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Air-Surface Exchange and Atmospheric Chemistry

Silver Spring, Maryland

The role of the NOAA Air Resources Laboratory in understanding the impact of anthropogenic related, atmospheric emissions on our environment requires us to determine the effectiveness of current regulations to mitigate negative impacts. It also requires us to anticipate how these effects will change in the future given current regulatory behavior. To this end, skills are required which combine traditional monitoring and modeling capabilities. The Air-Surface Exchange and Atmospheric Chemistry group addresses these issues by estimating the emission-deposition-fate of anthropogenically derive chemicals. While this group routinely collaborates with Silver Spring modelers and the Oak Ridge air-surface exchange scientists, unique skills include:

  • Measurement of precipitation chemistry from routine network as well as research perspectives. Network upgrades both in the U.S. and internationally are an important part of this effort.
  • Application of fast response trace gas measurements. This area of research allows modification of research-grade instruments for aircraft flux studies and to upgrade dry deposition monitoring programs.
  • Understanding of the cycling of atmospherically derived nutrients, with a focus on coastal regions. ARL- Silver Spring is the clear source of atmospheric information used to study coastal eutrophication issues.

The projects listed below give an indication of recent research efforts. You may click on any of the following in blue to go directly to the material you desire. We may also be reached by phone and E-mail as noted below.



The longest U.S. network record of precipitation chemistry in the modern era is that which started as the Department of Energy's Multistate Atmospheric Power Production Pollution Study (MAP3S) in 1976. This network was modified to follow a strict daily sampling protocol and was transferred to NOAA in 1991 where it remains a program of ARL, constituting one tier of the Atmospheric Integrated Research Monitoring Network (AIRMoN) program. Whereas the 200-site National Atmospheric Deposition Program (NADP) was designed to characterize long-term trends in the chemical climate of the U.S., AIRMoN was designed to provide data with a greater temporal resolution. This short-term resolution is critical for determining the effectiveness of emission controls mandated by the Clean Air Act, for Identifying source/receptor relationships using atmospheric models, and for evaluating the potential impacts of new sources of emissions on protected areas such as Class I Wilderness Areas.

AIRMoN-wet currently consists of nine sites operating in the Northeastern U.S., and in Tampa Bay, Florida. Measurements of the standard suite of major ions and additional supporting information (sulfate, nitrate, phosphate, chloride, calcium, magnesium, potassium, sodium, pH, conductivity, and rainfall amount) are measured at each station. Samples are immediately chilled upon collection, and remain chilled until analysis. Data are posted on the NADP/AIRMoN web page.

Gaseous Sulfur Intercomparison Experiment (GASIE)

Sulfur dioxide is the most abundant anthropogenic sulfur compound in the troposphere, and is emitted through coal and petroleum combustion, petroleum refining, and metal smelting operations. Sulfate deposition, especially downwind of large SO2 sources, leads to ecosystem acidification, while the presence of aerosol sulfates in both polluted and remote marine environments may mask the effects of CO2-induced global warming by increasing planetary albedo and lowering tropospheric temperatures. Sulfur dioxide concentrations in the troposphere range from several tens of parts per billion by volume (ppbv) in polluted urban areas to less than 50 parts per trillion by volume (pptv) in the clean marine troposphere. Thus, current measurement techniques must be sensitive, precise, and accurate enough to quantify [SO2] over a wide range of expected concentrations. Ongoing measurement intercomparison and technique validation activities are an integral component of atmospheric chemistry research, and the 1994 National Science Foundation (NSF)-sponsored GASIE experiment was designed to investigate the comparability of a number of SO2 measurement methodologies. The Air Resources Laboratory (ARL) fielded a commercial pulsed fluorescence (PF) detector during GASIE. While the PF instrument is widely used in pollution monitoring and intensive atmospheric chemistry research studies, its performance has rarely been assessed through formal intercomparison efforts, and its response to a number of potentially interfering compounds has never been documented in the literature. GASIE, and post-GASIE laboratory tests, provided the opportunity to explore more thoroughly the capabilities of this widely-used instrument.

Natural emissions of Oxidant precursors: Validation of techniques and Assessment (NOVA)

Nitrogen oxides (NOx) are known to play an important role as key precursors of the photochemical formation of tropospheric ozone (O3). While combustion sources dominate tropospheric NOx budgets, biogenic emission of NO from soils, particularly from heavily-fertilized agricultural soils, is also an important source of NOx. In agricultural-intensive areas of the U.S., however, the density of NO emissions emanating from fertilized soils may even rival NO emission densities found in urban areas [Williams, E.J. et al., J. Geophys. Res., 97, 7511-7519, 1992; Williams, E.J., et al., Global Biogeochem. Cycles, 6, 351-388, 1992]. Historically, NOx emissions from soils have been estimated using chamber, or enclosure, techniques. However, there is concern that enclosure methods may cause local environmental perturbations to the area under study, resulting in inaccurate or misleading flux estimates. In addition, enclosure methods by definition offer a means to estimate only emission fluxes; no information about net fluxes may be inferred.

In order to assess the validity of enclosure methods and other methods used to derive NO flux estimates, the Environmental Protection Agency (EPA) sponsored project NOVA in 1995 and 1996. Scientists from a variety of federal and university institutions gathered in rural northeastern North Carolina to conduct a joint experiment to compare enclosure methods (both static and dynamic) with micrometeorological techniques (eddy correlation). The eddy correlation technique provides an undisturbed direct measure of the flux and was selected to provide benchmark fluxes with which the results from chamber methods will be compared. While data analysis activities are still underway for the 1996 NOVA field experiment, some preliminary conclusions are detailed on the NOVA web page.

Southern Oxidants Study (SOS)

The Southern Oxidants Study (SOS) was initiated in 1988 following the Workshop on Atmospheric Photochemical Oxidants: A Southern Perspective. Additional impetus was provided by the landmark National Academy of Sciences report, Rethinking the Ozone Problem in Urban and Regional Air Pollution (NAS, 1991, National Academy Press, 500 pp.). Both publications highlighted the growing problem of urban and regional scale photochemical ozone pollution; despite progressively tighter controls on NMHC (VOC) emissions since 1970's, there has been no documented decrease in O3 concentrations in rural portions of the southeastern United States. SOS entered into the first of its 5-year Cooperative Agreements with the Environmental Protection Agency (EPA) in 1991; the cooperative agreement framework of SOS resulted in the collaborative research efforts of state and federal scientists acting in conjunction with their university counterparts. In 1995, the Air Resources Laboratory joined the ranks of SOS investigators by deploying the NOAA Twin Otter, one of six instrumented research aircraft, in a summertime intensive field experiment in Nashville, TN. The main goals of ARL involvement included the quantification of surface fluxes of sensible and latent heat, momentum, CO2, and ozone, and the study of ozone flux divergence in the mixed layer. The Twin Otter also carried a suite of sensitive trace gas detectors for the measurement of O3, CO, SO2, NO, NOx, NOy, and, in conjunction with scientists from the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, a grab sampling system for the measurement of C2-C10 hydrocarbons. Results of the chemistry measurements, whose goals included the characterization of near-field air quality in the Nashville region; the investigation of trace gas profiles in the mixed layer and the degree of correlation between surface and mixed layer concentrations; and an investigation of hydrocarbon distributions around Nashville, may be found on the SOS web page. Results from the flux measurement program of SOS may be found in the ATDD web pages.

The Chesapeake Bay Program Air Subcommittee

The Chesapeake Bay Program is a multi-agency program of targeted scientific research and integrated assessment, which has been instrumental in alerting policy makers to the need to couple air and water issues in their decision-making processes. Leadership of this activity within the CBP was initially in the hands of a specialized Air Quality Coordination Group, under the joint chairmanship of NOAA /ARL and the State of Maryland. Recently, the AQCG has been elevated in its position within the CBP -- it is now recognized as the Air Subcommittee. ARL provides coordination of the Subcommittee activities, and works directly with the EPA in arranging funding for projects of importance to the assessment goals of the CBP.

Characterizing the East and Gulf Coast Atmospheric Resource

It is clear that emissions from an "airshed" which serve as a regional origin of air pollutants affecting a given coastal waterbody also influence other coastal ecosystems. For example, if emissions inside the Chesapeake Bay airshed were reduced, then most of the major east coast estuarine and coastal ecosystems would benefit as well. The atmosphere is recognized as a "shared resource" that must be taken into account in developing coastal ecosystem restoration and protection strategies. In 1995, a formative meeting was held of representatives from federal agencies, States, industries, and environmentalist organizations, from which a cooperative movement was created -- the East Coast Atmospheric Resource Alliance (ECARA).

Estimating Air-water Exchange of Nitric Acid in Coastal Areas

Air-water exchange rates have been estimated for most nitrogen species over open ocean, however, these rates may not apply to coastal areas due to different meteorological conditions. A project was successfully undertaken which, I) developed and evaluated an iterative bulk exchange model to estimate air-water exchange of heat, water and momentum from buoy data, and ii) used the model outputs to estimate air-water transfer rates of nitric acid (HNO3).

Air-Surface Exchange and Atmospheric Chemistry Group Members

Name Phone E-mail
Richard S. Artz (Leader) (301) 713-0972
Winston T. Luke (301) 713-0295 ext 129

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