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.
Projects
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.
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.
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.
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).
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 |
richard.artz@noaa.gov |
| Winston T. Luke |
(301) 713-0295 ext 129 |
winston.luke@noaa.gov |
|
