资源环境科技发展态势分析平台

We provide new estimates of the air-sea flux of CCl4 using simulations from a global ocean biogeochemistry model (NEMO-PlankTOM) in combination with depth-resolved CCl4 observations from global oceanic databases. Estimates of global oceanic CCl4 uptake are derived from a range of model analyses, including prescribed parameterizations using reported values on hydrolysis and degradation, and analyses optimized using the global observational databases. We evaluate the sensitivity of our results to uncertainties in air-sea gas exchange parameterization, estimation period, and circulation processes. Our best constrained estimate of ocean CCl4 uptake for the period 1996-2000 is 20.1Gg/year (range 16.6-22.7), corresponding to estimates of the partial atmospheric lifetime with respect to ocean uptake of 124 (110-150) years. This new oceanic lifetime implies higher emissions of CCl4 than currently estimated and therefore a larger missing atmospheric source of CCl4.

Plain Language Summary Carbon tetrachloride (CCl4) is a trace gas emitted to the atmosphere during the industrial manufacture of refrigerants and solvents. CCl4 is also an ozone-depleting agent affecting loss of the atmosphere's protective ozone layer, and CCl4 emissions are now controlled by the Montreal Protocol. However, recent analyses of observed atmospheric CCl4 concentration conclude that the current rate of atmospheric decline is slower than expected, and inconsistent with recent estimates of CCl4 emissions to and removal from the atmosphere. Estimated oceanic uptake of CCl4 has been noted as potentially the most uncertain of the atmospheric loss processes, and here we provide new quantification of this flux. Our methodology employs a novel approach and uses a global ocean biogeochemistry model which includes representation of known physical and biogeochemical processes influencing oceanic CCl4 uptake, together with a compiled global ocean database of CCl4 observations. The observational database is used to evaluate model simulations, and to derive optimized estimates of the oceanic uptake flux by minimizing the discrepancies between the model and observations. We also evaluate the sensitivity of our estimates of ocean CCl4 uptake to known uncertainties in the model representation of processes, including air-sea gas transfer and oceanic chemical and biogeochemical loss. Our best constrained estimate of ocean CCl4 uptake for the 1996-2000 period is 20.1Gg/year (range 16.6-22.7), which is greater than previous recent estimates, and implies a larger missing source to the atmosphere of CCl4.