THE GLOBAL SOURCES OF NITROUS-OXIDE

We use atmospheric and ice core data on the concentrations of nitrous oxide to estimate that the present global anthropogenic emissions are 7+/-1 tg/yr. If the atmospheric lifetime of N2O is a hundred years or more, this estimate is virtually independent of the actual lifetime. The natural sources are estimated to be about 15 tg/yr. We also find that nitrous oxide started increasing rapidly only during the last century. The trends over the last decade are extremely variable; over 3-year periods the trends have ranged from 0.5 +/- 0.2 parts per billion by volume (ppbv/yr) to 1.2 +/- 0.1 ppbv/yr. The average rate of increase is about 0.80 +/- 0.02 ppbv/yr or 0.27 +/- 0.01 %/yr (1977-1988). There is an indication that N2O may be increasing faster in recent years than during the middle 1970s by about 0.2 +/- 0.1 ppbv/yr. It is likely that several small anthropogenic sources may be causing the present trends, all emitting between 0.1 and 1.5 Tg/yr.