Nitrous oxide, the new enemy of the ozone layer

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Since the ban on CFCs, which devoured stratospheric ozone, nitrous oxide (N 2 O), mass produced by agriculture, has become the main enemy of this protective layer, and is a powerful gas for greenhouse effect. Two studies show the very harmful effects.

Part of the stratosphere (whose floor is between 8 and 20 km altitude) contains a higher concentration of ozone (O3), of the order of one per thousand, which absorbs quite strongly ultraviolet rays from of the Sun. © NOAA

After the carbon dioxide (CO 2 ) hunt , should we declare war on N 2 O? The nitrous oxide , also known as nitrous oxide or laughing gas, is naturally produced (by land and oceans). But today one third of the emanations are due to human activities, and in particular to the spreading of manure and nitrogen fertilizers.

Two teams have just demonstrated the danger, both for maintaining a high concentration of ozonein the stratosphere , known as the ozone layer, which protects living beings from UV rays , and for the climate because nitrous oxide is a powerful greenhouse gas , 275 times more efficient than CO 2 .

Akkihebbal Ravishankara and his team from the  Earth System Research Laboratory at the National Oceanic and Atmospheric Administration ( NOAA ) have studied the impact of N 2 O on stratospheric ozone, which apparently has not never been done yet. The authors sought to determine the relative importance of nitrous oxide over the effects of other gases known to degrade ozone in the stratosphere.

In 1987, the Montreal Protocol banned CFCs (or chlorofluorocarbons, widely used in the cold industry or as a propellant ) and other molecules , such as HCFCs (hydrochlorofluorocarbons) and halogenated hydrocarbons . These substances, which degrade stratospheric ozone, have been progressively abandoned by a very large number of countries.

But nitrous oxide was not included in this protocol and, as a result, is now becoming the first enemy of the ozone layer , Akkihebbal Ravishankara and his colleagues conclude in an article published in  Science . According to the authors, it will remain so throughout the twenty-first century.

Nitrogen in the ground is nitrogen in the air and less ozone

Human activities, in fact, emit a lot and more and more. The main source is the spreading of slurry, manure and nitrogen fertilizers. This is the breeding and intensive farming again in the hot seat, after studies showing that the methane produced by cows increases the greenhouse effect …

In  Nature Geoscience , Eric Davidson, biogeochemist at the  Woods Hole Research Center inMassachusetts, has counted human productions. According to him, manure and manure release into the atmosphere 2% of the nitrogen they contain and nitrogen fertilizers 2.5%. In total, he explains, manure, through manure and manure, releases 2.8 million tonnes of N 2 O annually , in addition to the 2.2 million tonnes from synthetic fertilizers.

Far behind, the industry denies 0.8 million tonnes and the combustion of biomass 0.5 million tonnes. Taking into account the evolution of agriculture, Davidson estimated nitrous oxide injection into the atmosphere between 1860 and 2005. The concentration in the atmosphere would have increased from 270 to 319 ppb (parts per billion).

The author notes that as the proportion of animal protein in the human diet is increasing, manure management will become ”  an important component of efforts to reduce human production of nitrous oxide  .” Soon a tax N 2 O?

Dr. Kimberly Seltzer

Postdoctoral Scholar, UC Berkeley Research Assistant, MIT

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