The atmospheric partial lifetime of carbon tetrachloride with respect to the global soil sink

Abstract

The magnitude of the terrestrial soil sink for atmospheric carbon tetrachloride (CCl4) remains poorly constrained, with the estimated uncertainty range of CCl4 partial lifetimes between ~110 and 910 years. Field observations are sparse, and there are uncertainties in extrapolating these results to the global scale. Here we add to the published CCl4 fluxes with additional field measurements, and we employ a land cover classification scheme based on Advanced Very High Resolution Radiometer measurements that align more closely with the measurement sites to reevaluate the global CCl4 soil sink. We calculate an updated partial lifetime of CCl4 with respect to the soil sink to be 375 (288–536) years, which is 50 to 90% longer than the most recently published best estimates of the soil sink partial lifetime (195 and 245 years). This translates into a longer overall atmospheric lifetime estimate, which is more consistent with the observed atmospheric concentration trend and interhemispheric gradient.

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

“…This suggests additional emissions in the Northern Hemisphere, as the larger oceanic sink reported here for the Southern Hemisphere cannot account for it. Nevertheless, the overall budget of atmospheric CCl 4 is now much closer to being balanced, owing largely to the findings presented in this paper and to the re-evaluation of the soil sink (Happell et al, 2014;Rhew and Happell, 2016).…”

“…The oceanic sink, previously calculated as 94 yr (Yvon-Lewis and , also removes significant amounts of CCl 4 from the atmosphere. The CCl 4 lifetime owing to uptake by soils, previously determined at 90-195 yr, but recently assessed at 375 (288-536) yr, is considered a lesser component (Happell et al, 2014;Rhew and Happell, 2016). These additional sinks had previously brought the overall calculated lifetime of CCl 4 in the atmosphere down to 23-35 yr.…”

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

“…Using the most current estimates for the lifetime of CCl 4 in the atmosphere, soil and ocean (Liang et al, 2016;Rhew and Happell, 2016;Butler et al, 2016), global top-down emissions to the atmosphere were calculated as 40 ± 15 Gg yr −1 from 2007 to 2014 (Liang et al, 2016). A recent top-down study based on the observed temporal trend and interhemispheric gradient of atmospheric CCl 4 (Liang et al, 2014) consistently derived global CCl 4 emissions of 30 ± 5 Gg yr −1 from 2000 to 2012 when using the newly determined relative strength of oceanic sink versus soil loss (Liang et al, 2016).…”

Model sensitivity studies of the decrease in atmospheric carbon tetrachloride

“…(We also performed a simulation with the values presented in SPARC (2016) of 209 (157-313) years for tracers CTC1s, CTC2s and CTC3s). For the partial lifetime of CCl 4 loss over soil we used the recently published values of Rhew and Happell (2016), i.e. a best estimate of 375 years and an uncertainty range of 288-536 years.…”

“…Rhew and Happell (2016) re-evaluated the global CCl 4 soil sink using new observations and an improved land cover classification scheme. They derived the partial lifetime of CCl 4 with respect to soil loss to be 375 (288-536) years.…”