Deposition of nitrogen compounds can cause a number of deleterious effects, including changes in ecosystem function and surface water chemistry. The national deposition monitoring networks, measuring concentrations of certain molecular species in both their wet and dry forms, have been successful in furthering our understanding of ambient aerosols and selected trace gases across the United States; however, they also have important shortcomings. Key shortcomings of the current monitoring systems are their temporal resolution (one-week integrated samples), the accuracy of the split between ambient nitric acid and particulate nitrate, that NH3 is not measured, and that organic nitrogen (ON) is not routinely measured, either as total or speciated ON, in any of its wet, gaseous, or particulate forms. Organic nitrogen has been shown to contribute significantly to the total nitrogen deposition budget. Although some work has been done to characterize total ON in the atmosphere, little effort has been expended to characterize the molecular forms of ON, much less their origin. Measurements of the contribution of ON to total nitrogen in rain water in North American range from 10% to 60% with an average of 38%. Ambient measurements of particulate
ON at a few locations show that it can make up about 30% of particulate organic material, while measurements of aliphatic amines concentration near animal husbandry activities have shown them to be as high as ammonia. Oxidized forms of N such as peroxyacetyl nitrate and related alkyl nitrates have been shown to exist in significant concentrations. This presentation will review which of the many species contributing to total reactive N deposition can be routinely measured accurately, less accurately, at the research level, and not at all. Recommendations will be made as to what species to measure and with what time resolution to meet the overall objective of measuring and apportioning reactive nitrogen species to their emission sources.

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