Toward resolving the budget discrepancy of ozone-depleting carbon tetrachloride (CCl<sub>4</sub>): an analysis of top-down emissions from China

Abstract

Abstract. Carbon tetrachloride (CCl 4 ) is a first-generation ozone-depleting substance, and its emissive use and production were globally banned by the Montreal Protocol with a 2010 phase-out; however, production and consumption for non-dispersive use as a chemical feedstock and as a process agent are still allowed. This study uses the high frequency and magnitude of CCl 4 pollution events from an 8-year realtime atmospheric measurement record obtained at Gosan station (a regional background monitoring site in East Asia) to present evidence of significant unreported emissions of CCl 4 . Top-down emissions of CCl 4 amounting to 23.6 ± 7

Continued Emissions of the Ozone‐Depleting Substance Carbon Tetrachloride From Eastern Asia

“…The results of this work contrast with two separate studies using atmospheric data based on ISC to HCFC-22 ( Bie et al, 2017 ; Park et al, 2018 ). The ISC results from Bie et al (2017) used measurements of both compounds from Peking University in Beijing to derive emissions of around 4 Gg/year between 2011 and 2014, well below the lower uncertainty bounds of the estimates in this work.…”

“…Emissions from this sector should follow residential and business usage, and so may be broadly population based. In contrast, emissions of CCl 4 are thought to be primarily from industrial sources ( Park et al, 2018 ), and as we show in this work the spatial distribution of emissions is very different from a population distribution. Therefore, the assumption that sources of the two gases are colocated may not be valid and may help to explain the contrasting results between the different studies.…”

“…The ISC results from Bie et al (2017) used measurements of both compounds from Peking University in Beijing to derive emissions of around 4 Gg/year between 2011 and 2014, well below the lower uncertainty bounds of the estimates in this work. In contrast, the work of Park et al (2018) used the same data used in this study from Gosan, along with estimates of HCFC-22 emissions to derive average emissions of CCl 4 from China of 23.6 ± 7.1 Gg/year between 2011 and 2015, a total that is at the upper end of the estimates in this study. Potential biases in the ISC method lie in the emissions magnitude of the cotracer (HCFC-22, which was itself derived in an inversion), and in the assumption that emissions of CCl 4 and HCFC-22 are colocated.…”

“…Recent emission estimates based on CCl 4 consumption and production data in China suggest that this contribution has fallen dramatically, particularly after 2010 ( Bie et al, 2017 ). There have been a few recent studies that have used interspecies correlations (ISCs) of CCl 4 atmospheric mole fractions to carbon monoxide (CO) and HCFC-22 (CHClF 2 ) to infer emissions of CCl 4 ( Bie et al, 2017 ; Park et al, 2018 ; Wang et al, 2014 ). This method requires that the spatial distribution of CCl 4 emissions is similar to that of emissions of the correlating species (i.e., in the case that CO or HCFC-22 are used, it assumes that CCl 4 emissions are largely population weighted).…”

“…This method requires that the spatial distribution of CCl 4 emissions is similar to that of emissions of the correlating species (i.e., in the case that CO or HCFC-22 are used, it assumes that CCl 4 emissions are largely population weighted). However, the emissions estimates from the ISC methods may be prone to error in this assumption, and the two most recent studies estimate very different emission magnitudes of under 5 Gg/year ( Bie et al, 2017 ) and 23.6 ± 7.1 Gg/year ( Park et al, 2018 ) between 2011 and 2015. Therefore, the use of an independent inverse modelling method that is not subject to the same potential biases is important to evaluate which of these scenarios is most likely.…”