Nitrous Oxide - N2O
Nitrous oxide (N2O) gas should not be confused with nitric oxide (NO) or nitrogen dioxide (NO2). Neither nitric oxide nor nitrogen dioxide are greenhouse gases, although they are important in the process of creation of tropospheric ozone which is a greenhouse gas. There are several sources of nitrous oxide, both natural and anthropogenic (human), to the atmosphere with many of these sources difficult to measure. Because of this, there is general agreement that the atmospheric sources and sinks of nitrous oxide are difficult to bring into balance. Figure 10 shows the global biogeochemical of nitrous oxide involving transfers between Earth’s surface and atmosphere.
Figure 10. The global biogeochemical cycle of nitrous oxide. The major processes and fluxes involve transfer of nitrogen as nitrous oxide between the atmosphere and the surface of the Earth. Fluxes are millions of tons of nitrogen (MTN) per year, and the reservoir size of nitrous oxide is in millions of tons of nitrogen.
Natural production of nitrous oxide is from microbial activity in soils and in the ocean and after nitrous oxide production by the microbes the gas goes to the atmosphere. Human production of nitrous oxide is primarily due to combustion of fossil fuels, biomass burning, industrial production of nitric acid, and application of fertilizers to agricultural crops. Nitrous oxide enhances the greenhouse effect just as carbon dioxide does by capturing reradiated infrared radiation from the Earth’s surface and subsequently warming the troposphere (lower atmosphere). It is chemically inert in the troposphere and stays in the troposphere for about 120 years before moving into the stratosphere where it ultimately leads to destruction of stratospheric ozone. The atmospheric nitrous oxide concentration has been growing due to human activities (Figure 11).
Figure 11. Atmospheric nitrous oxide concentrations over time. There are two plots of nitrous oxide concentration over time with the main plot from the year 1000 to the year 2000 and the subplot from about the year 1980 to the year 2000. The left y-axis for both plots is nitrous oxide concentration in parts per billion and the y-axis for both plots is the year. The right y-axis for the main plot is a measure of the warming effect [in Watts (W) per square meter (m-2)] of the nitrous atmospheric concentration. For example, an atmospheric concentration of 300 ppb warms the Earth by 0.1 Watts per square meter.
