AIRMoN Wet Deposition Program
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Introduction
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. With the end of the acid deposition
decade, and with the cessation of a formal research program
under the National Acid Precipitation Assessment Program,
the MAP3S network was terminated by DOE and was eventually
transferred to NOAA where it
remains a program of ARL, constituting one tier
of the AIRMoN-Wet program.
Justification
The major wet deposition network -- the
National Atmospheric Deposition Program
(NADP)
-- has a large array of about 200 stations. Weekly samples
of precipitation are collected at these stations and then
sent to a single central laboratory for chemical analysis.
The weekly sampling network has three severe drawbacks:
- sample chemistry can be affected by biological activity
in precipitation that remains at ambient temperatures
for several days before analysis;
- week-long averaging means that several rainfall events
frequently are combined into single samples;
- while strict weekly sampling protocols ensure high
quality at a reasonable price, research to improve sample
quality is often not possible.
These drawbacks are important considerations for
NOAA. The first means that accurate quantification
of ammonium and (rarely) nitrate ion deposition is not
possible; the AIRMoN-Wet approach is to collect daily samples
and to keep them chilled until analysis so as to minimize
biological activity. The second complicates any interpretation
or analysis that involves a coupling with meteorology,
and the third tends to stifle innovation required to adapt
emerging technology to improve sampling methodologies,
to speed communication to keep sites on-line, or to reduce
labor expenses. None of these drawbacks should be construed
as complaints against the NADP weekly program. NADP provides
the routine monitoring required for long-term understanding
of trends and deposition across the entire country; prime
users of these data include ecologists, agriculturists,
foresters, and power companies affected by Clean Air Act
legislation. AIRMoN-Wet is a value added research program
designed to enhance the quality and utility of NADP data
while meeting the additional requirements required to meet
the NOAA mission.
AIRMoN-Wet Field and Laboratory Procedures
Routine aspects of the AIRMoN-Wet program are coordinated
carefully with NADP. Siting protocols, field equipment,
some sampling protocols, and most laboratory analysis protocols
are the same for both programs. Protocols in AIRMoN-Wet
differ from NADP National Trends Network (NTN) only to the extent required to ensure
temporally adequate (daily) sampling collection and enhanced
sample quality. AIRMoN protocols that differ from NADP NTN
include:
- daily collections
- chilling of samples until analysis
- reliance on a National
Weather Service "stick" gage instead of a Belfort
5-780 weighing gage for official precipitation amount
measurement
- no filtration of samples prior to analysis
- a sampling order for trace samples that emphasizes
analysis of anthropogenic substances over soil cations.
As with NADP NTN, AIRMoN-Wet
samples are analyzed by the Illinois State Water Survey
in Champaign, Illinois, and network coordination is handled
through the
National Resource Ecology Laboratory at
Colorado State University in Fort Collins, Colorado.
New equipment currently under evaluation for use with
the AIRMoN program includes the adaptation of several strain
gages as potential replacements for the aging Belfort 5-780.
Strain gages have fewer moving parts, no linkages to stick
or corrode, and are readily adapted to generate digital
signals that can be transmitted to a datalogger. Pending
the outcome of our current field study, AIRMoN will replace
the current recording gages with rain gages equipped with
dataloggers and cell phones. The new equipment will be
queried remotely, avoiding the time and agony of deciphering
information currently analyzed by hand from Belfort paper
charts. The new gages will be accompanied by software allowing
remote submission of field information by site operators.
The current system requires hardcopy submission of field
data followed by double punching of data by laboratory
personnel to ensure high levels of quality. After the initial
expenditures to upgrade equipment, it is anticipated that
AIRMoN-wet will produce more accurate data at a lower cost.
In 1996 all of the AIRMoN-Wet stations were equipped with
Canadian precipitation bulk gages to begin to address the
major discrepancies in chemical loadings that currently
exist at the border. Deposition biases differ for different
ions between the two countries; however, many of the biases
are statistically significant, amounting to about 14% for
sulfate deposition on an annual basis. Resolution of this
issue will allow refinement of chemical loadings from precipitation
for North America, issues of critical importance to the
Commission for Environmental Cooperation and
the
International Joint Commission. The Canadian Air and Precipitation
Monitoring Network (CAPMoN)-AIRMoN comparison
is an outgrowth of the longstanding CAPMoN-NADP comparison
begun in the mid-1980s (Vet et al., 1989; Sirois et al.,
1997).
As a first step to compare data from different networks,
NADP weekly data have been compared
to AIRMoN-wet data collected at collocated stations. For
some ions such as ammonium, differences between the weekly
and daily networks are systematic and amount to approximately
15% on an annual basis. (For the case of ammonium, the
differences are driven by biological decay of some samples.
Measured differences are in keeping with results found
between NADP and MAP3S during the early 1980s (Lamb and
Comrie, 1993). Other differences are more
difficult to quantify and are probably driven by contamination
problems. AIRMoN data clearly show that NADP bucket lid
seals occasionally contaminate samples with sodium; NADP
no longer ships samples in plastic buckets, largely because
of complaints from the AIRMoN/MAP3S community.
Research Plans
A number of projects will be attempted in the next year
or two, depending on available funding. We will continue
to upgrade electronics in motor box assemblies that drive
precipitation collectors, and we will attempt to complete
strain gage research so that we can move the equipment
to a permanent field position. A four-way field intercomparison
between NADP, AIRMoN-Wet, CAPMoN, and the
wet-side program under the EPA-led National Dry Deposition
Program is under consideration, with the likely establishment
of a proper comparison at Pennsylvania State University.
Further field studies with various biocide treatments are
still contemplated, but not planned for the next year or
two due to budget constraints. At some point, chilling
of samples should be replaced by introduction of a simple
biocide such as chloroform or thymol to cut shipping costs
and better stabilize samples.
Perhaps more importantly, we will attempt to move forward
with the early detection aspects of AIRMoN-Wet to detect
cleaner air due to mandated emissions reductions. Computation
of back trajectories in combination with cluster
analysis and gridded tabulations of trajectory has
continued at a low level for several years; some of this
work should come to fruition during the next year. The
main purpose of these efforts will be to reduce the uncertainty
in our analyses by removing variability introduced by meteorology.
Linkages with Other Parts of NOAA
The AIRMoN-Wet program is an integral part of the overall
AIRMoN program. AIRMoN-Wet is managed primarily from ARL
Silver Spring; the AIRMoN-Dry part of the program is managed
byARL/ATDD in
Oak Ridge, Tennessee. The ARL modeling community in
Silver Spring and
ASMD in
Research Triangle Park routinely apply these data to the
issue of nutrient deposition in coastal areas.
Linkages with Other Organizations
AIRMoN-Wet data are fully integrated into international
air quality studies as promoted by the
International Joint Commission between the U.S. and Canada,
the U.S.-Canada Air Accord, the Committee
for Environmental Cooperation (established
as a result of the North American Free Trade Agreement),
and the World Meteorological Organization Global Atmospheric
Watch program based in Geneva, Switzerland. U.S. agencies
involved in these international agreements include the
State Department, EPA, and the National Park Service. The
Atmospheric Environment Service and the Ontario Ministry
of the Environment are our Canadian counterpart agencies.
Through involvement with the
National Atmospheric Deposition
Program, AIRMoN scientists are part of a consortium of eight federal
agencies which require deposition data for a variety of
purposes.
Recent Publications
Hicks, B., and R. Artz, Estimating Background Precipitation
Quality from Network Data, Environmental Pollution, 75,
137-143, 1992.
Lamb, D., and L. Comrie, Comparability and Precision of
MAP3S and NADP/NTN Precipitation Chemistry Data at an Acidic
Site in Eastern North America, Atmospheric Environment, 27A,
1993-2008, 1993.
NADP/AIRMoN. The NADP/Atmospheric Integrated Research
Monitoring Network-wet Site Operator's Manual: Illinois
State Water Survey, Champaign, IL.
NADP/AIRMoN. The NADP/AIRMoN-wet Quality Assurance Manual." Illinois
State Water Survey, Champaign, IL.
Sirois, Alain, Robert Vet, and Dennis Lamb, A Comparison
of Precipitation Chemistry Measurements Obtained by the
CAPMoN and NADP/NTN Networks. Advances in Environmental
Research, In Press, 1997.
Vet, Robert J., A. Sirois, D. Lamb, and R. Artz. Intercomparison
of Precipitation Chemistry Data Obtained Using CAPMoN and
NADP/NTN Protocols. NOAA Technical Memorandum ERL ARL-174,
Air Resources Laboratory, Silver Spring, Maryland, 1989. |