2004 Annual Report

Prepared for:

U. S. Environmental Protection Agency

Office of Air and Radiation

Clean Air Markets Division 

Washington, DC November 2005

Clean Air Status and Trends Network 

(CASTNET)

Clean Air Status and Trends Network 

(CASTNET) 

2004 Annual Report 

Prepared by: 

Engineering and Consulting, Inc. 

Prepared for: 

U.S. Environmental Protection Agency 

Office of Air and Radiation 

Clean Air Markets Division 

Washington, DC 

November 2005 

Table of Contents 

Chapter 1 CASTNET Program Introduction........................................................................1

 Monitoring Network ................................................................................................3 

 CASTNET Measurements.......................................................................................4 

Modeling and Data Management.............................................................................5 

 Quality Assurance....................................................................................................6 

 Instrument Comparison Project ...............................................................................7 

Significant Events During 2004...............................................................................9 

 SO 

2 and NOx Emissions.........................................................................................10 

Chapter 2 Atmospheric Concentrations..............................................................................11

 Sulfur Dioxide........................................................................................................11 

 Particulate Sulfate ..................................................................................................13 

 Total Nitrate ...........................................................................................................15 

 Particulate Ammonium..........................................................................................16 

Bias in NO3 and HNO 

3 Measurements...................................................................18 

Chapter 3 Deposition of Sulfur and Nitrogen......................................................................19 

 Sulfur Deposition...................................................................................................20 

Contributors to Atmospheric Deposition Measured at CASTNET 

Eastern Reference Sites..........................................................................................24 

 Nitrogen Deposition...............................................................................................25 

African Saharan Aerosols (Dust) in CASTNET....................................................29 

Chapter 4 Ozone Concentrations .........................................................................................31 

Design Values for Ozone Concentrations for 2002 through 2004.........................31 

 Eight-Hour Ozone Concentrations.........................................................................33 

 Fifteen-Year Trends...............................................................................................34 

 CASTNET Ozone Measurements..........................................................................37 

Chapter 5 Data Quality .........................................................................................................39

 Precision.................................................................................................................40 

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

 CASTNET Sample Handling.................................................................................46 

 Completeness.........................................................................................................47 

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

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

Appendix A Locational and Operational Characteristics of CASTNET Sites................. A-1

CASTNET Annual Report – 2004 i Table of Contents 
List of Tables and Figures 

Chapter 1 CASTNET Program Introduction 

Figure 1-1 CASTNET Sites as of December 2004 

Figure 1-2 Three-Stage Filter Pack 

Figure 1-3 Multi-Layer Model 

Figure 1-4 Monitoring Instrument for Aerosols and Gases (MARGA)

Figure 1-5 Trends in SO 

2 and NO x Emissions 

Figure 1-6 Annual Utility SO 

2 Emissions (Phase I and Phase II Plants, only) for 2004

Figure 1-7 Annual Utility NO 

x Emissions (Phase I and Phase II Plants, only) for 2004

Table 1-1 Instrument Specifications for Semi-Continuous Monitoring 

Chapter 2 Atmospheric Concentrations 

Figure 2-1 CASTNET Reference Sites 

Figure 2-2 Annual Mean SO 

2 Concentrations (μg/m3

) for 2004 

Figure 2-3 Trend in Annual Mean SO 

2 Concentrations (μg/m3

) – Eastern United States

Figure 2-4 Annual Mean SO2-

4 Concentrations (μg/m3

) for 2004 

Figure 2-5 Trend in Annual Mean SO2-

4 Concentrations (μg/m3

) – Eastern United States

Figure 2-6 Annual Mean Total Nitrate (NO3 + HNO 

3) Concentrations (μg/m3

) for 2004

Figure 2-7 Trend in Annual Mean Total Nitrate (NO3 + HNO 

3) Concentrations (μg/m3

) – 

Eastern United States 

Figure 2-8 Annual Mean NH+ 

4 Concentrations (μg/m3

) for 2004

Figure 2-9 Trend in Annual Mean NH+ 

4 Concentrations (μg/m3

) – Eastern United States

Chapter 3 Deposition of Sulfur and Nitrogen 

Figure 3-1 Dry Sulfur (SO 

2 + SO2-4 ) Deposition (as S) (kg/ha/yr) for 2004

Figure 3-2 Total (Dry + Wet) Sulfur Deposition (kg/ha/yr) for 2004 

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

Figure 3-4 Trend in Total (Dry + Wet) Sulfur Deposition (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 

Figure 3-6 Dry Nitrogen (HNO 

3 + NO3 + NH+ 

4 ) Deposition (as N) (kg/ha/yr) for 2004 

Figure 3-7 Total (Dry + Wet) Nitrogen Deposition (as N) (kg/ha/yr) for 2004 

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

Figure 3-9 Trend in Total (Dry + Wet) Nitrogen Deposition (kg/ha/yr) – Eastern United States 

Figure 3-10 Trend in Dry, Wet, and Total Nitrogen Deposition (as N) (kg/ha/yr) with PrecipitationWeighted Mean Concentrations in Precipitation (mg/L) – Eastern United States 

Figure 3-11 Sand Storm

CASTNET Annual Report – 2004 ii Table of Contents 
List of Tables and Figures (continued)

Chapter 3 Deposition of Sulfur and Nitrogen (continued) 

Figure 3-12 Dust Transport 

Figure 3-13 Summer and Winter Dust Transport 

Figure 3-14 TOMS Aerosol Index for June 23, 2004

Figure 3-15 Time Series of Weekly Ca2+ Concentrations (μg/m3

) 

Figure 3-16 Time Series of Weekly Ca2+ Deposition (grams/ha/week) 

Chapter 4 Ozone Concentrations 

Figure 4-1 CASTNET Sites Above 1-Hour NAAQS 

Figure 4-2 Three-Year Averages of the Fourth Highest Daily Maximum 8-Hour O 

3 Concentrations 

(ppb) for 2002-2004 

Figure 4-3 Fourth Highest Daily Maximum 8-Hour O 

3 Concentrations (ppb) for 2004

Figure 4-4 Trend in Fourth Highest Daily Maximum 8-Hour O 

3 Concentrations (ppb) – 

Eastern United States 

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

Eastern United States 

Figure 4-6 Trend in Mean Seasonal Solar Radiation (W/m2

) (May through September) – 

Eastern United States 

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

Chapter 5 Data Quality

Figure 5-1 Historical and 2004 Precision Data for Atmospheric Concentrations 

Figure 5-2 Precision Data for Cation and Cl-

 Concentrations 

Figure 5-3 Precision Results for Laboratory Replicate Samples (2004)

Figure 5-4 Historical and 2004 Precision Data by Quarter for Ozone Concentrations 

Figure 5-5 Historical (1990-2003) and 2004 Percent Completeness of Measurements and Modeled 

Estimates 

Table 5-1 Data Quality Indicators for CASTNET Laboratory Measurements 

Table 5-2 Collocated Precision Results for 2004 by Quarter (MARPD) 

Table 5-3 Data Quality Indicators for CASTNET Field Measurements

Table 5-4 Filter Pack QC Summary for 2004 

Table 5-5 Accuracy Results for 2004 Field Measurements 

CASTNET Annual Report – 2004 iii Table of Contents 
List of Acronyms and Abbreviations 

°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 

CFR Code of Federal Regulations 

Cl- particulate chloride ion 

COC chain-of-custody 

CVS continuing verification samples 

DQI data quality indicator 

EPA U.S. Environmental Protection Agency 

grams/ha/week grams per hectare per week 

H 

2SO 4 sulfuric acid

HNO 

3 nitric acid 

Hz hertz 

IC ion chromatography 

K+ particulate potassium ion 

kg/ha/yr kilograms per hectare per year 

LAI leaf area index 

LiBr lithium bromide 

m meters 

MACTEC MACTEC Engineering and Consulting, Inc. 

MARCH Maryland Aerosol Research and Characterization

MARGA monitoring instrument for aerosols and gases 

MARPD aggregated mean of the absolute value of relative percent difference 

Mg2+

 particulate magnesium ion 

mg/L milligrams per liter 

MLM Multi-Layer Model 

mm millimeter 

Na+ particulate sodium ion 

NAAQS National Ambient Air Quality Standards 

NADP/NTN National Atmospheric Deposition Program/National Trends Network 

NAPAP National Acid Precipitation Assessment Program

NCore National Core Network 

CASTNET Annual Report – 2004 iv Table of Contents 
List of Acronyms and Abbreviations (continued) 

NDDN National Dry Deposition Network 

NH 

3 ammonia 

NH +

4 particulate ammonium

NH 

4NO 3 ammonium nitrate 

(NH 

4)

 

2SO 4 ammonium sulfate 

NIST National Institute of Standards and Technology

NO nitric oxide 

NO -

3 particulate nitrate 

NOx nitrogen oxides 

NOAA National Oceanic and Atmospheric Administration 

NPS National Park Service 

O 

3 ozone 

PM2.5 mass of particles with a mean diameter of less than 2.5 μm 

ppb parts per billion 

QA quality assurance 

QAPP Quality Assurance Project Plan 

QC quality control 

RH relative humidity 

RPD relative percent difference 

Sigma theta standard deviation of horizontal wind direction within one hour 

SLAMS State and Local Monitoring Stations

SO 

2 sulfur dioxide 

SO2-

4 particulate sulfate 

SOP standard operating procedures 

SR solar radiation 

TOMS Total Ozone Mapping Spectrometer 

μg/m3 

micrograms per cubic meter 

μm micrometer 

UPS uninterruptible power supply 

UV ultraviolet 

V 

d deposition velocity 

VAC volts alternating current

W/m2 watts per square meter 

CASTNET Annual Report – 2004 v Table of Contents 
CASTNET Annual Report – 2004 vi Table of Contents 
CChhaapptteerr 11::CCAASSTTNNEETTPPrrooggrraammIInnttrroodduuccttiioonn

CASTNET began operation in 1991 to provide long-term monitoring of air

quality in rural areas. The network, as of December 2004, features 85 site

locations throughout the continental United States and Alaska.

Rocky Mountain National Park, CO (ROM406/206)

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

(SO 

2) and nitrogen oxides (NO x) 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) was established by the U.S. Environmental Protection Agency (EPA) in 1991. At 

that time the National Dry Deposition Network (NDDN), EPA’s forerunner to CASTNET, was 

merged into CASTNET and the approximately 50 NDDN sites became the core CASTNET sites. 

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

between emissions, air quality, deposition, and ecological effects. CASTNET measures 

atmospheric sulfur and nitrogen pollutants that result from precursor emissions of SO 

2 and NOx

together with measurements of ozone (O 

3) concentrations and meteorological conditions at 

10 meters (m). This report summarizes CASTNET monitoring activities and the resulting 

concentration and deposition data for 2004. 

CASTNET Annual Report – 2004 1 Chapter 1: CASTNET Program Introduction 
CASTNET is sponsored by 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. Over the years, the number of NPS-sponsored CASTNET sites has grown to 29 sites as of 

the end of 2004. EPA, together with partners such as NPS, has added many sites to the network, 

which now comprises more than 80 sites across the United States. 

In addition to EPA and NPS, the principal sponsors, CASTNET operates in partnership with 

other rural long-term monitoring networks such as the National Atmospheric Deposition 

Program/National Trends Network (NADP/NTN). 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 25 measurement sites throughout Canada and one in 

the United States. CASTNET and CAPMoN both operate samplers at monitoring stations in 

Ontario, Canada and at monitoring stations located at Pennsylvania State University, pictured 

below. Together, CASTNET, NADP/NTN, and CAPMoN allow for a regional assessment of 

total (dry + wet) deposition throughout the United States and Canada. 

EPA relies on CASTNET and other long-term monitoring networks to generate the data and 

information used to assess the effectiveness of national air pollution control efforts under several 

different mandates, including Title IX of the CAAA, the National Acid Precipitation Assessment 

Program (NAPAP), the Government Performance and Results Act, and the United States – 

Canada Air Quality Agreement. 

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

on the EPA web site, www.epa.gov.castnet. 

Pennsylvania State University, PA (PSU106)

CASTNET Annual Report – 2004 2 Chapter 1: CASTNET Program Introduction 
Monitoring Network 

Figure 1-1 shows the locations of CASTNET monitoring sites as of December 2004. Eightyeight sites were operational at 85 distinct locations. Most CASTNET sites are located in rural or 

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

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 dividing line runs north to 

south across the states of North and South Dakota, Nebraska, Kansas, Oklahoma, and Texas. As 

a result, THR422, ND; WNC429, SD; and BBE401, TX are western sites while KNZ184, KS; 

CHE185, OK; and ALC188, TX are eastern sites. 

Figure 1-1 CASTNET Sites as of December 2004 

CASTNET Annual Report – 2004 3 Chapter 1: CASTNET Program Introduction 
CASTNET Measurements 

CASTNET sampling stations collect a variety of air 

pollutant concentrations and meteorological 

measurements on a weekly basis. 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 filter 

pack is changed out each Tuesday and shipped to the 

analytical chemistry laboratory for analysis. 

CASTNET measures concentrations of sulfur in the 

form of sulfur dioxide and sulfate and nitrogen as 

nitrate, nitric acid, and ammonium. In addition, it 

measures concentrations of chloride, calcium, sodium, 

magnesium, and potassium. 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 study the 

interaction of the pollutants with ecosystems in the atmospheric boundary layer and as part of the 

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

environment. The ozone and meteorological measurements are recorded continuously and 

archived as hourly averages. 

CASTNET Ambient 

Measurements

























Sulfur dioxide (SO 

2) 

Particulate sulfate (SO2-

4 ) 

Particulate nitrate (NO3) 

Nitric acid (HNO 

3) 

Particulate ammonium (NH+ 

4 ) 

Particulate calcium (Ca2+) 

Particulate sodium (Na +) 

Particulate magnesium (Mg

2+) 

Particulate potassium (K +) 

Particulate chloride (Cl –) 

Ozone (O 

3) 

Meteorological variables and

information on land use and 

vegetation 

Figure 1-2 Three-Stage Filter Pack 

CASTNET Annual Report – 2004 4 Chapter 1: CASTNET Program Introduction 
Modeling and Data Management 

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 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. 

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

www.epa.gov/castnet/data. The web site provides archives of the concentration and deposition 

data. Fully validated data are generally available approximately ten months following collection. 

Other documentation for the network, including information on all CASTNET sites, can be 

found at the CASTNET home page: www.epa.gov/castnet. 

Figure 1-3 Multi-Layer Model 

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

1 1 1

s b cut b a soil soil

a

r r r r r r

r

+ + + + +

+

,

V d C x

rb

ra

rsoil

Temp, RH, 

SR, LAI

Wind Speed, 

Sigma Theta

Wetness,

Precip

ra, soil

rb

rcut rs

CASTNET Annual Report – 2004 5 Chapter 1: CASTNET Program Introduction 
Quality Assurance 

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 CASTNET Quality Assurance Project Plan (QAPP) (MACTEC, 

2003b). The QAPP is comprehensive and includes standards and policies for all components of 

project operation from site selection through final data reporting. It can be downloaded from

www.epa.gov/castnet/library.html. 

Data quality indicators (DQI) have been formulated to gauge achievement of CASTNET 

objectives. DQI are quantitative and qualitative descriptors used to interpret the degree of

acceptability and utility of the data collected. The DQI for CASTNET are precision, accuracy, 

completeness, bias, representativeness, and comparability. Quantitative DQI are assessed by 

calculating statistical estimates of the precision, accuracy, and completeness of CASTNET 

measurements for both discrete and continuous data. Continual verification that the data obtained 

from both field and laboratory measurements meet specific criteria ensures that the data reliably

present a true picture of the quantity of those pollutants in the air sampled and of the 

meteorological conditions used in the MLM. The historical statistics have demonstrated that the 

QA program is adequate and followed strictly. The results show that the selected DQI parameters 

are within set limits, or boundaries, and that the long-term database satisfies CASTNET 

objectives. The CASTNET QA program is discussed in Chapter 5 of this report.

Cranberry, NC (PNF126)

CASTNET Annual Report – 2004 6 Chapter 1: CASTNET Program Introduction 
Instrument Comparison Project

CASTNET filter data have provided reliable information on 15-year trends in gaseous and 

aerosol pollutants. However, with improved measurement technology, data could be 

accessed in near real-time and available within 24 hours providing a much more timely 

data stream with improved capability for air quality assessment, including increased 

specificity and precision of reliable and highly resolved measurements of aerosols and 

atmospheric gases. Commercially available instrumentation is now capable of providing 

measurements on a semi-continuous basis for analytical cycles or time intervals ranging from

1 to 60 minutes. 

In order to consider deployment of semi-continuous monitoring systems in a long-term 

monitoring network such as CASTNET, EPA needs to critically evaluate any proposed 

instrumentation through intensive field testing and intercomparison with current CASTNET 

filter pack measurements. A joint project between EPA’s Emissions Monitoring and Analysis 

Division of the Office of Air Quality Planning and Standards and the Clean Air Market 

Programs, a division of the Office of Atmospheric Programs, was initiated to evaluate 

enhancements to rural multipollutant monitoring. 

CASTNET has been proposed as a 

platform for the expansion and 

enhancement of regional 

monitoring networks as part of the 

national CORE Network (NCORE) 

strategy, which includes multipollutant and toxics monitoring. 

An objective of NCORE is to 

improve rural air quality 

assessment and modeling. In 

addition to standard CASTNET 

measurements, inclusion of 

measurements of low-concentration 

carbon monoxide; total reactive 

oxides of nitrogen (which include 

oxides of nitrogen, composed of 

nitric oxide + nitrogen dioxide, and 

other reactive nitrogen oxide 

species); sulfur dioxide; and 

ammonia have been proposed to 

support NCORE’s objectives. 

1. Sample Collection Compartment

2. Analytical / Detection 

Compartment

3. Denuder

4. SJAC

5. Cold Trap

6. Tubing Pumps

7. Anion Eluent

8. Cation Eluent

9. Cation Ion Chromatograph

10. Anion Ion Chromatograph

11. Syringe Pump

12. Degasser

13. Conductivity Detectors

14. Regenerant Pump

15. Injection Valves

16. Column Heater

17. High Pressure Pump

18. Internal Standard

19. Suppressor Regenerant

20. Pulse Dampener

21. Anion Suppressor

22. Waste Bottle

23. Adsorption Solution

24. UPS

25. Flow Pump

26. Laptop Computer

27. Mass Flow Controller

28. Conductivity Meter

Cation 

Eluent

(HNO3)

Anion

Eluent Carbonate/

Bicarbonate

LiBr H2

SO4

MARGA 

ADI2080

1

2

3

6

5 4

8

7

19 18

13

9 10

15 16 15

14

17

12

11

26 20

17 21

Waste Bottle 

pH 3.5

Adsorption

Solution

22 23 24

25

27

28

1. Sample Collection Compartment

2. Analytical / Detection 

Compartment

3. Denuder

4. SJAC

5. Cold Trap

6. Tubing Pumps

7. Anion Eluent

8. Cation Eluent

9. Cation Ion Chromatograph

10. Anion Ion Chromatograph

11. Syringe Pump

12. Degasser

13. Conductivity Detectors

14. Regenerant Pump

15. Injection Valves

16. Column Heater

17. High Pressure Pump

18. Internal Standard

19. Suppressor Regenerant

20. Pulse Dampener

21. Anion Suppressor

22. Waste Bottle

23. Adsorption Solution

24. UPS

25. Flow Pump

26. Laptop Computer

27. Mass Flow Controller

28. Conductivity Meter

Cation 

Eluent

(HNO3)

Anion

Eluent Carbonate/

Bicarbonate

LiBr H2

SO4

MARGA 

ADI2080

1

2

3

6

5 4

8

7

19 18

13

9 10

15 16 15

14

17

12

11

26 20

17 21

Waste Bottle 

pH 3.5

Adsorption

Solution

22 23 24

25

27

Waste Bottle 

pH 3.5

Adsorption

Solution

22 23 24

25

27

28

 Figure 1-4 Monitoring Instrument for Aerosols 

and Gases (MARGA) 

CASTNET Annual Report – 2004 7 Chapter 1: CASTNET Program Introduction 
Table 1-1 Instrument Comparison Project: Instrument Specifications for Semi-Continuous Monitoring 

OPERATIONAL 

Species to Measure: 

• Particle Phase: Sulfate, nitrate, and ammonium, (chloride, sodium, potassium, calcium, and magnesium - desirable).

• Gas Phase: Sulfur dioxide, nitric acid, and ammonia (nitrous acid and hydrochloric acid - desirable).

Detection limit: Less than 0.1 μg/m3 for each species. 

Detection method: Ion chromatography (IC) with conductivity detection.

Resolution: One hour (sample accumulated for a one-hour period). 

Sample collection height: Four meters. 

Sample flow: Sufficient to achieve detection limit.

Flow control: Active instrument to log flow rate and sample volume. Concentrations to be based on actual sample volume.

Size selective inlet: PM2.5 optional.

One week unattended operation (7 consecutive days routinely): Instrument fault detection and catastrophic failure protection.

Consumables and Routine Maintenance: 

• Reservoir size and fluid consumption reasonable for weekly attendance at remote location; incorporate fluid recycle if practicable.

• Designed to minimize consumables and maintenance (pump design, columns, filters, etc.). 

• Designed for minimal maintenance on a weekly basis. Manufacturer to specify quarterly and annual maintenance requirements.

Operational Environment: 

• Shelter temperature: 25 ±5 °C; Outside temperatures: -30 to 40 °C 

Quality Assurance (QC checks): 

• Sample flow rate; Ion concentrations; Other critical parameters (temperature, pressure, etc.) 

Instrument Operation: 

• Designed for operators with little/no IC experience. Manufacturer to provide training on operation & maintenance documentation.

DATA HANDLING 

Display of current results: 48 hour graphical display and instrument operational parameters.

Storage: Store hourly concentrations, average flow rate, sample volume, and other instrument parameters.

Format: Data stored in CSV format.

Remote access: Via modem or internet; instrument parameters and data available remotely. 

PHYSICAL DIMENSIONS

Instrument must fit into existing CASTNET shelter with existing equipment. Footprint less than 8 square feet; Height less than 36 inches. 

POWER REQUIREMENTS 

110 VAC, 60 Hz, 20 amps.

 

The purpose of this project is to implement a program to evaluate emerging technically 

and scientifically advanced measurement techniques and to ultimately determine the

feasibility of enhancing the monitoring capacity of CASTNET through use of this 

instrumentation. The intent of this project is to replicate existing CASTNET measurements 

by utilizing different instruments and techniques as well as to expand the range of measured 

analytes at selected CASTNET project sites. The information obtained from this effort will 

help to further define regional atmospheric chemistry and decrease time required for 

resolution of atmospheric air quality measurements. By selecting one eastern, one western, 

and one central U. S. test site, the project will also improve understanding of the acidity of 

eastern aerosols versus those from western and central locations and the variability of the 

relative accuracy of CASTNET measurements of nitrate and nitric acid. The three evaluation 

site locations are Beltsville, MD (BEL116); Converse Station, CA (CON186); and 

Bondville, IL (BVL130).

CASTNET Annual Report – 2004 8 Chapter 1: CASTNET Program Introduction 
Significant Events During 2004 

January

Instrument Comparison Project initiated. 

NPS-sponsored site VII423, VI stopped sampling as of January 27.

CASTNET Quality Assurance Project Plan, Revision 2.0, was completed.

February

NPS-sponsored site POF425, AK stopped sampling as of February 3. 

Automated colorimetry analysis of particulate ammonium was switched to the new 

Bran+Luebbe AutoAnalyzer 3TM.

April

EPA-sponsored site ALC188, TX became operational. 

An automated daily screening procedure for screening continuous data from the sites was 

deployed. 

May

NPS-sponsored site KVA428, AK became operational.

H2NS Environmental’s DataLinkTM polling system replaced ENVICOM as the primary 

polling system.

June

CASTNET Quality Assurance Project Plan, Revision 2.1, completed. 

July

NPS-sponsored site HVT424, HI stopped sampling as of July 17. 

The recommendation for the Monitoring Instrument for Aerosols and Gases (MARGA)

submitted to EPA (Instrument Comparison Project). 

August

The annual “floor-to-ceiling” audit of CASTNET property conducted by EPA and the 

Defense Contract Management Agency at MACTEC’s Gainesville, FL location. 

Property management system approved by audit. 

September

Instrument recommendation for trace gas instruments submitted to EPA (Instrument 

Comparison Project). 

NPS-sponsored site KVA428, AK stopped sampling in late September. 

October

IRL141, FL reinstalled. The site had been dismantled in September prior to the arrival of 

Hurricanes Frances and Jeanne. 

CASTNET Annual Report – 2004 9 Chapter 1: CASTNET Program Introduction 
SO 

2 and NOx Emissions 

Figure 1-5 Trends in SO 

2 and NO x Emissions 

0

2000

4000

6000

8000

10000

12000

14000

16000

199019911992199319941995199619971998199920002001200220032004

Thousand Short Tons

SO2 - Phase I and II sources only

NOx - Phase I and II sources only

SO2 - Phase I and II sources only

NOX - Phase I and II sources only

Title IV of the 1990 Clean Air Act 

established the Acid Rain Program, which 

was designed to reduce emissions of sulfur 

dioxide (SO2) and nitrogen oxides (NOx) in 

two phases. Phase I ran from 1995 through 

1999 and required substantive emission 

reductions from 435 large electric 

generating plants involving approximately 

2,000 individual units (DOE, 1997). Phase II 

began in 2000 and includes more than 2,000 

generating stations. 

Figure 1-6 Annual Utility SO 

2 Emissions 

(Phase I and Phase II Plants, only) for 2004 

2004 Annual Emissions by State

(thousand short tons)

460 to 1,100

200 to 460

80 to 200

20 to 80

0 to 20

Figure 1-5 presents information on trends in 

SO 

2 and NO x emissions. The bars on the 

chart represent emissions from Phase I 

and II generating stations over the period 

1990 through 2004. The sharp decline in 

SO 

2 emissions in 1995 was a result of utility 

compliance with Phase I of the Acid Rain 

Program. 

Figure 1-6 presents information on state-bystate total annual Phase I and Phase II utility 

sulfur dioxide emissions for 2004. 

Figure 1-7 Annual Utility NO 

x Emissions 

(Phase I and Phase II Plants, only) for 2004 

2004 Annual Emissions by State

(thousand short tons)

150 to 360

90 to 150

70 to 90

20 to 70

0 to 20

Figure 1-7 presents the same information for 

emissions of nitrogen oxides. CASTNET’s 

34 reference sites (see Figure 2-1) are 

located in the eastern half of the United 

States where the heaviest emissions occur. 

CASTNET Annual Report – 2004 10 Chapter 1: CASTNET Program Introduction 
CChhaapptteerr22::AAttmmoosspphheerriiccCCoonncceennttrraattiioonnss

Bondville, IL (BVL130) 

Species measured by CASTNET include sulfur dioxide 

(SO 

2), sulfate (SO2-

4 ), nitric acid (HNO 3), nitrate (NO3), 

ammonium (NH+ 

4 ), several earth metals, and chloride 

(Cl-). Since 1990, measured concentrations of sulfur 

species have decreased. Concentrations of nitrogen species 

remained relatively steady until 2000 when they began 

showing a slow decline. 

This section presents maps illustrating the magnitude of concentrations across the United States. 

In addition, measurements from the 34 CASTNET reference sites (Figure 2-1) were analyzed for 

each pollutant in order to determine any trends in concentrations. These 34 sites have been 

reporting CASTNET measurements since 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). EPA’s procedures to 

interpolate and extrapolate quarterly mean 

data were also used. The data from the 34 

reference sites are presented using box 

plots for each year for the period 1990 

through 2004. 

Figure 2-1 CASTNET Reference Sites 

Sulfur Dioxide 

Mean sulfur dioxide (SO 

2) concentrations 

for 2004 are shown in Figure 2-2. The map 

shows a region of concentrations greater 

than 5.0 micrograms per cubic meter 

(μg/m3

) of air centered in the Ohio River 

Valley and extending to the East Coast. 

The Ohio River Valley is the major SO 

2

emission source region for the United 

States. Four sites measured concentrations 

greater than 10.0 μg/m3

. The single highest 

annual mean concentration (17.0 μg/m3

) 

CASTNET Annual Report – 2004 11 Chapter 2: Atmospheric Concentrations
observed at CASTNET sites in the continental United States was measured in eastern Ohio at 

Quaker City (QAK172). Only three western sites (i.e., sites west of 100 degrees west longitude), 

Olympic National Park, WA (OLY421); Petrified Forest National Park, AZ (PET427); and 

Theodore Roosevelt National Park, ND (THR422), measured an annual mean SO 

2 level above 

1.0 μg/m3

. 

Figure 2-3 provides box plots that show the trend in annual mean SO 

2 concentrations aggregated 

over the 34 reference sites for the period 1990 through 2004. Comparison of 3-year means from

the beginning of the period (1990-1992) to the end of the period (2002-2004) demonstrates a 

substantial 36 percent reduction in SO 

2 concentrations. 

Figure 2-2 Annual Mean SO 

2 Concentrations (μg/m3

) for 2004 

CASTNET Annual Report – 2004 12 Chapter 2: Atmospheric Concentrations
Figure 2-3 Trend in Annual Mean SO 

2 Concentrations (μg/m3

) – Eastern United States

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

4

8

12

16

20

199019911992199319941995199619971998199920002001200220032004

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

4

8

12

16

20

199019911992199319941995199619971998199920002001200220032004

Concentration

Particulate Sulfate 

Figure 2-4 shows a map of annual mean particulate sulfate (SO2-

4 ) concentrations measured 

during 2004. The map shows a relatively uniform distribution of atmospheric SO2-

4 in the center 

of the eastern monitoring network with values typically ranging from 3.0 to 5.0 μg/m3

. 

QAK172, OH, with a value of 5.4 μg/m3

, was the only site that measured a concentration greater 

than 5.0 μg/m3. Downward concentration gradients were observed from the center to the 

periphery of the network. The western monitoring sites measured relatively low annual mean 

concentrations with values ranging from 0.4 to 2.1 μg/m3

. Big Bend National Park (BBE401) in 

Texas measured the highest mean SO2-

4 concentration among the western sites. 

The trend in annual mean particulate sulfate concentrations is illustrated by the box plots in 

Figure 2-5. The diagram shows a significant reduction in SO2-

4 over the last 15 years. The 

difference between 3-year means at the beginning and end of the period is 24 percent. 

One of CASTNET’s two 

solar-powered monitoring 

sites, CAT175, NY is located 

in a remote area in the 

Catskills Mountains. 

CASTNET Annual Report – 2004 13 Chapter 2: Atmospheric Concentrations
Figure 2-4 Annual Mean SO2-

4 Concentrations (μg/m3

) for 2004

Figure 2-5 Trend in Annual Mean SO2-

4 Concentrations (μg/m3

) – Eastern United States 

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

2

3

4

5

6

7

8

199019911992199319941995199619971998199920002001200220032004

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

2

3

4

5

6

7

8

199019911992199319941995199619971998199920002001200220032004

Concentration

CASTNET Annual Report – 2004 14 Chapter 2: Atmospheric Concentrations
Total Nitrate 

Annual mean concentrations of total nitrate for 2004 are presented in Figure 2-6. Total nitrate is 

comprised of particulate nitrate (NO3) plus gaseous nitric acid (HNO 

3). Total nitrate 

concentrations respond to changes in nitrogen oxides (NOx) emissions and are more 

representative of ambient conditions caused by NOx emissions than either of its constituents 

alone. The uncertainty of measured concentrations of NO3 and HNO 

3 is discussed in the callout

box later in this chapter. 

The map in Figure 2-6 shows that concentrations above 4.0 μg/m3

 were measured at four sites in 

the three contiguous states of Illinois, Indiana, and Ohio. Total nitrate levels vary significantly 

from Georgia to Pennsylvania with a range of concentrations from 0.8 to 3.9 μg/m3

. Differences 

in deposition velocities, atmospheric scavenging rates, fresh nitric oxide (NO) emissions, and 

inversion heights influence the pattern of nitrate concentrations. Four CASTNET sites in 

southern California measured total nitrate levels greater than or equal to 2.0 μg/m3

. 

Box plots of annual total nitrate values are provided in Figure 2-7. The diagram shows an 

approximate 10 percent decline in total nitrate over the last 5 years. The mean concentration 

(3.2 μg/m3

) in 2000 declined to 2.6 μg/m3 in 2004. 

Figure 2-6 Annual Mean Total Nitrate (NO3 + HNO 

3) Concentrations (μg/m3

) for 2004

CASTNET Annual Report – 2004 15 Chapter 2: Atmospheric Concentrations
Figure 2-7 Trend in Annual Mean Total Nitrate (NO3 + HNO 

3) Concentrations (μg/m3

) – 

Eastern United States

 90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

2

4

6

8

199019911992199319941995199619971998199920002001200220032004

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

2

4

6

8

199019911992199319941995199619971998199920002001200220032004

Concentration

Particulate Ammonium 

A map of 2004 annual mean particulate ammonium (NH+ 

4 ) concentrations is provided in 

Figure 2-8. Lower concentrations were measured along the periphery of the network – northern 

New England, Minnesota, and Florida. The NH+ 

4 concentrations measured at western sites were 

relatively low with all but four western sites having annual mean NH+ 

4 concentrations below 

0.5 μg/m3

. 

Figure 2-9 presents box plots of annual mean NH+ 

4 concentrations. The measurements show a 

17 percent decline in mean NH+ 

4 concentrations between 3-year means at the beginning and end 

of the 15-year period. This decrease is believed to be due to the decrease in SO 

2 emissions and 

the concomitant lower production of ammonium sulfate [(NH 

4)

 

2SO 4]. 

Cedar Creek State Park, WV (CDR119)

CASTNET Annual Report – 2004 16 Chapter 2: Atmospheric Concentrations
Figure 2-8 Annual Mean NH+ 

4 Concentrations (μg/m3

) for 2004

Figure 2-9 Trend in Annual Mean NH+ 

4 Concentrations (μg/m3

) – Eastern United States

 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

199019911992199319941995199619971998199920002001200220032004

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

199019911992199319941995199619971998199920002001200220032004

Concentration

CASTNET Annual Report – 2004 17 Chapter 2: Atmospheric Concentrations
0

1

2

3

4

5

6

1999

Jul

1999

Oct

2000

Jan

2000

Apr

2000

Jul

2000

Oct

2001

Jan

2001

Jul

2002

Jul

Conc (μg/m3

)

MARCH NO3

CASTNET/BEL116 NO3

CASTNET/ARE128 NO3

CASTNET/BWR139 NO3

0

1

2

3

4

5

6

1999

Jul

1999

Oct

2000

Jan

2000

Apr

2000

Jul

2000

Oct

2001

Jan

2001

Jul

2002

Jul

Conc (μg/m3

)

MARCH HNO3

CASTNET/BEL116 HNO3

CASTNET/ARE128 HNO3

CASTNET/BWR139 HNO3

Bias in NO3 and HNO 

3 Measurements 

CASTNET utilizes a filter pack system to measure 

concentrations of atmospheric sulfur and nitrogen 

species. The filter pack contains four filters in

sequence. The Teflon® filter samples particle sulfate 

(SO2-

4 ), nitrate (NO-  3), chloride (Cl

-

), ammonium

(NH+ 

4 ), and other cations. The nylon filter collects 

nitric acid (HNO3) and some sulfur dioxide (SO2). 

The two cellulose filters collect the remaining SO2. 

Recent studies suggest that typically a fraction of the 

ammonium nitrate (NH 

4NO 3) collected on the 

Teflon® filter dissociates into HNO3 and ammonia 

(NH 

3). Also, NH 4NO 3 can react with acid SO2-4

particles on the Teflon® filter to produce HNO3. 

These reactions could result in an overestimate of 

HNO3 and an underestimate of particulate NO- 

 3 and 

NH+ 

4 . CASTNET data are being compared to data

from other measurement programs to estimate 

uncertainties in CASTNET filter pack measurements 

of HNO3, NO- 

 3, and NH+ 4 on a seasonal, annual, and 

geographic basis and the resulting uncertainties in

seasonal and annual dry deposition fluxes. 

The Maryland Aerosol Research and 

Characterization (MARCH) database is one of the 

data sets being compared to CASTNET data.

MARCH employed two sequential filter samplers 

and two sequential gas samplers (Chow et al., 1996) 

to collect 24-hour samples every third day. Each 

sampler had two channels, each of which contained a 

filter pack with one or two sampling filters. The two gas 

samplers also used diffusion denuders and appropriate 

filters to measure gas phase NH 

3 and HNO3. MARCH 

data collected from the monitoring site at Ford Meade, 

MD were compared with CASTNET data from the sites 

at Beltsville, MD (BEL116); Blackwater, MD 

(BWR139); and Arendtsville, PA (ARE128). Fort 

Meade is located about 15 kilometers from BEL116. 

Results indicate that CASTNET measures higher 

particulate NO3 and lower gaseous HNO 

3 concentrations 

than the other measurement systems. These results are 

somewhat counterintuitive in that opposite results were 

expected, i.e., lower NO3 on the Teflon® filter and

higher HNO 

3 on the nylon filter. An explanation is that 

the CASTNET filter pack collects larger NO3 particles 

because the instrument does not include a size selection 

inlet (e.g., cyclone). 

EPA will further investigate the effect of collecting

nitrate particles without a size selection inlet by

sponsoring additional measurements at the three 

CASTNET sites (BEL116, MD; BWR139, MD; and

ARE128, PA). Weekly nitrate concentrations will be

measured with and without cyclones. Several sized 

inlets will be utilized at BEL116. A 2.5 micrometer 

(μm) cut-off will be used at BWR139 and ARE128 and

compared to concentration measurements collected 

without a cyclone. 

Comparison of MARCH and CASTNET Data 

Particulate Nitrate Gaseous Nitric Acid 

 Note: CASTNET weekly and MARCH hourly measurements were aggregated to monthly mean concentrations 

CASTNET Annual Report – 2004 18 Chapter 2: Atmospheric Concentrations
CChhaapptteerr33:: DDeeppoossiittiioonnooffSSuullffuurraanndd NNiittrrooggeenn

CASTNET was designed to estimate dry deposition using 

measured atmospheric pollutant concentrations and 

deposition velocities. Dry deposition is responsible for 

approximately 20 to 80 percent of total atmospheric 

deposition depending on location and climate. Typical 

percentages are about 40 percent for dry sulfur deposition 

and 30 percent for dry nitrogen deposition. 

Clingmans Dome, TN (CLD303)

Great Smoky Mountains National Park

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

wet atmospheric processes. One of the unique components of CASTNET involves estimation of 

the rate of dry deposition from measured environmental conditions. Measured concentration data 

were combined with modeled dry deposition velocities to develop the flux estimates. 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 2004. Also, precipitation-weighted mean concentrations in precipitation of total 

atmospheric sulfur estimated for 2004 continued the downward trend that began in 1995 with 

implementation of Phase I of the Acid Rain Program. Nitrogen deposition rates show no 

significant trend. However, nitrogen concentrations in precipitation have declined since 1998. 

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

Meyers et al. (1998) and Finkelstein et al. (2000). 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 and were calculated for each hour with valid 

meteorological data for each CASTNET site for the entire period 1990 through 2004. 

The MLM has been evaluated for a limited number of vegetation types, terrain settings, and time 

periods (summarized by Baumgardner et al., 2002). 

CASTNET Annual Report – 2004 19 Chapter 3: Deposition of Sulfur and Nitrogen 
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 2004, 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 15.6 kg/ha/yr. The 

flux data show sharply declining gradients from the Ohio 

Valley northward into New England and also into Wisconsin 

and Minnesota. The highest dry sulfur deposition rates were 

coincidental to the major SO2 source region (Figure 1-6) and 

decline sharply with distance. Kodachrome Park, UT 

 

Figure 3-1 Dry Sulfur (SO 

2 + SO2-4 ) Deposition (as S) (kg/ha/yr) for 2004

CASTNET Annual Report – 2004 20 Chapter 3: Deposition of Sulfur and Nitrogen 
The dry deposition rates for the western sites were all less than 1.0 kg/ha/yr and generally 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. 

Wet deposition values used in trends 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 (yellow) shows dry deposition. A region with 

Figure 3-2 Total (Dry + Wet) Sulfur Deposition (kg/ha/yr) for 2004 

CASTNET Annual Report – 2004 21 Chapter 3: Deposition of Sulfur and Nitrogen 

Total Deposition

16

8

1.6

Dry Deposition

Wet Deposition

12.5

6.1

12.7

0.7

9.9

6.6

4.7

5.4

9.0

7.6

13.6

3.0

2.3

11.0

6.3

9.2

6.4

0.8

1.2

4.1

10.8

1.1

10.4

14.8

0.7

8.2

4.0

8.5

1.0

0.7

0.8

9.3

0.6

3.5

5.8

4.9

7.4

0.7

4.0

0.5

14.4

11.1

8.3

11.4

14.6

0.9

2.5 1.5

0.5

0.7

7.8

3.7

17.8

1.4 27.2

9.7

0.9

9.8

8.9

6.0

4.3

1.1

5.9

17.4

2.2

8.8

1.2

13.6

5.0

0.8

Sites not pictured:

DEN417, AK 0.3

Total Deposition

16

8

1.6

Dry Deposition

Wet Deposition

12.5

6.1

12.7

0.7

9.9

6.6

4.7

5.4

9.0

7.6

13.6

3.0

2.3

11.0

6.3

9.2

6.4

0.8

1.2

4.1

10.8

1.1

10.4

14.8

0.7

8.2

4.0

8.5

1.0

0.7

0.8

9.3

0.6

3.5

5.8

4.9

7.4

0.7

4.0

0.5

14.4

11.1

8.3

11.4

14.6

0.9

2.5 1.5

0.5

0.7

7.8

3.7

17.8

1.4 27.2

9.7

0.9

9.8

8.9

6.0

4.3

1.1

5.9

17.4

2.2

8.8

1.2

13.6

5.0

0.8

Sites not pictured:

DEN417, AK 0.3
sulfur deposition greater than 10.0 kg/ha/yr extends from southwestern Indiana, central Kentucky, 

and northern Tennessee, along the Ohio River into Pennsylvania, West Virginia, southwestern 

New York, Maryland, and New Jersey. Sulfur deposition at western sites was generally less than 

2.0 kg/ha/yr with the exception of Olympic National Park, WA (OLY421), which had an estimate 

of 2.5 kg/ha/yr, and Big Bend National Park, TX (BBE401) with a value of 2.3 kg/ha/yr. 

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 15 years, 1990 through 

2004. The box plots were based on data obtained from the 34 eastern CASTNET reference sites 

(Figure 2-1). Sulfur deposition at these sites declined significantly over the 15 years, although the 

dry and total fluxes were relatively constant over the last four 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 in sulfur concentration 

over the last few years.

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

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

2

4

6

8

10

12

199019911992199319941995199619971998199920002001200220032004

Deposition

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

2

4

6

8

10

12

199019911992199319941995199619971998199920002001200220032004

Deposition

CASTNET Annual Report – 2004 22 Chapter 3: Deposition of Sulfur and Nitrogen 
Figure 3-4 Trend in Total (Dry + Wet) Sulfur Deposition (kg/ha/yr) – Eastern United States 

0

5

10

15

20

25

199019911992199319941995199619971998199920002001200220032004

Deposition

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

5

10

15

20

25

199019911992199319941995199619971998199920002001200220032004

Deposition

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

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

2

4

6

8

10

12

14

16

199019911992199319941995199619971998199920002001200220032004

Dep

osition

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 – 2004 23 Chapter 3: Deposition of Sulfur and Nitrogen 
Dry SO2

Deposition

(as Sulfur)

Dry SO4

2-

Deposition

(as Sulfur)

Wet SO4

2-

Deposition

(as Sulfur)

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)

Deposition

(as Nitrogen)

Dry NO3

-

Deposition

(as Nitrogen)

Dry NH4

+

Deposition

(as Nitrogen)

Wet NO3

-

Deposition

(as Nitrogen)

Wet NH4

+

Deposition

(as Nitrogen)

Contributors to Atmospheric Deposition 

Measured at CASTNET Eastern Reference Sites 

 Sulfur Nitrogen 

Dry HNO3

 1990-1992 

13.5 kg/ha/yr 7.9 kg/ha/yr

 

Dry HNO3 2002-2004 

10.0 kg/ha/yr 7.4 kg/ha/yr

The four pie charts illustrate mean total (wet + dry) sulfur and nitrogen deposition rates for two 3-year 

periods, 1990 to 1992 and 2002 to 2004. 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 10.0 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 7.4 kg/ha/yr from the beginning three years to the final three years of the 15-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 38 percent over the 15 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 28 percent over the 15 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. 

CASTNET Annual Report – 2004 24 Chapter 3: Deposition of Sulfur and Nitrogen 
Nitrogen Deposition

Figure 3-6 presents a map of dry fluxes of nitrogen for 2004. 

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, although the geographic pattern is complex. The 

values range from 0.4 kg/ha/yr in New Hampshire to 

3.6 kg/ha/yr in eastern Ohio. Lower fluxes were observed along 

the periphery of the network. The values at the western sites 

ranged from 0.2 kg/ha/yr at Mount Rainier National Park, WA 

(MOR409) to 3.3 kg/ha/yr at Converse Station, CA (CON186). 

Colorado River, AZ

Figure 3-6 Dry Nitrogen (HNO 

3 + NO3 + NH+ 4 ) Deposition (as N) (kg/ha/yr) for 2004 

CASTNET Annual Report – 2004 25 Chapter 3: Deposition of Sulfur and Nitrogen 
A map (Figure 3-7) of total nitrogen deposition (as N) for 2004 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. Values above 

10.0 kg/ha/yr were observed in eastern Ohio and eastern Pennsylvania. 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 1.1 kg/ha/yr at MOR409, WA to 4.4 kg/ha/yr 

at CON186, CA. 

Figure 3-7 Total (Dry + Wet) Nitrogen Deposition (as N) (kg/ha/yr) for 2004 

CASTNET Annual Report – 2004 26 Chapter 3: Deposition of Sulfur and Nitr

Total Deposition

10

5

1

Dry Deposition

Wet Deposition

6.7

4.9

6.8

4.4

7.4

6.3

3.5

5.5

6.9

8.3

9.1

2.5

2.8

8.1

4.4

6.7

6.8

2.0

2.8

5.9

7.6

3.4

8.7

9.2

2.3

6.3

3.5

6.8

1.8

2.0

2.1

7.6

1.3

3.1

8.3

4.8

3.4

7.0

1.2

7.2

9.0

6.9

7.3

8.2

1.1

1.3 2.0

1.4

1.4

6.2

6.8

8.7

4.2 10.1

9.7

2.8

7.9

6.0

7.4

3.8

1.9

5.5

8.9

4.4

5.6

2.8

10.1

4.5

2.4

Sites not pictured:

DEN417, AK 0.4

Total Deposition

10

5

1

Dry Deposition

Wet Deposition

6.7

4.9

6.8

4.4

7.4

6.3

3.5

5.5

6.9

8.3

9.1

2.5

2.8

8.1

4.4

6.7

6.8

2.0

2.8

5.9

7.6

3.4

8.7

9.2

2.3

6.3

3.5

6.8

1.8

2.0

2.1

7.6

1.3

3.1

8.3

4.8

3.4

7.0

1.2

7.2

9.0

6.9

7.3

8.2

1.1

1.3 2.0

1.4

1.4

6.2

6.8

8.7

4.2 10.1

9.7

2.8

7.9

6.0

7.4

3.8

1.9

5.5

8.9

4.4

5.6

2.8

10.1

4.5

2.4

Sites not pictured:

DEN417, AK 0.4

ogen 
Figure 3-8 presents box plots that show the trend in dry nitrogen deposition, and Figure 3-9 shows 

the trend in total nitrogen deposition over the 15 years, 1990 through 2004. The box plots show no 

significant trend although the data suggest a decline in dry nitrogen deposition since 1999. 

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

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

199019911992199319941995199619971998199920002001200220032004

Deposition

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

199019911992199319941995199619971998199920002001200220032004

Deposition

Figure 3-9 Trend in Total (Dry + Wet) Nitrogen Deposition (kg/ha/yr) – Eastern United States 

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

199019911992199319941995199619971998199920002001200220032004

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

199019911992199319941995199619971998199920002001200220032004

Deposition

CASTNET Annual Report – 2004 27 Chapter 3: Deposition of Sulfur and Nitrogen 
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 over the last several 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 

0

2

4

6

8

10

12

199019911992199319941995199619971998199920002001200220032004

Dep

osition

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 – 2004 28 Chapter 3: Deposition of Sulfur and Nitrogen 
African Saharan Aerosols (Dust) in CASTNET 

Dust clouds from the Sahara Desert are produced throughout 

the year but most frequently in the summer. Dust clouds are 

produced when tropical waves pick up dust from the desert in 

North Africa and transport the dust through convection to 

heights of a few miles into 

the atmosphere. The dust 

clouds drift west in the 

easterly trade winds. Figure 3-11 illustrates a sand storm

over the African Sahel, the narrow border, or lightly 

vegetated “greenbelt,” between the Sahara and the 

agricultural areas to the south. Figure 3-12 shows a satellite 

photo of a dust cloud blowing off the African coast. 

Summer and winter dust transport patterns are illustrated in Figure 3-13. Summer patterns 

suggest the transport of the Saharan dust to the Caribbean and then veering northward around 

the Bermuda High to the United States. Satellite data from the Earth Probe Total Ozone 

Mapping Spectrometer (TOMS) aerosol index (Herman et al., 1997) detected Saharan dust 

events during several days of June and July 2004. Figure 3-14 shows the transport pattern on 

June 23, 2004. 

Figure 3-12 Dust Transport 

Figure 3-13 Summer and Winter Dust Transport 

Figure 3-11 Sand Storm 

CASTNET Annual Report – 2004 29 Chapter 3: Deposition of Sulfur and Nitrogen 
Figure 3-14 TOMS Aerosol Index for June 23, 2004 

CASTNET cation measurements document the appearance and transport of Saharan dust across 

the southeastern United States. Time series of weekly Ca2+ concentrations and depositions for 

three Florida sites are shown in Figures 3-15 and 3-16 for the period June 8 through July 13, 

2004. The dates represent the beginning of the sampling periods. The peak concentrations and 

deposition rates that were measured during the sampling weeks beginning June 22 and July 7 

indicate Saharan dust. The June event is illustrated by the TOMS data shown in Figure 3-14. 

The peak concentrations were approximately double annual mean values.

Figure 3-15 Time Series of Weekly Ca2+

Concentrations (μg/m3) 

CASTNET Annual Report – 2004 30 Chapter 3: Deposition of Sulfur and Nitrogen 

Figure 3-16 Time Series of Weekly Ca2+

Deposition (grams/ha/week) 

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

6/8/04 6/15/04 6/22/04 6/29/04 7/6/04 7/13/04

Deposition

SUM156, FL

IRL141, FL

EVE419, FL

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

6/8/04 6/15/04 6/22/04 6/29/04 7/6/04 7/13/04

Concentration

SUM156, FL

IRL141, FL

EVE419, FL
CChhaapptteerr44:: OOzzoonneeCCoonncceennttrraattiioonnss

Haze

CASTNET provides the primary vehicle for measuring 

rural ozone (O 

3) concentrations in the United States. 

Ozone concentration measurements during 2004 at 

the CASTNET reference sites were the lowest in the 

history of the network. 

Converse Station, CA (CON186)

CASTNET ozone (O 

3) data provide information on geographic patterns in regional O 3 and on the 

extent to which rural areas potentially exceed concentration values mandated by the National 

Ambient Air Quality Standards (NAAQS). Fourth highest 1-hour ozone concentrations above 

125 parts per billion (ppb) were measured at four sites over the period 2002-2004. These sites 

are located in the northeastern United States along the East Coast and in southern California. 

During the same period, 3-year averages of the fourth highest daily maximum 8-hour O 

3

concentrations were greater than or equal to 85 ppb at 11 sites. Measurements of 1-hour and 

8-hour concentrations during 2004 were considerably lower than previous years and are the 

lowest O 

3 concentrations in CASTNET history. 

Design Values for Ozone Concentrations for 2002-2004

Figure 4-1 provides the locations of the sites measuring daily maximum 1-hour O 

3 concentrations

greater than or equal to 125 ppb for the period 2002-2004. The number of days with 

measurements equaling or exceeding 125 ppb is listed with the fourth highest 1-hour value for 

the same time period included in parentheses. Four sites measured elevated concentrations – two 

on the East Coast and two in southern California. The fourth highest value constitutes the design 

value for achieving the 1-hour NAAQS. In other words, the value of 128 ppb measured at 

Beltsville, MD (BEL116) would have to be reduced to 125 ppb to meet the standard. 

CASTNET Annual Report – 2004 31 Chapter 4: Ozone Concentrations
Figure 4-1 CASTNET Sites Above 1-Hour NAAQS 

Three-year averages of the fourth highest daily 

maximum 8-hour O 

3 concentrations for 2002-2004 

are presented in Figure 4-2. These 3-year averages 

constitute design values for achieving the 8-hour 

NAAQS. Seven eastern sites and four sites in 

California observed a 3-year average concentration 

greater than or equal to 85 ppb. The sites and 

concentration values are listed in the table next to the 

map in Figure 4-2. The regions with elevated 

concentrations were located along the East Coast 

from Maryland to Connecticut and in Pennsylvania 

and Ohio. A value of 91 ppb was measured at Great 

Smoky Mountains National Park, TN (GRS420). 

Four sites in California observed elevated 8-hour O 

3

concentrations. 

Gothic, CO (GTH161)

CASTNET Annual Report – 2004 32 Chapter 4: Ozone Concentrations
Figure 4-2 Three-Year Averages of the Fourth Highest Daily Maximum 8-Hour O 

3

Concentrations (ppb) for 2002-2004 

Site ID

Conc. 

≥ 85 ppb 

CON186, CA 125 

JOT403, CA 107 

SEK402, CA 103 

WSP144, NJ 93 

BWR139, MD 92 

YOS404, CA 91 

GRS420, TN 91 

BEL116, MD 91 

ARE128, PA 89 

ABT147, CT 86 

LYK123, OH 86 

Eight-Hour Ozone Concentrations 

Figure 4-3 provides a map of the fourth highest daily 

maximum 8-hour O 

3 concentrations measured during 

2004. The sites with concentration values greater 

than or equal to 85 ppb are listed in the table next to 

the map in Figure 4-3. No eastern sites measured 

values greater than or equal to 85 ppb. Four 

California sites measured high 8-hour concentrations 

in 2004. The highest concentration (122 ppb) was 

measured at CON186, CA. The National Oceanic and 

Atmospheric Administration (NOAA) reported that 

much of the 2004 O 

3 season was dominated by a cool 

summer, the sixteenth coolest on record. Nationwide, 

June-August was the tenth wettest summer with 

Texas, Louisiana, Mississippi, Arkansas, Oklahoma, 

and Kansas recording their wettest summer and 

Pennsylvania its fourth wettest summer (NOAA, 2004). 

Indian River Lagoon, FL (IRL141)

CASTNET Annual Report – 2004 33 Chapter 4: Ozone Concentrations
Figure 4-3 Fourth Highest Daily Maximum 8-Hour O 

3 Concentrations (ppb) for 2004 

ite ID

Conc. 

≥ 85 ppb 

CON186, CA 122 

JOT403, CA 102 

SEK402, CA 95 

YOS404, CA 89 

Fifteen-Year Trends 

CASTNET measurements at the 34 eastern reference sites show a surprising and remarkable 

decline in O 

3 concentrations from 2002 to 2004. During 2002, 24 sites measured fourth highest 

8-hour O 

3 levels over 85 ppb, and 50 sites experienced at least one day with an 8-hour O 3 level 

greater than or equal to 85 ppb. Very high concentrations were measured along the East Coast 

from Maryland to Maine. During 2003, only six sites observed fourth highest 8-hour 

concentrations above 85 ppb. During 2004, no eastern sites observed O 

3 concentrations that were

higher than 85 ppb. 

Trends in 8-hour concentrations aggregated over the 34-station subset of reference sites show a 

significant decline from 2002 to 2003 and a further decline to 2004 (Figure 4-4). Median values 

decreased from 86 ppb in 2002 to 77 ppb in 2003 to 71 ppb in 2004. The decrease from 2002 to 

2003 is explained by unusually cool, cloudy, and wet weather during the 2003 ozone season 

(Figures 4-5 through 4-7). The additional, significant decrease from 2003 to 2004 is also 

associated with relatively cloudy and wet weather during the 2004 ozone season. However, 

trends in total nitrate – nitric acid plus particulate nitrate – also show a decline over the last few 

years, as shown in Figure 2-7. Figure 1-5 depicts a reduction in utility nitrogen oxides (NOx) 

emissions since 1997. Evidently, both weather and a decline in atmospheric nitrogen species 

contributed to the recent decline in ozone levels. This is the first evidence that a reduction in NOx

emissions is contributing to a decline in tropospheric ozone. 

CASTNET Annual Report – 2004 34 Chapter 4: Ozone Concentrations
Figure 4-4 Trend in Fourth Highest Daily Maximum 8-Hour O 

3 Concentrations (ppb) – 

Eastern United States 

60

80

100

120

199019911992199319941995199619971998199920002001200220032004

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

60

80

100

120

199019911992199319941995199619971998199920002001200220032004

Concentration

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

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

Eastern United States 

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

10

15

20

25

30

199019911992199319941995199619971998199920002001200220032004

Tem

peratur

e

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

10

15

20

25

30

199019911992199319941995199619971998199920002001200220032004

Tem

peratur

e

CASTNET Annual Report – 2004 35 Chapter 4: Ozone Concentrations
Figure 4-6 Trend in Mean Seasonal Solar Radiation (W/m2

) (May through September) – 

Eastern United States 

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

199019911992199319941995199619971998199920002001200220032004

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

199019911992199319941995199619971998199920002001200220032004

Solar Radiation

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

Eastern United States 

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

200

400

600

800

1000

1200

199019911992199319941995199619971998199920002001200220032004

Precipitation

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

200

400

600

800

1000

1200

199019911992199319941995199619971998199920002001200220032004

Precipitation

CASTNET Annual Report – 2004 36 Chapter 4: Ozone Concentrations
CASTNET Ozone Measurements

CASTNET Annual Report – 2004 37 Chapter 4: Ozone Concentrations

Quarterly Precision for ROM406/206, CO

0.00

5.00

10.00

15.00

20.00

25.00

Third Quarter 2001

Fourth Quarter 2001

First Quarter 2002

Second Quarter 2002

Third Quarter 2002

Fourth Quarter 2002

First Quarter 2003

Second Quarter 2003

Third Quarter 2003

Fourth Quarter 2003

First Quarter 2004

Second Quarter 2004

Third Quarter 2004

Fourth Quarter 2004

RPD

t

Although not a regulatory network, CASTNET O3 data provide information on measured concentrations in 

rural areas. To understand how these measurements compare to those measured by the regulatory

monitoring stations used for determination of NAAQS compliance, it is necessary to understand how well 

CASTNET data compare with data collected using regulatory methods. 

CASTNET evolved from the NDDN, a research network rather than a compliance monitoring network. As 

such, requirements established in the Code of Federal Regulations (CFR) to govern and uniformly

standardize state and local ozone monitoring stations were not followed. 

The essential difference between CASTNET O3 monitoring and regulatory monitoring is the regulatory

requirement that an independent verification check of a test atmosphere be performed with a second instation photometer at least once every two weeks. At regulatory monitoring stations, test concentrations for 

O3 must be obtained in accordance with the ultraviolet (UV) photometric calibration procedure specified in 

40 CFR part 50, Appendix D, or by means of a certified O3 transfer standard. CASTNET O3 analyzers 

perform weekly verification checks using a calibrated, internal O3 generator. The exceptions to this are the 

CASTNET sites sponsored by NPS and the Cherokee Nation site in Stilwell, OK (CHE185). The NPS sites 

are tasked with regulatory assessment of non-attainment areas in national parks, and therefore, conform to 

the regulatory methodology. All 

aspects of ambient O3 monitoring a

CHE185 are the responsibility of 

the Cherokee Nation. 

Over time CASTNET has 

implemented changes to improve 

the accuracy and precision of O3

monitoring. In 1998 all systems at 

EPA-sponsored sites were modified 

to route the test gases through the 

O3 inlet on the sampling tower. In 

this manner, the integrity of the 

entire sampling system can be 

verified during the checks. 

Previously, the test gases were 

introduced at the back of the 

analyzer and were not routed 

through the sampling system. Beginning in 2000, the calibration of each CASTNET O3 analyzer was 

independently verified using a transfer standard every six months. Prior to 2000, O3 analyzer calibrations 

were independently verified once per calendar quarter. 

In 2001, the NPS-sponsored site at Rocky Mountain National Park, CO (ROM406), a regulatory site, was 

collocated with an EPA-sponsored site (ROM206). ROM406 conforms to regulatory requirements while 

ROM206 is operated according to CASTNET protocol. Therefore, data collected from these sites provide 

an excellent opportunity to compare the method results. 

The figure above shows that the data compare very well. The precision goal for CASTNET O3

measurements is 10 percent. The results obtained when both systems are operating properly indicate that 

CASTNET O3 data can be used with confidence. The results for the third and fourth quarters of 2001, third

quarter 2003, and second and third quarters of 2004 were affected by various operating problems. 

Therefore, results for these quarters should be disregarded. 
CASTNET Annual Report – 2004 38 Chapter 4: Ozone Concentrations 
CChhaapptteerr55:: DDaattaa QQuuaalliittyy

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

are evaluated using data quality indicators (DQI). Both historical and current data can be 

used with confidence since CASTNET measurements are continually evaluated through the 

use of DQI. CASTNET has produced and continues to produce data of the highest quality. 

Bryce Canyon National Park, UT

The CASTNET 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) (MACTEC, 2003b). 

The QAPP is comprehensive and includes standards and policies for all components of project 

operation from site selection through final data reporting. 

DQI have been established to gauge achievement of CASTNET objectives. DQI are quantitative 

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 2004 data were 

analyzed and compared with historical data collected during the period 1990–2003. The 

information in this report is supplemented by analyses that are discussed in quarterly CASTNET 

Quality Assurance Reports (e.g., MACTEC, 2005). 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. CASTNET has produced and continues to produce data of the 

highest quality. 

CASTNET Annual Report – 2004 39 Chapter 5: Data Quality 
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 (1990–2003) and the 2004 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 5 percent for particulate sulfate (SO2-

4 ) to about 12 percent for particulate nitrate 

(NO3). The historical MARPD for SO2-

4 and ammonium (NH+ 4 ) each met the criterion, or DQI, for 

the CASTNET laboratory measurements shown in Table 5-1. The results for sulfur dioxide (SO2) 

and nitric acid (HNO3) 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 

(MACTEC, 2003a). 

Figure 5-1 Historical and 2004 Precision Data for Atmospheric Concentrations 

0

2

4

6

8

10

12

14

16

SO2 SO4 HNO3 NO3 NH4

MARPD

Overall - 1990 to 2003

Mackville, KY - 2004

Rocky Mtn, CO - 2004

SO2 SO4

2- HNO3 NO3-

 NH4

+

The 2004 precision results shown in Figure 5-1 indicate that the results for MCK131/231 were 

below historical results for all five parameters. Four parameters (SO2, SO2-

4 , HNO3, and NH+ 

4 ) met 

DQI precision criteria. The precision results for ROM406/206 were below historical results for 

two parameters, above for two, and about the same for one. Only the results for NH+ 

4 met the 

DQI criterion. 

CASTNET Annual Report – 2004 40 Chapter 5: Data Quality 
Table 5-1 Data Quality Indicators for CASTNET Laboratory Measurements 

Precision Accuracy 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 (Ca

2+) 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: 

ICP-AES = inductively coupled plasma-atomic emission spectrometry

 MARPD = mean absolute relative percent difference 

 N = nitrogen 

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

Revision 2.0 (MACTEC, 2003b).

Precision statistics for 2004 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 did not meet the DQI criterion of 5 percent, except for Cl-, 

which had a MARPD of 3.3 percent. As discussed 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, to limit the possibility of 

future contamination, acceptance testing was instituted for Na +, potassium (K +), magnesium

(Mg2+), calcium (Ca2+), and Cl-

. The 2004 precision results for cations and Cl- show that no 

parameter met the precision criterion. 

Figure 5-2 Precision Data for Cation and Cl- Concentrations

0

5

10

15

20

25

Ca K Mg Na Cl

Overall - 2000 to 2003

Mackville, KY - 2004

Rocky Mtn, CO - 2004

MARPD

Ca2+ K+ Mg2+ Na+ ClCASTNET Annual Report – 2004 41 Chapter 5: Data Quality 
The 2004 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 with the exception of the Whatman filter SO2-

4 analyses. 

A few samples with low values had very high relative percent difference (RPD) values. 

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

indicate a slight improvement in 2004 precision versus 2003 values for MCK131/231 and a 

slight decline in precision for ROM406/206 2004 values versus 2003. 

Figure 5-3 Precision Results for Laboratory Replicate Samples (2004)

0

1

2

3

4

5

6

Nylon SO4

Whatman SO4

Teflon SO4

Nylon NO3

Teflon NO3

Teflon NH4

Sodium

Potassium

Magnesium

Calcium

Chloride

Mean Absolute Relative Percent

Difference for InRun Replicates

Teflon

SO4

2-

contribute to SO 2

Nylon

SO4

2-

Nylon

NO3

-

Teflon

NH4

+

Whatman

SO4

2-

Teflon

NO3

-

Teflon

Na+

Teflon

K+

Teflon

Mg2+

Teflon

Ca2+

Teflon

ClTable 5-2 Collocated Precision Results for 2004 by Quarter (MARPD) 

Site Pairs SO2-

4 NO3 NH+ 4 Ca2+

Mg2+Na +K + HNO3 SO2

Total 

NO3 ClMCK 131/231, KY

Quarter 1 3.61 3.83 4.27 7.38 4.03 4.53 8.55 9.87 10.80 9.69 17.03 

Quarter 2 2.65 2.67 1.92 9.04 3.54 3.11 4.25 6.22 6.54 7.86 6.99 

Quarter 3 3.57 2.39 5.07 17.46 4.16 2.37 7.69 3.61 4.84 5.94 2.50 

Quarter 4 2.60 2.41 4.98 7.36 4.62 3.38 4.26 12.68 8.80 11.54 5.90 

2004 3.11 2.82 4.06 10.31 4.09 3.35 6.19 8.09 7.74 8.76 8.10 

ROM 406/206, CO

Quarter 1 9.39 6.54 8.21 10.27 5.78 6.61 6.48 13.03 7.50 20.05 16.12 

Quarter 2 13.56 4.91 4.44 6.95 4.27 4.85 5.56 9.17 9.53 7.37 3.74 

Quarter 3 9.56 4.28 5.66 10.34 4.08 4.03 6.55 9.90 6.34 6.24 2.62 

Quarter 4 11.65 4.63 4.70 12.80 4.99 7.10 8.36 23.02 13.86 17.50 4.75 

2004 11.04 5.09 5.75 10.09 4.78 5.65 6.74 13.78 9.31 12.79 6.81 

CASTNET Annual Report – 2004 42 Chapter 5: Data Quality 
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). However, the QA procedures for the O3 analyzers at the NPS-sponsored sites do meet the 

SLAMS QA requirements. 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. The precision criterion for O3 is 

10 percent. 

Table 5-3 Data Quality Indicators 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 2004. 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 

precision data show the results for all four quarters for MCK131/231 and for the first and last 

quarters for ROM406/206 met the 10 percent criterion. The results for ROM406/206 for the 

second and third quarters were unacceptable because the O3 analyzer at ROM206 experienced 

several intermittent problems from February through August 2004. The uninterruptible power 

supply was replaced in February and the O3 analyzer itself in March. A loose ground wire was 

found during April, and a loose card was discovered in August. However, the annual MARPD 

CASTNET Annual Report – 2004 43 Chapter 5: Data Quality 
for ROM406/206 was approximately 9.4 percent, indicating that the two independently operated 

O3 analyzers with different QA/quality control (QC) procedures produce nearly identical results. 

Figure 5-4 Historical and 2004 Precision Data by Quarter for Ozone Concentrations 

0

2

4

6

8

10

12

14

First

Quarter

Second

Quarter

Third

Quarter

Fourth

Quarter

Overall - 1990 to 2003

Mackville, KY - 2004

Rocky Mtn, CO - 2004

Mean Absolute Relative

Percent Difference

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 2004 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 2004 with the exception of the mean RPD 

(5.3 percent) for the Whatman SO2-

4 in-run replicates. Table 5-4 also lists the precision results 

that were shown in Figure 5-3. 

CASTNET Annual Report – 2004 44 Chapter 5: Data Quality 
Table 5-4 Filter Pack QC Summary for 2004 

Reference 

Sample1 Recovery (%R) 

Continuing Verification 

Samples (%R)

In-Run Replicate2 

(RPD) 

Filter Type Parameter 

Mea

n

Std. Dev. Count3 Mea

n

Std. Dev. Count3 Mea

n

Std. Dev. Count3 

Teflon® SO2-

4 99.32 1.53 170 100.16 0.98 871 0.91 1.34 283

NO3 102.23 0.95 170 100.03 1.27 872 3.20 3.70 283

NH+ 

4 100.36 2.63 176 100.04 1.94 853 0.85 1.36 249

Ca2+ 103.23 2.07 209 100.50 1.00 735 2.61 3.86 262

Mg2+ 100.18 1.59 209 99.86 0.76 735 2.37 3.97 265

Na+

94.65 1.42 209 99.84 0.91 735 1.31 1.44 265

K+

101.68 3.16 209 100.06 0.89 735 2.56 2.98 265

Cl

- 101.63 1.37 168 99.95 1.20 862 2.20 4.91 283

Nylon SO2-4 98.40 1.49 141 99.95 0.72 694 1.96 3.17 293

NO3 100.53 0.85 141 99.79 1.12 694 1.10 1.12 293

Whatman SO2-

4 100.64 0.66 188 99.10 0.63 708 5.30 7.98 260

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 

CASTNET Annual Report – 2004 45 Chapter 5: Data Quality 

Petrified Forest National Park, AZ (PET427)
CASTNET Sample Handling 

 Objectives

The sample handling system supporting CASTNET is 

intended to ensure the data collection rate and data 

quality objectives are met. CASTNET sample 

handling procedures include these operational goals: 

• Maintain a clear chain-of-custody (COC); 

• Safeguard sample integrity; 

• Recognize, document, and correct operational 

problems; and 

• Maximize the data capture rate. 

 Positive Controls 

CASTNET utilizes an open-face, three-stage filter 

pack to measure sulfur and nitrogen species. Filter 

pack handling procedures are designed to minimize 

handling and transfers (i.e., opportunities for 

contamination and misdirection). Sample integrity is 

maintained by ensuring that materials in contact with 

samples do not affect the analytes of interest in a way 

that could bias results. These materials must be 

traceable to a point to enable documentation of their 

contact with the sample. These goals are supported 

via documented COC and by incorporating filter 

acceptance tests, laboratory blanks, and field 

(trip) blanks. 

 Filter Acceptance Testing 

Maintenance of sample integrity begins prior to

preparation of the filter packs. Filters are purchased in 

lot quantities and subjected to acceptance testing. 

Filters that are found to be acceptable are then

provided to the filter pack technicians. Filter lot 

numbers and the results of the acceptance testing are 

documented. Positive control of all filters prior to

acceptance testing and of acceptable filters after 

testing is important in supporting the sample 

integrity goal. 

 Chain of Custody 

COC begins when the filter pack is prepared and

labeled. Filter packing is performed in a dedicated

clean area to minimize the contamination potential. 

Once the filter pack is prepared and loaded in 

accordance with standard operating procedures (SOP), 

a filter pack label is applied. A COC form, which

includes the filter pack lot number, site number, and

employee number of the employee who assembled the 

filter pack, is included in the shipping container, which

is sealed and labeled for shipment. 

 Quality Control Blanks 

Two laboratory blanks are prepared each week 

during the same time the filter packs are being

prepared for the field. Each blank contains a filter 

from the same lot as the filters used in preparation of 

the field filter packs. The filters selected for the 

laboratory blanks are placed directly into the 

extraction bottles, bypassing the handling involved 

in loading and unloading the filter packs. This is 

intended to provide an indication of the effects of

filter handling within the laboratory. 

Field blanks are prepared once each quarter for each 

sampling site. The filter packs used for the field

blanks contain a nonstandard connection that cannot 

be installed in the sampling system. The filter pack

is prepared and loaded according to SOP. The field 

blanks are clearly identified and labeled to prohibit 

their removal from the resealable plastic bag they 

are packed in. When the field blank is returned from

the site, it is unpacked and analyzed following the 

standard analytical procedures. These samples 

elucidate the potential for contamination from the 

filter pack loading and unloading process. 

Reagents used in laboratory analyses are analytical 

reagent grade, traceable to a commercial supplier. 

Method blanks, containing each reagent used in the 

analysis, are run with each analytical batch to assess

reagent integrity. Method blanks containing

detectable levels of analytes of interest and/or

interfering analytes indicate possible contamination 

of the reagent or contamination from other sources 

(i.e., glassware, carryover). These occurrences are 

investigated. Once identified, the source of the 

contamination is quarantined or eliminated. 

Future Direction 

MACTEC is evaluating the introduction of a routine

spiked reagent blank for laboratory analyses. A 

volume of deionized water identical to the routine 

aqueous volume used in the extraction of field 

samples would be spiked with a known 

concentration of target analytes and carried through 

the extraction and analysis process. The resulting 

concentration would elucidate potential gains or

losses from the preparation process. 

CASTNET Annual Report – 2004 46 Chapter 5: Data Quality 
Continuous Measurements 

CASTNET sites were calibrated every six months with NIST-traceable standards during 2004. 

Table 5-5 shows that all continuous parameters were within DQI criteria (Table 5-3) more than 

90 percent of the time, except for relative humidity > 85 percent. This parameter met established 

criteria 78 percent of the time. According to CASTNET project protocols, the associated data are 

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 

97 percent. Therefore, the completeness value for this parameter was not adversely affected. 

Table 5-5 Accuracy Results for 2004 Field Measurements 

Parameter Percent Within Criterion 

Temperature (0°C) 97 percent 

Temperature (ambient) 97 percent 

Delta Temperature (0°C) 94 percent 

Delta Temperature (ambient) 97 percent 

*Relative Humidity > 85% 78 percent 

Relative Humidity ≤ 50% 97 percent 

Solar Radiation 91 percent 

Wind Direction North 96 percent 

Wind Direction South 97 percent 

Wind Speed < 5 m/s 98 percent 

Wind Speed ≥ 5 m/s 98 percent 

Precipitation 99 percent

Wetness (w/in 0.5 volts) 100 percent 

Ozone Slope 96 percent 

Ozone Intercept 99 percent 

Flow Rate 93 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 this parameter was 

97 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 DQI 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 2004 

completeness data for all sites for measured filter concentrations, continuous measurements, and 

calculated parameters. The figure shows that the 2004 direct measurements met the 90 percent 

goal. The 2004 results show that atmospheric concentrations, filter pack flow values, and ozone 

CASTNET Annual Report – 2004 47 Chapter 5: Data Quality 
(O 

3) data completeness exceeded 95 percent. The four parameters derived from MLM results 

exceeded 85 percent completeness for 2004. The results for 2004 were better than historical 

completeness statistics with the exception of atmospheric concentrations, which were about one 

percentage point worse than the historical results.

Figure 5-5 Historical (1990-2003)* and 2004 Percent Completeness of Measurements and 

Modeled Estimates 

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

Note: 

* Black bars represent 1990-2003 data

Conclusion 

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

QA/QC procedures and generally free of systematic bias during 2004. Accuracy data met the 

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

> 85 percent. 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 ammonia 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 2004. 

CASTNET Annual Report – 2004 48 Chapter 5: Data Quality 
RReeffeerreenncceess

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. 

Chow, J.C., Watson, J.G., Zhiqlang, L., Lowenthal, D.H., Frazier, C.A., Soloman, P.A., 

Thuillier, R.H., Magliano, K. 1996. Descriptive Analysis of PM2.5 and PM1.0 at 

Regionally Representative Locations during SJVAQS/AUSPEX. Atmos. Environ. 30, 

2079-2112. 

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. 

Herman, J. R., Bhartia, P. K., Torres, O., Hsu, C., Seftor, C., and Celarier, E. 1997. Global 

Distribution of UV-Absorbing Aerosols From Nimbus 7/TOMS Data. J. Geophys. Res. 

102:16,911-16,922. 

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

Network (CASTNET) Quality Assurance Report: Fourth Quarter 2004 (OctoberDecember) with 2004 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). 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 2.0. 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. 

CASTNET Annual Report – 2004 R-1 References 
CASTNET Annual Report – 2004 R-2 References 

References (continued)

National Oceanic and Atmospheric Administration (NOAA). 2004. NOAA Reports Cool 

Summer, Seventh Coldest August on Record Across the Lower 48 States; Record Number 

of Named Atlantic Tropical Cyclones for August. NOAA News Online (Story 2319) 

http://www.noaanews.noaa.gov/ stories2004/s2319.htm. October 26. 

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). 2000. National Air Quality and Emissions 

Trends Report, 1998. EPA-454-R-00-003. OAQPS, Research Triangle Park, 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. 
AAppppeennddiixxAA

Locational and Operational Characteristics of CASTNET Sites

CASTNET Annual Report – 2004 A-1 

Table A-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter Pack1

O e and zon

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

AlabamaSND152 Sand Mountain 12/27/88 34.2894 85.9704 352 • • Agri. RAlaskaDEN417 Denali National Park 10/06/98 63.7258 148.9633 661 • • Forested CKVA428 Kobuk Valley National ParkΘ 05/27/04 67.0931 157.8689 88 • • Forested CArizonaCHA467 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 FlArkansasCAD150 Caddo Valley 10/04/88 34.1792 93.0989 71 • • Forested RCaliforniaCON186 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 CSEK402 Sequoia National Park 02/04/97 36.4292 118.7625 1225 • • Forested MYOS404 Yosemite National Park 09/25/95 37.7133 119.7061 1605 • • Forested C
CASTNET Annual Report – 2004 A-2 

Table A-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter Pack1

O e and zon

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

ColoradoGTH161 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 CConnecticutABT147 Abington 12/28/93 41.8402 72.0111 209 • • ◊ Urban-Agri. RFloridaEVE419 Everglades National Park 10/06/98 25.3911 80.6806 2 • • 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 FGeorgiaGAS153 Georgia Station 06/28/88 33.1812 84.4100 270 • • Agri. RIllinoisALH157 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 – 2004 A-3 

Table A-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter Pack1

O e and zon

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

IndianaSAL133 Salamonie Reservoir 06/28/88 40.8164 85.6608 250 • • Agri. FlVIN140 Vincennes 08/04/87 38.7406 87.4844 134 • • Agri. RKansasKNZ184 Konza Prairie 03/26/02 39.1021 96.6096 348 • • Prairie FlKentuckyCDZ171 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. RMaineACA416 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 RMarylandBEL116 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 – 2004 A-4 

Table A-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter Pack1

O e and zon

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

MichiganANA115 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. FlMinnesotaVOY413 Voyageurs National Park 06/13/96 48.4128 92.8292 429 • • Forested RMississippiCVL151 Coffeeville 12/27/88 34.0028 89.7989 134 • • Forested RMontanaGLR468 Glacier National Park 12/27/88 48.5103 113.9956 976 • • Forested CNevadaGRB411 Great Basin National Park 05/16/95 39.0053 114.2158 2060 • • Forested CNew HampshireWST109 Woodstock 12/27/88 43.9446 71.7008 258 • • Forested CNew JerseyWSP144 Washington’s Crossing 12/27/88 40.3133 74.8726 61 • • Urban-Agri. R
CASTNET Annual Report – 2004 A-5 

Table A-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter Pack1

O e and zon

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

New YorkCAT175 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 CarolinaBFT142 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 DakotaTHR422 Theodore Roosevelt National Park 10/06/98 46.8947 103.3778 850 • • Range ROhioDCP114 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. ROklahomaCHE185 Cherokee Nation 04/02/02 35.7507 94.6700 299 • • Agri. ROntarioEGB181 Egbert, Ontario 12/27/94 44.2317 79.7840 251 •6 •4 Agri. R
CASTNET Annual Report – 2004 A-6 

Table A-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter Pack1

O e and zon

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

PennsylvaniaARE128 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 DakotaWNC429 Wind Cave National Park 11/18/03 43.5578 103.4839 1292 • • Prairie RTennesseeESP127 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. RTexasALC188 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 CUtahCAN407 Canyonlands National Park 01/24/95 38.4586 109.8211 1809 • • Desert CVermontLYE145 Lye Brook 03/30/94 43.0510 73.0613 730 • •5 ◊ Forested M
CASTNET Annual Report – 2004 A-7 

Table A-1. Locational and Operational Characteristics of CASTNET Sites

Site ID Site Name 

Start date 

Latitude (°N) 

Longitude (°W) 

Elevation (m) 

Deposition Filter Pack1

O e and zon

Meteorology2 

Wet Deposition 

Primary Land Use 

Terrain 

VirginiaPED108 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 MWashingtonMOR409 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 COLY421 Olympic National Park 10/06/98 48.0975 123.4256 125 • • Forested CWest VirginiaCDR119 Cedar Creek State Park 11/10/87 38.8794 80.8478 234 • • ◊ Forested CPAR107 Parsons 01/19/88 39.0906 79.6614 510 • • Forested CWisconsinPRK134 Perkinstown 09/27/88 45.2066 90.5972 472 • • ◊ Agri. RWyomingCNT169 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 – 2004 A-8 

Site ran from late May through September, on

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)

Whatman = 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. 

Θ◊ 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

Denotes Sites Sponsored by EPA 

Denotes Sites New in 2004 Sponsored by EPA Denotes Sites Sponsored by NPS Denotes Sites New in 2004 Sponsored by NPS 

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/castnet www.epa.gov/airmarkets w.epa.gov/airmarkets www.epa.gov www.epa.gov

Source: NOAA