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Long‐term decrease in the global atmospheric burden of tetrachloroethene (C2Cl4)

We present a 14‐year record of tropospheric tetrachloroethene (C2Cl4) mixing ratios measured each season at remote surface locations throughout the Pacific Basin (71°N–47°S). Our calculated annual mean C2Cl4 mixing ratio for the extra‐tropical northern hemisphere (NH) was 13.9 ± 0.5 pptv in 1989, but declined to less than half this value (to 6.5 ± 0.2 pptv) by 2002. Mid‐latitude southern hemisphere (SH) mixing ratios, which were much smaller than NH values, showed interannual variations comparable to measured long‐term changes, and the SH annual mean was slightly less in 2002 than in 1989. Driven by the relatively large decrease in NH values, the global C2Cl4 mixing ratio declined from 6.3 ± 0.6 pptv in 1989 to 3.5 ± 0.2 pptv in 2002. These values suggest that the global C2Cl4 burden decreased by roughly 205 Gg between 1989–2002, which is consistent with industrial estimates of declining NH emissions over a similar period.