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Science 31 January 1992:
Vol. 255. no. 5044, pp. 581 - 583
DOI: 10.1126/science.255.5044.581
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Articles

Natural Vegetation as a Source or Sink for Atmospheric Ammonia: A Case Study

A. O. LANGFORD 1 and F. C. FEHSENFELD 2

1 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, and Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Boulder, CO 80303
2 Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Boulder, CO 80303, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, 80309

Measurements of gaseous ammonia above a montane-subalpine forest in the Colorado mountains show that the role of the forest as a source or sink depends on the atmospheric concentrations. The canopy appeared to be an ammonia source when exposed to air containing low concentrations, but a sink when exposed to air enriched by nearby agricultural sources. The forest-averaged compensation point was 0.8 part per billion by volume at 20°C. The net burden of ammonia and other nitrogen species of anthropogenic origin at this site was much less than at forest sites in the eastern United States and Europe and may provide a valuable resource for this nitrogen-limited ecosystem.

Submitted on July 22, 1991
Accepted on November 18, 1991


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Science. ISSN 0036-8075 (print), 1095-9203 (online)