Document: JAS-3-59-6

Organic nitrogen deposition; Is it time to reconsider the measurement of N in precipitation?

NEFF, J.* ¹, E.HOLLAND ², F.DENTENER ³, K.RUSSELL ⁴ and W.MCDOWELL ⁵

Colorado State University, Fort Collins, CO 80523, USA ¹
Max Planck Institute for Biogeochemistry, Jena, Germany, 07745 ²
Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, The Netherlands, NL-3508 TA 84. ³
University of Virginia, Charlottesville, VA 22903 ⁴
University of New Hampshire, Durham, NH 03824 USA ⁵

Abstract:
Organic forms of nitrogen are widespread in the atmosphere and the deposition of these compounds may contribute to the input of atmospheric N to ecosystems. However, atmospheric organic nitrogen (AON) is also infrequently measured and the processes that lead to the formation of organic nitrogen compounds are only partially understood. In this presentation, we summarize and synthesize data from 41 measurements of the concentrations and fluxes of AON. On average, organic N accounts for about one third of the total atmospheric N flux or concentration. The percentage contribution of organic N to total N loading varies from site to site and with measurement methodology but is consistently around a third of the total N load with a median value of 30% (Standard Deviation of 16%). There are no indications that AON is a proportionally greater contributor to N deposition in unpolluted environments and there are not strong correlations between fluxes of nitrate and AON or ammonium and AON. Possible sources for AON include byproducts of reactions between NOx and hydrocarbons, both of which are can be affected by human activity. Potentially important natural contributions of AON including marine and terrestrial sources of reduced (amino acid) N and long range transport of organic matter and bacteria. The reduced and bacterially-related forms of AON do not appear to play an important role in the overall flux of AON to the surface of the earth; however both dust and oxidized organic N species such as peroxyacetyl nitrates may be important. Our preliminary estimate of the magnitude of global AON fluxes places the flux between 10 and 50 Tg of N per year with substantial unresolved uncertainties but clear indications that AON deposition could be an important component of both site and global N balance.

Keywords: organic nitrogen, deposition, atmosphere

This abstract is being presented at: 4:45 PM in session:
Oral Session #28: Effects of N Deposition in Ecosystems.