Call to replace CH2Cl2 with less ozone depleting compounds

A popular industrial solvent, Dichloromethane is damaging the ozone layer over human populations. It’s already listed in the Montreal Protocol as a hazardous substance but it needs to be replaced with greener alternatives. While this solvent is classed as a very short lived substance, it is taking a large toll on the ozone layer.

When we combine this with the loading of atmospheric bromine and for every 5 ppt of that, we have an ozone loss of 1.3% and it could get as high as 350 ppt ( Impact of Very Short-Lived Substances on Stratospheric Bromine Loading, Jan Aschmann Doctoral Dissertation). Just the Bromine releases could wipe out 90% of the ozone layer.
“Several human-produced chlorocarbons not controlled by the Montreal Protocol are present in Earth’s atmosphere. Among the most abundant of these compounds is dichloromethane (CH2Cl2)—an industrial solvent also used as a feedstock in the production of other chemicals, among other applications 13,14. Unlike CFCs, which are virtually inert in the troposphere and have long atmospheric lifetimes (decades to centuries), CH2Cl2 is a so-called very short-lived substance (VSLS)15. Historically, VSLS have been thought to play a minor role in stratospheric ozone depletion due to their relatively short atmospheric lifetimes (typically <6 months) and therefore low atmospheric concentrations. However, substantial levels of both natural and anthropogenic VSLS have been detected in the lower stratosphere 15,16,17,18 and numerical model simulations suggest a significant contribution of VSLS to ozone loss in this region 19,20,21. Long-term measurements of CH2Cl2 reveal that its tropospheric abundance has increased rapidly in recent years 15,21,22,23. For example, between 2000 and 2012, surface concentrations of CH2Clincreased at a global mean rate of almost 8% per year, with the largest growth observed in the Northern Hemisphere (NH)21. Given that natural emissions of CH2Cl2 are small, this recent growth likely reflects an increase in industrial emissions 15. While the precise nature of the source remains poorly characterized, industrial CH2Cl2 emissions from Asia—in particular from the Indian subcontinent—appear to be growing in importance 23”   https://www.nature.com/articles/ncomms15962

These growth rates are exponential, and we seriously risk another ozone crisis in addition to the one addressed by the Montreal Protocol. In order to reduce the risk, a call to replace dichloromethane with alternatives needs to be made, and upgrade it to at least a partially-banned, controlled substance. If we do not take measures like this in the near term, we run the risk of even more dangerous UV radiation in the environment and cancelling out the benefit we see from the Montreal Protocol.

What’s worse, we run the risk of losing our ozone layer while we watch greenhouse gases and miss this very real risk which could lead to the need for an emergency oxygen airlift to replenish ozone.

Fig2-1

ncomms15962-f1

Observed trends and growth rate of surface CH2Cl2 and simulated stratospheric loading of chlorine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5490265/

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