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Carbon tetrachloride releases still too high, says NASA

Oi! Didn't you get the Montreal memo?

Somewhere, a dry cleaner didn't get the memo: someone is putting an awful lot of carbon tetrachloride into the atmosphere, and NASA would like them to stop.

Back in 1987, the compound was one of many ozone-depleting chemicals regulated under the Montreal Protocol. However, NASA said on Wednesday there's still too much of the stuff lingering in the atmosphere.

What NASA says it's now observing isn't some lingering hangover of the pre-Montreal Protocol days: worldwide emissions currently run at an average of “39 kilotons per year, approximately 30 percent of peak emissions prior to the international treaty going into effect,” the agency says.

Instead of declining at 4 per cent annually since 2007, the CCl4 concentrations in the atmosphere is only falling by 1 per cent per annum – even though reported emissions in that period were zero.

That leads NASA Goddard atmospheric scientist Qing Liang to conclude: “It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources.”

The NASA study also discovered that CCl4 remains in the atmosphere 40 per cent longer than was previously believed.

In the NASA release, the study's co-author Paul Newman (also of Goddard) says there is clearly “a major source” of CCl4 out there somewhere – either an ongoing industrial leakage, or emissions from contaminated sites.

The study was based on NASA's GEOS chemistry climate model, combined with global ground-based observations.

The good news is that while CCl4 is rising, it only accounts for 11 per cent of remaining ozone-depleting substances – and the overall trend is still downwards, which is good news for southern hemisphere countries affected by the Antarctic ozone hole. ®

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