Perfluorocarbons in the global atmosphere: tetrafluoromethane, hexafluoroethane, and octafluoropropane

Abstract

We present atmospheric baseline growth rates from the 1970s to the present for the long-lived, strongly infrared-absorbing perfluorocarbons (PFCs) tetrafluoromethane (CF<sub>4</sub>), hexafluoroethane (C<sub>2</sub>F<sub>6</sub>), and octafluoropropane (C<sub>3</sub>F<sub>8</sub>) in both hemispheres, measured with improved accuracies (~1–2%) and precisions (<0.3%, or <0.2 ppt (parts per trillion dry air mole fraction), for CF<sub>4</sub>; <1.5%, or <0.06 ppt, for C<sub>2</sub>F<sub>6</sub>; <4.5%, or <0.02 ppt, for C<sub>3</sub>F<sub>8</sub> within the Advanced Global Atmospheric Gases Experiment (AGAGE). Pre-industrial background values of 34.7±0.2 ppt CF<sub>4</sub> and 0.1±0.02 ppt C<sub>2</sub>F<sub>6</sub> were measured in air extracted from Greenland ice and Antarctic firn. Anthropogenic sources are thought to be primary aluminum production (CF<sub>4</sub>, C<sub>2</sub>F<sub>6</sub>, C<sub>3</sub>F<sub>8</sub>), semiconductor production (C<sub>2</sub>F<sub>6</sub>, CF<sub>4</sub>, C<sub>3</sub>F<sub>8</sub>) and refrigeration use (C<sub>3</sub>F<sub>8</sub>). Global emissions calculated with the AGAGE 2-D 12-box model are significantly higher than most previous emission estimates. The sum of CF<sub>4</sub> and C<sub>2</sub>F<sub>6</sub> emissions estimated from aluminum production and non-metal production are lower than observed global top-down emissions, with gaps of ~6 Gg/yr CF<sub>4</sub> in recent years. The significant discrepancies between previous CF<sub>4</sub>, C<sub>2</sub>F<sub>6</sub>, and C<sub>3</sub>F<sub>8</sub> emission estimates and observed global top-down emissions estimated from AGAGE measurements emphasize the need for more accurate, transparent, and complete emission reporting, and for verification with atmospheric measurements to assess the emission sources of these long-lived and potent greenhouse gases, which alter the radiative budget of the atmosphere, essentially permanently, once emitted

Recent increases in the atmospheric growth rate and emissions of HFC-23 (CHF<sub>3</sub>) and the link to HCFC-22 (CHClF<sub>2</sub>) production

“…The estimated accuracies of the calibration scales for HFC-23 and HCFC-22 are discussed below and a more detailed discussion of the measurement techniques and calibration procedures are reported elsewhere (Miller et al, 2008;O'Doherty et al, 2009;Mühle et al, 2010). HFC-23 and HCFC-22 measurements from all AGAGE sites are reported relative to the SIO-07 and SIO-05 primary calibration scales respectively, which are defined by suites of standard gases prepared by diluting gravimetrically prepared analyte mixtures in N 2 O to near-ambient levels in synthetic air (Prinn et al, 2000;Miller et al, 2008).…”

Global and regional emissions estimates of 1,1-difluoroethane (HFC-152a, CH<sub>3</sub>CHF<sub>2</sub>) from in situ and air archive observations

“…The estimated accuracy of the calibration scale for HFC152a is 4 %: a more detailed discussion of the measurement technique and calibration procedure is reported elsewhere (Miller et al, 2008;O'Doherty et al, 2009;Mühle et al, 2010). HFC-152a was determined using the MS in selected ion monitoring mode (SIM) with a target ion CH 3 CF + 2 (m/z 65) and qualifier ion CH 3 CF + (m/z 46).…”

“…We then compare these with HFC-152a emission estimates compiled from national reports to the United Nations Framework Convention on Climate Change (UNFCCC) and Emissions Database for Global Atmospheric Research (EC-JRC/PBL EDGAR v4.2; http://edgar.jrc.ec. europa.eu/), using the same techniques reported for other greenhouse gases Miller et al, 2010;Vollmer et al, 2011;Krummel et al, 2014;Rigby et al, 2014).…”

Evaluation of stratospheric age-of-air from CF<sub>4</sub>, C<sub>2</sub>F<sub>6</sub>, C<sub>3</sub>F<sub>8</sub>, CHF<sub>3</sub>, HFC-125, HFC-227ea and SF<sub>6</sub>; implications for the calculations of halocarbon lifetimes, fractional release factors and ozone depletion potentials

“…SIO CG CF4 and C2F6 time series have previously been published in Mühle et al (2010) and Trudinger et al (2016) and their SF6 time series in Rigby et al (2010). SIO CF4 and SF6 data 105 are reported on the SIO-05 scale and C2F6 on the SIO-07 scale (Mühle et al, 2010;Prinn et al, 2000). (Fig.…”

“…These samples were analysed on a 'Medusa' gas-chromatographic system with cryogenic pre-concentration and mass spectrometric detection (Arnold et al, 2012;Miller et al, 2008). SIO CG CF4 and C2F6 time series have previously been published in Mühle et al (2010) and Trudinger et al (2016) and their SF6 time series in Rigby et al (2010). SIO CF4 and SF6 data 105 are reported on the SIO-05 scale and C2F6 on the SIO-07 scale (Mühle et al, 2010;Prinn et al, 2000).…”