Australian carbon tetrachloride emissions in a global context

Abstract

Environmental context Carbon tetrachloride in the background atmosphere is a significant environmental concern, responsible for ~10% of observed stratospheric ozone depletion. Atmospheric concentrations of CCl4 are higher than expected from currently identified emission sources: largely residual emissions from production, transport and use. Additional sources are required to balance the expected atmospheric destruction of CCl4 and may contribute to a slower-than-expected recovery of the Antarctic ozone ‘hole’. Abstract Global (1978–2012) and Australian (1996–2011) carbon tetrachloride emissions are estimated from atmospheric observations of CCl4 using data from the Advanced Global Atmospheric Gases Experiment (AGAGE) global network, in particular from Cape Grim, Tasmania. Global and Australian emissions are in decline in response to Montreal Protocol restrictions on CCl4 production and consumption for dispersive uses in the developed and developing world. However, atmospheric data-derived emissions are significantly larger than ‘bottom-up’ estimates from direct and indirect CCl4 production, CCl4 transportation and use. Australian CCl4 emissions are not a result of these sources, and the identification of the origin of Australian emissions may provide a clue to the origin of some of these ‘missing’ global sources.

A comprehensive estimate for loss of atmospheric carbon tetrachloride (CCl<sub>4</sub>) to the ocean

“…Butler et al (1999) noted that the lowest firn air values were near detection limits in their samples and suggested that CCl 4 , though at times not differing from zero, could have been as high as 5-10 ppt in the atmosphere before 1900; recent, unpublished firn air data we have obtained, however, suggest that it is more likely between 3 and 4 ppt in the late 19th century. Consequently, most of the emission discrepancy must arise from heretofore unquantified, anthropogenic sources, predominantly in the Northern Hemisphere, to be consistent with the observed rate of decline for the global mole fraction, given our understanding of the global lifetime and the mean hemispheric difference measured for atmospheric CCl 4 (e.g., Fraser et al, 2014;Liang et al, 2014;Carpenter et al, 2014). Only with an excess of northern hemispheric sources would the deficit identified in this study and its distribution be fully consistent with the observed rate of decline of CCl 4 in the atmosphere (1.2-1.4 % yr −1 ), the observed interhemispheric gradient of ∼ 1.2 ppt in recent years, and an interhemispheric exchange time of the order of 1 year (Carpenter et al, 2014).…”

Current sources of carbon tetrachloride (CCl 4 ) in our atmosphere

“…emissions from old industrial sites and landfills) may also be important to the global overall CTC emissions (figure 1, Pathway D). Fraser et al (2014) estimated that unaccounted CTC emissions (legacy emissions and from chlor-alkali plants) could potentially contribute 10-30 Gg year −1 globally. Based on newly available information, SPARC (2016) revised this estimate to 5-10 Gg year −1 .…”

“…paper bleaching, disinfection (figure 1, left side, emissions Pathway A). Fraser et al (2014) used observations in an urban environment to estimate potential global emissions which could include this specific source, in addition to CTC legacy emissions. Although measurements cannot separate this source from legacy emissions, a combined emission estimate of as high as 10 Gg year −1 is possible (see section 5).…”

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

“…Annual Australian emissions are calculated from Victoria/Tasmania emissions using a population based scale factor of 3.7 and are shown in Fig. 10 and the 3rd column of Table 4 (Fraser et al, 2014b).…”