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Rapid Field Measurement of Airborne Ammonia/Ammonium
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Project Title:Development and Application of a Rapid and Robust Sensor to Determine Nitrogen Species in the Coastal
Atmosphere
Research Locations:Chesapeake Bay (Maryland)
Last Update: February 17, 2003
Atmospherically derived nitrogen can represent a significant fraction of the total nitrogen budget in East Coast estuaries. This pollution is primarily caused by fossil fuel emissions of nitrogen oxide and nitrogen dioxide (NOx), and volatilized ammonium and ammonia from animal waste (from agriculture and fertilizers). While a variety of commercial sensors exist for NOx species, ammonia and ammonium sensing still requires relatively slow sampling procedures that make it difficult to manage nitrogen inputs and apportion the source of airborne nitrogen pollution.
Approach
The goal of this project is to develop a field instrument that
reduces sampling time for particle-phase ammonium and gas-phase
ammonia. (Discrete sampling—taking samples in the field and
doing the analysis in the lab—can take 12-24 hours.) Researchers
accomplished this by looking at newly available technologies that
speed up sampling times, designing methods for integrating these
techniques into a field-deployable unit and testing the accuracy of
the prototype against other methods.
Design
The final design uses a two-channel flow-through mist chamber to
collect both gas-phase and particle-phase nitrogen. One of the
channels has a scrubber that removes the gas-phase ammonia, so
that the gas-phase portion can be obtained by subtracting the particle-
phase portion from the total. The sample is then converted
into an aqueous stream, which is then
analyzed using standard colorimetric
methods. The unit is relatively compact
and can be set up in a van (see Figure 2) to increase mobility.
Results
- The resulting instrument has demonstrated the ability to provide accurate results at a rate of 8-10 minutes per sample.
- Tests of the instrument near a dairy barn showed that the nitrogen concentration could vary by an order of magnitude with slight changes in wind, underscoring the need for a sub-hourly sampling system.
EPA Funds Further Application
The instrument developed for this project caught the eye of the
EPA, which has funded the researchers to use the device to measure
ammonia emissions from agricultural systems as well as urban
areas.
How Does the Instrument Compare?
The 8-10 minute sampling time is much faster than the 12-24
hours needed for discrete sampling. Some technologies are equal
to or faster than this newly developed device. However, this
instrument measures particulate-phase ammonium in addition to
gas-phase ammonium, which alternative technologies do not.
Adapting the Instrument for Other Nitrogen Species
Researchers believe that the device could be used to measure
nitrate/nitrite by changing the analytical system to one based on
long pathlength absorbance spectroscopy .
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Project Coordinator
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Joel Baker 410-326-7205
Ron Siefert 410-326-7386 |
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Start -End Date:
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09/01/1999 - 09/01/2003
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NERR Reserve(s):
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Chesapeake Bay (Maryland)
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For more information: |
Dolores Jalbert Leonard |