Atmospheric Deposition of Ammonia (ADAM) An Intercomparison Field Study

Atmospheric Deposition of Ammonia (ADAM)

An Intercomparison Field Study

Scientific Significance

Ammonia (NH₃) is a key atmospheric pollutant that may deteriorate ecosystem health and contribute to respiratory problems in humans. The lifetime of ammonia in the atmosphere is relatively short (a few days) because it readily reacts with acidic gases to form particulates or is deposited back to ecosystems through both wet and dry atmospheric processes. Atmospheric deposition of ammonia is a difficult parameter to measure since many atmospheric, biologic, and anthropogenic factors influence deposition rates. Since ammonia is a form of reactive nitrogen, it can contribute to a ‘cascade of effects’ in terrestrial and aquatic ecosystems, including soil acidification, loss of biodiversity, and hypoxia.
Global emissions of ammonia are rising as increased demands for food production result in more widespread fertilizer use and intensive livestock farming. In the U.S., agriculture accounts for greater than 80% of ammonia emissions. However, large uncertainties in emissions inventories persist, in part because ammonia emissions are not nationally regulated.
To help mitigate ammonia in the environment, emissions inventories need spatially representative measurements in a variety of ecosystems that will promote a better understanding of the factors that influence ammonia deposition. Studies of air-surface exchange of ammonia are hampered by a lack of suitable measurement techniques. Ammonia’s physical and chemical properties make it difficult to accurately measure in ambient concentrations and even more complex methods are necessary to measure air-surface exchange rates.

Project Plan

Scientists and engineers at NOAA/ARL/ATDD are partnering with researchers from the University of Tennessee(UT) at Knoxville to conduct a series of experiments to determine the suitability and robustness of a suite of ammonia measurement systems. A measurement testbed at the UT Plant Sciences Unit Campus (35°53'49.51"N, 83°57'28.50"W) has been designed to measure dry deposition of ammonia in proximity to well-characterized plots of fertilized vegetation. Varying concentrations of urea fertilizers are routinely distributed to the experimental plots surrounding the testbed; therefore, deposition rates from both pre- and post-fertilization periods can be monitored. Urea fertilizers have been shown to increase local ammonia emissions from vegetation by several orders of magnitude, providing a broad range for testing each measurement system.
The ADAM study will be conducted from February-March 2010. Currently, an IonPro Ion Mobility Spectrometer and a gradient configuration of annular denuder systems are available for testing along with a Picarro WS-CRDS Analyzer for Ammonia and a Pranalytica Nitrolux™-200 Ammonia Analyzer. Data from the ADAM study will be used to determine the applicability of the various methods to ammonia air-surface exchange research and to guide decisions for participation in the upcoming NOAA Biennial Field Campaign, CalNex 2010, in the San Joaquin Valley.
The overall objectives of the ADAM study are to (1) determine the suitability of a suite of ammonia measurement systems for air-surface exchange research; (2) measure the magnitude of ammonia deposition over an agricultural ecosystem during periods of pre- and post-fertilization; and (3) characterize the fundamental processes that influence ammonia air-surface exchange, including meteorological factors.

Collaborative Opportunities

The scientific research and engineering expertise at ATDD focuses on the chemistry and micrometeorology of ammonia deposition. However, to understand the entire process and determine what drives deposition or emission of ammonia, some knowledge of vegetation canopy dynamics and plant structure is necessary. It is anticipated that collaborations with researchers from the UT College of Agricultural Sciences and Natural Resources will contribute to a better understanding of how agricultural vegetation can be a sink (deposition) or source (emission) of atmospheric ammonia.

Points of Contact

LaToya Myles, Ph.D.
latoya.myles@noaa.gov
Mark Heuer
mark.heuer@noaa.gov