Stable carbon isotope fractionation in the UV photolysis of CFC-11 and CFC-12

Abstract

Abstract. The chlorofluorocarbons CFC-11 (CFCl 3 ) and CFC-12 (CF 2 Cl 2 ) are stable atmospheric compounds that are produced at the earth's surface, but removed only at high altitudes in the stratosphere by photolytic reactions. Their removal liberates atomic chlorine that then catalytically destroys stratospheric ozone. For such longlived compounds, isotope effects in the stratospheric removal reactions have a large effect on their global isotope budgets. We have demonstrated a photolytic isotope fractionation for stable carbon isotopes of CFC-11 and CFC-12 in laboratory experiments using broadband UV-C (190-230 nm) light. 13 C/ 12 C isotope fractionations (ε) range from (−23.8±0.9) to (−17.7±0.4) ‰ for CFC-11 and (−66.2±3.1) to (−51.0±2.9) ‰ for CFC-12 between 203 and 288 K, a temperature range relevant to conditions in the troposphere and stratosphere. These results suggest that CFCs should become strongly enriched in 13 C with decreasing mixing ratio in the stratosphere, similar to what has been recently observed for CFC chlorine isotopes. In conjunction with the strong variations in CFC emissions before and after the Montréal Protocol, the stratospheric enrichments should also lead to a significant temporal increase in the 13 C content of the CFCs at the surface over the past decades, which should be recorded in atmospheric air archives such as firn air.

Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air

“…The limited number and precision of these measurements make it premature at this stage to report a source δ( 37 Cl) change in these gases. Zuiderweg et al (2013) describe how the manufacturing processes used to synthesise chlorofluorocarbons have altered through industrial advances in the 20th century. The most significant change occurred in the production of the main feedstock (CCl 4 ).…”

“…They found a fractionation (ε) of −23.0 ‰ for CFC-11, compared to −55.3 ‰ for CFC-12 (at 233 K). Zuiderweg et al (2013) measured δ( 13 C, CFC-12) on North Greenland Eemian Ice Drilling (NEEM) firn air and reported a relative 13 C / 12 C enrichment of up to 80 ‰ from 1950 to the present day.…”

“…The strong stratospheric chlorine isotope fractionation of CFC-12 (Laube et al, 2010a) and the substantial change inferred from δ( 13 C) measurements (Zuiderweg at al., 2013) motivated us to conduct a more complete investigation of the chlorine isotope history of this species. This type of study has the potential to better constrain global sources and sinks (Röckmann et al, 2003).…”

Catalytic hydrolysis of Dichlorodifluoromethane over MoO3/ZrO2 -TiO2 solid acid

“…The advantage of solid superacid catalytic include their excellent catalytic activity, pollution-free, stability and reusability thus this type of materials also become very popular in catalyzing the hydrolysis Dichlorodi uoromethane (CFC-12) [13][14][15]. The catalytic behaviors, including the catalyst life of MoO 3 /ZrO 2 -TiO 2 solid acid catalyst calcined at different temperature for the catalytic hydrolysis of CFC-12 are investigated herein and the reaction condition of the effects of catalytic hydrolysis temperature and water vapor concentration has also been evaluated [16][17][18].The optimized conditions that catalyzed hydrolysis CFC-12 [19][20][21][22], for the large quantities of harmless treatment of CFC-12 to provide a theoretical basis. hours respectively, The baking temperature is 500 C and the baking time is 3 hours…”

Catalytic hydrolysis of Dichlorodifluoromethane over MoO3/ZrO2 -TiO2 solid acid

“…The advantage of solid superacid catalytic include their excellent catalytic activity, pollution-free, stability and reusability thus this type of materials also become very popular in catalyzing the hydrolysis Dichlorodifluoromethane(CFC-12) [13][14][15] . The catalytic behaviors, including the catalyst life of MoO 3 /ZrO 2 -TiO 2 solid acid catalyst calcined at different temperature for the catalytic hydrolysis of CFC-12 are investigated herein and the reaction condition of the effects of catalytic hydrolysis temperature and water vapor concentration has also been evaluated [16][17][18] . The optimized conditions that catalyzed hydrolysis CFC-12 [19][20][21][22] , for the large quantities of harmless treatment of CFC-12 to provide a theoretical basis.…”