycarbonyl peroxy nitrate, CF3OC(O)O2NO2

“…where k obs corresponds to the observed rate of disappearance of CF 3 OC(O)O 2 NO 2 , and [NO 2 ] and [NO] to the concentrations of NO 2 and NO in the cell where the reaction was followed by infrared spectroscopy. In all cases, the correction was carried out taking into account the temperature dependence of the rate constants for reactions (−1) and (3).…”

“…Christensen et al [8] determined the thermal stability of trifluoromethoxycarbonyl peroxy nitrate at 295.8 K in a mixture containing NO 2 and NO inside a smog chamber. von Ahsen et al [7] synthesized the pure peroxy nitrate in bulk quantities and characterized the molecule (vapor pressure, boiling, and melting points, UV cross sections, IR and Raman spectra, NMR, etc.).…”

“…Peroxy nitrates (RO 2 NO 2 ) are important species in the atmosphere because they act as reservoirs of NO 2 and RO 2 radicals. In particular, acyl peroxy nitrates (R C spheric thermal lifetimes (from 1 h to several days) [1] are sufficiently long that they can be transported from their sources to remote places or to the stratosphere [2][3][4].…”

The Trifluoromethyltrioxy Radical, CF3OOO

“…Furthermore, the CF 3 OOO trioxy radical has been suggested as an intermediate in an important ozone-depletion reaction in which CF 3 reacts with O 3 , but the proposed intermediate was not characterized. [12][13][14] In the 1960s trioxy radicals were invoked to explain patterns in the ESR spectra of solutions of CF 3 O [15] and (CH 3 ) 3 CO radicals in liquid oxygen at À196 8C. [16] In this communication we describe the nearly quantitative formation of CF 3 OOO and its isolation in an oxygen matrix at low temperatures.…”