Nitrous oxide (N2O) is another significant greenhouse gas due to its radiative effectiveness per unit mass (about 200 times higher than that of CO2) and its long lifetime of about 100 years in the atmosphere. N2O is emitted into the atmosphere from soil and oceans in areas of the world where nitrate and ammonium fertilizers are used, and from various industrial processes. It is photodissociated in the stratosphere by ultraviolet radiation.
Concentrations of atmospheric N2O exhibit a slight increase over time on a global scale. The results of WDCGG analysis show that the global mean annual atmospheric N2O mole fraction was 335.8 ppb in 2022, an increase of 1.4 ppb from the previous year. This is 24% higher than the pre-industrial level (about 270 ppb).
The figure below shows a time-series representation of N2O mole fractions at Ryori. It can be seen that short-term variations are very weak and there is no seasonal variation.
Time-series representation of N2O mole fractions recorded at JMA's Ryori observatory
Provisional values are included. It should be noted that the observation system was changed in 2004 and 2008.
The figure below shows a time-series representation of globally averaged N2O mole fractions as analyzed by the WDCGG using statistical methods.
Time-series representation of globally averaged N2O mole fractions
Blue: monthly mean mole fractions. Red: monthly mean with seasonal variations removed.
Atmospheric N2O mole fractions show an increase year by year with seasonal variations at all latitudes.
Time-series representation of zonally averaged N2O mole fractions