Aboveground Production across A Soil Resource Gradient: Potential Application of a Regional Air Quality Model to Simulate Dry Deposition of Total Nitrogen at National Parks

Michael G. Barna
Air Resources Division,
National Park Service,
Fort Collins, CO USA

Weekly estimates of dry deposited nitric acid (HNO3), particulate ammonium (NH4+) and particulate nitrate (NO3-) are provided by the Clean Air Status and Trends Network (CASTNet). There are, of course, many more nitrogen-containing species in the atmosphere that may play a role in dry deposition. These include “total reactive nitrogen” (NOy) which, in addition to nitric acid and particulate nitrate measured by CASTNet, is composed of nitrogen oxides (NOx), organic nitrogen (including peroxy acetyl nitrate, or PAN), nitrous acid (HONO), dinitrogen pentoxide (N2O5) and nitrate radical (NO3). Reduced forms of nitrogen, such as ammonia (NH3) and ammonia derivatives (e.g., amines), are other examples of potentially important nitrogen species. To quantify the impact of this “missing nitrogen” to dry deposition, the CAMx regional air quality model was used. Nitrogen species that 1) exist in appreciable concentrations in the atmosphere and 2) are characterized by rapid deposition velocities are anticipated to play a significant role in the total dry deposition budget.

Rocky Mountain National Park (RMNP), located approximately 100 km northwest of Denver in Colorado’s Front Range, is the subject of extensive atmospheric deposition research. Initial CAMx estimates of annual dry deposition at RMNP indicate that, during 2002, the estimated total nitrogen was 2.2 kg/ha/yr vs. 1.0 kg/ha/yr, as reported by CASTNet. This difference is largely attributed to the contribution of ammonia, and to a lesser extent nitrate radical and organic nitrates. This presentation will present more information regarding dry deposition at RMNP, as well as estimated values for other national parks.