Seminar

Abstract

National monitoring records reveal a dramatic shift in the balance of oxidized and reduced nitrogen species contributions to U.S. wet deposition of inorganic nitrogen over the past three decades, with a rapid increase in the fractional contribution by ammonium. This change partly reflects a decrease in wet nitrate deposition resulting from successful implementation of U.S. nitrogen oxides emissions reduction policies. Increases, however, have also been seen in wet deposition of ammonium. In the Rocky Mountain region, ammonium has contributed to rapid growth in reactive nitrogen deposition that threatens fragile alpine ecosystems. Ammonia is also a key ingredient in aerosol formation and the production of regional haze that sullies our skies and impairs scenic vistas. Despite its clear and increasing importance, atmospheric ammonia is not regulated and historically has seldom been measured. Data from a series of field studies will be examined to explore ammonia concentrations in the western U.S. and the importance of ammonia for nitrogen deposition and fine particle formation. Observations in Rocky Mountain and Grand Teton National Parks reveal large contributions of wet deposition of ammonium and dry deposition of gaseous ammonia to excess nitrogen inputs to high elevation ecosystems. Observations of recycling of ammonia through overnight cycles of dew formation and evaporation, however, highlight the difficulty of quantifying net inputs of ammonia to sensitive ecosystems. Research in oil and gas production regions of western Wyoming and the Bakken formation of North Dakota will be used to highlight the critical role ammonia plays in controlling the severity of winter haze episodes.

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Professor Jeff Collett received a Ph.D. degree in Environmental Engineering Science from Caltech. He worked at ETH-Zurich and the University of Illinois, before joining the faculty of Colorado State University. He currently serves as the head of the CSU Atmospheric Science Department. Dr. Collett's research interests include nitrogen deposition, air quality impacts from unconventional oil and gas development, emissions from wild and prescribed fires, regional air quality, aerosol impacts on visibility, instrument development, and other topics.