Trends and Distributions of Atmospheric Nitrous Oxide

Nitrous oxide (N2O) is an important atmospheric trace gas that is responsible for climate forcing as the third strongest greenhouse gas and depletion of stratospheric ozone. A recent study (Ravishankara et al., 2009, Science, 10.1126/science.1176985) has calculated the Ozone Depletion Potential (ODP) for N2O as 0.017. Using the new ODP coupled with current and future emissions they determined that N2O will be the dominant ozone depleting substance that will be emitted in the 21st century. Nitrous oxide emissions are dominated by the reduction of nitrate. The demand for nitrogenous fertilizers is expected to increase in response to greater demands for food production with increase in population. This will likely result in greater N2O emissions. NOAA/ESRL has been measuring N2O in the background atmosphere since 1977 using both flask and in situ instruments. Over the past 5 years, the trend of atmospheric nitrous oxide in the northern hemisphere has increased from 0.5 ppb per year to 1.2 ppb per year, but over the thirty year period the mean global growth rate has averaged about 0.75 ppb per year. We will examine whether this trend is significant or similar to fluctuations seen in the past. We will also compare our measurements to a larger global set of N2O flask measurements from the NOAA/ESRL Carbon Cycle flask network.