Hinterland Green

Sunday, August 30, 2009

NOAA Study Shows Nitrous Oxide Tops Ozone-Depleting Emissions

Layers of Earth's atmosphere
High resolution (Credit: NOAA)

According to a study by scientists at the National Oceanic and Atmospheric Administration (NOAA), nitrous oxide has become the largest ozone-depleting substance emitted through human activities and it is expected to remain the largest throughout the 21st century. The study, which was authored by A.R. Ravishankara, J.S. Daniel and Robert W. Portmann of NOAA's Earth System Research Laboratory (ESRL) chemical sciences division, evaluated nitrous oxide emissions from human activities, specifically as they relate to their potential impact on the Earth's ozone layer. The study found that as chlorofluorocarbon, or CFCs, which have been phased out by international agreement, ebb in the atmosphere, nitrous oxide will remain a significant ozone-destroyer. Nitrous oxide emissions from human activities are now more than twice as high as the next leading ozone-depleting gas.

How is nitrous oxide emitted? It is emitted from natural sources and as a byproduct of agricultural fertilization and other industrial processes. The researchers found when calculating the effect on the ozone layer now and in the future, that emissions of nitrous oxide from human activities erode the ozone layer and will continue to do so for many decades.

The ozone layer serves to shield plants, animals and people from excessive ultraviolet light from the sun. The thinning of the ozone layer allows more ultraviolet light to reach the Earth’s surface where it can damage crops and aquatic life and harm human health.
Nitrous oxide is also a greenhouse gas, so reducing its emission from manmade sources would be good for both the ozone layer and climate, the scientists said. In addition to soil fertilization, nitrous oxide is emitted from livestock manure, sewage treatment, combustion and certain other industrial processes. Dentists use it as a sedative (so-called “laughing gas”).

In nature, bacteria in soil and the oceans break down nitrogen-containing compounds, releasing nitrous oxide. About one-third of global nitrous oxide emissions are from human activities. Nitrous oxide, like CFCs, is stable when emitted at ground level, but breaks down when it reaches the stratosphere to form other gases, called nitrogen oxides, that trigger ozone-destroying reactions. Source: NOAA
This latest study is very revealing and though the role of nitrous oxide in ozone depletion has been known for several decades, it is the first study that explicitly calculated that role using the same measures that have been applied to CFCs, halons and other chlorine- and bromine-containing ozone-depleting substances.
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