This paper gives a brief overview of the current knowledge on atmospheric concentrations and emissions of N 2 O and discusses some aspects of future research. Although N 2 O occurs in the atmosphere in minute quantities compared to CO 2 and water vapor, its contribution to the greenhouse effect is considerable. This is caused by its long residence time in combination with the relatively large energy absorption capacity per molecule. Per unit mass the global warming potential of N 2 O is about 310 times greater than that of CO 2 . The global annual atmospheric CO 2 increase is about 3000 million ton CO 2 -C, primarily from fossil fuels.
Nitrous oxide is a long-lived gas because it is inert in the troposphere.
Analysis of Antarctic ice core samples indicates that the atmospheric N 2 O concentration has risen from about 275 ppbv in pre-industrial times to about 293 ppbv in the beginning of the 20th century and to 311 ppbv now. The atmospheric N 2 O concentration started to increase rapidly during this century, but an accelerated increase may have started only after 1940. However, the trends over the last decade are extremely variable, ranging from 0.5 to 1.2 ppbv per year. The atmospheric lifetime of N 2 O based on the destruction rates and the atmospheric burden amounts to 120 years. Most of the N 2 O in the Earth's atmosphere stems from microbiological processes.