Grantee Research Project Results
Final Report: Nitrogen Deposition onto Aqueous Media: Quantative Diagnostics, Laboratory Measurements, and Model Development
EPA Grant Number: R823333Title: Nitrogen Deposition onto Aqueous Media: Quantative Diagnostics, Laboratory Measurements, and Model Development
Investigators: Miller, John Houston
Institution: George Washington University
EPA Project Officer: Packard, Benjamin H
Project Period: September 15, 1995 through September 14, 1998
Project Amount: $182,227
RFA: Exploratory Research - Chemistry and Physics of Water (1995) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Safer Chemicals
Objective:
The deposition of nitrogen oxides from the atmosphere is expected to dramatically increase over the next 50 years and will have a profound effect on global tropospheric chemistry. In addition to acidification of terrestrial and marine ecosystems, this process is expected to lead to an increase in the quantity of tropospheric ozone and a decrease in the consumption rate of methane in forest soils. There is little fundamental data available for the rate of the deposition of individual oxidized nitrogen species or adequate models to account for the chemical interconversion of these species at or near absorbate surfaces. This lack of information has prompted further investigation into the relative contributions of wet versus dry deposition. A clearer understanding of the fundamental processes involved in dry deposition will allow for more accurate determination of atmospheric deposition and prove vital to environmental policy decisions.Summary/Accomplishments (Outputs/Outcomes):
With U.S. Environmental Protection Agency (USEPA) funds, we have conducted a study of nitrogen deposition which involves the development of laser-based diagnostics for the individual NOy species and laboratory measurements of their rates of dry deposition. Some key findings of the our experimental work to date are presented below:Nitric oxide, the thermodynamically favored emission from high temperature combustion showed a very slow deposition into water. Because of chemical transformation of NO that occur on the same time scale as the dry deposition, only an upper limit for the deposition velocity could be determined for NO.
Ammonia deposition was also investigated. Ammonia contributes as much as 50 percent of the total airborne nitrogen in farming regions. Nutrient overload from any nitrogen species leads to algae bloom, but ammonia is often thought to be a "high-octane nitrogen," causing even greater growth rates. In light of ammonia's rich aqueous chemistry, it was not surprising to find a dependence of NH3's deposition rate on pH. More surprising was the dependence of the deposition rate on anion concentrations (such as nitrate) in the aqueous phase. A possible explanation for this dependence is aerosol formation near the water surface.
Ammonia deposition rates were found to show a strong dependence on mixing in the gas phase. Our results indicate that deposition of ammonia, and by extension other species with rich aqueous chemistries, is limited by transport to the surface. A full order of magnitude difference was found for the deposition velocity measured in still and mixed air. In the case of extremely stagnant air (such as in our quiescent tank), the deposition rate is diffusion limited.
A model is being developed to account for the data observed in these experiments, which includes the interaction of mixing, diffusion, and chemistry during the deposition process. Model results confirm the measurements for NO that indicate that deposition is limited by gas phase diffusion and low solubility. In air containing ozone at typical tropospheric levels, NO's conversion to more soluble chemical forms occurs on a faster time scale than does the dissolution of NO itself.
It is anticipated that the models developed to explain our laboratory results will provide useful estimation tools for nitrogen deposition in the natural environment and thus, will provide valuable and necessary input for the development of global climate models.
The diagnostic capabilities afforded by the USEPA grant were leveraged in several additional studies of atmospheric chemistry relevance. We demonstrated the applicability of tunable diode laser absorption spectroscopy to stable isotope measurements for carbon monoxide. A difference in the ratio of 13C to 12C was found in the emissions of CO from a natural gas flame and in automobile exhaust, indicative of the different fossil sources of these fuels. Our laser systems were used to measure NO and NH3 in a simple laboratory flame system. These measured concentration profiles were then compared with models for flame chemistry. Finally, line strengths and broadening parameters were determined for nitrogen trifluoride (NF3). NF3 has become a dominant fluorine atom source for the electronic plasma etching community. Our measurements will be important to the USEPA in the determination of NF3's global warming potential.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 9 publications | 1 publications in selected types | All 1 journal articles |
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Hill DA, Tolocka MP, Miller JH. Measurement of CO isotopic ratios in combustion using tunable diode laser absorption spectroscopy. Chemical and Physical Processes in Combustion 1996:203-206. |
R823333 (Final) |
not available |
Supplemental Keywords:
acid deposition, absorption, chemical transport, marine, estuary, water, watersheds, nitrogen oxides, ammonia, monitoring, analytical, measurement methods, diode lasers., RFA, Scientific Discipline, Air, Water, Nutrients, Physics, Environmental Chemistry, Chemistry, Air Deposition, tropospheric ozone, Engineering, Chemistry, & Physics, aquatic ecosystem, aqueous impurities, quantitative models, nitrogen deposition, bioavailability, Chesapeak Bay, global warming calculations, ozone, laser based diagnostics, atmospheric nitrogen deposits, water quality, global climate models, ecosystem stress, troposphere, acid rain, atmospheric deposition, global tropospheric chemistryRelevant Websites:
http://www.gwu.edu/~combenvProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.