Laughing Gas: The Latest Environmental Threat

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The EarthNitrous oxide, more commonly known at your dentist’s office as laughing gas, is now the most prevalent man-made substance damaging the ozone layer. And it’s a greenhouse gas. Sadly, the joke’s apparently on us.

In a report published in Science on Friday, scientists at the National Oceanic and Atmospheric Administration (NOAA) located in Boulder, Colorado, have calculated the ozone-depleting potential (ODP) of the common gas nitrous oxide, N2O, and come to the conclusion that this previously ignored, naturally occurring substance is now a serious threat and likely will be for the rest of the century. About two-thirds of the nitrous oxide evolved every year comes from bacteria breaking down nitrogen-containing compounds. The other one-third is emitted by a large variety of human activities, including agricultural fertilization, livestock manure, the burning of both fossil and biofuels, and other industrial processes. They are increasing the atmospheric concentration of N2O by 1% every 4 years and have been essentially since the beginning of the Industrial Revolution.

There is some good news to accompany the words of doom and gloom, however. “The main reason for the large role of nitrous oxide is the success of the Montreal Protocol in that it has reduced the emissions of CFCs and other ozone-depleting chemicals,” said lead author A.R. Ravishankara. The Montreal Protocol is the international treaty of 1987 that aimed to protect the ozone layer by phasing out and banning known ozone-depleting chemicals such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs).

However, the reduction of CFCs is something of a double edged sword. The chlorine of CFCs and HCFCs competes with the nitrogen of N2O in the stratosphere; as the levels of chlorine decrease due to the reduction of CFCs according to international agreements, the remaining nitrogen from N2O will become about 50% more potent. N2O itself has an ODP comparable to that of HCFCs. And while the ODPs of the gases are similar, nitrous oxide is significantly more abundant that CFCs ever were. Globally, humans released just over 1 million tonnes of CFCs into the atmosphere at their peak. Today, we are releasing approximately 10 million tonnes of N2O, and that figure does not take into account the amount of the gas produced by natural sources.

The other bit of good news is that the Environmental Protection Agency (EPA) is already considering what to do about nitrous oxide emissions because of its role in global warming. In April, they declared six gases, including CO2 and N2O, pollutants that endanger public health, subjecting them to regulation under the Clean Air Act, and announced on Thursday that they are working on an emissions reporting system for all six.

Scientists have been aware of the ozone-depleting effects of nitrous oxide as well as its greenhouse gas status since the 1970s — when they were conducting research into the environmental effects of supersonic planes. “Nitrous oxide is kind of the forgotten gas,” according to Don Wuebbles of the University of Illinois at Urbana-Champaign, a scientist not involved in the report but who invented the method of quantifying a chemical’s ODP. “It was always thought of as a natural thing,” he said. Focused on the detrimental environmental effects of CFCs and CO2, “people have forgotten that [nitrous oxide has] been increasing.”

Photo Credit: woodleywonderworks at flickr

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