Direct nitrogen deposition. Revised January 2007

Report to CEMA (Alberta, Canada)
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\nThis report summarises the methods available for estimating the deposition of reactive (plant-available) nitrogen from the atmosphere, for comparison with Critical Loads, and as a means of assessing the environmental effects of the deposited nitrogen.
\nSources of atmospheric reactive nitrogen (NR) and its transformations in the atmosphere are briefly summarised, leading to several possible deposition pathways, both wet and dry. The principles behind direct measurements of wet deposition are explained, along with some of the factors that must be considered to avoid artefacts. Continuous direct measurement of dry deposition (i.e. the turbulent transfer of material from the atmosphere to the ground) is possible with the current state-of-the-art, but is expensive because of the need for fast-response analyzers, operating at concentrations of ppb (parts in 109 by volume) or less. Operation of this type of equipment, and analysis of the resultant data, is not a routine monitoring tool, but a research activity leading to measurement-based estimates of the parameters needed to model dry deposition on temporal and spatial scales that are inaccessible by current measurement methods. However, long-term integrating techniques are becoming available for routine monitoring use.
\nThe current available techniques are critically discussed, particularly in relation to practical deployment at a regional scale, with descriptions of what can be achieved using different techniques, and approximate estimates of the relative costs. A structured method for designing a possible monitoring network is described, listing the advantages and disadvantages of different approaches. Finally, a possible implementation plan is recommended, with an indication of costs. This would provide for a nested network across the oilsands region of Alberta comprising 20 sites; bulk wet deposition would be measured at all sites, air concentrations of major NR species at 10 of the sites, and long-term integrated flux measurements at 4 sites. The annual cost (excluding travel to sites for sampling) is estimated at $220,000. This would provide deposition estimates across the region to indicate whether or not Critical Loads for NR deposition are likely to be exceeded. Bibliographies for further reading and reference are provided for each section of the report.

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