Global observation of nitrous oxide: changes in growth rate and spatial patterns

Abstract:

Nitrous oxide (N₂O) currently exerts the third largest climate forcing of the long-lived greenhouse gases, after CO₂ and CH₄. N₂O is also involved in the destruction of stratospheric ozone. It is produced by microbial activity in soils and oceans, and also by industry. The atmospheric burden of N₂O has increased more than 20% from its preindustrial level of ~270 nmol mol^-1 (ppb). Much of this increase is related to the application of nitrogen-containing fertilizers, including manure. The NOAA Global Monitoring Division has measured the atmospheric mole fraction of N₂O at Earth’s surface in air samples collected around the globe (since the late 1970s) and at in situ sites mostly in the Western Hemisphere (since 1998). ). Measurements of the global burden and growth rate constrain global emissions, e.g. 18.2 ± 2.7 Tg N yr^-1 in 2013, where most of the uncertainty is related to uncertainty in the global lifetime. The average growth rate of N₂O from 1990 to 2010 was ~0.75 ppb yr^-1. Since 2004, however, the growth rate has been increasing, and is now about 25% higher than the 1990-2010 average. Between 2010 and 2013 the growth rate averaged ~0.95 ppb yr^-1. As the growth rate increased from 2004-2013, gradients derived from surface, zonal-mean N₂O mole fraction, such the mean pole-to-pole difference, and the difference between NH temperate latitudes and the southern polar region, decreased. This suggests a change in the distribution of N₂O emissions over this period. We will present our N₂O data and examine trends, gradients, and other features that could shed light on recent changes in the growth rate. We will also compare N₂O gradients to those of other trace gases, such as SF₆.