Organic Nitrogen (ON) in Wet Deposition in Rocky Mountain National Park

Florian M. Schwandner
Colorado State University,
Department of Atmospheric Sciences,
Fort Collins, CO USA

Measurements of inorganic and organic nitrogen deposition inside and near Rocky Mountain National Park during the Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) Study of spring and summer 2006 demonstrated that 11-53% of the total wet nitrogen deposition is as Organic Nitrogen (ON). Atmospheric organic nitrogen can include contributions from biological sources, oxidation products of combustion emissions, and reduced forms of nitrogen such as organic analogs of ammonia. For example, primary organic amines can react with organic acids to form secondary amides which themselves can partition into or adsorb onto particles and be transported significant distances before being deposited.

Our work on ON in wet deposition samples includes a systematic comparison between two methods: conventional UV-photo-oxidation with ON determined by difference of pre- and post-digestion inorganic nitrogen content from ion chromatography, and Total Nitrogen (TN) analyses using a Shimadzu TOC/TN analyzer. The individual handling, reagents, and laboratory procedures are being evaluated to assess the robustness of our method. In addition to systematic evaluation of the methods, we conduct time series measurements of blanks, natural samples, and standards, from laboratory, field, and controlled refrigerated storage, in order to understand storage and exposure differences in terms of sample and analyte stability.

To elucidate possible sources and processes responsible for the formation of organonitrogen compounds, work is also under way to speciate the organic nitrogen contents of both current and archive samples from the RoMANS study using various liquid and gas chromatographic methods, as well as quadrupole and Time-of-Flight mass spectrometry.