Science

Nitrous oxide’s chemical characteristics and interactions in the atmosphere contribute to its significance as a greenhouse gas. The following sections summarize some of these fundamental characteristics.

Greenhouse Gas Properties

Nitrous oxide (N2O) is a clear, colourless gas, with a slightly sweet odour. Due to its long atmospheric lifetime (approximately 120 years) and heat trapping effects - about 310 times more powerful than carbon dioxide on a per molecule basis - N2O is an important greenhouse gas.

Nitrous oxide has both natural and human-related sources, and is removed from the atmosphere mainly by photolysis (i.e., breakdown by sunlight) in the stratosphere. In the United States, the main human-related sources of N2O are agricultural soil management, mobile and stationary combustion of fossil fuel, adipic acid production, and nitric acid production. N2O is also produced naturally from a wide variety of biological sources in soil and water. On a global basis, it is estimated that natural sources account for over 60% of the total N2O emissions (IPCC, 2001c).

Global Warming Potentials

The concept of a global warming potential (GWP) was developed to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to another gas. The definition of a GWP for a particular greenhouse gas is the ratio of heat trapped by one unit mass of the greenhouse gas to that of one unit mass of CO2 over a specified time period.

As part of its scientific assessments of climate change, the Intergovernmental Panel on Climate Change (IPCC) has published reference values for GWPs of several greenhouse gases. While the most current estimates for GWPs are listed in the IPCC's Third Assessment Report (TAR), EPA analyses use the 100-year GWPs listed in the IPCC's Second Assessment Report (SAR) to be consistent with the international standards under the United Nations Framework Convention on Climate Change (UNFCCC) (IPCC, 1996). According to the SAR, nitrous oxide is 310 times more effective at trapping heat in the atmosphere when compared to CO2 over a 100-year time period. (See the table titled Global Warming Potentials and Atmospheric Lifetimes for a listing of GWPs and atmospheric lifetimes of N2O and the other major species of greenhouse gases for comparison.)

Atmospheric Concentrations

Global average atmospheric concentrations of N2O have increased from about 270 parts per billion by volume (ppbv) in 1750 to 314 ppbv in 1998, which equates to a 16% increase for the period. In the last two decades, atmospheric concentrations of N2O continue to increase at a rate of 0.25% per year. There has been significant multi-year variance in the observed growth of N2O concentrations, and the reasons for these trends are not yet fully understood (IPCC, 2001b). http://www.ghgonline.org/humaninfluencebig.htm

TT note! Note the 270 to 314 parts per BILLION, i.e. it is less than 1/1000 of CO2 current concentration. They claim that N2O has 200 to 300 times the greenhouse warming effect that CO2 has, (not exactly precise is it?).

Methane forms 1.5ppmv of the atmosphere and, in 'global warming' terms is said to be 20 times as dangerous as CO2.

It could therefore be said that methane = (1.5/380) x 20 = 0.00789 the danger of CO2. In other words, no danger at all!