Science for Solutions 

NOAA COASTAL 

Decision Analysis 

OCEAN PROGRAM 

Series No. 9 

ATMOSPHERIC 

COASTA 

REDUCING THE U/VCER 

Richard A. Valigura 

Winston T. Luke 

Richard S. Artz 

Bruce B. Hicks 

NOAA AIR RESOURCES 

LABORATORY 

JUNE 1996 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

Coastal Ocean Office 
The Decision Analysis Series has been 

established by NOAA's Coastal Ocean 

Program (COP) to present documents for 

coastal resource decision makers which 

contain analytical treatments of major 

issues or topics. The issues, topics, and 

principal investigators have been selected 

through an extensive peer review 

process. To learn more about the COP or 

the Decision Analysis Series, plezse 

write: 

NOAA 

Coastal Ocean Office 

131 5 East West Highway 

Silver Spring, MD 2091 0 

phone: 301 -71 3-3338 

fax: 30 1 -7 1 3-4044 

Cover photo: Convective coastal storms are an efficient mechanism 

for the transfer of atmospheric nitrogen to a given water body. 

Soluble nitrogen compounds in the atmosphere are dissolved into 

precipitation during storm formation as well as by falling rain. (Photo 

by Glenn Rolph, NOAA Air Resources Laboratory, 7992) 
Science for Solutions 

NOAA COASTAL OCEAN PROGRAM 

Decision Analysis Series No. 9 

ATMOSPHERIC NUTRIENT INPUT TO 

COASTAL AREAS 

REDUCING THE UNCERTAIN TIES 

Richard A. Valigura 

Winston T. Luke 

Richard S. Artz 

Bruce B. Hicks 

NOAA AIR RESOURCES LABORATORY 

JUNE 1996 

U.S. DEPARTMENT OF COMMERCE 

Michael Kantor, Secretary 

National Oceanic and Atmospheric Administration 

D. James Baker, Under Secretary 

Coastal Ocean Office 

Donald Scavia, Director 
This ~ublication should be cited as: 

Valigura, Richard A., Winston T. Luke, Richard S. Artz, and Bruce B. Hicks. 1996. Atmospheric 

Nutrient Input to Coastal Areas--Reducing the Uncertainties. NOAA Coastal Ocean Program 

Decision Analysis Series No. 9. NOAA Coastal Ocean Office, Silver Spring, MD. 24 pp. + 4 

appendices. 

This publication does not constitute an endorsement of any commercial product or 

intend to be an opinion beyond scientific or other results obtained by the National 

Oceanic and Atmospheric Administration (NOAA). No reference shall be made to 

NOAA, or this publication furnished by NOAA, in any advertising or sales 

promotion which would indicate or imply that NOAA recommends or endorses any 

proprietary product mentioned herein, or which has as its purpose an interest to 

cause directly or indirectly the advertised product to be used or purchased because 

of this publication. 
Note to Readers 

Atmospheric Nutrient Input to Coastal Areas--Reducing the Uncertainties by Richard A. 

Valigura, Winston T. Luke, Richard S. Artz, and Bruce B. Hicks of NOAA's Air Resources 

Laboratory is a synthesis of the findings and the management implications of research sponsored 

by the NOAA Coastal Ocean Program as part of its nutrient enhanced productivity activities. 

The atmospheric deposition of nutrients to estuaries, particularly along the U.S. East Coast, is 

being increasingly recognized as a significant contributor to eutrophication with its concomitant 

adverse impacts on living marine resources. This study by the Air Resources Laboratory is a 

seminal investigation of the subject particularly relating to the Chesapeake Bay. 

The NOAA Coastal Ocean Program (COP) provides a focal point through which the agency, 

together with other organizations with responsibilities for the coastal environment and its 

resources, can make significant strides toward finding solutions to critical problems. By working 

together toward these solutions, we can ensure the sustainability of these coastal resources and 

allow for compatible economic development that will enhance the well-being of the Nation now 

and in future generations. The goals of the program parallel those of the NOAA Strategic Plan. 

A specific objective of COP is to provide the highest quality scientific information to coastal 

managers in time for critical decision making and in a format useful for these decisions. To help 

achieve this, COP inaugurated a program of developing documents that would synthesize 

information on issues that were of high priority to coastal managers. A three-step process was 

used to develop such documents: 1) to compile a list of critical topics in the coastal ocean 

through a survey of coastal resource managers and to prioritize and select those suitable for the 

document series through the use of a panel of multidisciplinary technical experts; 2) to solicit 

proposals to do research on these topics and select principal investigators through a rigorous 

peer-review process; and 3) to develop peer-reviewed documents based on the winning 

proposals. Seven topics were selected in the initial round, and COP is planning a second round. 

Additionally, the series is being expanded to include the synthesis of findings from other COPfunded research. A list of titles in print appears on the inside back cover. 

As with all of its products, COP is very interested in ascertaining the utility of the Decision 

Analysis Series particularly in regard to its application to the management decision process. 

Therefore, we encourage you to write, fax, call, or E-mail us with your comments. Please be 

assured that we will appreciate these comments, either positive or negative, and that they will 

help us direct our future efforts. Our address and telephone and fax numbers are on the inside 

front cover. My Internet address is dscavia@cop.noaa.gov. 

1. Donald Scavia 

Director 

NOAA Coastal Ocean Program 
ACKNOWLEDGMENTS 

Numerous individuals and agencies contributed their time and/or resources toward the 

completion of this project. Special thaks go to the following individuals who provided 

unpublished datasets used in this report: Bill Matuszeski and Lewis Linker (EPA Chesapeake 

Bay Program Office); Paul Stacey (Connecticut Dept. of Environmental Protection); Holly 

Greening (Tampa Bay National Estuary Program); Mark Alderson (Sarasota Bay National 

Estuary Program); Bill Keene (University of Virginia); Joe Scudlark (University of Delaware); 

Kevin Civerolo, Bruce Dodridge, and Russ Dickerson (University of Maryland Meteorology 

Dept.); Russ Brinsfield, Ken Staver, and Mary Catherine Morrisey (University of Maryland's 

Wye River Education Center); Bill Boicourt (University of Maryrland's Horn Point 

Environmental Laboratory) ; Bob McMillan, Tylden Meyers, Jeff Mcqueen and Barbara Stunder 

(NOAA Air Resources Laboratory). 

The literature sysnthesis was facilitated by the Chesapeake Bay Research Consortium. Thanks is 

due to co-authors Laura McConnell, Joe Scudlark, and Joel Baker. 

The Mt. Washington Workshop was facilitated by the Chesapeake Bay Program's Scientific and 

Technical Advisory Committee. Special thanks must go to the participants at the Workshop, 

many of whom contributed to the text: Viney Aneja, Carmen Aquillar, Joel Baker, Richard 

Batuik, John Benedict, Brandon Bonanno, Owen Bricker, Mark Bundy, A1 Cimorelli, Dave 

Correll, Greg Cutter, Robin Dennis, Russ Dickerson, Rebecca Diclut, Bruce Dodderidge, Jim 

Galloway, Ricke Hood, Carolyn Hunsaker, Betsy LaRoe, Lewis Linker, Melissa McCollough, 

Laura McConnel, Jeff McQueen, Paul Miller, Ed Myers, John Ondov, Jess Parker, Eileen 

Rowan, Bill Ryan, Dan Salkovitz, Richard Scheffe, Terry Schemm, Joseph Scudlark, Sidney 

Steele, Robert Summers, Eric Van DeVerg, and Marv Wesely. 

The Airlie Workshop was facilitated by the Aliiance for Chesapeake Bay and the Chesapeake 

Bay Research Consortium. Thanks are due to all who participated in the Shared Resource 

Workshop, and especially to all who contributed material that found its way into the present text 

- Mark Alderson, Suzanne Aucella, Joel Baker, Richard Batiuk, Glen Besa, Rona Birnbaurn, 

Karl Blankenship, Donald Boesch, Walter Boynton, Peg Brady, Dail Brown, Diane Brown, John 

Calder, Mark Castro, James Collier, Chris Deacutis, Peter de Fur, Robin Dennis, Ellen Parr 

Doering, Fred Durham, Charles Ehler, Kelly Eisenman, Fran Flanigan, David Foerter, Elizabeth 

Gillelan, Normand Goulet, Holly Greening, Sonia Hamel, Patricia Harrington, Sheila Holman, 

Ricke Hood, Carolyn Hughes, Bill Keene, George Keller, Margaret Kerchner, Erica Laich, Lewis 

Linker, Jim Lynch, Gail MacKiernan, Tom Maslany, William Matuszeski, Paul Miller, Brian 

Morton, Kent Mountford, Thomas Noel, Marria O'Malley Walsh, Karen Rice, Barry Rochelle, 

Thomas Rogers, Eileen Rowan, Dan Salkovitz, Joseph Scudlark, Moira Schoen, Bill Sharp, John 

Sherwell, Deborah Shprentz, Paul Stacey, Ronald Stanley, Nancy Summers, Robert Talbot, 

Robert Thomann, Julie Thomas, Darryl Tyler, John Wickham, and Derek Winstanley. 
FOREWORD 

The overall goal of Atmospheric Nutrient Input to Coastal Areas (ANICA) Program was to 

develop methods for assessing the importance of atmospheric nutrient input, using the 

Chesapeake Bay as a first target of contemporary importance (as evidenced by specific mention of 

atmospheric deposition to the Bay, among other water bodies, in the Clean Air Act Amendments 

of 1990). 

As an atmospheric component of the nutrient research program of NOAA's Coastal Ocean 

Program, the long-term objectives of the research program were: 

To determine the wet and dry deposition of nitrogen to Chesapeake Bay and other East 

Coast estuarine areas selected for intensive study 

To develop a strategy for assessing the dry and wet deposition affecting other coastal 

watersheds in the Northeastern United States and Maritime Canala 

To apply the models that are developed or modified in this program to describe and 

predict present and future atmospheric deposition scenarios for catchment areas impacted 

by nitrogen deposition 

To link the findings from ANICA with the ecological components of NOAA's Coastal 

Ocean Program and the Clean Air Act's Great Waters Program objectives 

vii 
TABLE OF CONTENTS 

LIST OF FIGURES AND TABLES ................................................................................ xi 

... LIST OF TERMS AND ACRONYMS ........................................................................... xm 

EXECUTIVE SUMMARY ............................................................................................... xv 

CHAPTER 1 : INTRODUCTION ..................................................................................... 1 

Nitrogen in the Environment ................................................................................................... 1 

Atmospheric Nitrogen ............................................................................................................. 1 

Dejhing the Problem ............................................................................................................. 4 

CHAPTER 2: SCIENTIFIC FRAME WORK ............................................................... -7 

Mass Balance Paradigm ......................................................................................................... 7 

Sources and Emissions ............................................................................................................ 7 

Reactive Nitrogen: Nitrogen Oxides ............................................................................... 9 

Reduced Nitrogen: Ammonia and Ammonium ............................................................... 9 

Organic Nitrogen .......................................................................................................... 10 

Deposition Flux Estimates .................................................................................................... 11 

Wet Deposition ............................................................................................................ 11 

Dry Deposition .......................................................................................................... -12 

Loadings to Chesapeake Bay ............................................................................................... 13 

Direct Loadings ........................................................................................................... 13 

Indirect Loadings ...................................................................................................... -13 

Total Loadings Estimates ............................................................................................. 14 

Loadings Intercomparison Between Coastal Waters ............................................................. 16 

CHAPTER 3 : REMAINING ISSUES .......................................................................... 19 

The Literature Synthesis ..................................................................................................... 19 

The Mt . Washington Workshop ............................................................................................. 20 

The Airlie Workshop ............................................................................................................. 22 

APPENDICES: 

A . LIST OF ANICA TASKS ................................................................................... A-1 

B . SPECIFIC STUDIES ............................................................................................... B-1 

A Regression Approach for Estimating Precipitatiort Chemistry ............................... B-1 

Wet Deposition Over Chesapeake Bay ...................................................................... B-4 

Wet Deposition of Organic Nitrogen ......................................................................... B-6 
Dry Deposition Inferential Method (DDIM) Measurements at Wye. Md ..................... B-8 

Atmospheric Nitrogen Speciation Measurements ....................................................... B. 11 

Interconzparison of Filterpack and Denuder Techniques for HNo3 Measurements .... B-16 

Estimating Air- Water Transfer of HNO, .................................................................. B-19 

Operational RAMS 15 Km Forecasts over Chesapeake Bay ..................................... B-26 

C . ANICA ASSOCIATED SCIENTISTS ............................................................. c-i 

D . BIBLIOGRAPHY .................................................................................................. D-i 
LIST OF FIGURES AND TABLES 

Figures 

Figure 1.1 

Figure 2.1 

Figure 2.2 

Figure B. 1. 

Figure B.2. 

Figure B. 3. 

Figure B .4. 

Figure B. 5. 

Figure B.6. 

Figure B.7. 

Figure B. 8. 

Figure B.9. 

Atmospheric input of nitrogen to coastal areas 

A simplified schematic of the coastal nitrogen cycle 

A simplified schematic of the terrestrial nitrogen cycle 

Spatial distribution of the wet deposition of inorganic nitrogen across the 

Chesapeake Bay watershed 

A representation of the sequence of mechanisms influencing the deposition from 

the atmosphere of trace gases and diffusing particles 

The 48-hour back trajectories from Wye, Md. corresponding to periods of low 

measured NO, concentrations 

The 48-hour back trajectories from Wye, Md. corresponding to periods of high 

measured NO, concentrations 

The frequency distribution for 18 months (excluding winter) of estimated 

deposition velocities in Chesapeake Bay and the distribution for 1 week in 

December 1993 

Ten-minute deposition velocities calculated for December 1-8, 1993 

Ten-minute Monin-Obukhov dimensionless stability estimates versus measured 

windspeed, calculated from the Chesapeake Bay Observing System data for April 

1994 

Horizontal (vectors) and vertical (contours) windspeed simulations performed over 

the northern Chesapeake Bay employing the finest nested grid spacings (AX=2.5 

w 

Operational 15 km RAMS simulations of northern Chesapeake Bay 
Tables 

Table 2.1 Budget of global NO, emissions by source (Teragrams [l Tg=1012 g] N yr-l) 

Table 2.2 Budget of global NH, emissions by source (Tg N yfl) 

Table 2.3 Watershed retention values (in % of nitrogen loading) used in Bay loading studies 

to date 

Table 2.4 Proportion of total nitrogen loading to coastal waters attributed to atmospheric 

input 

Table B. 1. Regression coefficients of the selected models (p-values) 

Table B.2. Testing statistics for total nitrogen (NO, + NH,') deposition estimates (in 

percent) - 

Table B.3. Basic 0,, CO, daytime NO, NO,, NO,, and No,/NO, statistics for data collected at 

Wye, Md. between September 2-28, 1993 

Table B.4. Mean and maximum observed NO, mixing ratios for "Clean" and "Dirty" days 

measured at Wye, Md. between September 2-28, 1993 

Table B.5. Comparison between deposition (g HNO, m-,) estimates (V, * [HNO,]) derived 

using different averaging schemes and the time series average 

Table B.6. Summary of surface data available for RAMS 

Table B.7. RAMS operational configuration 
LIST OF TE S AND ACRONYMS 

CO 

Fd 

HCL 

Mg 

Norg 

N2O 

NH,' 

NO 

NO, 

NO,- 

p-NO,- 

03 

Rb 

RT 

so, 

v d 

dL 

AEOLOS 

AEROCE 

AIRMoN 

CAAA 

CAD 

CBOS 

CL 

DDIM 

HY-SPLIT 

GFC 

GPCP 

I C 

NADP 

NAPAP 

NCDC 

NCEP 

NDIR 

PMT 

RADM 

RAMS 

uv 

WATOX 

Carbon monoxide 

Dry deposition Flux 

Hydrochloric acid 

1 Megagram = 10' g 

Organic nitrogen 

Nitrous oxide 

Ammonium 

Nitrogen oxide 

Sum of NO and NO2 

Nitrate 

Particulate nitrate 

Ozone 

Quasi laminar resistance 

Total air-surface resistance 

Sulfur dioxide 

Deposition velocity 

Monin-Obukhov coefficient 

DH Heat transfer coefficient 

Gg 1 Gigagram = lo9 g 

m03 Nitric acid 

N2 Diatomic nitrogen 

NT Total nitrogen 

NH, Ammonia 

(NH4),S04 Ammonium sulfate 

NO2 Nitrogen dioxide 

NO, Total reactive nitrogen 

N0,NH4 Ammonium nitrate 

PAN Peroxyacetyl nitrate 

Ra Aerodynamic resistance 

Rc Canopy resistance 

SLM Standard lifers per minute 

Uz Windspeed at height z 

v, Gravitational settling velocity 

Atmospheric Exchange Over Lakes and Oceans Study 

AirlOcean Chemistry Experiment 

Atmospheric Integrated Research Monitoring Network 

Clean Air Act Amendments of 1990 

Citric Acid Denuder 

Chesapeake Bay Observing System 

Ozone Chemiluminecence technique for measuring NO 

Dry Deposition Inferential Method 

Hybrid Single Particle Lagrangian Integrated Trajectory Model 

Gas Filter Correlation 

Global Precipitation Chemistry Project 

Ion Chromatography Analysis 

National Atmospheric Deposition Program 

National Acid Precipitation Assessment Program 

National Climatic Data Center 

National Centers for Environmental Prediciton 

Non-Dispersive Infrared Adsorption 

Photomultiplier Tube 

Regional Acid Deposition Model 

Regional Atmospheric Modeling System 

Ultraviolet 

Western Atlantic Ocean Experiment 

. . . Xlll 
EXECUTIVE SUMMARY 

A significant fraction of the total nitrogen entering coastal and estuarine ecosystems along the 

eastern U.S. coast arises from atmospheric deposition; however, the exact role of atmospherically 

derived nitrogen in the decline of the health of coastal, estuarine, and inland waters is still 

uncertain. From the perspective of coastal ecosystem eutrophication, nitrogen compounds from 

the air, along with nitrogen from sewage, industrial effluent, and fertilizers, become a source of 

nutrients to the receiving ecosystem. Eutrophication, however, is only one of the detrimental 

impacts of the emission of nitrogen containing compounds to the atmosphere. Other adverse 

effects include the production of tropospheric ozone, acid deposition, and decreased visibility 

(photochemical smog). 

Assessments of the coastal eutrophication problem indicate that the atmospheric deposition 

loading is most important in the region extending from Albemarle/Parnlico Sounds to the Gulf of 

Maine; however, these assessments are based on model outputs supported by a meager amount of 

actual data. The data shortage is severe. The National Research Council specifically mentions the 

atmospheric role in its recent publication for the Committee on Environmental and Natural 

Resources, Priorities for Coastal Ecosystem Science (1994). It states that, "Problems associated 

with changes in the quantity and quality of inputs to coastal environments from runoff and 

atmospheric deposition are particularly important [to coastal ecosystem integrity]. These include 

nutrient loading from agriculture and fossil he1 combustion, habitat losses from eutrophication, 

widespread contamination by toxic materials, changes in riverborne sediment, and alteration of 

coastal hydrodynamics. " 

Much of the initial understanding of the atmospheric deposition problem derived from work of 

NOAA's Air Resources Laboratory (ARL). During the 1980s, under the auspices of the National 

Acid Precipitation Assessment Program (NAPAP), ARL conducted a major study (the Western 

Atlantic Ocean Experiment - WATOX) of the fate of air pollutants carried by the wind beyond 

the east coast of the continental U.S. This study revealed that almost all of these pollutants are 

deposited to the ocean, with greatest deposition rates occurring in the nearshore region. About 

30% of the total U.S. air emissions of nitrogen are deposited to the Atlantic, again with heaviest 

deposition to the near-shore region. Further impetus was added to the atmospheric transport 

issue by the passage of 1990 Clean Air Amendments which require that: 

7he Administrator [of the Environmental Protection Agency], in cooperation with 

the Under Secretary of Commerce for Oceans and Atmospheres, shall conduct a 

program to identlh and assess the extent of atmospheric deposition of hazardous 

air pollutants (and in the discretion of the Administrator, other air pollutants) to 

the Great Lakes, the Chesapeake Bay, Lake Champlain and coastal waters. 

To address the need for an objective methodology to assess the importance of the atmospheric 

input to coastal regions, the ARLIAtmospheric Nutrient Input To Coastal Areas (ANICA) 

program was developed through the NOAA Coastal Ocean Program. During the four-year 
lifetime of ANICA, methods for assessing the role of atmospheric nitrogen loadings to coastal 

areas were developed, and other stakeholders were alerted to the importance of the atmospheric 

deposition issue. 

Much of the progress under the ANICA program was made by cooperative effort with the 

Chesapeake Bay Program through alliance with the NOAA Chesapeake Bay Office. Through this 

alliance, ARL researchers were invited to assume the chairmanship of the multi-agency Air 

Quality Coordination Group (AQCG) of the Chesapeake Bay Program. Subsequently, the AQCG 

hosted two major atmospheric loadings workshops. The first was a scientific workshop at 

Baltimore, Md., in 1994 (the "Mt. Washington Workshop") which succeeded in defining and 

prioritizing immediate research needs to reduce existing uncertainty surrounding the atmospheric 

loadings issue. Six research areas were identified which refelected the need to: 

1) conduct integrated (intensive and coordinated) monitoring at specified locations 

2) work to improve atmospheric models 

3) work to improve biogeochemical watershed models - 

4) improve emissions inventories 

5) conduct process-oriented measurements to extend spatial representativeness 

6) develop an extensive network of less intensive measurements. 

Through its leadership role in the AQCG, the success of the Mt. Washington Workshop 

strategically positioned ARL at the head of coastal nutrientlatmospheric loadings research and 

assessment in the U.S. This position was strengthened in areas to the north and south of the 

Chesapeake Bay through a the second workshop of local, state, and federal policy makers 

conducted near Warrenton, Va., in 1995 (the "Airlie Workshop"). The Airlie Workshop 

concluded that there is need for: 

1) a better understanding of how all atmospheric nitrogen species affect coastal 

ecosystems and the related policy options 

2) a cross-media approach to the atmospheric deposition and loadings problem 

3) a coalition of interested parties extending from the north to the south of the potentially 

affected eastern coast of the continental U.S., including both terrestrial and biological 

interests as equals. 

Participants of the Airlie Workshop noted that the work needed is essentially multimedia, 

requiring attention by a consortium of workers rather than separate attention by specialists 

operating independently 

The ANICA program was designed as a targeted research program designed specifically to 

answer two particular q~iestions: To what extent is the perceived problem due to deposition 

from the atmosphere and how can this understanding be extrapolated to other circumstances? 

After several years of work on the Chesapeake Bay, there is now a strong recognition of the 

importance of the atmosphere among the scientific community which deal with Atlantic coastal 

xvi 
ecosystems. This is widely seen as an area of NOAA leadership, providing crucial guidance to 

EPA and the states to assure that regulatory controls on industry, agriculture, and waste 

treatment are considered in proper context with air quality controls. ANICA scientists have 

been exporting the lessons that have been learned. In fact, ANICA has been slowly expanding 

its horizons, with recent activity in all of the Great Lakes, Pamlico-Albemarle Sounds, the 

Gulf of Maine, and Tampa Bay. 

There have been approximately 35 studies around the world which addressed at least one aspect 

of atmospheric loadings, the majority of which were published since 1990. However, the 

measurement and modeling techniques used varies considerably between individual studies, 

making intercomparisons difficult. Though published estimates of the relative contribution from 

the atmosphere fall in an apparently constrained range (10-45%), the actual amount of 

atmospheric loadings vary widely depending, primarily, on the size of the waterbody and its 

watershed (as elucidated in this report). The uncertainties of the studies to date make it 

imperative that a better understanding be obtained of the processes that transport and deposit 

nitrogen to estuaries and coastal zones, and that the scope of this unders_tanding be extended to 

areas along both the East Coast and the Gulf of Mexico which remain to be investigated. The 

most recent estimate of a 27% contribution of atmospheric deposition to total nitrogen loadings 

to the Chesapeake Bay (Chesapeake Bay Program, 1996), falls within the range reported for other 

estuaries (10-45%). Projections for the coming decades estimate that the atmosphere will become 

a more significant source of nitrogen loadings to coastal areas with anticipated increases in 

population and land development resulting in more mobile and new power plant emissions. 

The results and recommendations of the two Workshops listed above, and the underlying science 

behind atmospheric nutrient loadings to coastal areas are substantiated in the documentation that 

follows. This report will: a) review the underlying framework needed for understanding 

atmospheric loadings issues, b) present the specific research conducted by ARL and associated 

scientists under the ANICA background/measurement/modeling framework, c) summarize the 

current state of the science, and d) suggest the remaining research and management needs. 
Chapter 1 

INTRODUCTION 

Nitrogen in the Environment 

Though the availability of nitrogen normally limits biological productivity in coastal waters, 

overabundance of nitrogen is of concern in areas which have developed nutrient enrichment 

problems (i.e., eutrophication). In addition to increasing productivity, nutrient enrichment 

generally alters the normal ratios of nitrogen to phosphorus and to other elements such as silicon. 

This alteration may induce changes in phytoplankton community structure. Species which 

normally occur in low abundances may be favored, and, in some cases, toxic and/or noxious algal 

blooms may result. For the New England coast in particular, the number of red and brown tides 

and shellfish problems from nuisance and toxic plankton blooms have increased over the past two 

decades. Furthermore, in coastal areas with poor or stratified circulation patterns (e.g., 

Chesapeake Bay, Long Island Sound) the "overproduction" of algae tends to sink to the bottom 

and decay, using all (anoxia) or most (hypoxia) of the available oxygen in the process, causing 

loss of habitat. In extreme cases, the increase in suspended matter due to overproduction 

decreases light infiltration, in turn causing a loss of submerged aquatic vegetation. 

There is some anecdotal evidence that nitrogen loadings have been an issue for longer than is 

generally appreciated. Paleoecological studies have revealed that there is a threshold up to which 

ecosystems can tolerate stress without obvious adverse consequences. Once this threshold is 

passed, however, the system may no longer be able return to its original equilibrium state. What 

is seen now could be a manifestation of a nitrogen problem that is just starting to be observable. 

In some cases (i.e., Chesapeake Bay, Long Island Sound), the overall nutrient loads have already 

tipped the balance and are producing obvious negative effects. The decline has been evident in 

seagrass and in fisheries productivity. Other estuaries may not have yet reached their balance 

points. Here, the emphasis will be on the role of atmospheric nitrogen compounds. 

Note that the following discussion uses a standardized distinction of the terms 

"deposition" and "loadings. " Deposition is the fZux of nitrogen from the 

atmosphere to whatever surface is beneath. Indirect loading is the portion of 

nitrogen deposited onto the terrestrial watershed which is transmitted to the water 

body itselJ; defined in terms offlow to the tidal waters. Deposition to the water 

surface itself constitutes a direct loading. 

Atmospheric Nitrogen 

The exact role of deposition of atmospheric nitrogen compounds as contributors to the decline of 

the health of coastal, estuarine, and inland waters is still uncertain. From the perspective of 

coastal ecosystem eutrophication, nitrogen compounds from the air, along with nitrogen from 

sewage, industrial effluent, and fertilizers, become a source of nutrients to the receiving ecosystem 

(Figure 1.1). Eutrophication, however, is only one of the detrimental impacts of the emission of 

nitrogen containing compounds to the atmosphere. These compounds are also 

significant contributors to decreased visibility (photochemical smog), acid deposition, and the 

production of tropospheric ozone. 

Atmospheric nitrogen compounds are ubiquitous. Diatomic nitrogen (N2) is the dominant 

component of the atmosphere, and is comparatively unreactive. However, nitrogen is also 

present in the atmosphere in other chemical forms, some of which are relatively reactive. These 

fate of these nitrogenous compounds are the central topic for the present report. 

Most atmospheric nitrogen compounds (other than N2 and nitrous oxide [N20]) fall into two 

categories: reactive nitrogen (composed primarily of nitrogen oxides), and reduced nitrogen 

(typically dominated by ammonia pH3]). There are also organic nitrogen species that are 

typically referred to as a subset of reactive nitrogen. These chemical species arise in the 

atmosphere from the interaction between nitrogen oxides and biogenic or anthropogenic 

hydrocarbons. Though available evidence suggests that organic nitrogen originates from both 

anthropogenic and natural sources, speciation of organic nitrogen in the atmosphere is very 

poorly understood. 

The dominant source of the reactive oxides of nitrogen present in air over North America is hightemperature combustion (industry, power plants, automobiles, etc.). Nitric oxide (NO) generated 

by combustion (some also derives from natural biological processes) reacts quickly in the lower 

atmosphere generating nitrogen dioxide (NO2), which is then the dominant nitrogen oxide in the 

lower atmosphere in polluted regions. NO2 slowly deposits to the underlying surface, but a large 

proportion of it remains in the atmosphere where it is subjected to further chemical reactions. 

One of these reactions generates nitric acid vapor (FINO3) which is easily and quickly deposited. 

Other reactions generate ozone; the ozone issue is therefore intimately related to the NO, 

(defined as NO + NO,) question. 

The different atmospheric nitrogen compounds deposit differently, and once deposited they vary 

greatly in their ability to move through a watershed to affect the water body it contains. Specific 

influencing factors, in addition to the chemical form in which the nitrogen compound is 

deposited - reactive, reduced, or organic nitrogen species - vary widely based on proximity to 

sources, receiving waters, transformations in the atmosphere as well as on the land surface and 

transfer through the watershed via surface runoff (Paerl, 1996). Current estimates are that 

nitrogen oxides are the largest contributor to atmospheric nitrogen loads to coastal waters of 

eastern North America (40-60%), with ammonia (20-40%) and organic nitrogen (about 20%) 

also contributing significant amounts on an annual basis. 
Defivling the Problem 

The initial impetus to investigate the importance of the atmosphere as a transport mechanism for 

nitrogen to estuarine areas was the 1988 Environmental Defense Fund (EDF) report (Fisher et al., 

1988). Based on one year of measurements (1984), and assuming relationships between wet and 

dry deposition that are likely to be conservative, the authors estimated that one-third of the 

inorganic nitrogen entering the Chesapeake Bay comes from the atmosphere. There have been 

several subsequent efforts to quantify the atmospheric nitrogen loadings to the Bay. However, 

the assumptions used in these studies overshadow the results; the error associated with these 

estimates is typically quoted as being a factor of two or sometimes as much as a factor of about 

three. Further impetus was added to the atmospheric transport issue by the passage of 1990 

Clean Air Amendments that require: 

The Administrator [of the Environmental Protection Agency], in cooperation with 

the Under Secretary of Commerce for Oceans and Atmosphere; shall conduct a 

program to identzfi and assess the extent of atmospheric deposition of hazardous 

air pollutants (and in the discretion of the Administrator, other air pollutants) to 

the Great Lakes, the Chesapeake Bay, Lake Champlain and coastal waters. 

In FY 1991 the NOAA Coastal Ocean Program initiated the Atmospheric Nutrient Input to 

Coastal Areas (ANICA) program. The ANICA program was proposed and managed through the 

NOAA Air Resources Laboratory (ARL). Through participation in the multiagency National 

Acid Precipitation Assessment Program, ARL scientists gained experience in creating data bases, 

techniques, and models useful for evaluating the atmospheric sources of nitrogen to coastal 

waters. The long-term goal of ANICA was to: 

Develop methods for assessing the importance of this atmospheric input, using the 

Chesapeake Bay as aJirst target of contemporary importance. 

ANICA was first proposed as a program to address scientific uncertainties involved in 

assessments of the kind put forward by the initial EDF report. When ANICA commenced, only a 

minimal data base existed with which to test computer models, and little experimental capability 

to obtain additional data. However, there was already a large, multi-state and federal 

organizational research effort addressing the Chesapeake Bay problem, the Chesapeake Bay 

Program. Most of attention was being directed at monitoring the flow of nutrients into the Bay 

via streams and rivers, monitoring changes in the Bay water quality and in its biology, and 

developing models to describe the interaction between such nutrient inputs and the recycling of 

nutrients within the Chesapeake Bay ecosystem. The ANICA program was designed to provide 

precisely the information that has previously been missing - direct experimental quantifications of 

areal deposition rates of atmospheric nutrients - and to introduce this new information into the 

models being developed. 

ANICA was a targeted research program designed specifically to answer two particular 
questions: To what extent is the perceivedproblem due to deposition@om the 

atmosphere and how can this understanding be extrapolated to other circumstances? 

After several years of work on the Chesapeake Bay, there is now a strong recognition of the 

importance of the atmosphere among the scientific community which deal with Atlantic coastal 

ecosystems. The specialization of ARL is widely recognized as being crucial to this science. This 

is all widely seen as an area of NOAA leadership, providing crucial guidance to EPA and the 

states to assure that regulatory controls on industry, agriculture, and waste treatment are 

considered in proper context with air quality controls. ANICA scientists have been exporting the 

lessons that have been learned. In fact, ANICA has been slowly expanding its horizons, with 

recent activity in all of the Great Lakes, Pamlico-Albemarle Sounds, the Gulf of Maine, and 

Tampa Bay. 

In FY 1991 ANICA was implemented as a series of 23 specific tasks (listed in Appendix A). 

These tasks were divided into three general areas of research: background development, 

measurement, and model and data evaluation. At the end of FY 1995, _nine (primarily background 

oriented) tasks were completed or implemented and six of the measurement and modeling phase 

tasks were initiated. Much of this progress was made through cooperative efforts with the 

Chesapeake Bay Program through the NOAA Chesapeake Bay Office. This report will: a) 

review the underlying framework needed for understanding atmospheric loadings issues, b) 

present the specific research conducted by ARL and associated scientists under the ANICA 

background/measurement/modeling framework, c) summarize the current state of the science, and 

d) suggest the remaining research and management needs. 
Chapter 2 

SCIENTIFIC FRAMEWORK 

Mass Balance Paradigm 

Biogeochemical cycling of nitrogen and contaminants on local, regional, and global scales is a 

complex system of emissions, transformations, dispersion, and deposition. This system is most 

complex in coastal environments, such as Chesapeake Bay, where landscape processes affect 

coastal processes and vice versa. Figure 2.1 is a simplified schematic that shows an idealized 

picture of a coastal ecosystem divided into four basic compartments or reservoirs, and the 

transfers among these compartments. This view provides a convenient basis for the current mass 

balance paradigm that attempts to quantify the transfers (loadings) between designated system 

components. To date, most emphasis has been placed on quantifying and identifying direct, 

well-defined emissions to each compartment (i.e., emissions from smokestacks, outfalls). 

However, the terrestrial watershed and the riverine and estuarine processes affect the transport of 

these emissions to the Bay both directly and indirectly. 

Atmospheric deposition includes wet deposition (through rain and snow) and dry deposition (as 

gases and aerosols). In each case, it also is necessary to consider whether the deposition is 

deposition to the water surface (i.e., direct deposition) or deposition to the watershed, with 

subsequent transport to the receiving stream (i.e., indirect deposition). Determining the 

magnitude of deposition is necessary but not always sufficient for addressing management issues. 

To deal efficiently with such issues requires an understanding of both the sources of atmospheric 

nitrogen (e.g., long-range versus short-range transport, emission source type, and associated 

meteorological conditions) and the relative magnitude of the atmospheric depositional loadings 

compared to that of all other sources of nitrogen surface waters. 

Sources and Emissions 

Most atmospheric nitrogen compounds (excluding N2 and N20, which are relatively inert in the 

lower atmosphere) fall into two categories: reactive nitrogen, sometimes referred to as oxides of 

nitrogen or odd nitrogen, and reduced nitrogen (typically dominated by ammonia [NH,]). Some 

organic nitrogen species arise in the atmosphere from the interaction between nitrogen oxides 

and biogenic or anthropogenic hydrocarbons, and are thus typically referred to as a subset of 

reactive nitrogen. The relative portions of the different forms nitrogen can take--i.e., nitrate, 

nitrite, ammonia, dissolved organic nitrogen--vary wideiy based on proximity of sources to 

receptors, receiving waters, and atmospheric transformations as well as on the land surface and 

transfer through the watershed via surface runoff (Paerl, 1996). Current estimates are that 

reactive nitrogen is the largest contributor to atmospheric nitrogen loads to coastal waters (40- 

60%), with ammonia (20-40%) and organic nitrogen (0-20%) also contributing significant 

amounts. 
Anthropogenic 

Sources 

Figure 2.1. A simplified schematic of the coastal nitrogen cyle. 

8 
Reactive Nitrogen: Nitrogen Oxides 

Reactive nitrogen compounds (primarily oxides of nitrogen) are emitted to the atmosphere 

through both natural and anthropogenic pathways, overwhelmingly (95%) as nitric oxide, or NO. 

Natural sources of NO include emission from soils and generation by lightning; dominant 

anthropogenic sources include emission from automobiles, power plants, and biomass burning. 

On a global basis, anthropogenic and natural sources of reactive nitrogen are approximately equal 

in strength (Table 2.1). In North America, and especially in northeastern North America, the 

overwhelming majority of nitrogen oxides is of anthropogenic origin. 

Table 2.1. Budget of global NO, emissions by source (Teragrams [l Tg = lo1' g] N yr-I). 

Ada~ted from Watson et al.. 1992. 

Sources of NO, = NO + NO, 

Fossil fuel combustion 

Lightning 

Tg N yr-' 

14-28 

- 

2-20 

Microbial activity in soils 

Biomass burnine: 

11 Stratospheric input <1 

I 

5-20 

3-13 

Oxidation of ammonia 

Oceans 

Once in the atmosphere, NO is transformed via a multitude of secondary reactions to form higher 

oxides of nitrogen. Of the reactive nitrogen components, HNO, and particulate nitrate (p-NO,') 

are believed to dominate nitrogen deposition (Huebert and Robert, 1985; Huebert et al., 1988; 

Meyers et al., 1989). However, deposition of NO, also may be significant in near-urban 

environments where concentrations are high; its spatial and temporal extent is an important 

question being addressed. Peroxy acetyl nitrate (PAN) is a compound which arises from the 

reaction of NO, with the photo-oxidation products of both natural and anthropogenic 

hydrocarbons. PAN is efficiently produced in polluted urban air due to the reactive nature of 

many anthropogenic hydrocarbons. Few studies of PAN deposition have been conducted. 

Smullen et al. (1 982) views PAN deposition as insignificant; however, Singh (1987) states that it 

may be important near polluted urban and semi-rural locations. 

0-10 

< 1 

Reduced Nitrogen: Ammonia and Ammonium 

Ammonia is emitted into the atmosphere through both natural and anthropogenic pathways. 

Natural sources of NH, include microbial decomposition of organic nitrogen compounds in soils 

and ocean waters and volatilization from animal and human wastes. Anthropogenic sources 
include the manufacture and release of commercial and organic fertilizers during and after 

application and fossil fuel combustion. Human activities such as manure management and 

biomass burning exacerbate emissions from otherwise natural processes. Two estimates of the 

global emission budget are presented in Table 2.2. The uncertainties apparent in these estimates 

are related to the intrinsically local nature of ammonia emissions, which make regional estimates 

highly difficult to construct. 

Ammonia is a highly reactive compound and has a short residence time in the atmosphere. It is 

primarily emitted at ground level and quickly deposits to the area near its source unless it reacts 

with other gaseous chemicals (e.g., SO?, HNO,) and converted to ammonium (NHC) aerosol 

(Langland, 1992; Asman, 1994). Ammonium can be transferred regionally as an ammonium salt 

(e.g., ammonium nitrate [N03NH4]) and is the primary contributor to ammonium concentrations 

measured in precipitation. 

Organic Nitrogen 

Table 2.2. Budget of global NH, emissions by source (Tg N yr"). Adapted from Schlesinger 

and Hartley, 1992 (numbers in parenthesis indicate range); Dentener and Crutzen, 1994. 

To date, studies of atmospheric nitrogen deposition have almost exclusively addressed dissolved 

inorganic nitrogen (reactive and reduced nitrogen). Because of the paucity of reliable 

measurements, the historical variability in analytical techniques and results, and the current lack 

of suitable and uniform analytical measurement techniques, only limited work has been reported 

Source 

Domestic animals 

Sea surface 

Undisturbed soils 

Wild animals 

Vegetation 

Fertilizers 

Biomass burning 

Human 

Coal combustion 

Automobiles 

Total 

Schlesinger and Hartley, 1992 

32.0 (24-40) 

13.0 (8-18) 

10.0 (6-45) 

9.0 (5-10) 

5.0 (1-9) 

4.0 

2.0 

0.2 

75.2 (50-128) 

Dentener and Crutzen, 

1994 

22.0 

7.0 

2.5 

5.1 

6.4 

2.0 

45.0 
on the deposition of organic nitrogen. In fact, only wet deposition of organic nitrogen has been 

addressed. 

This dearth of information is becoming widely recognized by the scientific community and is 

receiving increased attention. Recent reports (Gorzelska et al., 1992; Milne and Zika, 1993; 

Cornell et al., 1995; Scudlark et al., 1995) suggest that organic nitrogen is a significant fraction 

of the total nitrogen measured in precipitation. Various estimates for the relative flux of organic 

versus total N via wet deposition range from -4 0% to >60%. These recent data suggest that the 

contribution of the unresolved organic fraction may significantly augment the atmospheric 

deposition of nitrogen to coastal waters. However, in addition to the lack of dry deposition data, 

there remain many conceptual questions related to source identification and bioavailability of 

deposition organic nitrogen. 

Current analytical techniques are unable to speciate specific organic N compounds measured in 

precipitation. Therefore, it is difficult to determine relative contributions of biogenic versus 

anthropogenic sources. Cornell et al. (1 995) speculated from their open ocean studies that the 

higher concentrations in continental rains, the need for a relatively large sea-surface fractionation 

to sustain a marine source, and the isotope results all suggest that a continental source is more 

likely. They also suggest that industrial combustion sources could contribute to dissolved 

organic nitrogen formation via reactions of soot with NO, and NH,. 

Deposition Flux Estimates 

The process by which atmospheric nitrogen is transferred to terrestrial and water surfaces is 

generally termed atmospheric deposition. Deposition is divided into two categories: wet and dry. 

Wet deposition involves the incorporation of gaseous or particulate nitrogen into cloud/rain 

formations (including fog), and the subsequent deposition of this water onto an underlying 

surface. Dry deposition involves the exchange of gaseous and particulate nitrogen between the 

atmosphere and a surface either through settling or by impact deposition. 

Wet Deposition 

With the exception of organic nitrogen compounds, the analytical techniques for major nitrogen 

species in precipitation are well established and can be considered fairly routine. Most of the 

current debate over the appropriate approach for measurement of wet nitrogen deposition is 

centered around field sampling protocols (i.e., the process by which the sample is collected and 

transported to the analytical laboratory). The question of precipitation sample collection 

frequency remains a topic of active debate. Many precipitation sampling networks have adopted 

a one-week sampling protocol as a reasonable compromise between high data quality and 

reasonable operational costs. Shorter collection intervals are generally not required to quantify 

trends in the wet deposition of stable chemical compounds; ecosystems do not usually respond 

rapidly to changes in deposition. On the other hand, longer-term sampling (e.g., monthly) is 

usually avoided because of difficulty in maintaining adequate quality control over precipitation 
samples which remain in the field for long periods of time. Overall, weekly sampling provides 

data which are quite adequate for long-term trend detection and ecosystem input assessment, but 

which are of limited use in coupling with meteorological models, and are often useless for 

process-oriented studies. In addition, while many ions in precipitation are relatively stable for 

periods of weeks or months, nitrogen compounds are more chemically labile and so require more 

frequent sample collection and analysis intervals to ensure sample stability and, by extension, a 

proper assessment of their environmental impacts. Thus, as the questions posed to the research 

community become more difficult, the demand for daily sampling is increasing. 

Wet deposition is chaotic in nature, which makes estimating short-term patterns difficult. 

However, review of nitrogen deposition data shows that deposition at one site is much the same 

as at a neighboring site when long-term averages are evaluated. This fact allows meaningful 

areal (isopleth) maps of wet deposition and nitrogen chemistry to be constructed using long-term 

data. 

Dry Deposition 

When considering total atmospheric deposition of nitrogen to a given watershed, the largest 

uncertainties are associated with the ability to estimate the spatial distribution of dry deposition. 

Enough is known about the processes that control dry deposition to permit deposition to be 

estimated on a point-by-point basis. However, in contrast to wet deposition, long-term averaging 

does not reduce differences between sites; it clarifies the differences. This fact makes 

understanding large-scale dry deposition patterns difficult. Thus, it is not possible to extract 

meaningful site-specific dry deposition data from large-area, time-averaged data without detailed 

consideration of the site in question. 

The mechanisms that control dry deposition are tied to biological and land surface features that 

are highly variable from one specific location to another. The problems with estimating dry 

deposition are further complicated by the fact that the capability for long-term, continuous 

monitoring is limited by both scientific and economic factors. In an effort to circumvent these 

problems, investigators have used mathematical models to estimate the distribution of dry 

deposition. However, even detailed, site-specific models used to estimate dry deposition from 

field measurements at a site under investigation are limited in their ability. Comparative 

measurement and modeling studies have shown that site-specific models - at good sites and in 

selected conditions - perform well a little over half the time. The reasons for the inadequacies 

are known to be associated with hard-to-quantify surface characteristics (e.g., leaf wetness, 

moisture conditions). These issues are not new, and they have been the subject of considerable 

debate. Efforts to resolve these problems have been made and continue to be made, but a 

universally acceptable spatial dry deposition model is still far distant. 

The primary assumption made by published loading studies is that dry deposition is equal to wet 

deposition. This assumption is necessary because there is no independent measurement basis for 

estimating areal dry deposition rates. This same lack of data also means that there is no existing 
evidence that this estimate is grossly misleading. It would seem obvious, considering the vastly 

dissimilar atmospheric and surface mechanisms that cause dry and wet deposition, that equality 

between them would be an extremely unlikely and quite fortuitous finding, in practice. 

Loadings to Chesapenke Bay 

Direct Loadings 

Studies have explored the idea that atmospheric deposition may contribute a significant 

proportion of phytoplankton nitrogen demands in coastal areas (Paerl, 1985; Paerl, 1988; Paerl et 

al., 1990). Fogel and Paerl(1991), for example, have estimated that 20-50% of annual new 

nitrogen demands for Pamlico-Albemarle Sound may be supplied by direct atmospheric 

deposition to the water surface (wet and dry). Furthermore, there have been two recent, and 

opposing, papers published on the effects of wet-deposited nitrogen effects on phytoplankton off 

Bermuda (Owens et al., 1992; Michaels et al., 1993). It is not currently known if the over-land 

measurements are representative of over-water deposition, but it is suspected that this is not the 

case. To investigate this question, a daily precipitation chemistry site was established on Smith 

Island, Md., in late 1995. This site will provide the first time series measurements of over-water 

wet deposition along the East Coast. Estimates of wet deposition to the Chesapeake Bay surface 

range from 3.45 to 4.2 Gg NO,-N yr-' (1 Gigagram = 1 * 1 09g) (Fisher and Oppenhiemer, 1991 ; 

Hinga et al., 1991; Tyler, 1988). 

Although the airlsurface exchange of nitrogen has been estimated for most nitrogen species over 

open ocean (Galloway, 1985; Duce et al., 1991), these rates may not apply to coastal situations in 

that coastal areas involve different meteorological processes (NRC, 1992). 

Through the use of instrumented Chesapeake Bay Observing System (CBOS) buoys, owned by 

the University of Maryland, estimates of nitrogen (HNO,, NO,, NH,) dry deposition rates to the 

Bay surface have been developed (Valigura, 1995). These estimates corroborate those given by 

other investigators to some extent, but still cover a wide range of values, from 745 Mg y-' (1 

Megagram = 1 * 106g) to 2.24 Gg y-I. From this data set, calculations were performed to 

determine the effect of atmospheric dry deposition on phytoplankton dynamics. This analysis 

demonstrated that dry-deposited nitrogen may provide 10% of the annual "new nitrogen" 

demands in Chesapeake Bay, and that individual events could supply up to 75% of the new 

demands for periods of several days (Malone, 1992; Owens et al., 1992). 

Indirect Loadings 

The greatest uncertainty in the quantification of loadings to coastal areas such as Chesapeake Bay 

is how much is transferred through the terrestrial watershed to the surface waters, and how much 

is subsequently transported downstream to the Bay. Nitrogen activity within a given watershed 

depends on the amount of soil nitrogen, historical acidic deposition, physical characteristics of 

the soil, site rainfall and temperature characteristics, the elevation and slope of the land, and the 

type and age of the vegetative cover (see Figure 2.2). These characteristics vary at all scales, 
Oxidation, 

Fixation by lightning 

+ ( N , NITKOGEN OXIDES NII , NITROGEN OXIDES 

Industrial -8 

fixation d 

.# (fertilizer) - 

Atmospheric Volitalization 

deposition 

I SOIL 

ANIMAL 

PLANT N 

e Death and wastes 

No Nitiification + Arnrnonification 

-4 , NII 1 ORGANIC N - 

I 

v 

LEACHING 

EROSION 

RUNOFF 

SUBSURFACE 

now 

Figure 2.2. A simplified schematic of the terrestrial nitrogen cycle. 

14 
making it difficult to determine the general fate of atmospherically deposited nitrogen over any 

area of significant size. However, using these criteria, a classification scheme for forested sites 

has been developed to evaluate a site's potential to retainlleach nitrogen (Melillo et al., 1989; 

Johnson and Lindberg, 1992). For example, sites in the Chesapeake Bay watershed generally fall 

into the zero-to-low leaching classifications (Hunsaker et al., 1994). 

A central difficulty in all discussion of watershed retention relates to the use of average values in 

assessments. Watershed retention assumptions used in the Chesapeake Bay studies (see above) 

are presented in Table 2.3. These estimates vary over several orders of magnitude, primarily 

because of the lack of adequate evaluation data. Assembling an adequate understanding of longterm behavior when the processes involved are fundamentally episodic is one of the major 

challenges, and represents an area in which contemporary 

Table 2.3. Watershed retention values (in % of nitrogen loading) used in Bay loading 

Land Use Tyler, 1988 Fisher and Hinga et al., 1991 

Oppenheimer, 199 1 

Forest 95.2-1 00.0 80.0 (5 1 .O-100.0) 80.0 (25.0-95.0) 11 

Pasture 93.7-99.96 70.0 (5 1 .O-90.0) 80.0 (25.0-95.0) 11 

Cropland 

models are sorely deficient. It is apparent from measurements that the majority of the 

atmospheric wet deposition occurs during a few episodes (Dana and Slinn, 1988; Fowler and 

Cape, l984), such that the wet-deposited nitrogen (as well as previously dry-deposited nitrogen) 

is deposited directly to or can flow quickly into the surface waters without intermediate reduction 

in concentration. 

Residential 

Total Loading Estimates 

76.0-99.97 

The role of atmospheric transport in providing an important path for nitrogen to estuarine areas 

was publicized in the EDF report (Fisher et al., 1988). Based on one year of measurements 

(1 984), and assuming relationships between wet and dry deposition that are likely to be 

conservative, the authors estimated that one-third of the inorganic nitrogen entering the 

Chesapeake Bay comes from the atmosphere. There have been several subsequent efforts to 

quantify the atmospheric nitrogen loadings to Chesapeake Bay (Fisher and Oppenhiemer, 1991; 

Hinga et al., 1991; Tyler, 1988). The approach taken in these studies can be divided into two 

components: estimating wet and dry deposition and estimating watershed retention. However, 

the assumptions used in these studies overshadow the results; the error associated with these 

estimates is typically quoted as being a factor of 2 or sometimes as much as a factor of about 

three. The most recent and best estimate of atmospheric nitrogen loads (i.e., 27% of the annual 

62.0-95.3 

70.0 60.0 (45.0-75.0) 

35.0 (0.0-70.0) 25.0 (10.0-50.0) 
load) to the Bay were developed through the Chesapeake Bay Program (CBP; Chesapeake Bay 

Program, 1996). This estimate falls within the range reported for other estuaries (10-45%), see 

below. To estimate wet deposition, the CBP combines output from a regression model developed 

from NADP weekly and daily precipitation chemistry measurements with data from the high 

density NOAA rainfall network. This approach yields daily estimates of rainfall to 74 sub-basins 

of the Chesapeake Bay watershed. Dry deposition is assumed to be equal to wet deposition for 

over-land areas and 44% of wet for over-water areas. Indirect atmospheric loadings from the 

terrestrial watershed are estimated with the CBP Watershed Model, a bulk-parameter model. In 

the coming decades, it is predicted that the atmosphere will become a more significant source of 

nitrogen loadings to the Chesapeake Bay with anticipated increases in population and land 

development resulting in more mobile and new power plant emissions (Fisher et al., 1988; 

Pechan, 1991). 

Loadings Intercomparison Between Coastal Waters 

There have been approximately 40 studies around the world which addressed at least one aspect 

of atmospheric loadings, the majority of which were published since 1990. However, the 

measurement and modeling techniques used vary considerably between individual studies, 

making intercomparisons difficult. Table 2.4 presents a summary of selected studies performed 

along the U.S. East Coast which are comparable in broad terms. There were two criteria for 

selection based not on scientific merit but on the approach and information content. These 

criteria required that the results were either: 

- published in a credible peer reviewed journal 

- advocated by a major management organization (e.g., an EPA National Estuary Program) 

These studies can be divided into two groups: those which considered both direct and indirect 

nitrogen loads and those which considered only direct loads. Table 2.4 confirms the common 

belief that the amount of atmospheric nitrogen input is related to the size of a waterbody and its 

watershed. 

It is interesting to note that although the percentages listed in Table 2.4 have an apparently 

constrained range (1 0-45%), the numerical estimates of atmospheric loadings vary widely. This 

point highlights the danger of using percentages as the basis for large scale management 

decisions. Many areas along both the East Coast and the Gulf of Mexico remain to be 

investigated. The uncertainties of the studies to date make it imperative that a better 

understanding be obtained of the processes that transport and deposit nitrogen to estuaries and 

coastal zones. 
I I I I 

LZ OLI SP 62 91 

69 0068E LOIOS 

SLI OOPI I 988591 

6E - PSLL L6I6S 

Sb OZ8P ISPEP 

ES 9b8I S069E 

Z'P 8ZE 80LP 
Chapter 3 

REMAINING ISSUES 

As the ANICA Program progressed it became clear that there is a large need for information 

dissemination regarding atmospheric nitrogen issues. ANICA scientist were directly involved in 

three such informational projects. In early 1994, a literature synthesis entitled, "Atmospheric 

Deposition of Nitrogen and Contaminants to the Chesapeake Bay and Its Watershed" (Valigura et 

al., 1995) was completed for and published by the Chesapeake Bay Program Scientific and 

Technical Advisory Committee. The second effort was a scientific workshop (referred to as the 

Mt. Washington Workshop) entitled, "Atmospheric Loadings to Coastal Areas - Resolving 

Existing Uncertainties, " and was held in June 1994 in Baltimore, Maryland. The third effort was a 

policy-oriented workshop (referred to as the Airlie House Workshop) entitled, "Airsheds and 

Watersheds - The Role of Atmospheric Nitrogen Deposition," and was held in October 1995 in 

Warrenton, Virginia. 

The Literature Synthesis 

The literature synthesis concluded with the following recommendations for steps to reduce 

uncertainties associated with prediction of atmospheric loadings. Depending on chemical species, 

the current uncertainties in estimates of atmospheric loading of nitrogen and contaminants to 

Chesapeake Bay and its watershed range from * 20% to orders of magnitude. However, if ways 

are to be found to reduce such atmospheric deposition, it is essential that the processes be better 

understood and that the quality and reliability of the estimates be improved. Accordingly, it is 

recommended that the following steps be initiated. These steps are not comprehensive or specific 

suggestions, but one list of key areas of uncertainty which will serve as discussion points in fbture 

deliberations. They are: 

Conduct monitoring and research experiments focused on improving measurements and 

modeling techniques to fbrther understand and quantifjl the emission cycles of the key 

chemical species 

Develop and perform nitrogen speciation experiments including on organic nitrogen and 

ammonia compounds; subsequently, conduct intensive studies of the dry deposition rate of 

nitrogen compounds from air crossing the watershed zone of the Chesapeake Bay region 

Investigate the effect of localized contaminant deposition in both urban and near-urban 

environments; specifically, develop estimates of surface-water loadings attributable to 

urban runoff and investigate the temporal and spatial distribution of NO, deposition 

Establish. integrated monitoring sites of atmospheric emission and deposition; initial focus 

should be on the concurrent measurement of the chemistry, intensity, and duration of 

precipitation and streamflow events 
Establish over-water precipitation chemistry sites and compare the results with those from 

land-based precipitation chemistry sites 

Establish common data bases to process and store data that can be used as input to models 

and/or to test specific predictions of the models; this effort should include emission 

inventories (anthropogenic and natural), wet and dry deposition rates at specific locations 

to be covered by the model, spatial distributions of soil and atmospheric moisture, 

chemical concentration distributions, and relevant meteorological supporting data 

ClarifL the role of urban areas as a source of atmospheric contaminants to surface waters; 

conduct research on sampling methods for small particle deposition and source attribution 

for organic contaminants 

Investigate the bioavailability of materials deposited from the atmosphere; conduct 

exposure studies to learn how chemical speciation influences exposure 

The Mt. Washington Workshop: Developing Science Priorities 

To focus attention on the problem, and to take a first step towards ordering scientific programs to 

reduce existing uncertainties in the quickest manner, a meeting of active scientists from different 

contributing disciplines was conducted at Mt. Washington, Maryland, on June 29-30, 1994. The 

workshop was sponsored by the Scientific and Technical Advisory Committee and the Air Quality 

Coordination Group of the Chesapeake Bay Program (CBP). The gathering included 

representation from the Great Lakes research community and federal and state agencies. 

The challenge given to the workshop was simple -- to construct a prioritized listing of practical 

studies that would make the greatest impact on reducing the current uncertainty in estimates of 

the contribution of atmospheric deposition to declining aquatic ecosystem health. The workshop 

was constructed to produce such an ordering through meetings of interacting working groups and 

concluding with extensive plenary discussion of the working group conclusions. 

The listing that resulted is summarized below and substantiated in the documentation that follows. 

It was concluded, however, that scientific investigations that are already under way are making 

considerable progress; in essence, any new efforts should be arranged to build on existing 

programs rather than risk new starts that compete with older ones. It was also concluded that 

there is a general need for improvement in the scientific programs already ongoing for all 

measurement methods, models, and evaluation of pollution reduction strategies. 

The emphasis of the workshop discussion was on all nitrogen species, toxic chemicals, trace 

metals, precipitation chemistry, airborne aerosols, and supporting meteorological investigation. In 

every one of these cases the general call for a new focus applies, although with different weights 

according to the particular emphasis. The workshop put priorities in the following order: 
Priority 1 -- Conduct intensive, coordinated integrated monitoring at special locations 

within the watershed, with wet deposition, dry deposition, and local catchment area 

characterizations. It was concluded that the single most limiting factor in assessing the 

adequacy of current models is the lack of quality data on actual deposition within the 

target watershed. Until an integrated monitoring station is operational, there will be no 

comprehensive data set for evaluating model performance. 

Priority 2 -- Work to improve existing atmospheric models. In brief, there are many limitations 

of current models, especially including their limited grid size (smaller grid cells are 

desired) and their inability to handle orographic and chemical factors that are likely to be 

of critical importance. 

The above top priorities reflect the workshop's recognition that current models are likely to be 

misleading, but that the extent of any errors cannot be judged because the key observations of 

deposition are not yet made. 

Priority 3 -- Improve biogeochemical watershed models. The workshop recognized the 

important role of watershed chemical retention and emphasized the need for close linkages 

with the appropriate expert scientific community. 

Priority 4 -- Improve emissions inventories and projections. It was noted that assessments of 

atmospheric deposition are necessarily at the mercy of emissions estimates and that such 

estimates are currently highly imperfect both in the adequacy of reporting requirements 

and the spatial resolution used to report the emission values. 

Priority 5 -- Conduct process-oriented measurements to extend vertical and spatial 

meteorological and chemical concentration coverage and to quantify 

representativeness. The models that are now needed for assessment purposes need more 

advanced input data than do the simpler models used in early assessments. As time 

progresses and as these models evolve hrther, input data requirements will increase. It 

was concluded that measurement programs to provide the data required by the models 

should be established. 

Priority 6 -- Establish an extensive array of less intensive measurements. This item follows 

from Priority 1. In essence, a nested network is envisioned with a small number of 

Priority 1 intensive stations supporting a denser array of simple stations designed to 

provide improved spatial resolution for some selected variables. 

The workshop considered the needs for uncertainty reduction in two distinct contexts: 

to build confidence by separate attention to individual parts of the source-emissiondispersion-deposition-delivery-effects process 
to test the accuracy of overall understanding and model predictions 

In addition, it was pointed out that a quality assurance program to consolidate the existing 

network of wet and dry deposition (for nitrogen) sites is currently not in place. Therefore, 

deposition must be monitored, keeping ecological considerations in mind. 

The meeting noted that current assessments are almost entirely based on large-grid model outputs 

without the benefit of actual deposition observations to the coastal areas that are thought to be 

affected. Consequently, the top research priority was associated with the need for one (or 

preferably several) Integrated Research Sites where actual deposition measurements could be 

made at locations where supporting ecological data are collected. Other priorities reflected the 

current state of science and the relative importance of different areas of uncertainty. In general, 

each participant was encouraged to think in terms of the science at the highest possible level 

leaving personal agendas and agency perspectives behind. 

In general, it was concluded that work should continue on the development of 

atmospheric models which produce output offiner-grid resolution for the airshed 

affecting the Chesapeake Bay. Ancillary work should focus on studying the influence of 

key urban areas on the atmospheric loading to the watershed and tidal waters and to 

develop spatially-detailed wetfall and dryfall atmospheric-deposition input data for the 

watershed, tributaries, and coastal waters off the Bay mouth. Coordination of this 

activity appears to be an appropriate role for the CBP Air Quality Coordination Group. 

Finally, it was noted that no part of the workshop deliberations should be considered relevant only 

to the Chesapeake Bay. It was specifically concluded that the ordering listed above would be 

equally appropriate for other affected coastal areas. 

The Airlie House Workshop: Identifying Implications for Management 

A workshop was conducted at Airlie House Conference Center, Warrenton, Virginia, in October 

1995, where leading scientists and key policy and regulatory officials assembled to explore 

mechanisms by which air and water pollution control programs can work together to help protect 

coastal ecosystems. The focus of the workshop was on atmospheric nitrogen compounds, but 

many of the conclusions would apply equally well to other pollutants occurring in the air, such as 

toxic chemicals, trace metals, and persistent organic compounds. In all such instances, the 

atmosphere constitutes a resource that is shared among many different coastal jurisdictions and 

between the air and water regulatory communities. 

Scientific uncertainty has historically been an obstacle to proactive management response. The 

Airlie House Workshop reported here benefitted from the ability to draw upon scientific 

conclusions and recommendations about the coastal atmospheric deposition problem that were 

developed following the Mt. Washington Workshop. Given this information, participants 

concluded that scientific uncertainty has been reduced to the extent that some new or modified 
regulations and controls can be justifiably implemented. 

Atmospheric deposition of nitrogen species is recognized by all East Coast estuarine programs as 

either a significant contributor to estuarine eutrophication or a mechanism of possible concern. 

The region from which the atmospheric nitrogen pollution arises is much larger than the water 

surface that is potentially affected, and even much larger than the watershed that drains into it. 

The extent of "airsheds" are now starting to be recognized. The Chesapeake Bay airshed, 

depending on the definition used, is up to 600,000 square miles (lo6 krn2) in area, extending 

upwind of and bordering the water body itself. Emissions from an airshed of this magnitude affect 

more than a single estuary. For example, the emissions from the Chesapeake Bay airshed may 

affect the entire coastline such as from the Carolinas to New York. Thus, airsheds constitute an 

important "shared resource" that must be recognized. Reductions in emissions in airsheds benefit 

many downwind ecosystems, and assessments of the benefit of such reductions must take all 

benefitting water bodies into account, not just one single ecosystem that is especially favored. 

It was noted that some reductions in nitrogen emissions have already been made as a result of the 

controls mandated by the Clean Air Act Amendments (CAAA) of 1990. However, participants 

expressed concern that political pressures may not permit the full emissions reductions proposed 

by the CAAA to be realized. Water quality scenarios need to be weighed carefully, since some 

assume full implementation of the CAAA controls whereas others disregard them. Current 

assessments of projected water quality (and of ecosystem viability) do not take the additional 

controls proposed by the Ozone Transport Commission into account. It should be noted that the 

CAAA, and therefore the present document, concentrates on the deposition of the products of 

emissions of nitric oxide (NO) into the atmosphere - essentially nitrates (NO,-). Very little is said 

about the role of products of ammonia emission - essentially ammonium compounds - which are 

of considerable importance but about which relatively little is known. The role of organic 

nitrogen species is also not emphasized; these are poorly understood but are known to be strongly 

influenced by biological sources that cannot be regulated. 

The following five recommendations summarize the conclusions drawn by the participants of the 

Shared Resources Workshop. 

Efforts to resolve scientific uncertainties associated with the quantification of atmospheric 

deposition and the resulting loadings should be continued. The priorities identified at the 

1994 Mt. Washington workshop serve as a useful reference for planning future work. 

Future research should also focus on quantifling atmospheric nitrogen fluxes to the 

coastal ocean and characterizing the biochemical cycle of organic nitrogen through the 

Chesapeake Bay watershed. 

o Although there is uncertainty in many areas, enough is known to determine a general 

direction for action. Managers and regulators should move forward and not wait for all of 

the uncertainties to be resolved. Accuracy is possibly most needed when weighing costs 

of controls versus benefits. 
A set of basic information for use in explaining the cause for concern about atmospheric 

deposition and waterbody effects to the public, politicians, regulators, etc., should be 

generated. It was considered likely that a single set of basic material could be used as the 

core of issue-related material addressing current understanding about emissions, 

atmospheric deposition loadings by watershed and water body, areas of greatest 

uncertainty, etc. This would promote cooperation and coordination across the 

organizations involved and avoid sending mixed messages. 

A cross-media approach to quantifling atmospheric deposition and resulting loadings 

needs to be developed. Greater cooperation across issues, estuaries and bays, scientific 

disciplines, and governmental units is essential. Barriers to greater cooperation should be 

identified and eliminated. 

In order to assure that such coordination continues, a future meeting of the present kind 

(but with representation from an enlarged group of organizations) should be held in about 

a year's time. 

The workshop concluded that there is need for: a) a better understanding of how all atmospheric 

nitrogen species affect coastal ecosystems and of the related policy options, b) a cross-media 

approach to the atmospheric deposition and loadings problem, and c) a coalition of interested 

parties extending from the north to the south of the potentially affected East Coast of the 

continental U.S., including both terrestrial and biological aspects as equals. The work that is 

needed is essentially multi-media, requiring attention by a consortium of workers rather than 

separate attention by specialists operating independently. 

The workshop resulted in a clear and loud call for more cooperation across different 

issues, estuaries and bays, scientzfic disciplines, and state and federal agencies. 

Outreach to state and federal agencies, non-government organizations, induse, and the 

public at large, is critically needed. 

Even in these days of calls for cooperation and integration, the close association reqaired in the 

present context calls for attention by teams of workers that has classically been difficult to arrange 

and maintain. In the present case, there seems to be no option; the importance of the issue and its 

environmental sphere of influence combine to make it more important than ever before to build a 

working alliance of researchers and regulators addressing the atmospheric deposition issue. The 

role of atmospheric deposition is known to be important in many areas of concern, the 

atmosphere does indeed constitute a genuine shared resource, and a coordinated attack on the 

problem is recognized as an essential element rather than a desired goal. The Airlie House 

workshop was a start along a road to more extensive cooperation specifically intended to 

lead to more accurate assessments of atmospheric deposition to all East Coast estuaries and 

to arrange for the results to be presented in an optimal format for assimilation by policy 

and regulatory processes. 
Appendix A 

LIST OF ANICA TASKS 

TASK 3.1.1 : Bring together data from various wet deposition networks, examine quality 

assurance, and assemble appropriate information into a single data set for further analysis. 

TASK 3.1.2: Assess deposition of organic nitrate using specially-equipped monitors at a single 

site, and later using a number of sites as determined on the basis of the initial exploration. 

TASK 3.1.3: Sort deposition data according to event precipitation rates and amounts, and 

reported in a probabilistic manner as well as in terms of long-term average deposition 

rates. 

TASK 3.1.4: Set up new sampling sites. Sites will be sought that provide precipitation data 

representative of the central portions of the Chesapeake Bay, and precipitation records 

will be compared against values interpolated from terrestrial isopleths. If no existing sites 

that are suitable can be located, then special sites will be set up. 

TASK 3.1.5: Central-bay sites will be sought for data on wet deposition on an event basis. If no 

existing sites can be located, then special sites will be set up to test the hypothesis that wet 

deposition to the water surface of the Chesapeake Bay can be estimated adequately by 

interpolating terrestrial wet deposition isopleth maps. 

TASK 3.2.1 : Measure HNO, concentrations routinely at the Wye River site. 

TASK 3.2.2: Conduct intensive intercomparisons against annular denuder methodologies to 

evaluate the quality of HNO, data reported by the NOAA filterpack techniques. 

TASK 3.2.3: Conduct intensive air chemistry investigations of other airborne nitrogen 

compounds, especially NO,. 

TASK 3.2.4: Assess the spatial variability of air chemistry across the Chesapeake Bay watershed 

by use of Regional Acid Deposition Model or some better modeling capability 

benchmarked against the Wye River data. 

TASK 3.2.5: Initiate Dry Deposition Inferential Method operation at the Wye River site and 

commence archiving deposition velocities for HNO, and NO,. 

TASK 3.2.6: Obtain satellite imagery and derive land-use categorized depiction of the 

Chesapeake Bay catchment area. 

TASK 3.2.7: Produce modeled wind fields and related meteorological data for the Chesapeake 

Bay catchment area. 
TASK 3.2.8: Produce areal representations of deposition velocities for the entire catchment area. 

TASK 3.2.9: Benchmark the DDIM predictions for the Wye River sites for both NO, and HNO,. 

TASK 3.2.10: Instrument water buoys to monitor the stability regime over the water surface. 

Use the data obtained to compute deposition velocities for NO, and HNO, appropriate for 

the water surface itself. 

TASK 3.2.1 1 : Derive probabilistic representations of deposition velocity regimes in order to 

express water surface deposition of NO, and HNO, (primarily) as a function of month and 

season. 

TASK 3.2.12: Combine terrestrial deposition velocity fields (from Task 3.2.8) with air 

concentration fields (Task 3.2.4) to provide monthly and seasonal quantifications of the 

dry deposition of nitrogen species to the terrestrial watershed. 

TASK 3.2.13 : Combine aquatic deposition velocity fields (from Task 3.2.1 1) with air 

concentration fields (Task 3.2.4) to provide monthly and seasonal quantifications of the 

dry deposition of nitrogen species to the water surface of the Bay. 

TASK 3.2.14: Conduct intensive field studies as required to evaluate the accuracy and adequacy 

of these quantifications. 

TASK 3.3.1 : Assemble a data base giving weekly, monthly, and seasonal values representing: 

a) dry deposition to the water body, b) wet deposition to the water body, c) dry deposition 

to the surrounding watershed, d) wet deposition to the surrounding watershed, 

e) precipitation quantity, f) riverine nutrient input, and g) representative Bay water 

concentrations of related nutrients. 

TASK 3.3.2: Conduct multiple lag correlation analyses of the assembled data so as to deduce 

statistical relationships among the variables as a function of season. 

TASK 3.4.1 : 'conduct aircraft assessments of the horizontal fluxes of nitrogen species in air 

flowing across the Chesapeake Bay watershed as a function of altitude and season. 

TASK 3.4.2: Utilize the ANICA data set to improve regional deposition models for future use in 

assessing atmospheric nutrient deposition to vulnerable ecosystems. 
Appendix B 

ESTIMATING DEPOSITION: S 

A Regression Approach for Estimating Precipitation Chemistry 

Background 

The modeling subcommittee of the Chesapeake Bay Program was interested in an immediate 

improvement to the input of atmospheric nitrogen from NO,- and NH,' into the Bay Watershed 

model via precipitation (i.e., wet deposition). Data from 15 National Atmospheric Deposition 

Program (NADP) sites within and around the Chesapeake Bay watershed were used to investigate 

statistical relationships between the amount of precipitation and the concentration of nitrogen 

species in the rainfall. Using these statistical relationships and NOAA precipitation records, 

improved methods for estimating wet deposition nitrogen loading to the Chesapeake Bay were 

developed. Although statistical methods are not complete solutions to the problem both are an 

improvement over older approaches used by the Bay Program. 

Method 

Two datasets were used to develop the proposed methods; one from the NADP and another from 

the MAP3 S precipitation chemistry network. The primary network collecting precipitation 

chemistry data is coordinated by the NADP. The NADP was initiated in 1978 and is still in 

operation, consisting of some 193 sites funded on a site-to-site basis by a variety of organizations. 

These sites have identical siting and sampling criteria, and all data are analyzed in the same 

laboratory and using the same methodology. Precipitation samples are collected for one week 

with wet-only samplers and then sent to the Illinois State Water Survey for analysis. The 

proposed methods were either developed from or directly use the dataset collected by the NADP 

during 1984- 1992 from the 15 NADP sites in and nearest to the Bay watershed. 

The MAP3 S network was begun in 1976 and collected data until 1990 from nine sites along the 

Northeast United States. The MAP3S sites, like the NADP sites, had coordinated siting, 

sampling, and'analytical criteria to allow intercomparisons between sites. However, precipitation 

samples were collected on a event basis using wet-only samplers. The regression method was 

tested using datasets collected from 1978-1986 by three MAP3S sites located within the 

watershed. 

The regression method is based on the basic logarithmic relationship between amount of 

precipitation (mm ha-') and the NO,' and NH,' concentrations in the precipitation (mg mm-I). A 

relationship was developed using weekly data collected over an eight year period at the 15 NADP 

sites. Due to the weekly sampling protocol of NADP, the data were quality controlled by 

selecting those data where the precipitation event occurred only on the last day of the weekly 

sample. These data can be interpreted as daily samples, analyzed by the NADP network. Using 

this criterion, 265 samples were obtained from the approximately 5020 samples collected from the 
NADP sites, and these samples were used to develop the regression model. The coefficients of 

the final regression model are shown in Table B. 1. The final model was chosen from a list of 

variables which included log of precipitation, month, month2, sine of month, cosine of month, 

latitude, and longitude. This model was then tested (estimated vs. measured) on 8 years of event 

based data (approximately 1800 samples) collected independently at three MAP3S sites in and 

around the watershed (Table B.2). Estimates of annual total nitrogen (NO, + NH,) deposition 

were within 20% of that measured. On an individual event basis, estimates generally fell within 

a factor of two. 

Table B.1. Repression coefficients of the selected models (D values). 

- 

Table B.2. Testing statistics for total nitrogen (NO, + NH;) deposition estimates (in 

NO3 

NH4 

Site Location & Network Mean Error Mean Error in Error Variance 

in Annual Event in Event Event Errors 

11 Estimates I Estimates / Estimates I 

Intercept 

-1.289 (.0811) 

- 1.226 (.OOOO) 

State College, Pa. 11 -19 I 5 I 77 1 998 1-80 

- 18 2 1 95 649 / -94 

- 2 44 339 973 / -8 1 

15 Sites -19 17 65 490 / -80 

In(ppt) 

-.3852 (.OOOO) 

-.3549 (.OOOO) 

Implementation 

The Watershed Model used by the Chesapeake Bay Program is a bulk parameter model which 

divides the Chesapeake Bay watershed into 70 segments related to small-and-intermediate-scale 

watersheds. Each of the watershed segments has an associated hourly precipitation data record. 

To develop wet deposition estimates for the entire watershed, the regression method was 

employed using the precipitation data records. The result was a daily wet deposition data set for 

each segment. Figure B. 1 shows the average annual deposition estimates by watershed segment. 

month 

.3966 (.OOOO) 

month2 

-.0037 (.OOOO) 

-.0337 (.OOOO) 

Latitude 

.0744 

(.OOO 1) 

R2 

.4 1 

.3 1 
Dissolved Inorganic N 

Wet Deposition (@/Ha) 

Figure B. 1. Spatial distribution of the wet deposition of inorganic nitrogen across the Chesapeake 

Bay watershed. 
Wet Deposition Over Clzesapeake Bay 

Background 

The Mt. Washington Workshop listed as a top priority the need to provide actual data against 

which to compare model predictions and assessments. Wet-fall deposition of nitrogen has 

traditionally been estimated by creating isopleths of deposition between over-land precipitation 

chemistry sites. It is currently suspected that over-land wet deposition data do not adequately 

represent direct wet deposition rates to large waterbodies, primarily due to the complex 

meteorology in coastal areas such as Chesapeake Bay. The dearth of data concerning wet 

deposition of nitrogen to the Chesapeake Bay surface waters prompted ANICA scientists to 

propose the establishment of an overwater precipitation chemistry site. The site was established 

in September 1995. The resulting data set will provide a first opportunity to evaluate the 

effectiveness of over-land based sampling for estimating over-water deposition to large 

waterbodies, and to test model outputs against actual data obtained over the target area. The 

project will provide measurements of wet deposition of nitrogen spe~ies to the waters of the 

Chesapeake Bay using a wet-only collector erected on Smith Island in the lower Bay. Samples 

will be collected and analyzed using the National Atmospheric Deposition Program's (NADP) 

- Atmospheric integrated Besearch Monitoring Network (NADPIAIRMoN) field and laboratory 

protocols. 

Wet deposition is the result of scavenging of airborne particles and trace gases by clouds, fog, 

condensation, and by the collection of other particles and gases by hydrometeors as they fall from 

the clouds in which they were formed. These processes are sometimes referred to as "in-cloud" 

and "sub-cloud" scavenging, or alternatively as "rainout" and "washout" respectively. In general, 

scavenging of nitrogen by precipitation processes is highly efficient. Concentrations in collected 

precipitation samples are easily measured, although rapid chemical reactions occurring after 

samples are collected can give rise to misleading concentration data if analysis is not performed 

soon after collection, or if adequate steps are not quickly taken to chemically preserve sample 

integrity. The most widely accepted method for precipitation sampling is the wet-only collector, 

which is designed to remain covered until precipitation is occurring and returns to covered 

condition after rainfall. To quantify trends in the wet deposition of stable chemical compounds, 

short-term deposition data are generally not required; ecosystems do not usually respond rapidly 

to changes in deposition. However, long-term (e.g. monthly) sampling is usually avoided 

because of difficulty in maintaining adequate quality control over samples that remain in the field 

for long periods of time. Many networks have adopted a one-week sampling protocol as a 

reasonable compromise between high sample quality and reasonable operational costs. Weekly 

sampling provides data that are quite adequate for long-term trend detection and for assessing 

ecosystem inputs for stable ions, but are limited in their utility for coupling with meteorological 

models, and are often useless for process-oriented studies. In addition, while many of the 

heretofore studied ions are relatively stable for periods of weeks or months, problems such as 

nitrogen loading to estuaries and other coastal ecosystems require even shorter period collections 

as well as special handling to adequately ensure sample stability. As the questions posed to the 
research community become more difficult, the demand for daily sampling is increasing. 

With the exception of organic nitrogen compounds, the analytical techniques for major nitrogen 

species in precipitation are well established and can be considered fairly routine. Most of the 

current debate over the appropriate approach for measurement of wet nitrogen deposition is 

centered around field-sampling protocols (i.e., the process by which the sample is collected and 

transported to the analytical laboratory). 

Objectives 

Field protocols for the major networks around the world have been developed over 40 years of 

experimentation and debate. In the United States, the national network is the NADP. As of 

1993, NADP consisted of 193 weekly sampling sites, and seven daily sampling sites (affiliated 

with the NOAA AIRMoN Program). The NADP weekly and AIRMoN sites have identical siting 

criteria for precipitation chemistry measurements, and all data are analyzed in the same 

laboratory using similar methodologies. The one major difference is that the weekly NADP 

samples are filtered at the laboratory to stabilize sample chemistry; AIRMoN samples are 

stabilized through continuous refrigeration beginning immediately after collection. In general, 

the site operator will visit the site on a daily basis. By evaluating the collector function record on 

each visit, the operator will check for precipitation during the previous 24 hours, excessive 

bucket lid openings other than during precipitation, and if more than one week has passed 

without a bucket change. If one of these events has occurred the site operator will change the 

bucket. If a sample has been collected, field chemistry (as appropriate) will be done, and the 

sample will be prepared and shipped to the central NADP analytical laboratory (the Illinois State 

Water Survey). The sample will be analyzed using NADPIAIRMoN guidelines. Quality 

assurance/quality control will be performed before the data is entered into the NADPIAIRMoN 

electronic database housed at Colorado State University. 

The goal is to produce two years of data on wet deposition of central nitrogen compounds 

(nitrates, nitrites, and ammonium) to the waters of the Chesapeake Bay, with daily time 

resolution. 
Wet Deposition of Organic Nitrogen 

Background 

Wet-deposition fluxes of inorganic N (primarily NO,- and NH,') to coastal eastern North America 

are well characterized and the corresponding dry-deposition fluxes, though substantially less 

certain, are reasonably constrained. However, the deposition fluxes of organic nitrogen (N,J 

compounds are very uncertain. The lack of reliable measurement techniques and the associated 

dearth of field data are responsible for the poor state of current understanding. Various estimates 

for the relative flux of organic versus total N via wet deposition range from <lo% to >60%. The 

four types of methods currently being evaluated for atmospheric investigations of No, are those 

commonly used to analyze total nitrogen (N,) in seawater. These methods include: persulfate wet 

chemical oxidation (most widely used), UV photo-oxidation, high-temperature oxidation, and 

high-temperature catalytic oxidation. In all cases, No, is determined by subtraction from N, the 

sum of the ammonium, nitrate, and nitrite concentrations. Recent findings (Suzuki, 1993) suggest 

that the agreement between methods is reasonably good. The pyro-cbemiluminescent method 

currently shows the most promise due to advantages of rapid and automated analysis, and small 

sample (100 pl) requirements. Other techniques are labor intensive and require approximately 

100 rnl of sample -- potentially a very serious constraint when studying small-volume precipitation 

events. With support from ANICA and the EPA Great Waters Program, the University of 

Virginia (UVa) has developed a pyro-chemiluminescent technique to reliably measure total N and 

organic N in dilute aqueous solutions, and is currently investigating sampling artifacts and 

assessing sample stability. 

Analytical Method 

Wet-only precipitation is sampled using an Aerochem Metrics collector. As indicated above, 

sampling techniques and sample stability assessments are currently under investigation; specific 

sampling and handling procedures may be refined as a result of these investigations. Preliminary 

results suggest that organic N in precipitation is very unstable; to generate representative data, it 

may be necessary to subsample precipitation events in stainless steel containers and to preserve 

samples immediately against microbial degradation. 

Samples are analyzed for NT using a modified ANTEK model 7000 analyzer. All N compounds 

are converted to NO via high-temperature combustion, and NO is subsequently quantified via 

chemiluminescence. Over the past several years, this approach has been used with increasing 

frequency to analyze atmospheric and marine samples. As described below, however, potentially 

serious problems may compromise resulting data. Few data generated using this approach have 

been published in the peer-reviewed literature. 

Initial studies by UVa revealed that data generated using a range of "standard" conditions 

(recommended for application by the manufacturer and by other users) and an off-the-shelf 

instrument (configured for application by the manufacturer) were subject to large, significant 
positive and negative artifacts; all compounds were not recovered with equal efficiency. The 

direction and magnitude of bias varied as a hnction of the chemical composition of the test 

solution and the corresponding method of calibration. "Standard" operating conditions also 

resulted in poor reproducibility and low precision. Because the organic fraction is calculated by 

difference, reliable results require highly precise and unbiased analytical data; performance using 

"standard" configurations and procedures was unacceptable. 

UVa subsequently modified the instrument and the analytical procedure and are now able to 

generate unbiased and highly precise results at expected concentrations for a representative range 

of test compounds including NH,', NO,', urea (CH4N20), and ethylamine (C2H,N). 

Proposed Research 

UVa has applied to several hnding sources for hnds to conduct a subsequent and more 

comprehensive analysis (i.e., over space and time) of NT, inorganic, and (by difference) No, in wet 

deposition to eastern North America and to the western North Atlantic-Ocean using this new and 

well-characterized technique. NH,' and NO, will be measured by automated colorimetry and ion 

chromatography, respectively, using standard procedures for the Global Precipitation Chemistry 

Project (GPCP) and the AirIOcean Chemistry Experiment (AEROCE); resulting inorganic data 

are precise to approximately +I-4% and unbiased. The above approach would comprise the most 

reliable and precise method currently available for measuring the wet-deposition flux of NT and 

Norg. 

The goal of this investigation will provide the first comprehensive assessment of the 

atmospheric deposition of No, in eastern North America and the northwestern Atlantic 

Ocean thereby providing critical information concerning atmospheric N inputs to the 

Chesapeake Bay and other coastal waters in polluted regions. 
Dry Deposition Inferential Method (DDIM) Measurements at Wye, Md 

Background 

As of 1992, the NOAA Dry Deposition Inferential Measurement (DDIM) network was composed 

of 1 1 dry deposition sites. In December 1992, a DDIM site was established at Wye, Md., 

constituting the second NOAAIDDIM site in the Chesapeake Bay watershed, the first being at 

Leading Ridge, Pa. Both Chesapeake Bay sites are collocated with NADP weekly and 

NADPIAIRMoN stations, thereby allowing estimates of total nitrate nitrogen deposition. The 

DDIM network was designed to develop methods of deposition estimation at a three core sites, 

and then expand these methods throughout the DDIM network. Concentrations of sulphur 

dioxide, particulate sulfate, particulate nitrate, and nitric acid are measured via heated inlet 

filterpacks. The filterpack samples are exposed for one week with an air flow of three liters per 

minute. Meteorological variables (e.g., wind speed and direction, standard deviation in wind 

direction, global radiation, air temperature and humidity, surface wetness, precipitation) are also 

measured at each site, thereby allowing dry deposition to be estimated via the inferential 

technique. These techniques were developed over several years of intensive research at the core 

network prior to network initialization. However, the core sites are not representative of the 

coastal environment, and it was not clear, a priori, if the DDIM method would work in a coastal 

areas. 

The DDIM Method 

This method estimates dry deposition using air concentration data and calculating deposition rate 

based on measurement of atmospheric and surface factors or by consideration of land-use type 

(i.e., forest, cropland, etc.). For nitrogen compounds, this method is applicable only to those 

species that can be considered to be depositing at all times -- primarily HNO,, but also particulate 

nitrate (p-NO,-; Meyers et al., 1989). These chemicals allow surface deposition fluxes to be 

treated as essentially uni-directional (toward the surface), and thereby inferred from atmospheric 

concentration data, provided that the characteristics of the situation in question can be formulated 

in terms of properties that can be measured. In this technique, the transfer coefficient is termed a 

deposition velocity (V,). The value of V, is computed from field observations and used to 

estimate the dry deposition rate (F,) from air concentration measurements C: 

Estimation of V, involves a balanced consideration of atmospheric and particle physics, 

chemistry, and biology (see Figure B.2). The deposition velocity is normally considered as an 

overall "conductance" of the pollutant to the surface and, consequently, the inverse of V, is 

described as the total resistance to pollutant transfer, RT. This basic "resistance analogy" 

commonly specifies four major resistances: 
Acrodynarnic 

Factors 

Near-Susfacc 

Phoretic 

Effects 

Quasi-Laminar 

Layer 

Factors 

Surface 

Propcstics 

Tusbulcnce 'l'usbulence "r" - - -7 

Slephan Flow 1 

I I Interception I 

7 Brownian Diffusion - - - + Brownian DiI'Susion 

I 

Slo~nata 

I 

Waxiness I 

Vestilurc 

I 

Exudaks 

Rcccptor 

I 

Welness 

I I 

Chc~nistry 

I 

Emissions 

Figure B.2. A representation of the sequence of mechanisms influencing the deposition from 

the atmosphere of trace gases (right side) and diffusing particles (left). Not all 

processes are identified. (adapted from Hicks, 1986). 
- an aerodynamic resistance, %, that is a fknction only of atmospheric properties, such as 

atmospheric turbulence and stratification; - a near surface "quasi-laminar" resistance, %, that relates to the diffusion of pollutants 

across the near-surface layers where molecular and Brownian properties are important; 

- a surface canopy, or residual, resistance, &, that expresses the consequences of the 

chemical, morphological, and biological processes influencing pollution adsorption or 

"capture" by the surface itselc 

- gravitational settling, Vg, as modified by particle growth due to humidity interactions, is 

used to incorporate particle dynamics into R, and % (note that Vg is zero for gases). 

It is important to note that these resistances are conceptually independent so that they may be 

considered in series, thereby allowing the calculation of V,: 

There are three major areas of concern with this approach: i) the accur-acy of the concentration 

data, ii) the accuracy of the deposition velocity, and iii) the applicability of the deposition velocity 

concept in the experimental circumstance. The first two issues have been and are currently being 

addressed by a variety of air chemistry and research programs; current estimates of the error 

associated with them is about k 25%. The third concern points to the conceptual unidirectionality of V, as a potentially severe limitation, important to both modeling and measuring 

programs. The V, concept is derived from relationships developed to describe turbulent transport 

to surfaces that are effectively horizontal and uniform. When considering non-uniform landscape 

patterns (i.e., checkerboard forest and croplands), edge effects will be of considerable importance. 

The mechanisms involved will be largely advective, once again making the problem three 

dimensional. This is an over-riding problem in that a one-dimensional description is used by 

almost all existing deposition models. It is especially a problem in the coastal zone where the 

majority of the landscape is broken and varied. 

Results 

Data from the Wye site have been collected, archived and analyzed from December 1992 through 

December 1994. These analyses revealed deposition rates which were similar to those reported 

from other DDIM stations in the region, and that dry deposition of nitrate (ICNO,/p-NO,) was 

approximately 46% of total nitrate deposition. However, fkrther analysis indicated that the filter 

pack (chemical concentration) data may be suspect due to artifacts associated with high ammonia 

and sea salt concentrations over Maryland's Eastern Shore. Additional studies are planned to 

quantifL errors associated with filterpack measurements in coastal areas. 
Atmospheric Nitrogen Speciation Measurements 

Background 

Reactive nitrogen compounds are emitted to the atmosphere through both natural and 

anthropogenic pathways, overwhelmingly (95%) as NO. Nitrogen oxide is highly reactive in the 

atmosphere and is transformed into a variety of higher oxides of nitrogen. Understanding these 

transformations and their by-products is crucial to the understanding of tropospheric ozone 

production, air quality, and atmospheric nitrogen effects on coastal ecosystems. Through 

ANICq NOMARL developed the ability to perform research quality measurements of nitrogen 

oxides and their associated chemicals (i.e., 0, and CO). Furthermore, several speciation 

experiments were performed, two of which are relevant to Chesapeake Bay. The first was a 

cooperative effort with the University of Maryland's Meteorology Department in September 19%. 

The second experiment, in August 1995, consisted of shipbourne nitrogen speciation 

investigations as part of the Atmospheric Exchange Over Lakes and Oceans (AEOLOS) 

Experiment in Chesapeake Bay. The University of Maryland performed a experiment 

investigation into NO,/NO, speciation from September 2-28, 1993 at Wye, Md., making 

simultaneous measurements of NO, NO,, NO,, 0,. Concurrently, NOMARL's Hybrid Single 

Particle Langrangian Integrated Trajectory (HY-SPLIT) model was used to run 24 hour "back 

trajectories in an attempt to determine the geographic history of the air-mass being sampled. 

Analytical Method 

The accurate determination of NO, speciation is an intricate and complex undertaking which 

necessitates the use of several experimental techniques. NO, NO,, and NO, may all be measured 

with a single instrument, a standard ozone chemiluminescence NO detector (Luke and Valigura, 

1996). The ozone chemiluminescence (CL) technique is, for all practical purposes, the only 

widely used method of measuring atmospheric levels of nitric oxide. The technique is a 

continuous measurement method based upon the detection of photons released through the 

reaction of ozone (0,) with NO. Ambient air is drawn into a reaction vessel at a controlled flow 

rate by a mechanical vacuum pump and mass flow controller. Ozone is generated within the 

instrument as a reagent by passing a flow of pure, dry oxygen through a high-voltage electrode; it 

is then directed into the reaction vessel where it reacts with NO in the sample flow to form NO,. 

Approximately 10% of the NO, is formed in an electronically excited state (NO,") (e.g., Fontijn et 

al., 1970), a fraction of which relaxes back to the ground state by emitting a photon. The 

broadband emission spectrum ranges in wavelength from about 600-3000 nm, and the photons are 

detected by a red-sensitive photomultiplier tube (PMT). Because thermal emission and 

amplification of electrons by the PMT can overwhelm detection of the low-energy photons, it is 

necessary to cool the PMT with dry ice or thermoelectric junctions to minimize background noise. 

As long as ozone is in great excess in the reaction chamber, the amount of light detected at the 

PMT is proportional to the mixing ratio of NO in the sample air stream and the instrument 

pumping speed. NO, (NO, = NO + NO,) is measured by first passing the air through a photolytic 

conversion cell, where a fraction of the ambient NO, is photolyzed to NO and subsequently 
detected. NO, is measured by first passing the ambient sample air through either a gold or 

molybdenum catalyst which efficiently reduces all NO, species to NO. The detector provides 

real-time, continuous output of NO, NO,, and NO, concentrations. 

Given the strong photochemical links between NO, and O,, ozone concentration was measured 

using continuous UV photometric technique. Carbon monoxide was also be measured using a 

continuous technique, gas filter correlation (GFC), non-dispersive infrared (NDIR) absorption. 

Carbon monoxide is one of several compounds which participate in the photochemical oxidation 

of NO, and production of ozone. It is also an excellent tracer of incomplete combustion and can 

provide information on the severity of pollution events. 

The HY-SPLIT Model 

Grouping of trajectories into common spatial clusters is a method to classifl different 

meteorological situations associated with pollutant transport from different source regions. These 

regimes can then be identified with specific periods of time, such as those associated with an air 

sample or deposition measurement. 

As with many models using gridded meteorological data fields, the trajectory calculations (HYSPLIT model; Draxler, 1992) follow a geometric approach. The trajectories' 3-dimensional 

motion is computed from the u,v, and o (dpldt) component winds output and archived every two 

hours from NOAA1s National Centers for Environmental Prediction's Nested Grid Model (NGM). 

The time series consists of twice-daily consecutive model forecast fields from +2 h after 

initialization to +12 h. Archives of the 2-hour fields are available since 1991 from the National 

Climatic Data Center (NCDC; reference TD-6140). The fields are given on a 180 krn polar 

sterographic grid at 10 model sigma levels from 0.982 to 0.434. There are about 4 levels within 

the boundary layer. 

Results 

The fraction of NO, which is most reactive is NO,. Air influenced by fresh NO, emissions will by 

characterized by high NO,/NO, ratio. Table B.3 shows that the mean ratio for the project was 

about 0.65. ~uring the day this ratio varied from a broad morning maximum of -0.80 to an 

afternoon minimum of <O.5O. Polluted air arriving at the site mixes downward to the surface 

when the sun rises and instability occurs, but photochemistry is still weak. Later in the day, 

photochemistry dominates and NO, is converted to higher oxides of nitrogen (e.g., HNO,). In the 

late afternoon to early evening, HNO, deposition combined with NO emissions from the soil lead 

to an increased ratio later in the day. 

Results from the HY-SPLIT model back trajectories gave some insight into the origin of 

pollutants arriving to the Wye site. Figures B.3 and B.4 show the outputs from six model runs; 

three low NO, ("clean") days and three high NO, ("dirty") days, respectively. Note that the air 

highest in NO, came from Pennsylvania or the Baltirnore~Washington region, while low-NO, air 
Figure B.3. The 48-hour back trajectories from Wye, Md. corresponding to periods of low 

measured NO, concentrations. 
Figure B.4. The 48-hour back trajectories from Wye, Md. corresponding to periods of high 

measured NO, concentrations. 
originated from the more rural south. Table B.4. contains the mean and observed maximum NO, 

mixing ratios during each 24-hour trajectory run. 

Table B.3. Basic 0,, CO, daytime NO, NO,, NO,, and NoJNO, statistics for data collected 

at Wve. Md. between Se~tember 2-28.1993. 

During the trajectory for September 1 1, the lowest CO/NOx and CO/NO, ratios were observed. 

The trajectory came from the industrial midwest. Relatively low CO mixing ratios coupled with 

high NO, mixing ratios suggest emissions from coal-burning power plants. Concurrent high SO, 

mixing ratios would further suggest that power plant emissions influence this particular 

trajectory. 

Mean 

Median 

Minimum 

Maximum 

Mid 67% 

Mid 90% 

Table B.4. Mean and maximum observed NO, mixing ratios for "Clean" and "Dirty" days 

measured at Wye, Md. between September 2-28,1993. 

I I 1 

0, ppb 

2 8 

26 

1 

76 

1 1-45 

3-59 

Day I Mean Concentration (ppb) I Maximum Concentration (ppb) 

CO ppb 

21 1 

196 

9 5 

628 

142-274 

117-334 

"Clean1' Days 

NO,,, ppb 

0.56 

.1 

-0 

14.78 

0.03-0.76 

0.02-2.14 

1.47 

9/27 

2.58 

NO, ppb 

4.20 

3.05 

0.52 

20.68 

1.21-7.39 

0.90-1 1.78 

"Dirtv" Davs 

2.03 3.28 

NO, PP~ 

7.67 

5.24 

1 .07 

48.66 

2.97-12.14 

2.01-20.81 

NOx/NOv 

0.65 

0.65 

0.26 

- 1 

0.40-0.84 

0.33-0.95 
Intercomparison of Filterpack and Denuder Techniques for HNO, Measurement 

Background 

Despite the importance of HNO, to overall N deposition, there are remarkably few suitable 

techniques for its measurement. Real-time instruments typically employ spectroscopic methods of 

detection, and are often complex, expensive, and power consuming. Integrated, or batch 

techniques (e.g., filterpacks) have been widely used due to their simplicity and low cost. 

However, the time resolution of these techniques is limited. Furthermore, artifact formation 

arising from collection or volatilization of HNO, from ammonium nitrate aerosols is a perennial 

worry in filterpack methods, and can pose a problem whenever long sampling times are used. In 

coastal areas the adsorption of HNO, on coarse-mode seasalt aerosols can carry the nitrate flux in 

large particles; therefore, traditional gas-phase filterpack HNO, measurements may be inadequate 

in coastal environments. 

The perceived need to evaluate the filterpack technique in coastal areas was reinforced by the 

results from the Wye, Md., Dry Deposition Inferential Measurement (DDIM) station which 

indicated that it may not be possible to use traditional inferential techniques for estimating dry 

deposition in the near-coastal environment. The DDIM station pushes the filterpack methodology 

to its theoretical limit by using low flow rates and a weekly sampling protocol. This is especially 

true in areas with high NH, and/or seasalt concentrations (both a problem on Maryland's Eastern 

Shore). In these areas the chemical equilibrium between HN03/NH,/NH4N03 on the initial 

particle filter can influence the amount of nitrogen trapped by the secondary nylon filter (see 

below). Through ANICA and the Great Waters Program denuders and support equipment have 

been acquired for a filterpaclddenuder intercomparison. 

Filter Pack 

The most widely used method for routine HNO, concentration and flux measurements is the nylon 

filterpack (FP) technique (e.g., Goldan et al., 1983). In this method, two filters are typically 

employed; a Teflon prefilter is typically used to trap particles (NhNO,, (NHJ2SO,, etc.) and pass 

HNO,, which is quantitatively scrubbed by reaction with basic -NH, active sites on the nylon 

filter. Both filters are extracted after collection and NO, is usually analyzed by ion 

chromatography. Fast air flow rates and filter pore sizes of 1 pm are typically used, and the openfaced, inlet-less filterpack assembly is faced directly into the wind to avoid surface losses of 

HNO,. The nylon filter technique showed no interferences in laboratory tests (Goldan et al., 

1983) and has been successhlly used in a variety of gradient measurements of HNO, flux (e.g., 

Huebert and Robert, 1985; Huebert et al., 1988). Side-by-side deployment of the Teflonlnylon 

filterpacks demonstrated a precision of ca 1%, more than adequate for the successhl 

measurement of HNO, gradients over Illinois grassland (Huebert et al., 1988). Provided that 

sample collection intervals are kept short, however, the problem with artifact formation from the 

collection and volatilization of ammonium nitrate aerosols can be minimized (e.g., Spicer et al., 

1982; Huebert et al., 1988). 
Denuders 

Denuder measurements of NH, are based upon the concept of selective scavenging by passing the 

sample airstream through an acid-coated tube (simple denuder) or concentric tubes (annular 

denuder). Gas-phase ammonia rapidly diffuses to the walls, is absorbed, and is extracted aRer 

sampling for analysis by ion chromatography (IC), colorimetry, or other methods. Ammoniumcontaining aerosols and vapor phase HNO, pass unimpeded through the denuder and are collected 

on Teflon and nylon backup filters (Luke and Valigura, 1996). 

The denuder method employed for this study will utilize a citric acid-coated denuder (CAD), 

followed by a traditional filter pack assembly, with extraction and analysis of ammonia (as NH,') 

by IC. An inverted quartz tube, 60-70 cm long, is suspended vertically from a sampling tower. 

Air is drawn through the denuder at a flow rate of about 2-10 standard liters per minute (SLM) 

using a small pump and electronic mass flow controller. Gas-phase ammonia in the sample 

airstream rapidly diffuses to the walls of the denuder and is absorbed by the citric acid coating. 

After sampling, a small aliquot of deionized water or 5 mM HCL is used to rinse the walls of the 

tube and extract the ammonia in the form of an ammonium salt. The backup filter is also 

extracted. Ammonium concentrations in the tube and filter extracts are quantified by ion 

chromatography, referenced to independent calibration standards. The concentration in air may 

be calculated from the measured (NH,'), air sampling rate, and length of the sampling interval. 

Although free of readily identifiable interferences, the CADIIC method may suffer from artifacts 

under some conditions. Turbulent particle impaction at the inlet and walls of the denuder, as well 

as particle settling, can artificially increase measured (NH,). These artifacts can be virtually 

eliminated, however, by maintaining laminar flow through the tube and positioning the denuder 

vertically (Ferrn, 1979). Potentially severe artifacts may arise from the evaporation of ammonium 

nitrate within the denuder as gas phase NH, is depleted at the denuder walls. The magnitude of 

this error will depend strongly upon temperature and residence time of the sample air within the 

denuder. While this error is difficult to quantify, Langford et al. (1989) estimated its magnitude 

under conditions of high aerosol loading using the measured NH,NO, evaporation rates of 

Richardson and Hightower (1987). At denuder residence times of 1 s (typical residence times for 

the research proposed here is less than 0.5 s) and temperatures of 25-35 "C, Langford et al. 

(1992) estimated that particle evaporation will introdace approximately 6% error in measured 

(NH,) at high aerosol concentrations ((NH,NO,)/O\TH,) = 70). At the lower aerosol loadings 

typical of the rural and remote troposphere, artifact formation from aerosol evaporation should be 

small. Exceptions may occur at locations near strong local NH, sources (such as agricultural 

areas) where aerosol loadings may be high. 

Previous Intercomparisons 

A multitude of HNO, intercomparison campaigns have been conducted over the last 10-1 5 years, 

and results have not always been consistent. In general, the various chemical techniques have 

shown substantial agreement at HNO, concentrations greater than a few ppbv. At lower 

concentrations the results begin to diverge. In a 1979 study in Claremont, Ca. (Spicer et al., 
1982), a variety of filter pack and denuder methods were compared with the NO, conversion 

difference and FTIR techniques (Luke and Valigura, 1996). At HNO, concentrations of 4-20 

ppbv, good agreement was found among most of the methods. Hering et al. (1988) compared the 

results of HNO, measurements using several integrated (denuder, thermal denuder, FP) and 

spectroscopic methods. At HN03 concentrations of several ppbv agreement was generally good, 

but scatter increased below 3 ppbv. Overall agreement among all methods was a factor of two. 

The demonstrated precision of the denuder method was poor, and the denuder method yielded 

consistently lower results than the spectroscopic methods used. Artifact formation arising from 

ammonium nitrate volatilization in filterpacks exposed for long periods of time resulted in 

overprediction of HNO, by FP techniques. However, for short sampling intervals the FP method 

agreed well with the spectroscopic techniques. In areas where the majority of nitrate is present as 

gas-phase nitric acid, intercomparison campaigns suggest that agreement between filterpack and 

denuder measurements of HNO, are generally good, owing to the lack of artifact formation from 

volatilization of ammonium nitrate aerosols (e.g., Benner et al., 1991). 

Measurement Strategies 

The first priority is to deploy the CAD system alongside the DDIM filterpack and conduct 

calibration, collection efficiency, and artifact formation tests to judge the suitability of the CAD 

technique for longer term measurements. Collection efficiency of the denuder system will be 

determined by spiking the ambient airflow with a quantified source of -N&, obtained either from a 

calibration gas mixture or a permeation tube. Measured efficiencies will be compared to those 

calculated from the Gormley-Kennedy relationship (e.g., Ferm, 1979; Bollinger et al., 1983). 

Side-by-side CADIfilterpacks will be deployed in parallel to assess the representativeness of daily 

integrated samples by comparing results from a single CADIfilter sample collected for 24 hours 

with those from 8 (6) denuders sampled for 3 (4) hours each. Daylnight effects could similarly be 

studied and may be important considerations when sampling in a humid environment where 

condensation may be a problem. 

The secondary priority is to evaluate the importance of NH,NO, artifact formation in high 

concentration areas such as Chesapeake Bay. Collection efficiency and "breakthrough" tests will 

be performed by connecting denuders in series and comparing the amounts of NH,' collected on 

front and back tubes. Artifact formation from particle impaction andlor evaporation may be 

explored by comparing results from parallel samplers, where a Teflon prefilter is placed at the 

inlet of one denuder and the outlet of the other. In a parallel effort, base-impregnated denuders 

for HNO, will be deployed alongside the CAD denuders, and will be used in conjunction with 

filterpack measurements to assess the importance of aerosol NH4N03 formation at the sampling 

sites and its effects upon long-term filterpack measurements of HNO, carried out routinely at the 

Wye Institute. Analytical recovery of the extraction and IC analysis will also be evaluated. 
Estimating Air- Water Transfer ofHNO, 

Background 

When considering the atmosphere as a pathway for nitrogen input, it is necessary to consider 

whether the nitrogen is transferred directly to the water surface, or indirectly to the watershed, 

with subsequent transport to the receiving waters. Several ongoing research programs seek to 

estimate the amount of nitrogen entering the coastal waters via precipitation and indirect 

deposition; however, rigorous studies of directly deposited nitrogen are few. Air-water exchange 

has been estimated for most nitrogen species over open ocean (Galloway, 1985; Duce et al., 

1991), however, these rates may not apply to coastal situations because coastal areas experience 

meteorological processes not found over the open ocean (NRC, 1992). 

To date, the primary obstacle to estimating coastal air-water nitrogen exchange has been the lack 

of near-surface, over-water coastal meteorological data. These data are needed to generate 

improved computer models, which will then be able to simulate existing small-scale coastal 

conditions. In response to this need, there has been an increased deployment of measurement 

buoys along the East Coast of the United States. One such network of buoys is the Chesapeake 

Bay Observing System (CBOS) owned and operated by the University of Maryland's Horn Point 

Laboratory. Through ANICA, the instrumentation aboard a CBOS buoy was augmented to 

include relative humidity and water temperature measurements. The results of this project are 

published in the Journal of Geophysical Research (Valigura, 1995). The two primary objectives 

were to: i) develop and evaluate an iterative bulk exchange model to estimate air-water exchange 

of heat, water and momentum from buoy data, and ii) use the model outputs to estimate air-water 

transfer rates of nitric acid (HNO,). 

The Iterative Bulk Exchange Model 

Because of a high affinity for water and relatively high ambient concentrations in coastal areas, 

HNO, is considered to be the primary nitrogen species of interest for deposition directly to water 

surfaces. Given its affinity for water, HNO, transfer can be considered uni-directional (i.e., 

downwards). Furthermore, for transfer to water, the quasi-boundary layer resistance (I&,) is small 

(Garratt and Hicks, 1973; Kanemasu et al., 1979) relative to the aerodynamic resistance (R,rnO3) 

even in very light wind conditions. Consequently, the arguments here will focus on R, mo3 alone, 

and the resistance form of the general flux (Fmo3) equation can be written 

where the surface concentration, [HNO,],, is taken to be zero and the deposition velocity, V, (m 

s-l), is the inverse of the aerodynamic resistance qmO3 (s m-I). 

Air-water exchange of sensible heat is similarly regulated by aerodynamic resistance (%d, 

allowing for the assumption that qmO3 is equivalent to %,. Using this assumption, it was 
therefore possible to use the heat transfer coefficient, estimated with general bulk-transfer 

equations, to estimate the deposition velocity of HNO, 

where D, is the dimensionless heat transfer coefficient, see below, and u, is the measured 

windspeed (m s-I) at height (2). 

Model Evaluation Results 

Three days of eddy correlation measurements of heat, moisture and momentum fluxes were 

collected on tower, boat, and airplane platforms from June 16-20, 1990 near NOAA's Looe Key 

National Marine Sanctuary in Florida (Crawford et al., 1993). During the first day, data 

collection was taken in shallow gulf waters (1 0 m), 500 m upwind of shore. During the next two 

days, data collection was performed 13.5 km offshore, 100 m outside the barrier reef in 25 m of 

water. Mean meteorological variables (wind speed, air temperature, and relative humidity) were 

recorded from all platforms, with water surface temperature measured by infrared temperature 

sensor from the boat, for the duration of the experiment. These mean data were incorporated into 

the bulk exchange model and the resulting output was compared against the eddy correlation data 

collected from the airplane (Crawford et al., 1993). 

Model versus measurement intercomparisons of friction velocity, latent heat flux, and sensible 

heat flux were quite favorable. Average differences between measured and modeled friction 

velocities and latent heat fluxes were small, h 1 cm and h 10 W mV2 respectively. Sensible heat 

fluxes were very small and intercomparisons were inconclusive. This was due to an apparent 

disconnect between eddy correlation data measured on the airplane and local water- surface data 

collected by boat. The disconnect can be attributed to the inherently local nature of the surface 

temperature measurements and the fact that eddy correlation integrates surface characteristics for 

some considerable distance upwind. The noise in the water surface temperature measurements 

was directly translated into noise in the model output, thereby resulting in the measurement 

versus model differences. Further comparisons are being conducted as data becomes available. 

Experimental Set-Up 

In late March 1992, the CBOS buoy was anchored in the north Chesapeake Bay, off Howell 

Point, Maryland (39.36"NY 76. low) for 3 periods between April 1992 and July 1994 (excluding 

the winter months) totaling 18 months. The CBOS buoy is owned and operated by the Horn 

Point Laboratory, Center for Environmental and Estuarine Studies, a member of the University of 

Maryland system. The buoy is of the wave-follower variety, and allowed data to be telemetered 

to a central computer system for remote access. The cross-section of the Bay narrows to 4.5 krn 

in the area of the buoy, making the fetch 4.5 km or greater in the geographical window from 210" 

to 50°, and 1 krn or less in the window from 5 1' to 209'. Water depth is variable across this 

section of Chesapeake Bay (average depth 5 m), but the buoy is anchored in the deep channel 
where the depth of water is 12.5 m. 

Deposition Velocity Estimation Results 

Deposition velocities were calculated for the approximately 25,000 10-minute periods that 

comprise the CBOS dataset to date. The overall frequency distribution is presented in Figure 

B.5. When viewed on shorter time scales, the distribution begins to change, as is shown for the 

first week in December 1993 (Figure B.5). The potential danger of using averagelgeneral 

deposition velocities in short term analysis becomes apparent when the actual time series of V, is 

reviewed for the same week in December 1993, Figure B.6. Meyers and Yuen (1987) found that 

concurrent, high resolution V, and concentration data improved estimates of 0, deposition, but 

did not improve estimates of SO, deposition. The primary reason for the difference between the 

two chemicals was that the measured variability in O, concentration was significantly correlated 

with the corresponding measured variability in V, (i.e, concentrations were proportional to 

deposition rates), and concentrations of SO, were not correlated with corresponding V, (i.e., 

concentrations were not proportional to deposition rate). It is unknown if HNO, concentrations 

([HNO,]) over Chesapeake Bay are correlated with V, ([HNO,] was not measured during this 

study). To illustrate the potential errors associated with using average or time series V,, a simple 

matrix analysis was performed using the December 1993 time series, Table B.5. Deposition was 

estimated using three different V, regimes (the actual times series V,, the time series average V,, 

Table B.5. Comparison between deposition (g HNO, me2) estimates (V, * [HNO,]) derived 

and the 1993 average V,), and three different HNO, concentrations representative of [HNO,] 

using different averaging schemes and the time series averages estimate for the first two 

weeks of December 1993 (% differences are shown in parenthesis). 

commonly measured within the Bay region. The concentrations were i) switched from a constant 

low (1.2 ppb) to a constant high (2.7 ppb) after the front, ii) switched from a constant high to a 

constant low after the front, and iii) maintained at the average (1.95 ppb). The deposition 

estimate derived from using the time series average V, and average [HNO,] was used as the 

reference value for intercomparisons, Table B.5. The analysis shows that if V, and [HNO,] are 

Low-High 

1.2-2.7 ppb 

High-Low 

2.7-1.2 ppb 

Average 

1.95 ppb 

Time Series V, 

Time Series Average V, 

(.0049 ms") 

1993 Annual Average V, 

(.0065 ms-') 

.485 ( 4.5) 

.429 (- 7.5) 

.567 ( 22.0) 

.443 (- 4.5) 

.499 ( 7.5) 

.661 ( 42.0) 

.464 ( 0.0) 

.464$ 

.614 ( 32.0) 
% .O 1.5 2.0 

Deposition Velocity (ern fl) 

Figure B.5. The frequency distribution for 18 months (excluding winter) of estimated 

deposition velocities in Chesapeake Bay (solid line) and the distribution for 1 week 

in December 1993 (dotted line). 
1 2 3 4 5 6 7 8 

Date 

Figure B.6. Ten-minute deposition velocities calculated for December 1-8, 1993. 

B-23 
not correlated, the error in deposition estimates is primarily driven by errors in estimating mean 

values of V, and [HNO,]. If they are correlated, determining the source the associated errors is 

more complex. If [HNO,] and V, are correlated, adequate estimation of deposition can only be 

obtained by concurrent measurements of [HNO,] and V,. These analyses demonstrate the need 

to determine if variability in HNO, concentration is significantly correlated with the 

corresponding variability in transfer rate to Chesapeake Bay. 

The V, distribution (Figure B.5) is likely to be conservative for two reasons. The first and most 

important reason is that the winter months are not accounted for because the buoy is removed 

due to ice. During the winter, air-water temperature differences are likely to be at a maximum 

(with water being consistently warmer than air), causing transfer rates to be at their peak. 

Therefore, any distribution that excludes this period is likely to be conservative. Another reason 

to believe that these estimates are conservative is that assuming equivalent transfer rates for 

HNO, and heat does not adequately account for scavenging of HNO, by aerosol water droplets 

and particles, which tend to increase deposition rates. 

There are theoretical limitations with this approach as well: lack of homogeneous conditions in 

the coastal zone and the inadequacy of similarity theory to describe turbulent conditions 

measured. Because the northern Chesapeake Bay is narrow, the local landscape tends to affect 

the meteorology. These effects make fetch assumptions unreasonable, thereby making it difficult 

to assume that the "local" buoy measurements are representative of any sizeable area. Estimating 

large-scale deposition patterns will require deployment of buoys at a range of different sites with 

concurrent mesoscale modeling efforts. The second theoretical consideration concerns the 

Monin-Obukhov similarity theory upon which the bulk transfer equations are based. This theory 

has been evaluated, and is considered valid, over a certain range (-1 zlL 1) of meteorological 

conditions. Beyond this range, the atmosphere is either extremely stratified so that the flow is 

effectively disconnected from the surface or so unstable that it is under free convection 

conditions. During the two years of data collection, there were periods where model outputs 

showed that conditions were too stable/unstable to be considered in the "normal" MoninObukhov frame. These periods were closely related to low wind speeds, as shown in Figure B.7 

for the month of April 1994. 

The approach used in this study has been shown to be applicable to SO, and should be applicable 

to other hygroscopic chemicals such as ammonia. To improve upon this technique, further eddy 

correlation projects must be performed to evaluate/modify the bulk transfer equation assumptions 

under low wind conditions. In future investigations, concurrent evaluation of HNO, 

concentrations will allow for the quantification of the actual differences between the time-series 

and the single-deposition velocity approaches. 
0 2 4 6 8 10 

Wind Speed (m/s) 

Figure B.7. Ten-minute Monin-Obukhov dimensionless stability estimates versus measured 

windspeed, calculated from the Chesapeake Bay Observing System data for April 

1994. Solid lines denote outer ranges of applicability for Monin-Obukhov 

similarity theory. 
Operntionnl RAMS 15 Km Forecasts over Chesapeake Bay 

Background 

The Regional Atmospheric Modelling System (RAMS) version 3a, developed at Colorado State 

University, has been configured to simulate mesoscale atmospheric circulations on both 

IBMl6000 workstations at the Air Resources Lab (ARL). The software developed at ARL allows 

the user to setup and initialize RAMS anywhere in the world using the ARL packed 

meteorological fields and global land and water surface data sets. The ARL modeling system is 

described in detail by McQueen et al. (1 994, 1995). 

RAMS Description 

Grid Structure 

RAMS utilizes an Arakawa-C grid stagger of the thermodynamic and momentum variables to 

reduce finite differencing error. An oblique stereographic horizontal grid coordinate can be 

specified. This varies from the normal polar stereographic coordinates in that the grid is true at 

the center of the RAMS domain with the "pole" position defined at that center as well. A twoway interactive multiple nested grid scheme exists so that scale interactions can be incorporated. 

This nested grid approach also allows for a finer mesh to resolve local-scale circulations in the 

area of interest and a coarser mesh outside this area. Simulations performed over the northern 

Chesapeake Bay employed the finest nested grid spacings to date (AX=2.5 km), Figure B.8. A 

15 km finest mesh grid spacing is used to produce operational 24-36 hour forecasts. Grid 

domains of the finest mesh have ranged from 50 to 600 km depending on the grid spacing. The 

model can be run in 1,2 or 3 dimensions. 

Initialization 

The model can be initialized from spatially inhomogeneous meteorological observations and, 

therefore, simulations are not limited to synoptically undisturbed cases. A program to ingest 

ARL packed National Centers for Environmental Prediction's (NCEP) model gridded fields into 

RAMS was developed. More than one input NCEP dataset can be used by combining these 

fields to create a complete input through the troposphere. Alternatively, NCEP model gridded 

data and surface and rawinsonde sites can be objectively analyzed to isentropic surfaces before 

being interpolated to the model grid using the RAMS ISAN package. Objective analysis follows 

the widely used Barnes approach. Currently, the model defaults to using NCEP model data on a 

2.5 degree latitude-longitude horizontal grid and mandatory pressure levels. 

The user can choose constant or spatially varying surfaces for RAMS ingest. Spatially varying 

surface variables such as soil moisture, soil and vegetation type, canopy temperature and water 

content, terrain height, land roughness, land percentage and water surface temperature can be 

ingested into RAMS on the model grid. Table B.6 summarizes the available ground surface data 

sets and their coverage. Over the U.S., surface data exists at a higher (30" latitude-longitude grid 

or about 1 km resolution) than available globally (10' latitude-longitude grid or about 18 km 
RAMS Fine grid domain (2KM) 

Figure B.8. Horizontal (vectors) and vertical (contours) windspeed simulations performed over 

the northern Chesapeake Bay employing the finest nested grid spacings (AX=2.5 

km). Note the high vertical motions on the western shore of the Bay indicating the 

beginnings of a "Bay Breeze" (Triangle indicates position of CBOS buoy). 
resolution). Soil moisture is predicted by first computing an Antecedent Precipitation Index 

(API) derived from the last few months of observed or model gridded precipitation archived at 

ARL. 

Table B.6. Summaw of surface data available for RAMS. 

Type 

Topography 

11 

SST 

soil type 

soil moisture 

Land use 

Roughness 

Coverage 

Global 

U.S. 

Global 

Global 

Global 

U.S. 

global 

U.S. 

global 

Operational Capabilities 

NMC forecasts 

Resolution 

10' latllon grid 

30" latllon grid 

lo latllon 

Range 

10 m 

10 m 

.1 K 

observed precip 

1 degree 

1 degree 

I1 

167 H-S 

categories 

1km 

Update I 

weekly 

daily 

- daily 

167 H-S 

categories 

RAMS has been used operationally for air quality dispersion forecasts. At ARL, RAMS is run in 

both a forecast and hindcast mode. Table B.7 summarizes the current operational configuration. 

Table B.7. RAMS operational configuration. 

RAMS is normally run over the Chesapeake Bay and Mid Atlantic region when it is not required 

for an emergency, exercises, or to support air quality experiments. The RAMS domain can easily 

be moved through the Real time Emergency Application and Display system (READY; Rolph 

Workstation 

Mid Atlantic1 

Ches. Bay 

Mid Atlantic1 

Ches. Bay 

Mode 

2400 km2 

680 km2 

2400 km2 

680 km2 

Location 

.33 

.16 

80 km 

20 km 

60 km 

15 km 

Domain cpdwall 

time 

AX 
et al., 1993; Draxler et a1.,1993) by simply specifling the center latitude and longitude of the 

coarse grid through the READY menu. On RISC2, RAMS is configured to produced 24-36 

hour forecasts twice-per-day after the latest ETA model fields are available. On RISC1, RAMS 

is configured in a hindcast mode while also assimilating four dimensionally surface wind data 

normally available every hour. An example of operational RAMS predicted winds and 

temperatures on the fine 15 km domain are shown in Figure B.9. RAMS outputs are available in 

real-time on a one week rotating archive on the ARL work stations. 
FN RAMS Operational Fine Grid (15 km) Archive 

Figure B.9. Operational 15 km RAMS simulations of northern Chesapeake Bay 

B-3 0 
Appendix C 

ANICA ASSOCIATED SCIENTISTS 

University of Delaware 

Thomas Church - College of Marine Studies: Member of the Chesapeake Bay 

Atmospheric Deposition Study (CBADS) group within the Chesapeake Bay 

Program. Specializing in wet deposition of nutrients and heavy metals. 

Jin Wu - Director, Air-Sea Interaction Laboratory: Investigating physical interactions 

during low wind speed conditions. 

University of Marvland 

Joel Baker - Chesapeake Biological Laboratory: Head of the CBADS group. Specializing 

in wet deposition of organic compounds, including nutrients. 

William Boicourt - Horn Point Environmental Laboratory: Head of the Chesapeake Bay 

Observational System (CBOS) buoy project. Specializing in the physical 

hydrodynamics of the Chesapeake Bay. 

Russell Brinsfield - Director, Wye Research Center: Investigating nitrogen cycling 

through cropped watersheds within the Chesapeake Bay area. 

Russell Dickerson - Department of Meteorology: Specialist in the measurement of 

atmospheric nitrogen species. 

John Ondov - Department of Chemistry, College Park: Member of the CBADS group 

within the Chesapeake Bay Program. Specializing in particle chemistry and 

transfer. 

Universih, of Virginia 

James Galloway - Professor, Department of Environmental Sciences: Investigating wet 

deposition of organic nitrogen to the coastal ocean. 

William Keene - Department of Environmental Sciences: Investigating wet deposition of 

organic nitrogen to the coastal ocean. Specializing in atmospheric chemistry. 

Universit_v of North Carolina 

Hans P'aerl - Professor, Institute of Marine Sciences: Specializing in nitrogen-production 

interactions in coastal waters. 

Smithsonian Environmental Research Center 

Dave Correll - Director: Specialist in forest watershed nutrient dynamics. 

Jess Parker - Forest Ecologist: Specialist in forest canopy Structure dynamics. 

Donald Weller - Forest Ecologist: Specialist in forest watershed dynamics modeling. 
Appendix D 

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Parameters. 

No. 2. Matthews, Geoffrey A. and Thomas J. Minello. 1994. Technology and Success in 

Restoration, Creation, and Enhancement of Spartina alternzjlora Marshes in the United States. 2 

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Bibliography of Synthesis Documents on Selected Coastal Ocean Topics. 

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No. 5. Lipton, Douglas W., Katharine F. Wellman, Isobel C. Sheifer and Rodney F. Weiher. 

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No. 6. Vestal, Barbara, Alison Rieser et al. 1995. Methodologies and Mechanisms for 

Management of Cumulative Coastal Environmental Impacts. Part I -- Synthesis, with Annotated 

Bibliography; Part I1 -- Development and Application of a Cumulative Impacts Assessment 

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No. 7. M~~rphy, Michael L. 1995. Forestry Impacts on Freshwater Habitat of Anadromous 

Salmonids in the Pacific Northwest and Alaska--Requirements for Protection and Restoration. 

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Involvement in California.