NOAA warns about nitrogen's effect on ozone layer

NOAA Scientists have gained new insight into the role of nitrous oxide, N2O, in the atmosphere.

According to a new study released by NOAA scientists, nitrous oxide, N2O, is now the leading future threat to atmospheric ozone health; a growing threat in relation to CFCs, which began being phased out from industrial processes in the late 1980's due to the Montreal Protocol. N2O is not included in the treaty's regulations.

Chloroflourocarbons, CFCs, are still the leading cause of ozone depletion and are responsible for the annual hole that opens up over Antarctica. Researchers found that N2O was one-fiftieth as effective as CFCs in destroying ozone; may not sound that bad, but with the amount of N2O released into the atmosphere from natural and manmade systems, scientists are beginning to worry about the role N2O will play in decreasing the atmosphere's ability to block out harmful UV rays from the sun.

The ozone layer is a layer in the earth's atmopshere that absorbs up to 99% of the sun's high frequency ultraviolet light. It is mainly located in the lower portion of the stratosphere from approximately 6 to 31 miles above the Earth's surface. The thickness of the ozone layer can vary seasonally and geographically.

Ultraviolet radiation is dangerous to humans; in fact, versions of it are potentially damaging to all life on earth. It comes in three forms based upon its wavelength: UV-A, UV-B, and UV-C. UV-C radiation is completely blocked out in stratosphere about 22 miles above the earth's surface; some UV-A and UV-B radiation reaches the earth. It is the UV-B radiation that causes sunburn and skin cancer in high doses.

It was thought, up until now, that the ozone was recovering. By decreasing the use of CFCs, we thought we had avoided a serious problem to humans and other biological life on earth (as referenced in this ScienceDaily article earlier this year). "We are at the point where we have to ask: Were we right about ozone? Did the Montreal Protocol work? What kind of world was avoided by phasing out ozone-depleting substances?"; but now research scientists from NOAA are saying that increased use of nitrogen is set to have a larger impact than CFCs ever did, even suggesting that nitrogen will play a bigger role affecting climate change and human health than CO2 if left unregulated.

Nitrous oxide, this time around, is not bringing humanity the giggles. While N2O is produced by natural processes as bacteria converts compounds containing nitrogen in rivers and forests into the gas, it is also coming from manmade sources including sewage treatment, fuel combustion, and fertilizer. By far, agricultural activities are the highest source of nitrogen use. (EPA statistics on nitrogen)

The report came from NOAA's Earth Systems Research Laboratory. "Though the role of nitrous oxide in ozone depletion has been known for several decades, the new study is the first to explicitly calculate that role using the same measures that have been applied to CFCs, halons, and other chlorine and bromine compounds containing ozone-depleting substances." (NOAA press release)

By eliminating or severely limiting other ozone damaging manmade substances like CFCs, halons, and other chlorine and bromine compounds through the Montreal Protocol, nitrous oxide has risen in status to become a larger fraction of the ozone damaging pie; but this is not just a problem of relativity. The Montreal Protocol's success may also end up increasing the potency of N2O in the atmosphere and its ability to destroy the protective ozone layer.

One of the researchers explains why limiting CFCs increases N2O's potency. "Solar ultraviolet radiation breaks CFC molecules apart, creating chlorine and chlorine oxides. These are what destroy ozone. Similarly, N2O doesn't directly damage ozone. Chemical reactions in the stratosphere must first strip away one of that molecule's nitrogen atoms, forming nitric oxide, or NO. This stripped down molecule is what actually wreaks havoc with ozone."

"Nitrogen oxides and chlorine oxides kind of oppose each other in destroying stratospheric ozone,” researchers explained further. “In other words, N2O offsets the ability of chlorine oxides to destroy ozone. And vice versa. We have calculated the ozone-depleting potential of N2O to be roughly 50% larger when chlorine levels return to the year-1960 level.” Since chlorine oxides limit the ability of NO to destroy ozone, by simultaneously limiting CFCs and other chlorine compounds and increasing the use of nitrogen compounds in societal activities over the past half century, we have begun disturbing the fragile chemical mixture in the earth's atmosphere that protects us from dangerous UV radiation from the sun.

The report shows that nitrogen emissions from natural processes are basically static, while manmade emissions such as the nitrogen fertilization of agricultural soils and fossil-fuel combustion have been growing steadily, "to where they now boost atmospheric concentrations of N2O by roughly 1% every four years". (Science News article)

Nitrous oxide is also a greenhouse gas responsible for trapping heat in the earth's atmosphere and regulating climate on the planet.

For more info:
Nitrogen challenges CO2 for media spotlight; Energy Examiner