December 2006

Clean Air Status and Trends Network

(CASTNET)

2005 Annual Report

Prepared for:

U.S. Environmental Protection Agency

Office of Air and Radiation 

Clean Air Markets Division

Washington, DC

0

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1990199119921993199419951996199719981999200020012002200320042005

Year

kg/ha

Dry Sulfur Deposition

Dry Nitrogen Deposition

Air Quality Measurements Long-Term Trends Environmental Results
Clean Air Status and Trends Network 

(CASTNET) 

2005 Annual Report 

Prepared by: 

MACTEC Engineering and Consulting, Inc. 

Prepared for: 

U.S. Environmental Protection Agency 

Office of Air and Radiation 

Clean Air Markets Division 

Washington, D.C. 

December 2006 
CASTNET Annual Report – 2005 - i - Table of Contents 

Table of Contents

 Executive Summary .................................................................................................................... ii 

Chapter 1 CASTNET Overview .................................................................................................................. 1 

Locations of Monitoring Sites....................................................................................................... 3 

CASTNET Monitoring Sites on Tribal Lands .............................................................................. 4 

 Measurements Collected at CASTNET Sites................................................................................ 5 

 Calculating Dry Deposition........................................................................................................... 6 

 CASTNET Reference Sites........................................................................................................... 7 

 SO 

2 and NOx Emissions ................................................................................................................ 8 

Chapter 2 Atmospheric Concentrations.................................................................................................... 10 

Sulfur Dioxide............................................................................................................................. 10 

 Particulate Sulfate ....................................................................................................................... 12 

 Total Nitrate................................................................................................................................ 13 

 Particulate Ammonium ............................................................................................................... 15 

Continuous Measurements of Trace Concentrations of CO, NOy, and SO 

2 ................................ 16 

Chapter 3 Atmospheric Deposition ........................................................................................................... 17 

 Sulfur Deposition ........................................................................................................................ 18 

Contributors to Atmospheric Deposition .................................................................................... 22 

 Nitrogen Deposition.................................................................................................................... 23

Chapter 4 Ozone Concentrations............................................................................................................... 26

National Ambient Air Quality Standards for Ozone................................................................... 27 

Eight-Hour Ozone Concentrations.............................................................................................. 28

Sixteen-Year Trends ................................................................................................................... 30 

Nitrogen Oxides and Ozone........................................................................................................ 32 

Trends in Ozone Concentrations along the Washington, D.C. to Coastal Maine Corridor......... 36 

Chapter 5 Data Quality .............................................................................................................................. 38 

Precision...................................................................................................................................... 39 

Accuracy ..................................................................................................................................... 44 

Completeness .............................................................................................................................. 46 

 Laboratory Intercomparison Studies ........................................................................................... 47 

Conclusion .................................................................................................................................. 48 

References .................................................................................................................................................. R-1 

Appendix A Significant Events During 2005 

Appendix B Locational and Operational Characteristics of CASTNET Sites 

Appendix C Acronyms and Abbreviations 

On the cover: 

The site pictured is Parsons, WV (PAR107). 

The graph depicts mean dry deposition values from the 34 CASTNET reference sites (see page 7). 
CASTNET Annual Report – 2005 - ii - Executive Summary 

Executive Summary 

Created by the Environmental Protection Agency (EPA) to establish long-term monitoring of air 

quality and meteorological conditions in rural areas, the Clean Air Status and Trends Network 

(CASTNET) began operation in 1991. CASTNET measures rural, regionally representative 

concentrations of sulfur and nitrogen species and ozone in order to evaluate the effectiveness of 

national and regional air pollution control programs. 

Key Results through 2005 

♦ Mean annual sulfur dioxide (SO 

2) and particulate sulfate (SO2-4 ) concentrations aggregated 

over the 34 eastern reference sites have declined significantly over the 16-year period 

1990 through 2005. 

♦ Over the 16-year period, wet, dry, and total deposition of atmospheric sulfur have 

declined. 

♦ Mean annual concentrations of total nitrate (nitric acid plus particulate nitrate) showed 

almost no change from 1990 through 2000. Since then, total nitrate has declined 

approximately 10 percent. 

♦ Estimates of wet, dry, and total nitrogen deposition show no significant trend over the 16 

years. However, the data suggest a slight decline in dry nitrogen deposition and in mean 

nitrogen concentrations in precipitation since 1999. 

♦ The median fourth highest daily maximum 8-hour ozone concentration for 2005 was the 

second lowest in the history of the network despite the return to normal weather 

conditions during the ozone season. The recent decline in rural ozone and nitrate levels 

has been attributed to the documented decline in nitrogen oxides (NOx) emissions as well 

as weather conditions. Nitrogen oxides emissions in the eastern United States have 

declined over the last several years because of the Acid Rain Program, EPA’s NOx State 

Implementation Plan (SIP) Call, and several other NOx control programs. 

Significant operational events during 2005 are listed in Appendix A. The location and 

operational characteristics of each site by state is provided in Appendix B. Appendix C provides 

a list of acronyms and abbreviations. 

Mackville, KY (MCK131/231) 
CASTNET Annual Report – 2005 - iii - Executive Summary 

Initiated: 

Network Summary 

1987 

Number of Sites: 

 (as of December 2005) 

87 

Sampling Schedule: Filters exposed over seven days to produce 7-day averages 

(Tuesday to Tuesday) 

Ambient Measurements: 

 Gaseous: Sulfur Dioxide (SO 

2), Nitric Acid (HNO 3), Ozone (O 3) [hourly] 

 Particulate: Sulfate (SO2-

4 ), Nitrate (NO3), Ammonium (NH+ 4 ), Other 

relevant ions 

Meteorological 

Parameters: 

 (Hourly averages) 

Temperature (2 and 9 meters), Wind Speed and Direction, 

Standard Deviation of Wind Direction (Sigma Theta), Solar 

Radiation, Relative Humidity, Precipitation, Surface Wetness 

Land Surface Features: Leaf Area Index and Vegetation, Land Use, Terrain 

Note: 

 The National Dry Deposition Network (NDDN) was established in 1986 and field measurements began in 1987. With the passage of the 

1990 Clean Air Act Amendments, NDDN was subsumed by CASTNET in 1991. 
CASTNET Annual Report – 2005 1 Chapter 1: CASTNET Overview

Chapter 1: CASTNET Overview

The CASTNET database is available to the public via EPA’s CASTNET data web page:

www.epa.gov/castnet/data. 

The 1990 Clean Air Act Amendments (CAAA) mandated significant reductions in sulfur dioxide 

(SO 

2) and nitrogen oxides (NOx) emissions from electric utility plants. In addition, the CAAA 

directed that a national air monitoring network be established to track real-world environmental 

results as the reductions were implemented. The Clean Air Status and Trends Network 

(CASTNET) is a national air monitoring network that provides data for determining relationships 

between emissions, air quality, deposition, and ecological effects. This report summarizes 

CASTNET monitoring activities and the resulting concentration and deposition data for 2005. 

CASTNET started as the National Dry Deposition Network (NDDN), which began operation in 

1986. The 50 NDDN sites were transferred to CASTNET in 1991. One of the major strengths of 

CASTNET is the long-term data record with more than 40 sites operating since the late 1980s. 

The network, as of December 2005, included 87 monitoring stations at 83 site locations 

throughout the continental United States and Alaska. CASTNET sites measure rural, regionally 

representative concentrations of sulfur and nitrogen species and ozone (O 

3) in order to detect and 

quantify trends, define the spatial distribution of rural pollutants, and estimate dry deposition 

fluxes. The goal of estimating dry deposition also requires the measurement of several 

meteorological parameters and information on vegetation and land use. 

CASTNET is a national air 

monitoring network that provides 

data for determining relationships 

between emissions, air quality, 

deposition, and ecological effects.

Perkinstown, WI (PRK134) 
CASTNET Annual Report – 2005 2 Chapter 1: CASTNET Overview

To satisfy the CASTNET objectives and to support the investigation of the relationships between 

emissions and concentrations/depositions, efforts were made to select regionally representative 

sites, especially in the eastern United States. "Regionally representative" refers to the overall 

similarity – in terms of air pollutant concentrations and land use – of the site to a characteristic 

area, typically 100 kilometers (km) by 100 km, surrounding the site. For the western United 

States, the limited number of sites and higher geographic diversity preclude rigorous 

determination of spatial patterns. Therefore, site selection focused on locations where specific 

research issues could be addressed and where natural resources were at risk (e.g., national parks). 

CASTNET is sponsored by the Environmental Protection Agency (EPA) and the National Park 

Service (NPS). NPS began its participation in CASTNET in 1994 under an agreement with EPA. 

NPS is responsible for the protection and enhancement of air quality and related values in 

national parks and wilderness areas. The number of NPS-sponsored CASTNET sites was 27 as 

of the end of 2005. In addition to EPA and NPS, the principal sponsors, CASTNET operates in 

partnership with other rural long-term monitoring networks: 

♦ National Atmospheric Deposition Program/National Trends Network (NADP/NTN)

operates monitoring stations with wet deposition samplers to measure the concentrations 

and deposition rates of air pollutants that are removed from the atmosphere by 

precipitation. NADP/NTN operates wet deposition samplers at or near virtually every 

CASTNET site. 

♦ The Canadian Air and Precipitation Monitoring Network (CAPMoN) operates 28 

measurement sites throughout Canada and one in the United States. CASTNET and 

CAPMoN both operate samplers at monitoring stations in Ontario, Canada and also at 

Pennsylvania State University. 

♦ The Interagency Monitoring of Protected Visual Environments (IMPROVE)

measures aerosol pollutants near more than 30 CASTNET sites. IMPROVE measures 

particulate air pollutants that affect visibility and visual air quality. 

♦ Mercury Deposition Network (MDN) samplers are operated at multiple CASTNET 

sites. MDN samplers measure mercury in precipitation. 

State agencies also operate special purpose air pollutant measurement devices at some 

CASTNET sites. EPA uses CASTNET in conjunction with these other long-term monitoring 

networks to assess the effectiveness of national and regional air pollution control programs. 

Additional information, previous annual reports, and other CASTNET documents can be found 

on the EPA Web site, www.epa.gov/castnet. The CASTNET database is also available to the 

public by accessing the "Data" link on EPA's CASTNET Web page. The Web site provides 

archives of the concentration and deposition data. Fully validated data are generally available 

approximately ten months following collection. 
CASTNET Annual Report – 2005 3 Chapter 1: CASTNET Overview

Locations of Monitoring Sites 

Figure 1-1 shows the locations of CASTNET monitoring sites as of December 2005. Eightyseven sites were operational at 83 distinct locations. Most CASTNET sites are located in rural or 

remote locations away from pollution emission sources and heavily populated areas. Appendix B 

provides the location and operational characteristics of each site by state, including information 

on start date, latitude, longitude, elevation, and the types of measurements taken at each site. For 

the purposes of this report, CASTNET sites are called “western” or “eastern” depending on 

whether they are west or east of 100 degrees west longitude. The line runs north to south 

dividing the states of North and South Dakota, Nebraska, Kansas, Oklahoma, and Texas. 

Figure 1-1 CASTNET Sites as of December 2005 
CASTNET Annual Report – 2005 4 Chapter 1: CASTNET Overview

CASTNET Monitoring Sites on Tribal Lands 

Three CASTNET monitoring sites are located on tribal 

lands as a result of a unique cooperative effort among EPA 

Headquarters (HQ), EPA Regions, tribal governments, and 

the Inter-Tribal Environmental Council (ITEC), a non-profit 

agency which provides member tribes with technical 

support and training in environmental fields. This 

collaborative effort has resulted in monitoring sites 

operating on the tribal lands of the Cherokee Nation in 

eastern Oklahoma (CHE185), the Alabama-Coushatta in 

eastern Texas (ALC188), and the Santee Sioux in northern 

Nebraska (SAN189). 

All three tribes initially received grants from EPA Regions 6 

and 7 to establish sites and purchase monitoring equipment. 

EPA Regional staff and ITEC then worked with the local 

tribal environmental staff to help with the installation of the 

site, operation of instruments, and the interpretation of results. EPA HQ and Regions continue to 

support the tribes in the operation, instrument calibration, and maintenance of each site as part of 

CASTNET. 

Having CASTNET monitoring sites on tribal lands provides benefits to both tribes and EPA. For 

the tribes involved, it enhances their ability to develop and run their own environmental 

programs that help to protect their communities and environment. Locating these sites on tribal 

lands also helps EPA (both HQ and Regions) obtain regional data that are used to monitor longterm trends in air pollution and understand the behavior of atmospheric pollutants. 

Paynes Prairie State Park, FL 
CASTNET Annual Report – 2005 5 Chapter 1: CASTNET Overview

Measurements Collected at CASTNET Sites 

CASTNET was designed primarily to measure seasonal and annual average concentrations and 

depositions over many years. Consequently, measurement of weekly average concentrations was 

selected as the basic sampling strategy. Over the course of the week, air is drawn through a 

three-stage filter pack (Figure 1-2) at a controlled flow rate to collect air pollutants in the form of 

gases and particles. The first stage of the filter pack encloses a Teflon® filter, the second a nylon 

filter, and the third holds two potassium carbonate (K 

2CO 3)-impregnated cellulose filters. The 

filter pack is changed out each Tuesday and shipped to the analytical chemistry laboratory 

for analysis. 

Figure 1-2 Three-Stage Filter Pack 

CASTNET measures concentrations of sulfur in the form of 

sulfur dioxide (SO2) and sulfate (SO2-

4 ) and nitrogen as 

nitrate (NO3), nitric acid (HNO3), and ammonium (NH+ 

4 ). In 

addition, it measures concentrations of chloride (Cl –), 

calcium (Ca2+), sodium (Na +), magnesium (Mg2+), and 

potassium (K +). Sulfate, NH+ 

4 , NO3, Cl –, and the earth 

metals are collected on the Teflon® filter. The nylon filter 

collects HNO3 and some SO2 . The cellulose filters collect 

the remaining SO2. 

Previous studies have suggested that the CASTNET filter 

pack system overestimates HNO3 and underestimates 

particulate NO3 and NH+ 

4 . This suggestion is based on the 

hypothesis that typically a fraction of the ammonium nitrate 

(NH4NO3) collected on the Teflon® filter dissociates to 

ammonia (NH 

3). Also, NH4NO3 can react with acid sulfate 

particles on the Teflon® filter to produce HNO3. Data from 

CASTNET and three other measurement programs 

CASTNET Ambient 

Measurements

 Sulfur dioxide (SO2) 

 Particulate sulfate (SO2-

4 ) 

 Particulate nitrate (NO3) 

 Nitric acid (HNO3) 

 Particulate ammonium (NH+ 

4 ) 

 Particulate calcium (Ca2+) 

 Particulate sodium (Na +) 

 Particulate magnesium (Mg2+) 

 Particulate potassium (K +) 

 Particulate chloride (Cl –) 

 Ozone (O3) 

 Meteorological variables and 

information on land use and 

vegetation 
CASTNET Annual Report – 2005 6 Chapter 1: CASTNET Overview

(e.g., Ames, et al., 2001) are being used to address this hypothesis and to estimate uncertainties 

in CASTNET filter pack measurements of HNO3, NO3, and NH+ 

4 on a seasonal, annual, and 

geographic basis. Information from these analyses will be available in late 2006. Preliminary 

results (Rogers, et al., 2006b) indicate that total nitrogen measurements are comparable among 

different monitoring programs but that differences exist among measurements of individual 

species (e.g., NO3). 

CASTNET also measures ozone, one of the major components of smog. In addition to the air 

pollutants, CASTNET sites record meteorological measurements of temperature, solar radiation, 

relative humidity, precipitation, wind speed and direction, and surface wetness. These 

meteorological measurements are used to gauge the transport of air pollutants and as input to the 

mathematical model (the Multi-Layer Model or MLM) used for estimating dry deposition to 

ecosystems in the atmospheric boundary layer. The ozone and meteorological measurements are 

recorded continuously and archived as hourly averages. 

Calculating Dry Deposition 

The original network design was based on the assumption that dry deposition or flux could be 

estimated as the linear product of measured pollutant concentration (C) and modeled deposition 

velocity (Vd): 

Flux = C x Vd

Measured atmospheric concentrations are calculated based on the mass of each analyte in each 

filter extract and the volume of air sampled. The rate of deposition of a pollutant, also known as 

deposition velocity, is influenced by meteorological conditions, vegetation, and chemistry. Dry 

deposition processes are modeled as resistances to deposition. The deposition velocity values are 

calculated for each hour of each year using the mathematical computer model, the Multi-Layer 

Model (MLM). The MLM was described by Meyers et al. (1998) and Finkelstein et al. (2000). 

An improved version of the MLM (Schwede, 2006) will be delivered to MACTEC during 2006. 

This version includes changes to the soil moisture factor, which affects the stomatal and soil 

resistances (see Figure 1-3), and to the radiation algorithm, which also affects the stomatal 

resistance. The data used in the MLM to estimate dry deposition are derived from meteorological 

measurements and pollutant concentrations taken at the site together with an estimation of the 

vegetation leaf-out and leaf area index (LAI). The schematic of the MLM in Figure 1-3 shows 

the relationships among the various resistances and illustrates the meteorological and other data 

that are required as model input. 
CASTNET Annual Report – 2005 7 Chapter 1: CASTNET Overview

Figure 1-3 Multi-Layer Model 

CASTNET Reference Sites 

Chapters 2 through 4 present maps 

illustrating the magnitude of pollutant 

concentrations and deposition fluxes across 

the United States. In addition, 

measurements from 34 CASTNET 

reference sites (Figure 1-4) were analyzed 

for each pollutant in order to determine 

trends in concentrations and trends in rates 

of dry, wet, and total deposition. These 34 

sites have been reporting CASTNET 

measurements since at least 1990 and are 

used for determining long-term trends. The 

reference sites were selected using criteria 

similar to those used by EPA in its 

National Air Quality and Emission Trends 

Report (2000). The criteria include site 

longevity and data completeness. EPA’s 

procedures to interpolate and extrapolate 

quarterly mean data were also used. In 

chapters 2 through 4, the data from the 34 

reference sites were aggregated and then 

presented using box plots for the period 

1990 through 2005. 

Figure 1-4 CASTNET Reference Sites 

Multi-Layer Model (MLM)

Flux =

1/Vd = 

ra = turbulence

ra, soil = turbulence near soil

rb = thin layer at surface

rcut = cuticular

rs = stomatal

rsoil = soil

1

11 1

s b cut b a soil soil

a

rr r r r r

r

+

+

+

+

+

+

,

VxC d

rb

ra

rsoil

Temp, RH, 

SR, LAI

Wind Speed, 

Sigma Theta

Wetness,

Precip

ra, soil

rb

rcut rs
CASTNET Annual Report – 2005 8 Chapter 1: CASTNET Overview

SO 

2 and NO x Emissions 

The Acid Rain program (ARP), established under Title IV of the 1990 Clean Air Act 

Amendments, requires major reductions of sulfur dioxide (SO 

2) and nitrogen oxides (NOx) 

emissions from the electric power industry. The SO 

2 program sets a permanent cap on the total 

amount of SO 

2 that may be emitted by electric generating units in the contiguous United States. 

The program began in 1995 and is being phased in, with the final 2010 SO 

2 cap set at 8.95 

million tons, a level equal to about one-half of the emissions from the power sector in 1980. 

Using a market-based cap and trade mechanism to reduce SO 

2 emissions allows flexibility for 

individual combustion units to select their own methods of compliance. Currently, one allowance 

provides a regulated unit limited authorization to emit one ton of SO 

2. The Clean Air Act 

allocates allowances to regulated units based on historic fuel consumption and specific emission 

rates prior to the start of the program. The total allowances allocated for each year equal the SO 

2

emission cap. The program encourages early reductions by allowing sources to bank unused 

allowances in one year and use them in a later year. 

The ARP has closer to a traditional approach to achieve NOx emission reductions. Rate-based 

limits apply to most of the coal-fired electric utility boilers subject to the ARP. No nationwide 

cap has been placed on NOx emissions. Other NOx emissions control programs have resulted in 

significant reductions in NOx emissions during the ozone season (see Chapter 4). Two prominent 

control programs are the Ozone Transport Commission (OTC) NOx Budget (1999-2002), and the 

NOx State Implementation Plan (SIP) Call, which began in 2003 and will continue through 2007. 

The ARP is composed of two phases for SO 

2 and NOx. Phase I applied primarily to the largest 

coal-fired electric generation sources from 1995 through 1999 for SO 

2 and from 1996 through 

1999 for NOx. Phase II for both pollutants began in 2000. In 2005, the SO 

2 Phase II requirements 

applied to 3,456 operating units; the Phase II NOx requirements applied to 982 of those operating 

units that are ≥ 25 megawatts and burned coal between 1990 and 1995 (EPA, 2005a). 

Figure 1-5 presents state-by-state total annual SO2 and NOx emissions for Phase I and Phase II 

electric utility plants for 2005. The heaviest emissions occurred in the eastern United States with 

major SO2 sources centered around the Ohio River Valley. 
CASTNET Annual Report – 2005 9 Chapter 1: CASTNET Overview

Figure 1-5 Annual Utility SO 

2 and NOx Emissions (Phase I and Phase II Plants only) for 2005 

2005 Annual Emissions

(thousand short tons)

1,000

Sulfur Dioxide

Nitrogen Oxide

2005 Annual Emissions

(thousand short tons)

1,000

Sulfur Dioxide

Nitrogen Oxide
 

CASTNET Annual Report – 2005 10 Chapter 2: Atmospheric Concentrations

Chapter 2: 

Atmospheric Concentrations 

This chapter presents maps illustrating the geographic distribution and magnitude of annual 

mean concentrations across the United States. Maps are provided for sulfur dioxide (SO 

2), sulfate 

(SO2-

4 ), total nitrate (NO3), and ammonium (NH+ 4 ) concentrations. Maps of other filter pack 

measurements are provided in CASTNET quarterly reports (MACTEC, 2005b; 2005c; 2006a; 

2006c). In addition, concentration data from the 34 CASTNET reference sites (Figure 1-4) were 

analyzed to determine any trends in concentrations over the period 1990–2005. The data from 

the 34 reference sites are presented using box plots for each year of the 16-year period. 

Sulfur Dioxide 

Figure 2-1 presents annual mean sulfur dioxide (SO 

2) concentrations for 2005. The map shows a 

large region in the eastern United States with concentrations greater than or equal to 

5.0 micrograms per cubic meter (μg/m3). The region extends from southwestern Illinois and 

western Kentucky to eastern Michigan to New Jersey, Maryland, and Virginia. Concentrations 

above 5.0 μg/m3

 were also observed at Sand Mountain, AL (SND152) and Georgia Station, GA 

(GAS153). Several sites along and downwind of the Ohio River Valley recorded SO 

2

concentrations in excess of 10.0 μg/m3. The Ohio River Valley is the major SO 

2 emission source 

region (see Figure 1-5) in the United States. The single highest SO 

2 concentration (16.2 μg/m3

) 

was measured in eastern Ohio at Quaker City (QAK172). Only three western sites (i.e., sites 

west of 100 degrees west longitude) measured an annual mean SO 

2 concentration greater than 

CASTNET uses filter pack technology to measure concentrations of sulfur dioxide (SO 

2), 

sulfate (SO2-

4 ), nitric acid (HNO 3), nitrate (NO3), ammonium (NH+ 4 ), chloride (Cl –), and 

several earth metals. Since 1990, measured concentrations of sulfur species have generally 

decreased. However, annual mean SO 

2 and SO2-4 concentrations increased in 2005 relative 

to 2004. There were no concurrent increases in electric utility emissions in the eastern 

United States. Concentrations of nitrogen species remained relatively steady from 1990 

until 2000 when they began a slow decline. However, mean annual total nitrate and NH+ 

4

concentrations increased in 2005.

Cedar Creek State Park, WV (CDR119) 
 

CASTNET Annual Report – 2005 11 Chapter 2: Atmospheric Concentrations

1.0 μg/m3. These sites include Theodore Roosevelt National Park, ND (THR422), Petrified 

Forest National Park, AZ (PET427), and Sequoia National Park, CA (SEK430). 

Figure 2-2 provides box plots that show the 1990–2005 trend in annual mean SO 

2 concentrations 

aggregated over the 34 reference sites. The diagram shows an overall downward trend with some 

interannual changes. The 2005 mean concentration was slightly higher than the 2004 level. 

Three-year means for 1990-1992 and 2003–2005 were 9.0 μg/m3 and 5.9 μg/m3, respectively. 

This change demonstrates a significant reduction of 34 percent in annual mean SO 

2

concentrations. 

Figure 2-1 Annual Mean SO 

2 Concentrations (μg/m3

) for 2005 

Figure 2-2 Trend in Annual Mean SO 

2 Concentrations (μg/m3

) – Eastern United States 

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CASTNET Annual Report – 2005 12 Chapter 2: Atmospheric Concentrations

Particulate Sulfate 

A map of annual mean sulfate (SO2-

4 ) concentrations for 2005 is presented in Figure 2-3. The map 

shows a region of concentrations greater than or equal to 5.0 μg/m3 along the Ohio River Valley 

from western Kentucky to southwestern Pennsylvania. An annual concentration of 5.1 μg/m3

also was recorded at SND152, AL. Sulfate concentrations were generally higher in 2005 than in 

2004. In 2004 only one site recorded a value above 5.0 μg/m3

. That site was QAK172, OH, 

which also recorded the highest concentration of 5.6 μg/m3

 in 2005. Sulfate concentrations 

greater than or equal to 1.0 μg/m3 were measured at five sites in California and along the 

southern tier to Chiricahua National Monument, AZ (CHA467) and Big Bend National Park, TX 

(BBE401). The CASTNET site in North Dakota (THR422) also measured a SO2-

4 level of 

1.0 μg/m3. The five relatively high SO2-

4 concentrations in California were higher than the 

respective SO 

2 levels for the same sites. 

Figure 2-4 provides box plots of 2005 annual mean SO2-

4 data from the CASTNET eastern 

reference sites in order to illustrate the trend in atmospheric sulfate. Overall, the figure depicts a 

significant reduction in SO2-

4 over the last 16 years with some interannual changes. The 2005 

mean level was higher than the 2004 value. The difference between 3-year means at the 

beginning and end of the period is 23 percent, a change from 5.4 μg/m3

 for 1990–1992 to 

4.2 μg/m3

 for 2003–2005. 

Figure 2-3 Annual Mean SO2-

4 Concentrations (μg/m3

) for 2005 
 

CASTNET Annual Report – 2005 13 Chapter 2: Atmospheric Concentrations

Figure 2-4 Trend in Annual Mean SO2-

4 Concentrations (μg/m3

) – Eastern United States 

Total Nitrate 

Figure 2-5 provides a map of annual mean total nitrate (NO3) concentrations for 2005. Total NO3

is defined as the sum of gaseous nitric acid (HNO 

3) and particulate NO3. Total NO3 better 

measures the response to changes in nitrogen oxides (NOx) emissions than either of its 

constituents alone. Also, the individual constituents are thought to include measurement 

uncertainties. EPA is currently sponsoring a work assignment to investigate the uncertainties in 

CASTNET HNO 

3 and NO3 measurements and to compare CASTNET measurements with 

nitrogen data from other networks. Final results of this study will be presented in the CASTNET 

2006 Annual Report and in a separate project report and/or paper. 

The map in Figure 2-5 shows a complex pattern of total nitrate concentrations along the 

Appalachian chain from Georgia to eastern Ohio and Pennsylvania. Mean concentrations ranged 

from 0.8 μg/m3 at the CASTNET site at Coweeta, NC (COW137) to 3.5 μg/m3 at QAK172, OH. 

The geographic variability in concentrations is caused by changes in the elevations of the 

monitoring stations and the associated differences in deposition velocities, inversion heights, and 

exposure to fresh nitric oxide emissions. The highest annual mean total nitrate values were 

recorded in Illinois, Indiana, and Ohio. Seven sites measured concentrations greater than or equal 

to 4.0 μg/m3

. Concentrations greater than or equal to 4.0 μg/m3 were also observed at 

Arendtsville, PA (ARE128) and Blackwater Wildlife Refuge, MD (BWR139). Three CASTNET 

sites in California measured total nitrate concentrations above 3.0 μg/m3

. One of these sites, 

SEK430, is located in the Sierra Nevada Mountains adjacent to the agricultural Central Valley. 

The other two sites -- Converse Station (CON186) and Joshua Tree National Monument 

(JOT403) -- are located downwind of the Los Angeles Basin. 

Box plots of annual total nitrate values from the 34 CASTNET reference sites are provided in 

Figure 2-6. The data show a decline from 2000 to 2004 but a slight increase in 2005. The overall 

trend depicts a 12 percent reduction in total nitrate from 1990-1992 to 2003-2005. 

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CASTNET Annual Report – 2005 14 Chapter 2: Atmospheric Concentrations

Figure 2-5 Annual Mean Total Nitrate (NO3 + HNO 

3) Concentrations (μg/m3

) for 2005 

Figure 2-6 Trend in Annual Total Nitrate (NO3 + HNO) Concentrations (μg/m3) – 

 Eastern United States 

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10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
 

CASTNET Annual Report – 2005 15 Chapter 2: Atmospheric Concentrations

Particulate Ammonium 

A map of annual mean ammonium (NH+ 

4 ) concentrations is presented in Figure 2-7. The map 

shows annual levels greater than or equal to 2.0 μg/m3

 in the agricultural states of Illinois, 

Indiana, and Ohio and also at three sites representative of agricultural areas in Pennsylvania, 

Kentucky, and Alabama – Penn State University, PA (PSU106); Mackville, KY (MCK131); and 

SND152, AL. The NH+ 

4 concentrations measured at western sites were relatively low with all 

sites measuring concentrations below 1.0 μg/m3

. 

The trend diagram for annual mean NH+ 

4 values is provided in Figure 2-8. The box plots show a 

16 percent decline in NH+ 

4 concentrations from the 3-year period 1990-1992 to the three years at 

the end of the period (1.79 μg/m3 to 1.49 μg/m3). However, the 2005 mean was higher than the 

2004 value. This increase might be related to relatively higher SO2-

4 and NO3 concentrations in 

2005 and the resulting higher ammonium sulfate [(NH 

4)

 

2SO 4] and ammonium nitrate (NH 4NO 3) 

concentrations. 

Figure 2-7 Annual Mean NH+ 

4 Concentrations (μg/m3

) for 2005 
 

CASTNET Annual Report – 2005 16 Chapter 2: Atmospheric Concentrations

Figure 2-8 Trend in Annual Mean NH+ 

4 Concentrations (μg/m3

) – Eastern United States 

Continuous Measurements of Trace Concentrations of 

CO, NOy, and SO 

2

In addition to filter pack measurements, continuous measurements of low-concentration 

(i.e., trace) carbon monoxide (CO), total reactive oxides of nitrogen (NOy), and sulfur 

dioxide (SO 

2) are collected at the CASTNET Beltsville, MD (BEL116) site. Data from 

these continuous gas analyzers were extracted from the entire 7-month database and 

plotted. The data show some interesting results. The following figure is a plot of hourly 

CO, NOy, and SO 

2 data from the low-concentration analyzers for the first two weeks of 

November 2005. Separate scales are provided for each pollutant. The CO and NOy

measurements are correlated, suggesting an urban source of these two pollutants. The SO 

2

measurements are unrelated to the CO and NOy data. This result suggests that the SO 

2

sources are not collocated with the urban sources of the CO and NOy. These simple 

interpretations suggest that the low-concentration measurements could be utilized for other 

types of analyses and also for the evaluation of filter pack measurements. 

CO BEL116 

NOY BEL116 

SO2 BEL116 

0

1

2

3

4

1990199119921993199419951996199719981999200020012002200320042005

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Mean

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90th Percentile

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Median

Mean

25th Percentile

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0

1

2

3

4

1990199119921993199419951996199719981999200020012002200320042005

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Mean

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90th Percentile

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Median

Mean

25th Percentile

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CASTNET Annual Report – 2005 17 Chapter 3: Atmospheric Deposition 

Chapter 3: 

Atmospheric Deposition 

CASTNET was designed to estimate dry deposition as the product of measured pollutant 

concentrations and modeled deposition velocities. The Multi-Layer Model (MLM) is the 

computer model used to calculate hourly deposition velocities based on meteorological 

measurements and information on vegetation and its annual evolution. Total deposition is 

the sum of estimated dry deposition and measured wet deposition. Since 1990, total sulfur 

deposition has declined significantly. The data show a 27 percent reduction in 3-year mean 

sulfur fluxes over the period from 1990-1992 to 2003-2005. Total nitrate deposition 

declined by 9 percent over the same period. Dry deposition is responsible from 

approximately 20 to 80 percent of total deposition depending on location and climate. The 

percentage is higher in major source regions. Typical percentages are 40 percent for dry 

sulfur and 30 percent for dry nitrogen deposition. 

Gaseous and aerosol sulfur and nitrogen pollutants are deposited into ecosystems through dry and 

wet atmospheric processes. One of the most critical and unique components of CASTNET 

involves estimation of the rate, or flux, of dry deposition from measured environmental 

conditions. Measured concentration data are combined with modeled dry deposition velocities to 

develop the flux estimates. For this report, wet deposition measurements were obtained from 

NADP/NTN and combined with CASTNET’s dry deposition data to estimate total deposition. 

Total sulfur and nitrogen deposition rates decreased during 2005. Precipitation-weighted mean 

concentrations in precipitation of total atmospheric sulfur remained about the same in 2005 as 

2004, while nitrogen concentrations in precipitation continued the slow decline that began 

in 1998. 

Dry deposition processes were simulated using the MLM (Figure 1-3) as described by 

Meyers et al. (1998) and Finkelstein et al. (2000). An improved version of the MLM (Schwede, 

2006) will be provided to MACTEC in 2006. For this report, the MLM was run using CASTNET 

meteorological measurements and information on land use, vegetation, and surface conditions to 

calculate deposition velocities for sulfur dioxide (SO2), nitric acid (HNO3), ozone (O3), and the 

particles, sulfate (SO2-

4 ), nitrate (NO3), and ammonium (NH+ 4 ). The deposition velocities were 

assumed to be identical for all particle species. Deposition velocity values were calculated for 

Lassen Volcanic National Park, CA (LAV410)
CASTNET Annual Report – 2005 18 Chapter 3: Atmospheric Deposition 

each hour with valid meteorological data for each CASTNET site for the entire period 1990 

through 2005. For a deposition velocity to be estimated, temperature, solar radiation, relative 

humidity, wind speed, and standard deviation of the wind direction (sigma theta) must all be valid 

for the hour. Aggregation rules for CASTNET require three valid quarters for the calculation of 

an annual value. If an annual value is not available for a specific site, results are not included on 

maps presented in this chapter. For trends analyses, missing values are replaced by interpolation 

or extrapolation using valid annual estimates. The MLM has been evaluated for a limited number 

of vegetation types, terrain settings, and time periods (summarized by Baumgardner et al., 2002). 

Sulfur Deposition 

MLM simulations were done separately for sulfur dioxide (SO2) and sulfate (SO2-

4 ). The model 

calculations were summed to obtain estimates of dry sulfur deposition [as sulfur (S)] for 2005, 

which are shown in Figure 3-1. The magnitude of a deposition rate is illustrated by the size of the 

circle. The map shows a narrow region with fluxes greater than 5.0 kilograms per hectare per year 

(kg/ha/yr) centered around and downwind of the Ohio River Valley from southern Indiana to 

New Jersey. The highest deposition rate was estimated for Quaker City, OH (QAK172) with a 

flux of 13.3 kg/ha/yr. The highest dry sulfur deposition rates were coincidental to the major SO2

source region (Figure 1-5) and declined sharply with distance. 

 

Figure 3-1 Dry Sulfur (SO 

2 + SO2-4 ) Deposition (as S) (kg/ha/yr) for 2005 

The dry deposition rates for the western sites were all less than 1.0 kg/ha/yr with the majority of 

sites less than 0.5 kg/ha/yr. The MLM was not run for those sites in Figure 3-1 having no 

numerical value adjacent to the site location because of incomplete data. 

0.8

6.5 2.3

6.3

0.3

2.0

0.7

1.7

2.6

0.8

0.9

5.0

3.0

1.0

0.3

0.4

4.7

2.4

0.3

3.6

1.5

6.0

0.3

1.9

1.8

0.8

3.9

0.2

0.3

2.4

0.2

0.7

1.3

0.5

1.1

0.4

3.3

1.1

0.1

5.4

5.6

3.5

6.0 0.4

0.1

4.5

0.3

2.4

0.8

0.3 13.3

3.0

3.8

3.0

0.5

3.3

7.4

0.4

4.4

0.4

5.5

0.3

0.1

Sites not pictured:

DEN417, AK 0.1

Deposition

10

5

1
CASTNET Annual Report – 2005 19 Chapter 3: Atmospheric Deposition 

Wet deposition values used in these analyses represent a combination of historical CASTNET wet 

deposition data with NADP/NTN wet deposition data. For CASTNET sites where wet 

concentrations were measured prior to January 1999 (when responsibility for wet deposition 

monitoring activities at CASTNET sites was transferred to NADP/NTN), those values were used 

in the data set. For sites where no wet concentrations were measured and for all sites after January 

1999, values were obtained from a grid of concentration estimates derived from available 

NADP/NTN sites by using an inverse distance weighting function. Estimated concentrations were 

multiplied by the precipitation measured at the CASTNET sites to obtain estimates of 

wet deposition. 

Figure 3-2 provides a map of estimates of total sulfur deposition. The map was constructed by 

adding dry and wet deposition. The circles in the figure illustrate the magnitude of total sulfur 

deposition and also the relative contributions from wet and dry deposition. The dark shading 

(blue) signifies wet deposition and the light shading (tan) shows dry deposition. For 2005, a 

region with total (dry + wet) sulfur deposition (kg/ha/yr) greater than 10.0 kg/ha/yr extended from 

southwestern Indiana and central Kentucky, along the Ohio River into Ohio, West Virginia, 

Virginia, Maryland, New Jersey, Pennsylvania, and New York. Sulfur deposition at western sites 

was less than 2.0 kg/ha/yr. The contribution of dry deposition was much more significant in and 

near major source regions. For example, the contribution of dry sulfur deposition ranged from 

about half of total sulfur deposition at Vincennes, IN (VIN140) to only a small fraction at sites 

in Florida. 

Figure 3-2 Total (Dry + Wet) Sulfur Deposition (as S) (kg/ha/yr) for 2005 

7.5

9.9

12.1

13.7

1.2

6.0

4.1

5.5

7.3

3.7

1.9

10.8

7.7

4.9

0.7

1.1

10.0

7.8

1.1

10.1

5.4

12.2

0.9

7.6

7.4

6.5

9.1

0.9

0.9

8.2

0.9

3.6

6.3

4.4

6.6

1.3

8.3

4.8

0.7

9.8

12.5

8.6

10.6 1.4

1.2

10.4

0.5

8.1

3.7

1.1 22.5

7.9

9.1

6.5

1.6

6.9

15.5

2.2

11.4

1.3

12.0

0.7

0.4

Sites not pictured:

DEN417, AK 0.9

Total Deposition

16

8

1.6

Dry Deposition

Wet Deposition

7.5

9.9

12.1

13.7

1.2

6.0

4.1

5.5

7.3

3.7

1.9

10.8

7.7

4.9

0.7

1.1

10.0

7.8

1.1

10.1

5.4

12.2

0.9

7.6

7.4

6.5

9.1

0.9

0.9

8.2

0.9

3.6

6.3

4.4

6.6

1.3

8.3

4.8

0.7

9.8

12.5

8.6

10.6 1.4

1.2

10.4

0.5

8.1

3.7

1.1 22.5

7.9

9.1

6.5

1.6

6.9

15.5

2.2

11.4

1.3

12.0

0.7

0.4

Sites not pictured:

DEN417, AK 0.9

Total Deposition

16

8

1.6

Dry Deposition

Wet Deposition
CASTNET Annual Report – 2005 20 Chapter 3: Atmospheric Deposition 

Figure 3-3 presents box plots that show the trend in dry sulfur deposition (as S), and Figure 3-4 

shows the trend in annual total (dry + wet) sulfur deposition (as S) over the 16 years, 1990 

through 2005. The box plots were based on data obtained from the 34 eastern CASTNET 

reference sites (Figure 1-4). Sulfur deposition at these sites declined significantly over the 

16 years, although the dry fluxes have been relatively constant for the last five years. Figure 3-4 

shows a decline in total sulfur deposition over the last two years. Figure 3-5 presents estimates of 

trends in dry, wet, and total deposition of sulfur (as S) on the same diagram. The trend line for 

mean sulfur concentrations in precipitation shows a continuing decrease over the last several 

years with a small increase in 2005. The influence of precipitation on total sulfur deposition is 

illustrated by comparing the solid (top) line to the dotted blue line in Figure 3-5. The solid line 

shows total deposition, which depends on sulfur concentrations in precipitation and precipitation 

amounts. The dotted line shows concentrations in precipitation, which reflect changes in SO 

2

emissions. Total sulfur deposition declined from a 1990-1992 mean of 13.5 kg/ha/yr to a 

2003-2005 mean of 9.9, a 27 percent reduction. 

Figure 3-3 Trend in Dry Sulfur Deposition (as S) (kg/ha/yr) – Eastern United States 

0

2

4

6

8

10

12

1990199119921993199419951996199719981999200020012002200320042005

Deposition

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90th Percentile

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Median

Mean

25th Percentile

10th Percentile

0

2

4

6

8

10

12

1990199119921993199419951996199719981999200020012002200320042005

Deposition

90th Percentile

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Median

Mean

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10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

Big Meadows National Park, VA (SHN418) 

Photos: NPS 
CASTNET Annual Report – 2005 21 Chapter 3: Atmospheric Deposition 

Figure 3-4 Trend in Total (Dry + Wet) Sulfur Deposition (as S) (kg/ha/yr) – 

Eastern United States 

Figure 3-5 Trend in Dry, Wet, and Total Sulfur Deposition (as S) (kg/ha/yr) with PrecipitationWeighted Mean Concentrations in Precipitation (mg/L) – Eastern United States

0

5

10

15

20

25

1990199119921993199419951996199719981999200020012002200320042005

Deposition

90th Percentile

75th Percentile

Median

Mean

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90th Percentile

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Median

Mean

25th Percentile

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0

5

10

15

20

25

1990199119921993199419951996199719981999200020012002200320042005

Deposition

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Mean

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0

2

4

6

8

10

12

14

16

1990199119921993199419951996199719981999200020012002200320042005

Deposition

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Concentration

Wet Deposition

Dry Deposition

Concentration in Precipitation

Total Deposition
CASTNET Annual Report – 2005 22 Chapter 3: Atmospheric Deposition 

Contributors to Atmospheric Deposition 

1990-1992: CASTNET Eastern Reference Sites 

Sulfur Nitrogen 

2003-2005: CASTNET Eastern Reference Sites 

 

The four pie charts illustrate mean total (wet + dry) sulfur and nitrogen deposition rates for two 

3-year periods, 1990 to 1992 and 2003 to 2005. The mean values were obtained for the 34 reference 

sites. The pie charts show a significant decline in mean total sulfur deposition from about 13.5 to 

9.9 kg/ha/yr from the beginning to the ending three years. The charts show a relatively small decline 

in total nitrogen deposition, from 7.9 to 7.2 kg/ha/yr from the beginning three years to the final three 

years of the 16-year period. The data show that wet SO2-

4 deposition was the major contributor to 

total sulfur deposition, followed by dry SO 

2 and a much smaller contribution from dry SO2-4 . The 

percentage of dry deposition in total deposition changed from 41 percent to 39 percent over the 16 

years. Wet NO3 deposition was the major contributor to total nitrogen deposition followed by wet 

NH+ 

4 , dry HNO 3, dry NH+ 4 , and dry NO3. The percentage of dry nitrogen deposition changed slightly 

from 29 percent to 27 percent over the 16 years. For both sulfur and nitrogen, dry deposition 

contributed from about 20 to 80 percent of total deposition at individual CASTNET sites, depending 

on location and climate. Typical deposition percentages are about 40 percent for dry sulfur and 

30 percent for dry nitrogen. 

Dry SO2

Deposition

(as Sulfur)

Dry SO4

2-

Deposition

(as Sulfur)

Wet SO4

2-

Deposition

(as Sulfur)

Dry HNO3

Deposition

(as Nitrogen)

Dry NO3

-

Deposition

(as Nitrogen)

Dry NH4

+

Deposition

(as Nitrogen)

Wet NO3

-

Deposition

(as Nitrogen)

Wet NH4

+

Deposition

(as Nitrogen) 13.5 kg/ha 7.9 kg/ha

Dry SO2

Deposition

(as Sulfur)

Dry SO4

2-

Deposition

(as Sulfur)

Wet SO4

2-

Deposition

(as Sulfur)

Dry HNO3

Deposition

(as Nitrogen)

Dry NO3

-

Deposition

(as Nitrogen)

Dry NH4

+

Deposition

(as Nitrogen)

Wet NO3

-

Deposition

(as Nitrogen)

Wet NH4

+

Deposition

(as Nitrogen)

Dry SO2

Deposition

(as Sulfur)

Dry SO4

2-

Deposition

(as Sulfur)

Wet SO4

2-

Deposition

(as Sulfur)

Dry HNO3

Deposition

(as Nitrogen)

Dry NO3

-

Deposition

(as Nitrogen)

Dry NH4

+

Deposition

(as Nitrogen)

Wet NO3

-

Deposition

(as Nitrogen)

Wet NH4

+

Deposition

(as Nitrogen) 13.5 kg/ha 7.9 kg/ha

Dry HNO3

Deposition

(as Nitrogen)

Dry NO3

-

Deposition

(as Nitrogen)

Dry NH4

+

Deposition

(as Nitrogen)

Wet NO3

-

Deposition

(as Nitrogen)

Wet NH4

+

Deposition

(as Nitrogen)

Dry SO2

Deposition

(as Sulfur)

Dry SO4

2-

Deposition

(as Sulfur)

Wet SO4

2-

Deposition

(as Sulfur)

9.9 kg/ha 7.2 kg/ha

Dry HNO3

Deposition

(as Nitrogen)

Dry NO3

-

Deposition

(as Nitrogen)

Dry NH4

+

Deposition

(as Nitrogen)

Wet NO3

-

Deposition

(as Nitrogen)

Wet NH4

+

Deposition

(as Nitrogen)

Dry SO2

Deposition

(as Sulfur)

Dry SO4

2-

Deposition

(as Sulfur)

Wet SO4

2-

Deposition

(as Sulfur)

9.9 kg/ha 7.2 kg/ha
CASTNET Annual Report – 2005 23 Chapter 3: Atmospheric Deposition 

Nitrogen Deposition 

Figure 3-6 presents a map of dry fluxes of nitrogen [as nitrogen (N)] for 2005. Nitrogen fluxes are 

comprised of nitric acid (HNO3) + nitrate (NO3) + ammonium (NH+ 

4 ). This map was constructed 

by summing the individual MLM simulations for the three species. Almost all of the CASTNET 

sites in the eastern United States had estimated dry nitrogen deposition rates greater than 

1.0 kg/ha/yr. The nitrogen fluxes were more uniform than the sulfur fluxes, reflecting a wider 

distribution of NOx sources. The flux values ranged from 0.5 kg/ha/yr in New Hampshire and 

Maine to 3.6 kg/ha/yr in eastern Ohio. The values at the western sites ranged from 0.2 kg/ha/yr at 

North Cascades National Park, WA (NCS415) to 3.0 kg/ha/yr at Converse Station, CA 

(CON186). 

Figure 3-6 Dry Nitrogen (HNO 

3 + NO3 + NH+ 4 ) Deposition (as N) (kg/ha/yr) for 2005 

A map (Figure 3-7) of total nitrogen deposition (as N) for 2005 was constructed by summing the 

estimates of dry (light shading) and wet (dark shading) deposition. The figure shows that a large 

majority of the eastern sites recorded deposition rates greater than 5.0 kg/ha/yr. No values above 

10.0 kg/ha/yr were observed in 2005. Lower fluxes were recorded along the periphery of the 

network (e.g., in New England and Florida and throughout the West). The values at the western 

sites ranged from 1.3 kg/ha/yr in central California at Yosemite National Park (YOS430) and in 

Wyoming at Yellowstone National Park (YEL408) to 5.0 kg/ha/yr in southern California 

at CON186. The contributions of dry nitrogen deposition to total nitrogen were lower than the 

corresponding contributions of dry sulfur deposition. Dry nitrogen deposition typically 

contributed less than 50 percent of total deposition in the East. Interestingly, dry nitrogen 

0.8

2.9 1.0

2.2

3.0

2.4

0.7

1.8

2.5

0.5

1.4

2.4

1.6

1.3

0.9

0.9

2.9

2.3

0.8

2.4

1.9

3.4

1.1

1.5

1.5

0.8

2.3

0.3

0.9

3.2

0.3

0.6

1.4

0.5

0.8

2.6

1.5

1.9

0.5

1.4

3.0

2.0

2.9 1.1

0.2

1.5

1.0

1.9

0.9

0.8 3.6

2.7

2.7

2.8

0.6

1.6

2.6

0.7

2.2

1.2

2.7

0.3

0.4

Sites not pictured:

DEN417, AK 0.1

Deposition

3.0

1.5

0.3
CASTNET Annual Report – 2005 24 Chapter 3: Atmospheric Deposition 

deposition contributed more than half of total nitrogen deposition in southern California, a region 

with elevated concentrations of nitrogen species and limited rainfall. The CASTNET site at 

QAK172, OH had the distinction of measuring the highest total sulfur and nitrogen 

deposition rates. 

Figure 3-7 Total (Dry + Wet) Nitrogen Deposition (as N) (kg/ha/yr) for 2005 

Figure 3-8 presents box plots that show the trend in dry nitrogen deposition (as N), and Figure 3-9 

shows the trend in annual total (dry + wet) nitrogen deposition over the 16 years, 1990 through 

2005. The box plots in Figure 3-8 show little overall trend although the data suggest a decline in 

dry nitrogen deposition since 1999. Total nitrogen deposition (Figure 3-9) decreased since 2003. 

Figure 3-8 Trend in Dry Nitrogen Deposition (as N) (kg/ha/yr) – Eastern United States 

0

1

2

3

4

5

6

1990199119921993199419951996199719981999200020012002200320042005

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0

1

2

3

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6

1990199119921993199419951996199719981999200020012002200320042005

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6.1

6.2

7.6

8.4

5.0

5.6

3.3

5.1

7.4

3.3

2.5

7.0

4.9

5.0

1.9

2.2

7.1

7.7

2.7

7.8

5.7

8.2

2.6

7.6

5.9

4.9

6.9

1.6

2.1

7.5

1.7

2.9

7.4

4.2

4.4

4.6

6.0

7.5

1.6

4.5

9.4

6.3

6.9 2.8

1.4

6.0

1.3

6.8

6.5

2.7 9.9

8.6

6.8

7.7

3.0

5.6

9.2

4.5

7.7

3.7

7.8

1.3

1.3

Sites not pictured:

DEN417, AK 0.4

Total Deposition

10

5

1

Dry Deposition

Wet Deposition

6.1

6.2

7.6

8.4

5.0

5.6

3.3

5.1

7.4

3.3

2.5

7.0

4.9

5.0

1.9

2.2

7.1

7.7

2.7

7.8

5.7

8.2

2.6

7.6

5.9

4.9

6.9

1.6

2.1

7.5

1.7

2.9

7.4

4.2

4.4

4.6

6.0

7.5

1.6

4.5

9.4

6.3

6.9 2.8

1.4

6.0

1.3

6.8

6.5

2.7 9.9

8.6

6.8

7.7

3.0

5.6

9.2

4.5

7.7

3.7

7.8

1.3

1.3

Sites not pictured:

DEN417, AK 0.4

Total Deposition

10

5

1

Dry Deposition

Wet Deposition
CASTNET Annual Report – 2005 25 Chapter 3: Atmospheric Deposition 

Figure 3-9 Trend in Total (Dry + Wet) Nitrogen Deposition (as N) (kg/ha/yr) - 

 Eastern United States 

Estimates of trends in wet, dry, and total deposition of atmospheric nitrogen (as N) are presented 

in Figure 3-10. The trend in precipitation-weighted mean nitrogen concentrations in precipitation 

is also provided on the same figure. The trend line for precipitation-weighted mean nitrogen 

concentrations in precipitation shows a slight downward trend since 1998. This trend line 

illustrates the effect of changes in NOx emissions. Total nitrogen deposition declined from a 

3-year (1990-1992) average of 7.9 kg/ha/yr to a 2003-2005 value of 7.2 kg/ha/yr. This constitutes 

a 9 percent decline over the 16 years. 

Figure 3-10 Trend in Dry, Wet, and Total Nitrogen Deposition (as N) (kg/ha/yr) with 

Precipitation-Weighted Mean Concentrations in Precipitation (mg/L) – 

Eastern United States 

4

6

8

10

12

14

1990199119921993199419951996199719981999200020012002200320042005

Deposition

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

4

6

8

10

12

14

1990199119921993199419951996199719981999200020012002200320042005

Deposition

90th Percentile

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Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

2

4

6

8

10

12

1990199119921993199419951996199719981999200020012002200320042005

Deposition

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Concentration

Wet Deposition

Dry Deposition

Concentration in Precipitation

Total Deposition
 

CASTNET Annual Report – 2005 26 Chapter 4: Ozone Concentrations

Chapter 4: 

Ozone Concentrations 

CASTNET ozone (O 

3) measurements provide information on geographic patterns in regional O 3. 

Each monitoring site operates an ozone analyzer to measure O 

3 concentrations continuously. 

Ozone data are recorded and archived as hourly averages. 

The CASTNET O 

3 database constitutes a long-term 

record of O 

3 levels in rural areas with more than 40 sites 

operating since the late 1980s. While CASTNET is not a 

compliance network, the 8-hour O 

3 standard is a useful 

metric in assessing status and trends in rural O 

3. The 

analyses presented in this section examine trends in the 

fourth highest daily maximum 8-hour average O 

3

concentrations, consistent with the metric used in the 

8-hour standard (see call out box on following page). 

During the period 2003-2005, 3-year averages of the 

fourth highest daily maximum 8-hour O 

3 concentrations 

were greater than or equal to 85 parts per billion (ppb) at 

seven sites in California, Maryland, New Jersey, and 

Tennessee. Measurements of 8-hour concentrations 

during 2005 were somewhat higher than 2003 and 2004 

but were considerably lower than concentrations measured over the period 1990-2002. Ozone 

levels measured in 2005 continue to show a downward trend that began in 2002.

Death Valley National Park, CA (DEV412) 

CASTNET provides the primary means for monitoring rural ozone (O 

3) concentrations 

in the United States. The median fourth highest daily maximum 8-hour O 

3 concentration 

for 2005 was the second lowest in the history of the network despite the return to 

normal weather conditions during the ozone season (May through September). The 

decline in rural ozone levels over the last few years has been attributed to the 

documented decline in NOx emissions, as well as weather conditions not conducive to 

ozone formation during some of those years. 
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 27

National Ambient Air Quality Standard for Ozone 

8-Hour Ozone Standard 

To better protect public health, EPA (1997) revised its national air quality standards for 

ozone in 1997, establishing an 8-hour standard. The 8-hour standard is 0.08 parts per 

million (ppm). An area meets the standard if the 3-year average of the annual fourth 

highest daily maximum 8-hour average concentration is less than or equal to 0.08 ppm. 

For more information on the 8-hour ozone standard and ozone nonattainment areas in 

the United States, visit www.epa.gov/air/oaqups/glo/designations/index.htm. 

What Does It Mean? 

EPA collects ozone data on an hourly basis. Essentially, 8-hour average ozone 

concentrations at a monitor cannot exceed 0.08 ppm more than three days per year. For 

compliance purposes: 

♦ Hourly ozone measurements are used to compute 8-hour average concentrations. 

♦ The daily maximum 8-hour average is recorded for each day. 

♦ For each year, the fourth highest daily maximum concentration is calculated. 

♦ These annual fourth highest daily maximum concentrations are averaged over threeyear periods. 

♦ If the average exceeds 0.084 ppm (0.085 rounds up to 0.09 thus exceeding the 

standard criteria) or 85 ppb in practice, the area is designated as a “nonattainment 

area.” 
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 28

Eight-Hour Ozone Concentrations 

Figure 4-1 presents 3-year averages of the fourth highest daily maximum 8-hour O 

3

concentrations for 2003-2005. The sites with concentration levels greater than or equal to 85 ppb 

are listed in a table next to the map in Figure 4-1. Three eastern and four sites in California 

measured 3-year average concentrations greater than or equal to 85 ppb. These 3-year average 

concentrations constitute current design values for achieving the 8-hour National Ambient Air 

Quality Standard (NAAQS) for O 

3. For example, the estimated value of 124 ppb at CON186 

would have to be reduced to 84 ppb to achieve the standard. Design values change as a new 

3-year database becomes available. 

For comparison, 3-year averages of the fourth highest daily maximum 8-hour O 

3 concentrations 

for the previous 3-year period, 2002-2004 are presented in Figure 4-2. The area with standard 

exceedances was larger during this earlier period. Six eastern and the same four California sites 

recorded 3-year averages greater than or equal to 85 ppb. The period 2003-2005 represents an 

improvement in air quality. 

Fourth highest daily maximum 8-hour O 

3 concentrations for 2005 are shown in Figure 4-3. 

Concentrations greater than or equal to 85 ppb were recorded along the East Coast in the 

Washington, D.C. to Boston corridor; Great Smoky Mountains National Park, TN (GRS420); 

and Alhambra, IL (ALH157). In addition, five California CASTNET sites monitored 

exceedances of the 8-hour ozone NAAQS. The California sites include Converse Station 

(CON186), Sequoia National Park (SEK430), Joshua Tree National Monument (JOT403), Death 

Valley National Monument (DEV412), and Yosemite National Park (YOS404). The 8-hour level 

of 123 ppb at CON186 was the highest value that was measured in the network during 2005. 

Rocky Mountains National Park, CO (ROM406/206) 
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 29

Figure 4-1 Fourth Highest Daily Maximum 8-Hour Ozone Concentrations (ppb) for 

2003-2005

Figure 4-2 Fourth Highest Daily Maximum 8-Hour Ozone Concentrations (ppb) for 

2002-2004

Figure 4-3 Fourth Highest Daily Maximum 8-Hour Ozone Concentrations (ppb) for 2005

Site ID 

Conc ≥ 85 

ppb 

CON186, CA 124 

SEK430, CA 107 

JOT403, CA 106 

YOS404, CA 88 

BWR139, MD 88 

WSP144, NJ 86 

GRS420, TN 86 

Site ID 

Conc ≥ 85 

ppb 

CON186, CA 125 

JOT403, CA 107 

SEK430, CA 103 

WSP144, NJ 93 

BWR139, MD 92 

GRS420, TN 91 

YOS404, CA 91 

ARE128, PA 89 

ABT147, CT 86 

LYK123, OH 86 

Site ID 

Conc ≥ 85 

ppb 

CON186, CA 123 

SEK430, CA 107 

JOT403, CA 104 

WSP144, NJ 89 

ALH157, IL 88 

BWR139, MD 87 

ABT147, CT 87 

GRS420, TN 86 

DEV412, CA 85 

YOS404, CA 85 
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 30

Sixteen-Year Trends 

Since 2002, CASTNET ozone measurements have shown a significant decline in annual fourth 

highest daily maximum 8-hour concentrations throughout the 34 eastern reference sites (Figure 

1-4) used to track trends in concentrations. During 2002, 24 of the reference sites measured 

fourth highest daily maximum 8-hour O 

3 concentrations greater than or equal to 85 ppb. The 

number of reference sites with exceedances was reduced to six in 2003, followed by further 

reduction to none in 2004. As shown in Figure 4-3, five eastern reference sites recorded elevated 

8-hour concentrations in 2005. 

Figure 4-4 shows the 16-year trend in 8-hour O 

3 concentrations aggregated over the 34 reference 

stations. The box plots show a significant decline from 2002 to 2003 and a further decline in 

2004. The 2005 data show a small increase. Median values for the aggregated measurements for 

the four years 2002 through 2005 were 88 ppb, 79 ppb, 70 ppb, and 76 ppb, respectively. Trends 

in temperature, solar radiation, and precipitation for the reference sites are shown in Figures 4-5 

though 4-7. These box plots were produced for the ozone season, May through September, when 

sunlight and warm weather promote the chemical reactions that form ozone. The meteorological 

influence on O 

3 concentrations is evident from the three figures. The 2003 and 2004 ozone 

seasons, which measured significantly lower concentrations of ozone than the preceding years 

(1990-2002), were unusually cool, cloudy, and wet. For example, total precipitation measured in 

2003 and 2004 was well above the amounts recorded during the previous 13 years. Interestingly, 

ozone season weather returned to normal in 2005. Yet the median 8-hour O 

3 concentration was 

the second lowest in the 16-year period. 

Figure 4-4 Trend in Fourth Highest Daily Maximum 8-Hour Ozone Concentrations (ppb) – 

Eastern United States 

60

80

100

120

1990199119921993199419951996199719981999200020012002200320042005

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 31

Figure 4-5 Trend in Mean Seasonal (May through September) Temperature (°C) – 

 Eastern United States 

Figure 4-6 Trend in Mean Seasonal (May through September) Solar Radiation (W/m2

) – 

Eastern United States 

10

15

20

25

30

1990199119921993199419951996199719981999200020012002200320042005

Temperature

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

150

175

200

225

250

275

300

1990199119921993199419951996199719981999200020012002200320042005

Solar Radiation

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

150

175

200

225

250

275

300

1990199119921993199419951996199719981999200020012002200320042005

Solar Radiation
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 32

Figure 4-7 Trend in Total Precipitation (mm) (May through September) – 

 Eastern United States 

Nitrogen Oxides and Ozone 

EPA recently analyzed changes in NOx emissions and O 

3 concentrations. The findings were 

published in two excellent reports (EPA, 2005b and 2006), which evaluated the effectiveness of 

NOx and volatile organic compound (VOC) emission control programs in the eastern United 

States and reported subsequent changes in ozone levels. Figure 4-8, which was taken from the 

2006 EPA report, depicts annual NOx and VOC emissions in the eastern United States from 1990 

through 2005. Figure 4-9 shows ozone season NOx emissions for five baseline years during this 

time period. The figure illustrates emissions from large electric generating and industrial sources 

in the NOx Budget Trading Program (NBP) region, which is illustrated in light green in 

Figure 4-10. The region includes 19 eastern states and the District of Columbia. The emissions 

were totaled for 2,570 units in the region. The decline in NOx emissions over the last several 

years is evident in the figures. In the report, EPA attributed the decline in emissions to several 

effective control programs: 

Mobile source controls, 

VOC Reasonably Available Control Technology (RACT) and Maximum Available 

Control Technology (MACT), 

New Source Review, 

Acid Rain Program, 

Ozone Transport Commission (OTC) NO 

x Budget (1999-2002), and 

NO 

x State Implementation Plan (SIP) Call (2003 - current). 

200

400

600

800

1000

1200

1990199119921993199419951996199719981999200020012002200320042005

Precipitation

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 33

Figure 4-8 Annual Emissions in the Eastern United States, 1990-1995 and 1997-2005 

Figure 4-9 NBP NOx Emissions in the Eastern United States, Ozone Season 

(May through September), 1990-2005 

Figure 4-10, which was taken from the 2006 EPA report, shows the relationship between 

emission reductions from power industry sources and changes in O 

3 concentrations at CASTNET 

and EPA Air Quality System sites in the eastern United States over the period 2002 through 

2005. The figure shows declines in ozone concentrations in all NBP states. 
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 34

Figure 4-10 NOx Emission Reductions and Changes in 8-hour Ozone, 2002-2005 

Note: 

 Shaded region shows areas affected under the NBP as of 2005. Source: EPA 

Trends in CASTNET measurements of total nitrate concentrations (Figure 4-11) show a 

relationship between the decline in ozone and a decline in atmospheric nitrogen (Rogers et al., 

2006a). The box plots show a significant reduction in total nitrate concentrations during the 

ozone season since 1999. Figure 4-12 illustrates this decline by comparing ozone season mean 

total nitrate concentrations for 2000 and 2005 for the CASTNET reference sites. Both weather 

and a reduction in NO 

x emissions and total nitrate concentrations contributed to the decline in O 3

concentrations. 

Figure 4-11 Trend in Ozone Season (May through September) Mean Total Nitrate 

 (NO3 + HNO 

3) Concentrations (μg/m3 ) – Eastern United States 

0

1

2

3

4

5

6

7

1990199119921993199419951996199719981999200020012002200320042005

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

1

2

3

4

5

6

7

1990199119921993199419951996199719981999200020012002200320042005

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 35

Figure 4-12 2000 and 2005 Ozone Season (May through September) Mean Total Nitrate 

 (NO3 + HNO 

3) Concentrations (μg/m3 ) – CASTNET Eastern Reference Sites 

3.8 / 3.1 4.1 / 3.2

3.9 / 3.5

4.3 / 4.0

1.4 / 0.9

2.9 / 2.3

1.9 / 1.4

3.6 / 3.2

3.9 / 3.8

3.8 / 3.2

3.2 / 2.5

1.8 / 1.5

3.3 / 2.5

1.5 / 1.1 4.5 / 3.2

2.6 / 2.0 2.8 / 2.2

1.9 / 1.5

3.4 / 2.4

0.5 / 0.4

1.8 / 1.5

2.3 / 1.7 0.9 / 0.6

2.1 / 2.0

1.8 / 1.2

2.4 / 1.7

1.8 / 1.2

1.3 / 1.5 1.3 / 1.5

3.0 / 2.4

1.5 / 1.0

3.5 / 3.0

0.5 / 0.5
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 36

Trends in Ozone Concentrations along the 

Washington, D.C. to Coastal Maine Corridor 

Historically, elevated ozone 

concentrations have been recorded along 

the East Coast from metropolitan 

Washington, D.C. to Acadia National 

Park in Maine. Within the last five years, 

3-year averages of the fourth highest 

daily maximum O 

3 concentrations have 

been more than 90 ppb at the CASTNET 

sites in Maryland, eastern Pennsylvania, 

New Jersey, and Connecticut and as high 

as 87 ppb in Maine. Recent studies by 

EPA (2005b) demonstrated a decline in 

O 

3 concentrations in the eastern United 

States that is related to the decline in NOx

emissions, which resulted from a number 

of NOx emission control programs. The 

analyses discussed by Rogers et al. 

(2006a) together with the analyses in this 

chapter demonstrate a significant 

reduction in O 

3 levels at the 34 eastern 

CASTNET reference sites. This 

reduction is attributed to the significant 

decline in NOx emissions, as manifested 

by the decline in total nitrate 

concentrations, and cool, cloudy, and wet 

weather conditions during the “ozone 

season” (i.e., May through September) of 

2003 and 2004. More typical ozone 

season weather was observed in 2005. 

60

70

80

90

100

110

120

1990199119921993199419951996199719981999200020012002200320042005

ppb

Ozone

10

15

20

25

1990199119921993199419951996199719981999200020012002200320042005

Degrees Celsius

150

250

350

450

550

650

750

850

W/m2 or millimeters

Temperature

Solar Radiation

Precipitation

0

1

2

3

4

5

6

7

1990199119921993199419951996199719981999200020012002200320042005

μg/m3

Total Nitrate

60

70

80

90

100

110

120

1990199119921993199419951996199719981999200020012002200320042005

ppb

Ozone

10

15

20

25

1990199119921993199419951996199719981999200020012002200320042005

Degrees Celsius

150

250

350

450

550

650

750

850

W/m2 or millimeters

Temperature

Solar Radiation

Precipitation

0

1

2

3

4

5

6

7

1990199119921993199419951996199719981999200020012002200320042005

μg/m3

Total Nitrate
CASTNET Annual Report – 2005 Chapter 4: Ozone Concentrations 37

Fourth highest daily maximum O 

3 concentrations measured at six CASTNET sites indicate 

that ozone peaked in 2002, and the lowest concentrations occurred during the last three 

years. The trend was calculated from 1990-2005 measurements from Beltsville, MD 

(BEL116); Blackwater Wildlife Refuge, MD (BWR139); Arendtsville, PA (ARE128); 

Washington’s Crossing State Park, NJ (WSP144); Abington, CT (ABT147); and Acadia 

National Park, ME (ACA416). The data were aggregated over the six sites. Ozone season 

temperature, solar radiation, and precipitation data show that the 2002 O 

3 peak was 

observed during an exceptionally warm, sunny, and dry summer. Much lower O 

3

concentrations were recorded in 2003 and 2004. The weather conditions during these two 

ozone seasons were cool, cloudy, and wet. Weather conditions returned to normal during 

the 2005 O 

3 season. Yet O 3 concentrations remained low. 

Ozone season mean nitrate concentrations have shown a significant decline in atmospheric 

nitrogen along the East Coast since 1999. The trend in total nitrate concentrations along the 

East Coast is comparable to the trend in total nitrate levels for the 34 reference sites 

(Figure 4-11), but the decline in concentrations along the East Coast is more significant. 

The 3-year mean total NO3 level for 1990-1992 of 4.4 μg/m3 declined to 3.2 μg/m3 in 

2002-2005, a 27 percent reduction. The 1999 peak in mean nitrate was 4.5 μg/m3 . EPA has 

estimated about a 25 percent reduction in annual NOx emissions in the eastern United 

States over the period 1997-2004 (see Figure 4-9) and an approximate 50 percent decline 

in power industry NOx emissions during the ozone season for the same period. The 

relationship between low ozone along the East Coast and weather is clear from the trends. 

The decline in ozone, especially in 2005, is also related to the decline in NOx emissions 

and the corresponding decline in nitrate concentrations. 
CASTNET Annual Report – 2005 38 Chapter 5: Data Quality

Chapter 5: 

Data Quality 

The CASTNET Quality Assurance (QA) program was designed to ensure that all reported data 

are of known and documented quality in order to meet CASTNET objectives and to be 

reproducible and comparable with data from other monitoring networks and laboratories. The 

QA program elements are documented in the Quality Assurance Project Plan (QAPP), Revision 

2.1, (MACTEC, 2003b). The QAPP is comprehensive and includes standards and policies for all 

components of project operation from site selection through final data reporting. 

Estimating dry deposition requires the measurement of several meteorological parameters and 

information on vegetation and land use. The CASTNET data collection process and QA efforts 

were designed to ensure that the data collected meet program objectives. 

Data quality indicators (DQI) are quantitative statistics and qualitative descriptors used in 

interpreting the degree of acceptability and utility of the data collected. The DQI for CASTNET 

are precision, accuracy, completeness, bias, representativeness, and comparability. Precision, 

accuracy, and completeness for CASTNET 2005 data were analyzed and compared with 

historical data collected during the period 1990–2004. The information in this report is 

supplemented by analyses that are discussed in quarterly CASTNET Quality Assurance Reports 

(e.g., MACTEC, 2006b). These QA reports are produced four times per year with the fourth 

quarter report including an annual summary. Both historical and current data can be used with 

confidence since CASTNET data are always verified and validated through the use of the DQI 

and associated measurement criteria. CASTNET has produced and continues to produce data of 

the highest quality. 

Joshua Trees in Nevada 

The CASTNET quality assurance program is based on specified data quality objectives, 

which are evaluated using data quality indicators (DQI). Historical data and measurements for 

2005 can be used with confidence since CASTNET measurements are continually evaluated 

through the use of DQI and their associated measurement criteria. CASTNET has produced 

and continues to produce data of the highest quality. 
CASTNET Annual Report – 2005 39 Chapter 5: Data Quality

Figure 5-1 Historical and 2005 Precision Data for Atmospheric Concentrations 

Precision 

Exposed Filter Concentrations 

Figure 5-1 provides a bar chart in which the bars represent precision statistics for each 

CASTNET analyte in terms of mean absolute relative percent difference (MARPD) for both the 

historical (1990–2004) and the 2005 data for the collocated sites at Mackville, KY 

(MCK131/231) and Rocky Mountain National Park, CO (ROM406/206). Trace cations and 

chloride are excluded from this figure but are shown later in Figure 5-2. The historical results 

vary from about 4 percent for particulate sulfate (SO2-

4 ) to about 12 percent for particulate nitrate 

(NO3). The historical MARPD for SO2-

4 met the criterion for the CASTNET laboratory 

measurements shown in Table 5-1. The historical results for sulfur dioxide (SO2), nitric acid 

(HNO3), and ammonium (NH+ 

4 ) were above the 5 percent criterion but were considered 

reasonable. The results for NO3 were significantly above the 5 percent goal. Historically, the 

precision of NO3 measurements has been consistently worse than for the other analytes, possibly 

because NO3 concentrations are the lowest of all the pollutants, and nitrate species include 

sampling artifacts (Harding ESE, 2003). 

The 2005 precision results shown in Figure 5-1 indicate that the results for MCK131/231 were 

below (i.e., better than) the historical results for all five parameters. Four parameters (SO2, SO2-

4 , 

HNO3, and NH+ 

4 ) met precision criteria. The precision results for ROM406/206 were better than 

historical results for one parameter, HNO3. Only the result for NH+ 

4 met the DQI criterion.

Overall, the filter pack precision results for 2005 were about the same as 2004. 

0

2

4

6

8

10

12

14

16

SO2 SO4 HNO3 NO3 NH4

MARPD

Overall - 1990 to 2004

Mackville, KY - 2005

Rocky Mtn, CO - 2005

SO2 SO4

2- HNO3 NO3-

 NH4

+
CASTNET Annual Report – 2005 40 Chapter 5: Data Quality

Table 5-1 Data Quality Indicator Criteria for CASTNET Laboratory Measurements 

 Precision1 Accuracy2 Nominal 

Analyte Method (MARPD) (%) Reporting Limits 

Ammonium (NH +

4 ) Automated colorimetry 10 90 - 110 0.020 mg-N/L 

Sodium (Na +) ICP-AES 5 95 - 105 0.005 mg/L 

Potassium (K +) ICP-AES 5 95 - 105 0.005 mg/L 

Magnesium (Mg2+) ICP-AES 5 95 - 105 0.003 mg/L 

Calcium (Ca2+) ICP-AES 5 95 - 105 0.003 mg/L 

Chloride (Cl-) Ion chromatography 5 95 - 105 0.020 mg/L 

Nitrate (NO3) Ion chromatography 5 95 - 105 0.008 mg-N/L 

Sulfate (SO2-

4 ) Ion chromatography 5 95 - 105 0.040 mg/L 

Note: 1 This column lists precision goals for both network precision calculated from collocated filter samples and laboratory precision based 

on replicate samples. The goal for the ICP-AES precision RPD criterion changed from 10 percent to 5 percent at the onset of the new 

contract beginning on July 30, 2003. The precision criterion is applied as described below: 

 QC conditions: (v1 = initial response; v2 = replicate response; RL = nominal reporting limit) 

 Condition 1: if (v1 or v2 < RL and the absolute value of (v1 – v2) < RL) = OK 

 Condition 2: if (v1-v2) < RL and v1 < 5 x RL) = OK 

 Condition 3: if (v1 > 5*RL and RPD < 5%) = OK 

 Status: one of the conditions is OK = Precision QC Passes 

2

 This column lists laboratory accuracy goals based on reference standards and continuing calibration verification spikes. The goal for 

the ICP-AES accuracy criterion changed from 90 – 110 percent to 95 – 105 percent for continuing calibration verification spikes at 

the onset of the new contract beginning on July 30, 2003. The criterion remains 90 – 110 percent for ICP-AES reference standards. 

 

 ICP-AES = inductively coupled plasma-atomic emission spectrometry 

 MARPD = mean absolute relative percent difference 

 N = as nitrogen 

For more information on analytical methods and associated precision and accuracy criteria, see the CASTNET Quality Assurance Project Plan – 

Revision 2.1 (MACTEC, 2003b). 

Precision statistics for 2005 for four cations and chloride (Cl –

 ), based on collocated ambient 

concentrations, are summarized in Figure 5-2. The historical MARPD statistics for both 

MCK131/231 and ROM406/206 do not meet the DQI criterion of 5 percent, except for Cl –

 , 

which had a MARPD of approximately 5 percent. As discussed in the CASTNET 2002 QA 

Report (MACTEC, 2004) and in the CASTNET 2002 Annual Report (MACTEC, 2003a), the 

very high historical MARPD for sodium (Na +) was the result of sample bottle contamination. 

These bottles are no longer purchased. Also, acceptance testing of the Teflon® filter was 

instituted for the trace cations and Cl –

 in 2003. The 2005 precision results for cations and Cl – 

show that potassium (K +), Na +, and Cl –

 met the precision criterion at MCK131/231 and that Cl – 

met the criterion at ROM406/206. The MARPD for potassium measured by the two filter packs 

at ROM406/206 was about 18 percent. This relatively poor precision was caused by very low K +

concentrations at the park. Potassium is analyzed at a wavelength of 766.4 nanometers (nm) by 

the inductively coupled plasma-atomic emission spectrometry (ICP-AES) instrument. This is a 

difficult wavelength for the ICP-AES instrument because it is close to the wavelength of the 

carrier gas. Low concentration levels show more noise for K + and lower precision through 

repeatability as a result. 
CASTNET Annual Report – 2005 41 Chapter 5: Data Quality

Table 5-2 summarizes 2005 precision results by quarter for the two sets of collocated sites. The 

results indicate comparable performance in 2005 precision versus 2004 for MCK131/231 and a 

slight decline in precision for ROM406/206 2005 values versus 2004 (MACTEC, 2005a). 

Figure 5-2 Precision Data for Cation and Cl –

 Concentrations 

Table 5-2 Collocated Precision Results for 2005 by Quarter (MARPD) 

Site Pairs SO2-

4 NO3 NH+ 

4 Ca2+ Mg2+ Na + K + HNO3 SO2

Total 

NO3 Cl-

 MCK 131/231, KY

Quarter 1 2.16 8.50 3.60 19.38 8.78 4.84 5.42 7.74 4.97 4.24 5.38 

Quarter 2 2.29 8.34 2.15 6.74 6.88 2.64 4.52 3.08 1.64 4.05 0.76 

Quarter 3 2.43 14.38 3.41 5.39 5.58 7.47 4.86 3.32 2.64 4.46 0.76 

Quarter 4 3.68 8.93 3.30 7.62 11.16 5.31 5.77 4.06 3.01 5.23 7.58 

2005 2.64 10.04 3.12 9.79 8.10 5.07 5.14 4.55 3.07 4.50 3.62 

 ROM 406/206, CO

Quarter 1 4.41 13.65 3.40 9.77 13.81 6.18 26.70 5.64 9.10 4.76 2.93 

Quarter 2 7.08 11.78 7.87 8.08 8.15 8.83 8.77 6.92 10.95 6.18 2.89 

Quarter 3 7.67 15.89 7.22 10.28 11.62 8.51 15.04 2.63 7.17 3.25 2.59 

Quarter 4 5.49 12.69 5.50 12.31 9.13 7.75 21.17 5.37 8.43 4.89 5.18 

2005 6.16 13.50 6.00 10.11 10.68 7.82 17.92 5.14 8.91 4.77 3.40 

0

5

10

15

20

25

Ca K Mg Na Cl

Overall - 2000 to 2004

Mackville, KY - 2005

Rocky Mtn, CO - 2005

MARPD

Ca2+ K+ Mg2+ Na+ Cl-
CASTNET Annual Report – 2005 42 Chapter 5: Data Quality

The 2005 analytical precision results for five analytes and the three filter types are presented in 

Figure 5-3. The results were based on analysis of five percent of the samples that were randomly 

selected for replication in each batch. The results of in-run replicate analyses were compared 

to the results of the original concentrations. The laboratory precision data met the 5 percent 

measurement criterion listed in Table 5-1. 

Figure 5-3 Precision Results for Laboratory Replicate Samples (2005) 

Ozone Concentrations 

CASTNET QA procedures for the EPA-sponsored ozone (O3) analyzers are different from the 

EPA QA requirements for State and Local Monitoring Stations (SLAMS) monitoring 

(EPA, 1998). The QA procedures for the O3 analyzers at the NPS-sponsored sites also do not 

meet the SLAMS requirements. While NPS utilizes the appropriate procedures and equipment, 

the NPS sites are calibrated twice per year versus the SLAMS requirements of four times per 

year. In any event, the operation of the collocated O3 analyzers at ROM406/206, CO provides an 

opportunity to evaluate the precision of the independent systems. Table 5-3 provides the DQI 

criteria for the CASTNET continuous measurements including O3. The precision criterion for the 

collocated O3 data is 10 percent. 

0

1

2

3

4

5

Nylon SO4

Cellulose SO4

Teflon SO4

Nylon NO3

Teflon NO3

Teflon NH4

Sodium

Potassium

Magnesium

Calcium

Chloride

Mean Absolute Relative Percent

Difference for In-Run Replicates

Teflon

SO4

2-

contribute to SO 2

Nylon

SO4

2-

Nylon

NO3

-

Teflon

NH4

+

Cellulose

SO4

2-

Teflon

NO3

-

Teflon

Na+

Teflon

K+

Teflon

Mg2+

Teflon

Ca2+

Teflon

Cl-
CASTNET Annual Report – 2005 43 Chapter 5: Data Quality

Table 5-3 Data Quality Indicator Criteria for CASTNET Field Measurements 

Measurement Criteria* 

Parameter Method Precision Accuracy 

Wind Speed Anemometer ± 0.5 m/s The greater of ± 0.5 m/s for winds < 5 

m/s or ± 5% for winds ≥ 5 m/s 

Wind Direction Wind Vane ± 5° ± 5° 

Sigma Theta Wind Vane Undefined Undefined 

Relative Humidity Thin Film Capacitor ± 10% (of full scale) ± 5%, relative humidity > 85% 

± 20%, relative humidity ≤ 85% 

Solar Radiation Pyranometer ± 10% (of reading taken at local 

noon) ± 10% 

Precipitation Tipping Bucket Rain Gauge ± 10% (of reading) ± 0.05 inch† 

Ambient Temperature Platinum RTD ± 1.0°C ± 0.5°C 

Delta Temperature Platinum RTD ± 0.5°C ± 0.5°C 

Surface Wetness Conductivity Bridge Undefined Undefined 

Ozone UV Absorbance ± 10% (of reading) ± 10% 

Filter Pack Flow Mass Flow Controller ± 10% ± 5% 

Note: 

 °C = degrees Celsius 

 m/s = meters per second 

 RTD = resistance-temperature device 

 UV = ultraviolet 

 * Precision criteria apply to collocated instruments, and accuracy criteria apply to calibration of instruments. 

 † For target value of 0.50 inch. 

MARPD statistics were calculated from hourly O3 measurements obtained from the collocated 

sites MCK131/231, KY and ROM406/206, CO during 2005. In addition, quarterly historical 

precision statistics were compiled for all collocated sites. Quarterly precision results are 

summarized in Figure 5-4. The data show the historical results met the 10 percent criterion. The 

2005 precision data also met the 10 percent criterion for all four quarters for both MCK131/231 

and ROM406/206. The results for ROM406/206 indicate that the two independently operated O3

analyzers with different QA/quality control (QC) procedures produce nearly identical results.

MCK131/231, KY ROM406/206, CO 
CASTNET Annual Report – 2005 44 Chapter 5: Data Quality

Figure 5-4 Historical and 2005 Precision Data by Quarter for Ozone Concentrations 

Accuracy 

Laboratory Filter Concentrations 

Accuracy of laboratory measurements is assessed through the analysis of reference samples and 

continuing verification samples (CVS). Reference samples and CVS are procured from 

independent suppliers and are National Institute of Standards and Technology (NIST) traceable. 

Reference samples are analyzed at the beginning and end of each analytical batch to verify the 

accuracy and stability of the calibration curve. The target value of the CVS solution is set to 

the midrange of the calibration curve. The CVS in 2005 were analyzed every tenth sample to 

verify no drift in the calibration curve. Table 5-4 presents the percent recoveries and standard 

deviations for reference samples and CVS relative to target concentrations. The table shows 

that the DQI goals (see Table 5-1) were met in 2005. Table 5-4 also lists the precision results 

that were shown in Figure 5-3. 

0

2

4

6

8

10

12

14

First

Quarter

Second

Quarter

Third

Quarter

Fourth

Quarter

Overall - 1990 to 2004

Mackville, KY - 2005

Rocky Mtn, CO - 2005

MARPD

Shenandoah National Park, VA Photo: NPS 
CASTNET Annual Report – 2005 45 Chapter 5: Data Quality

Table 5-4 Filter Pack QC Summary for 2005 

Reference 

Sample1 Recovery (%R) 

Continuing Verification 

Samples (%R) 

In-Run Replicate2

(RPD) 

 Filter Type  Parameter 

 Mean  Std. Dev.  Count3  Mean  Std. Dev.  Count3  Mean  Std. Dev.  Count3 

Teflon® SO2-

4 100.08 2.07 171 99.57 1.04 879 0.55 0.86 303 

 NO3 102.45 1.02 171 99.01 1.19 879 2.16 2.50 303 

 NH+ 

4 98.83 2.53 180 100.70 2.48 838 0.62 0.62 193 

 Ca2+ 103.27 2.19 201 100.65 0.99 768 1.95 3.28 316 

 Mg2+ 101.40 1.31 201 100.10 0.77 768 2.01 2.47 316 

 Na+

94.58 1.05 201 100.04 0.88 768 1.45 1.79 316 

 K+

103.14 2.28 201 100.34 0.88 768 2.87 2.92 316 

 Cl- 101.78 1.63 171 99.28 1.31 875 1.69 2.92 303 

Nylon SO2-

4 101.16 2.39 142 99.41 1.79 690 2.13 3.00 283 

NO3 101.68 1.06 147 99.04 1.46 697 1.18 1.57 285 

Cellulose SO2-

4 101.38 0.70 180 99.12 0.70 696 4.12 6.60 253 

Note: % R = percent recovery 

 RPD = relative percent difference 

1

 Results of reference sample analyses provide accuracy estimates 

2 Results of replicate analyses provide precision estimates 3

 Number of QC Samples 

Continuous Measurements 

Table 5-5 presents field accuracy results for 2005 based on instrument challenges performed 

using independent reference standards during site calibration visits. CASTNET sites were 

calibrated every six months with NIST-traceable standards. Each parameter was within its 

criterion with at least 90 percent frequency with the exception of high (> 85%) relative humidity 

at 80.3 percent and solar radiation at 86.6 percent. However, these results did not adversely 

affect data collection because data are not considered invalid unless criteria are exceeded by 

more than two times the criterion. Using the two times standard, relative humidity passed with 

95 percent frequency and solar radiation passed with 97 percent frequency. During 2006, a 

portable relative humidity chamber will be used as the calibration transfer for testing the 

accuracy of the relative humidity sensors. Using a humidity chamber instead of transfer salts will 

provide a better gauge of the relative humidity sensor performance. 
CASTNET Annual Report – 2005 46 Chapter 5: Data Quality

Table 5-5 Accuracy Results for 2005 Field Measurements 

 Parameter Percent Within Criterion 

Temperature (0°C) 95 percent 

Temperature (ambient) 97 percent 

Delta Temperature (0°C) 96 percent 

Delta Temperature (ambient) 95 percent 

*Relative Humidity > 85% 80 percent 

Relative Humidity ≤ 50% 98 percent 

*Solar Radiation 87 percent 

Wind Direction North 92 percent 

Wind Direction South 94 percent 

Wind Speed < 5 m/s 99 percent 

Wind Speed ≥ 5 m/s 98 percent 

Precipitation 100 percent 

Wetness (w/in 0.5 volts) 99 percent 

Ozone Slope 97 percent 

Ozone Intercept 99 percent 

Flow Rate 94 percent 

Note: °C = degrees Celsius. 

 m/s = meters per second.

 * = Per CASTNET project protocols, data are flagged as “suspect” (S) but still considered valid if the calibration criterion is not 

exceeded by more than its magnitude (i.e., if within 2x the criterion). The percent within 2x criterion for relative humidity 

> 85 percent was 95.1 percent. The percent within 2x criterion for solar radiation was 96.6 percent. 

Completeness 

Completeness is defined as the percentage of valid data points obtained from a measurement 

system relative to total possible data points expected to be obtained. The CASTNET 

measurement criterion for completeness requires a minimum completeness of 90 percent for 

every measurement for each quarter. In addition, data aggregation procedures require 

approximately 70 percent completeness for hourly fluxes and weekly concentrations/fluxes. 

Figure 5-5 presents historical and 2005 completeness data for all sites for measured filter 

concentrations, continuous measurements, and calculated parameters. The figure shows that the 

2005 direct measurements met the 90 percent goal. The 2005 results show that data completeness 

exceeded 95 percent for six parameters, including filter pack flow. The four parameters derived 

from model results exceeded 75 percent completeness for 2005. Historical results are better for 

atmospheric concentrations, wind speed, temperature, ozone, and annual mean atmospheric 

concentrations. 
CASTNET Annual Report – 2005 47 Chapter 5: Data Quality

Figure 5-5 Historical* and 2005 Percent Completeness of Measurements and Modeled 

Estimates 

Note: 

 * Black bars represent 1990-2004 data 

Laboratory Intercomparison Studies

MACTEC participates in the U.S. Geological Survey (USGS) interlaboratory comparison 

program. Overall, eight laboratories participate in the program, receiving four samples for 

chemical analysis from USGS every two weeks. The samples are a mix of synthetically 

prepared samples, deionized water, and natural wet deposition samples. MACTEC 

reported the eight parameters of interest for CASTNET for 104 USGS samples during 

2005. MACTEC 2005 median values for all of the parameters analyzed were within 

10 percent of the target values. 

 

MACTEC generally participates in two studies by the National Water Research Institute 

(NWRI) of Canada’s Proficiency Testing QA Program each year in addition to 

interlaboratory comparison studies for the USGS. During the 2005 studies, MACTEC’s 

laboratory achieved the “Ideal” rating (i.e., results were within two standard deviations of 

the study’s assigned value) for seven of the eight CASTNET parameters tested with one 

sample result for sulfate listed between two and three standard deviations. The 

performance of the laboratory was rated as being free of systematic bias for all eight 

parameters. MACTEC was ranked number 5 out of 39 participating laboratories as of the 

end of 2005. 

65 70 75 80 85 90 95 100

Annually Aggregated Flux Estimates

Annual Mean Deposition Velocities

Annual Mean Atm. Concentrations

Hourly Flux Estimates

Surface Wetness

Filter Pack Flow

Ozone

Delta Temperature

Ambient Temperature

Precipitation

Solar Radiation

Relative Humidity

Sigma Theta

Wind Direction

Scalar Wind Speed

Vector Wind Speed

Atmospheric Concentrations

Percent Completeness

Meteorological

Parameters

DQI Measurement Criterion

Model

Results
CASTNET Annual Report – 2005 48 Chapter 5: Data Quality

Conclusion 

DQI results demonstrate that field and laboratory processes were adequately monitored through 

QA/QC procedures and generally free of systematic bias during 2005. Accuracy data met the 

established criteria for field and laboratory parameters with the exception of relative humidity 

> 85 percent and solar radiation. However, since the criterion was exceeded by a value less than 

its own magnitude, the associated continuous data collected are considered valid. 

Precision data for sulfur constituents and ammonium are considered acceptable. Precision data 

for nitrate analyses of collocated field samples have not met the established criterion due, most 

likely, to the low concentrations generally measured and the unpredictable nature of the 

gas-particle equilibrium of the nitrate species. Completeness criteria were met for all parameters 

in 2005. 
CASTNET Annual Report – 2005 R-1 References

References 

Ames, R.B. and Malm, W.C. 2001. Comparison of Sulfate and Nitrate Particle Mass 

Concentrations Measured by IMPROVE and the CDN. Atmospheric Environment. 

Vol. 35(5) 905-916. 

Baumgardner Jr., R.E., Lavery, T.F., Rogers, C.M., and Isil, S.S. 2002. Estimates of the 

Atmospheric Deposition of Sulfur and Nitrogen Species: Clean Air Status and Trends 

Network, 1990-2000. Environmental Science and Technology. 36(12):2,614-2,629. 

Finkelstein, P.L., Ellestad, T.G., Clarke, J.F., Meyers, T.P., Schwede, D.B., Hebert, E.O., and 

Neal, J.A. 2000. Ozone and Sulfur Dioxide Dry Deposition to Forests: Observations and 

Model Evaluation. J. Geophys. Res. 105:D12:15,365-15,377. 

Harding ESE, Inc., now known as MACTEC Engineering and Consulting, Inc. (MACTEC). 

2003. Clean Air Status and Trends Network (CASTNET) 2001 Quality Assurance Report. 

Prepared for U.S. Environmental Protection Agency (EPA), Office of Air and Radiation, 

Research Triangle Park, NC, Contract No. 68-D-98-112. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2006a. Clean Air Status and Trends 

Network (CASTNET) Fourth Quarter 2005 Data Report. Prepared for U.S. 

Environmental Protection Agency (EPA), Office of Air and Radiation, Clean Air Markets 

Division, Washington, D.C. Contract No. 68-D-03-052. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2006b. Clean Air Status and Trends 

Network (CASTNET) Quality Assurance Report: Fourth Quarter 2005 (OctoberDecember) with 2005 Annual Summary. Prepared for U.S. Environmental Protection 

Agency (EPA), Office of Air and Radiation, Clean Air Markets Division, Washington, 

D.C. Contract No. 68-D-03-052. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2006c. Clean Air Status and Trends 

Network (CASTNET) Third Quarter 2005 Data Report. Prepared for U.S. Environmental 

Protection Agency (EPA), Office of Air and Radiation, Clean Air Markets Division, 

Washington, D.C. Contract No. 68-D-03-052. Gainesville, FL. 
CASTNET Annual Report – 2005 R-2 References

References (continued) 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2005a. Clean Air Status and Trends 

Network (CASTNET) 2004 Annual Report. Prepared for U.S. Environmental Protection 

Agency (EPA), Office of Air and Radiation, Clean Air Markets Division, Washington, 

D.C. Contract No. 68-D-03-052. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2005b. Clean Air Status and Trends 

Network (CASTNET) First Quarter 2005 Data Report. Prepared for U.S. Environmental 

Protection Agency (EPA), Office of Air and Radiation, Clean Air Markets Division, 

Washington, D.C. Contract No. 68-D-03-052. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2005c. Clean Air Status and Trends 

Network (CASTNET) Second Quarter 2005 Data Report. Prepared for U.S. 

Environmental Protection Agency (EPA), Office of Air and Radiation, Clean Air Markets 

Division, Washington, D.C. Contract No. 68-D-03-052. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2004. Clean Air Status and Trends 

Network (CASTNET) 2002 Quality Assurance Report. Prepared for U.S. Environmental 

Protection Agency (EPA), Research Triangle Park, NC, Contract No. 68-D-03-052. 

Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2003a. Clean Air Status and Trends 

Network (CASTNET) 2002 Annual Report. Prepared for U.S. Environmental Protection 

Agency (EPA), Research Triangle Park, NC, Contract No. 68-D-03-052. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2003b. Clean Air Status and Trends 

Network (CASTNET) Quality Assurance Project Plan (QAPP), Revision 2.1. Prepared 

for U.S. Environmental Protection Agency (EPA), Research Triangle Park, NC, Contract 

No. 68-D-98-112. Gainesville, FL. 

Meyers, T. P., Finkelstein, P., Clarke, J., Ellestad, T.G., and Sims, P.F. 1998. A Multilayer 

Model for Inferring Dry Deposition Using Standard Meteorological Measurements. 

J. Geophys. Res. 103D17:22,645-22,661. 

Rogers, C.M., Howell, H.K., and Lavery, T.F. 2006a. The Surprising Decline in Rural Ozone 

Concentrations in the Eastern United States. Electric Utility Environmental Conference. 

Tucson, January 22-25. 
CASTNET Annual Report – 2005 R-3 References

References (continued) 

Rogers, C.M., Howell, H.K., and Lavery, T.F. 2006b. Uncertainties in CASTNET NO3 and 

HNO 

3 Measurements. Paper # 06-C-858-AWMA. Air & Waste Management 

Association (AWMA) 99th Annual Conference. New Orleans, June 20-23. 

Schwede, D.B. 2006. A Comparison of the Deposition Velocity Estimates from the CASTNET 

and CAPMoN Networks. (Working paper). Research Triangle Park, NC. 

U.S. Department of Energy (DOE). 1997. The Effects of Title IV of the Clean Air Act 

Amendments of 1990 on Electric Utilities: An Update. Energy Information 

Administration, Office of Coal, Nuclear, Electric and Alternate Fuels, U.S. Department 

of Energy, Washington, DC. DOE/EIA-0582(97). 

U.S. Environmental Protection Agency (EPA). 2006. NOx Budget Trading Program. 2005 

Program Compliance and Environmental Results. EPA 430-R-06-013. September 2006. 

U.S. Environmental Protection Agency (EPA). 2005a. Acid Rain Program 2004 Progress 

Report. EPA 430-R-05-012. October 2005. 

U.S. Environmental Protection Agency (EPA). 2005b. Evaluating Ozone Control Programs in 

the Eastern United States. EPA 454-K-05-001. August 2005. 

U.S. Environmental Protection Agency (EPA). 2000. National Air Quality and Emissions 

Trends Report, 1998. EPA-454-R-00-003. OAQPS, RTP, NC 27711. 

 

U.S. Environmental Protection Agency (EPA). 1998. Quality Assurance Requirements for State 

and Local Air Monitoring Stations (SLAMS). 40 CFR 50, Appendix L. 

U.S. Environmental Protection Agency (EPA). 1997. National Ambient Air Quality Standards 

for Ozone. 40 CFR 50. 
AAppppeennddiixxAA

Significant Events During 2005
CASTNET Annual Report – 2005 Appendix A

Significant Events During 2005

January 

Ozone monitoring was discontinued at NPS-sponsored site EVE419, FL beginning January 1, 2005. 

February 

NPS-sponsored site SEK402, CA temporarily stopped sampling on February 24, 2005, when the site was dismantled 

and relocated. 

NPS-sponsored site OLY421, WA stopped all sampling at the end of February 2005. 

April 

NPS-sponsored site SEK402, CA was moved to another location in Sequoia National Park and resumed sampling on 

April 7, 2005 with the new designation of SEK430. 

June 

Low-power ozone analyzers were installed at the solar-powered sites, LYE145, VT and CAT175, NY. 

The first two Monitoring Instruments for Aerosols and Gases (MARGA) were installed at the BEL116, MD site. 

July 

An independent audit of the CASTNET field operations center in Gainesville, FL was conducted by Environmental 

Forward Observer, LLC. CASTNET operations were judged as satisfactory. 

Preliminary, screened data became available within 48 hours of collection on the CASTNET web page: 

www.epa.gov/castnet 

August 

The annual “floor-to-ceiling audit of CASTNET property was conducted by EPA and the Defense Contract 

Management Agency at MACTEC’s Gainesville, FL location. The property management system was approved 

by the audit. 

Hurricane Katrina damaged a CASTNET site in Mississippi (CVL151). 

September 

Hurricane Rita damaged a CASTNET site in Texas (ALC188). 

KVA428, AK stopped all sampling at the end of September 2005. 

October 

External audits of EPA- and NPS-sponsored CASTNET sites began. 

Hurricane Wilma damaged CASTNET sites in Florida (EVE419 and IRL141). 

December 

After testing and evaluation, a new laboratory information management system (LIMS) was approved for use with 

CASTNET data. 
AAppppeennddiixxBB

Locational and Operational Characteristics of CASTNET Sites
CASTNET Annual Report – 2005 B-1 

Table B-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter 

Pack1 

Ozone and 

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

Alabama SND152 Sand Mountain 12/27/88 34.2894 85.9704 352 • • Agri. RAlaska DEN417 Denali National Park 10/06/98 63.7258 148.9633 661 • • Forested CArizona CHA467 Chiricahua National Monument 04/25/89 32.0092 109.3892 1570 • • ◊ Range CGRC474 Grand Canyon National Park 05/16/89 36.0597 112.1822 2073 • • Forested CPET427 Petrified Forest National Park 09/24/02 34.8225 109.8919 1723 • • Desert FlArkansas CAD150 Caddo Valley 10/04/88 34.1792 93.0989 71 • • Forested RCalifornia CON186 Converse Station 06/17/03 34.1941 116.9130 1837 • • Agri./Forested CDEV412 Death Valley National Monument 02/21/95 36.5092 116.8481 125 • • Desert CJOT403 Joshua Tree National Monument 02/16/95 34.0714 116.3906 1244 • • Desert CLAV410 Lassen Volcanic National Park 07/25/95 40.5403 121.5764 1756 • • Forested CPIN414 Pinnacles National Monument 05/16/95 36.4850 121.1556 335 • • Forested CSEK430 Sequoia National Park 04/07/05 36.4894 118.8269 457 • • Forested MYOS404 Yosemite National Park 09/25/95 37.7133 119.7061 1605 • • Forested C
CASTNET Annual Report – 2005 B-2 

Table B-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter 

Pack1 

Ozone and 

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

Colorado GTH161 Gothic 05/16/89 38.9573 106.9854 2926 • • ◊ Range CMEV405 Mesa Verde National Park 01/10/95 37.1983 108.4903 2165 • • Forested CROM206 Rocky Mountain National Park 07/03/01 40.2778 105.5453 2743 • • Forested CROM406 Rocky Mountain National Park 12/20/94 40.2778 105.5453 2743 • • Forested CConnecticut ABT147 Abington 12/28/93 41.8402 72.0111 209 • • ◊ Urban-Agri. RFlorida EVE419 Everglades National Park 10/06/98 25.3911 80.6806 2 • •4 Swamp FIRL141 Indian River Lagoon 07/09/01 30.1065 80.4554 2 • • Beach FSUM156 Sumatra 12/28/88 30.1065 84.9938 14 • • ◊ Forested FGeorgia GAS153 Georgia Station 06/28/88 33.1812 84.4100 270 • • Agri. RIllinois ALH157 Alhambra 06/28/88 38.8690 89.6229 164 • • ◊ Agri. FBVL130 Bondville 02/09/88 40.0520 88.3725 212 • • Agri. FSTK138 Stockton 12/28/93 42.2872 89.9998 274 • • Agri. R
CASTNET Annual Report – 2005 B-3 

Table B-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter 

Pack1 

Ozone and 

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

Indiana SAL133 Salamonie Reservoir 06/28/88 40.8164 85.6608 250 • • Agri. FlVIN140 Vincennes 08/04/87 38.7406 87.4844 134 • • Agri. RKansas KNZ184 Konza Prairie 03/26/02 39.1021 96.6096 348 • • Prairie FlKentucky CDZ171 Cadiz 10/01/93 36.7841 87.8500 189 • • Agri. RCKT136 Crockett 08/24/93 37.9211 83.0658 455 • • Agri. RMAC426 Mammoth Cave National Park 07/24/02 37.1319 86.1478 243 • • Agri./Forested RMCK131 Mackville 07/31/90 37.7044 85.0483 353 • • Agri. RMaine ACA416 Acadia National Park 12/01/98 44.3769 68.2608 158 • • Forested CASH135 Ashland 12/20/88 46.6039 68.4142 235 • • Agri. FlHOW132 Howland 11/24/92 45.2158 68.7085 69 • • Forested RMaryland BEL116 Beltsville 11/01/88 39.0283 76.8175 46 • • Urban-Agri. FlBWR139 Blackwater National Wildlife Refuge 07/04/95 38.4448 76.1115 4 • • Forest-Marsh C
CASTNET Annual Report – 2005 B-4 

Table B-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter 

Pack1 

Ozone and 

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

Michigan ANA115 Ann Arbor 06/28/88 42.4164 83.9019 267 • • ◊ Forested FlHOX148 Hoxeyville 10/31/00 44.1809 85.7390 298 • • Forested FlUVL124 Unionville 06/28/88 43.6139 83.3597 201 • • ◊ Agri. FlMinnesota VOY413 Voyageurs National Park 06/13/96 48.4128 92.8292 429 • • Forested RMississippi CVL151 Coffeeville 12/27/88 34.0028 89.7989 134 • • Forested RMontana GLR468 Glacier National Park 12/27/88 48.5103 113.9956 976 • • Forested CNevada GRB411 Great Basin National Park 05/16/95 39.0053 114.2158 2060 • • Forested CNew Hampshire WST109 Woodstock 12/27/88 43.9446 71.7008 258 • • Forested CNew Jersey WSP144 Washington’s Crossing 12/27/88 40.3133 74.8726 61 • • Urban-Agri. R
CASTNET Annual Report – 2005 B-5 

Table B-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter 

Pack1 

Ozone and 

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

New York CAT175 Claryville 05/10/94 41.9423 74.5519 765 • •5 Forested CCTH110 Connecticut Hill 09/28/87 42.4010 76.6535 515 • • ◊ Forested RHWF187 Huntington Wildlife Forest 05/28/02 43.9732 74.2232 502 • • Forested CNorth Carolina BFT142 Beaufort 12/28/93 34.8843 76.6213 2 • • ◊ Agri. FlCND125 Candor 09/25/90 35.2643 79.8382 198 • • ◊ Forested RCOW137 Coweeta 11/04/87 35.0605 83.4302 686 • • Forested CPNF126 Cranberry 12/27/88 36.1040 82.0448 1250 • • ◊ Forested MNorth Dakota THR422 Theodore Roosevelt National Park 10/06/98 46.8947 103.3778 850 • • Range ROhio DCP114 Deer Creek State Park 09/28/88 39.6358 83.2600 267 • • ◊ Agri. RLYK123 Lykens 01/10/89 40.9169 82.9981 303 • • ◊ Agri. FlOXF122 Oxford 08/18/87 39.5314 84.7231 284 • • Agri. RQAK172 Quaker City 09/28/93 39.9431 81.3378 372 • • Agri. ROklahoma CHE185 Cherokee Nation 04/02/02 35.7507 94.6700 299 • • Agri. ROntario EGB181 Egbert, Ontario 12/27/94 44.2317 79.7840 251 •6 •4 Agri. R
CASTNET Annual Report – 2005 B-6 

Table B-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter 

Pack1 

Ozone and 

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

Pennsylvania ARE128 Arendtsville 06/28/88 39.9231 77.3078 269 • • ◊ Agri. RKEF112 Kane Experimental Forest 01/03/89 41.5981 78.7683 622 • • Forested RLRL117 Laurel Hill State Park 12/15/87 39.9883 79.2522 615 • • Forested CMKG113 M.K. Goddard State Park 01/12/88 41.4250 80.1447 384 • • Forested RPSU106 Penn. State University 01/06/87 40.7209 77.9316 376 • • Agri. RSouth Dakota WNC429 Wind Cave National Park 11/18/03 43.5578 103.4839 1292 • • Prairie RTennessee ESP127 Edgar Evins State Park 03/22/88 36.0389 85.7330 302 • • Forested RGRS420 Great Smoky Mountains National Park 10/06/98 35.6331 83.9422 793 • • Forested CSPD111 Speedwell 06/12/89 36.4698 83.8265 361 • • ◊ Agri. RTexas ALC188 Alabama-Coushatta 04/02/04 30.4210 94.4045 101 • • Forested RBBE401 Big Bend National Park 07/18/95 29.3022 103.1772 1052 • • Forested CUtah CAN407 Canyonlands National Park 01/24/95 38.4586 109.8211 1809 • • Desert CVermont LYE145 Lye Brook 03/30/94 43.0510 73.0613 730 • •5 ◊ Forested M
CASTNET Annual Report – 2005 B-7 

Table B-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter 

Pack1 

Ozone and 

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

Virginia PED108 Prince Edward 11/03/87 37.1653 78.3070 150 • • ◊ Forested RSHN418 Shenandoah National Park 06/28/88 38.5231 78.4347 1073 • • Forested MVPI120 Horton Station 06/02/87 37.3300 80.5573 920 • • Forested MWashington MOR409 Mount Rainier National Park 08/29/95 46.7583 122.1244 415 • • Forested CNCS415 North Cascades National Park 02/14/96 48.5397 121.4472 109 • • Forested CWest Virginia CDR119 Cedar Creek State Park 11/10/87 38.8794 80.8478 234 • • ◊ Forested CPAR107 Parsons 01/19/88 39.0906 79.6614 510 • • Forested CWisconsin PRK134 Perkinstown 09/27/88 45.2066 90.5972 472 • • ◊ Agri. RWyoming CNT169 Centennial 08/19/91 41.3722 106.2422 3178 • • Range CPND165 Pinedale 12/27/88 42.9214 109.7900 2388 • • Range RYEL408 Yellowstone National Park 06/26/96 44.5597 110.4006 2400 • • Forested R
CASTNET Annual Report – 2005 B-8 

1. The dry deposition filters are analyzed for the following constituents: 

Teflon® = SO2-4 , NO- 3, NH+ 4 , Cl -, K +, Na +, Mg2+, Ca2+

Nylon = SO2-4 , NO- 3 (reported as HNO3)

Cellulose = SO2-4 (reported as SO2)

2. Meteorological sensors: temperature, delta temperature, relative humidity, solar radiation, 

vector wind speed, scalar wind speed, wind direction, sigma theta, surface wetness, and precipitation via tipping bucket rain gauge. 

3. N = No; Y = Yes; M = Marginal; N/A = Not Applicable. 4. O3 not measured. 

5. Solar-powered sites. 6. Composite filter pack, day filter pack, and night filter pack. 

• Indicates current monitoring. 

◊ Indicates discontinued monitoring. 

 Measurements were discontinued at the variou

including: 

(1) rotate limited number of instrum(2) redundant measurements (e.g.(3) funding limitations. 

100 and 200 series = EPA – Operated Sites 400 series = NPS – Operated Sites 141 site = St. Johns River Water M
AAppppeennddiixxCC

Acronyms and Abbreviations
CASTNET Annual Report – 2005 Appendix C C-1 

List of Acronyms and Abbreviations

ARP Acid Rain Program 

°C degrees Celsius 

Ca2+

 particulate calcium ion 

CAAA Clean Air Act Amendments 

CAPMoN Canadian Air and Precipitation Monitoring Network 

CASTNET Clean Air Status and Trends Network 

Cl- particulate chloride ion 

CO carbon monoxide 

CVS continuing verification samples 

DQI data quality indicator 

EPA U.S. Environmental Protection Agency 

HNO 

3 nitric acid 

HQ EPA Headquarters 

ICP-AES inductively coupled plasma-atomic emission spectrometry 

IMPROVE Interagency Monitoring of Protected Visual Environments 

ITEC Inter-Tribal Environmental Council 

K+ particulate potassium ion 

K 

2CO 3 potassium carbonate 

kg/ha/yr kilograms per hectare per year 

km kilometer 

LAI leaf area index 

LIMS laboratory information management system 

MACT maximum available control technology 

MACTEC MACTEC Engineering and Consulting, Inc. 

MARGA monitoring instrument for aerosols and gases 

MARPD mean absolute relative percent difference 

MDN Mercury Deposition Network 

Mg2+

 particulate magnesium ion 

mg/L milligrams per liter 

MLM Multi-Layer Model 

mm millimeter 

N nitrogen 

Na+ particulate sodium ion 

NAAQS National Ambient Air Quality Standards 

NADP/NTN National Atmospheric Deposition Program/National Trends Network
CASTNET Annual Report – 2005 Appendix C C-2 

List of Acronyms and Abbreviations (continued) 

NBP NOx Budget Trading Program 

NDDN National Dry Deposition Network 

NH3 ammonia 

NH +

4 particulate ammonium 

NH 

4NO 3 ammonium nitrate 

(NH 

4)

 

2SO 4 ammonium sulfate 

NIST National Institute of Standards and Technology 

nm nanometer 

NO -

3 particulate nitrate 

NO 

x nitrogen oxides 

NO 

y total reactive oxides of nitrogen 

NPS National Park Service 

NWRI National Water Research Institute 

O 

3 ozone 

OTC Ozone Transport Commission 

ppb parts per billion 

ppm parts per million 

QA quality assurance 

QAPP Quality Assurance Project Plan 

QC quality control 

RACT reasonably available control technology 

S sulfur 

SIP State Implementation Plan 

SLAMS State and Local Monitoring Stations 

SO 

2 sulfur dioxide 

SO2-

4 particulate sulfate 

total NO3 gaseous nitric acid (HNO 

3) + particulate nitrate (NO3) 

μg/m3 micrograms per cubic meter 

USGS U.S. Geological Survey 

V 

d deposition velocity 

VOC volatile organic compounds 

W/m2 watts per square meter
For More Information

U.S. Environmental Protection Agency

Office of Air and Radiation

Clean Air Markets Division

Washington, D.C.

On the Web:

CASTNET Home Page: Clean Air Markets EPA Home Page:

Division Home Page:

www.epa.gov/castnet www.epa.gov/airmarkets www.epa.gov