Fourth Highest Daily Maximum 8-Hour Ozone Concentrations (ppb) for 2008

Clean Air Status and Trends

Network (CASTNET)

2008 Annual Report

Trend in Fourth Highest Daily Maximum 8-Hour Average Ozone Concentrations (ppb) − Eastern United States
Clean Air Status and Trends Network 

(CASTNET) 

2008 Annual Report

Prepared by: 

MACTEC Engineering and Consulting, Inc. 

Prepared for: 

U.S. Environmental Protection Agency 

Office of Air and Radiation 

Clean Air Markets Division 

Washington, D.C. 

EPA Contract No. EP-W-09-028 

February 2010
CASTNET Annual Report – 2008 ~ i ~ Table of Contents 

Table of Contents 

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

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

 Background ..................................................................................................................................................... 1 

 Cooperating Networks ................................................................................................................................ 3 

 Locations of Monitoring Sites ..................................................................................................................... 4 

 CASTNET Reference Sites .......................................................................................................................... 5 

 Measurements Collected at CASTNET Sites .......................................................................................... 6 

 Delivery of CASTNET Ozone Measurements to the EPA Air Quality System ................................................... 7 

 Calculating Dry Deposition ......................................................................................................................... 8 

 Sulfur Dioxide and Nitrogen Oxides Emissions ...................................................................................... 9 

 2008 Significant Events ................................................................................................................................................ 12 

Chapter 2 Atmospheric Concentrations ........................................................................................ 13 

Sulfur Dioxide .............................................................................................................................................. 13 

Ammonia Monitoring Network (AMoN) ...................................................................................................... 15 

 Particulate Sulfate ........................................................................................................................................ 17 

 Total Nitrate ................................................................................................................................................ 18 

 Particulate Ammonium ............................................................................................................................... 19 

 Trends in Air Quality at CASTNET Western Reference Sites ............................................................................ 21 

Chapter 3 Atmospheric Deposition ................................................................................................ 22 

 Sulfur Deposition ......................................................................................................................................... 23 

 Using CASTNET Data to Assess Quantity of Atmospheric Deposition Compared with Critical Loads ... 27 

 Nitrogen Deposition ................................................................................................................................... 29 

 Uncertainties in NO3 and HNO 

3 Concentrations and Their Effect on Dry Nitrogen Deposition ............. 32 

Chapter 4 Ozone Concentrations ................................................................................................... 34 

 National Ambient Air Quality Standards for Ozone ............................................................................................ 35 

 Eight-Hour Ozone Concentrations ......................................................................................................... 35 

 Impacts of NOx Budget Program and Clean Air Interstate Rule on Rural and Urban Ozone 

 Levels in the Eastern United States ........................................................................................................................... 39 

 Nitrogen Oxides and Ozone .................................................................................................................... 41 

 Ozone Episode in the Great Smoky Mountains, TN (GRS420) in July 2008 ................................................ 44 

Chapter 5 Data Quality .................................................................................................................... 47 

 Precision ........................................................................................................................................................ 47 

 Accuracy ........................................................................................................................................................ 54 

 Completeness ............................................................................................................................................... 56 

 Interlaboratory Comparison Results .......................................................................................................................... 58 

 Summary of Data Quality Results ............................................................................................................ 59 

References 

Appendix A Locational and Operational Characteristics of CASTNET Sites 

Appendix B Acronyms and Abbreviations 
CASTNET Annual Report – 2008 ~ ii ~ Executive Summary 

Executive Summary 

This report summarizes Clean Air Status and Trends Network (CASTNET) data collected 

during 2008 and examines trends in air quality since 1990. The report presents maps of the 

geographic distribution of pollutants measured in 2008. The report also discusses significant 

network events and presents an analysis of data quality. CASTNET began collecting 

measurements in 1991 with the incorporation of 50 sites from the National Dry Deposition 

Network, which had been in operation since 1987. CASTNET measures rural, regionally 

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

effectiveness of national and regional air pollution control programs. 

Key Results through 2008 

 The air quality, as represented by CASTNET pollutant measurements, was the best in 

the history of the network. 

 Mean annual sulfur dioxide and particulate sulfate concentrations declined significantly in 

the eastern United States over the 19-year period 1990 through 2008. Sulfur dioxide 

levels declined 48 percent while sulfate concentrations declined 26 percent. 

 Total (dry + wet) sulfur deposition declined by 38 percent from 1990 through 2008. 

 Mean annual concentrations of total nitrate (nitric acid plus particulate nitrate) declined 

25 percent in the eastern United States over the 19-year period. 

 Total nitrogen deposition declined by 19 percent from 1990 through 2008. 

 Ozone levels measured at CASTNET sites in 2008 continue to show a downward trend 

that began after a peak in 2002. The mean fourth highest daily maximum 8-hour average 

ozone concentration (69 ppb) for 2008 was the lowest in the history of the network. 

Only two eastern and four California sites recorded exceedances of the 8-hour 

standard of 0.08 ppm during the most recent 3-year period (2006–2008). During 2008, 

no eastern site recorded a fourth highest daily maximum 8-hour ozone concentration 

above 85 ppb. The recent declines in rural ozone and nitrate levels have been attributed 

to the documented decline in nitrogen oxide emissions in the eastern United States. 

 Measurements taken during 2008 and historical data collected over the period 

1990–2007 were analyzed relative to data quality objectives and their associated 

metrics. These analyses demonstrate that CASTNET data can be used with confidence 

and that CASTNET continues to produce information of the highest quality. 
CASTNET Annual Report – 2008 ~ 1 ~ Chapter 1: CASTNET Overview 

Chapter 1: CASTNET Overview 

CASTNET is a national air quality monitoring network designed to provide data to 

assess trends in air quality, atmospheric deposition, and ecological effects due to 

changes in air pollutant emissions. CASTNET began operation in 1991 to provide 

long-term monitoring of air quality in rural areas and to determine trends in 

regional atmospheric nitrogen, sulfur, and ozone concentrations and deposition 

fluxes of sulfur and nitrogen pollutants. CASTNET was preceded by the National 

Dry Deposition Network, which began in 1987. The primary sponsors of 

CASTNET are the Environmental Protection Agency and the National Park 

Service. As of December 2008, the network operated 84 monitoring stations 

throughout the contiguous United States, Alaska, and Canada. Air quality 

measurements collected in 2008 show the continuing decline in pollution levels 

throughout the network. Mean annual sulfur dioxide concentrations and mean 

fourth highest daily maximum 8-hour average ozone concentrations were the 

lowest in the history of CASTNET. 

Background 

The U.S. Congress, under a provision in the 1990 Clean Air Act Amendments (CAAA), 

directed the Environmental Protection Agency (EPA) to establish the Clean Air Status and 

Trends Network (CASTNET) to assess the effectiveness of the Acid Rain Program (ARP), 

which was promulgated to reduce emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) 

from electric generating units (EGUs). Congress recognized the need to assess and track realworld environmental results as the ARP was implemented, and emission reductions became 

effective. Congress mandated that CASTNET provide consistent, long-term measurements for 

determining relationships between changes in emissions and any subsequent changes in air 

quality, atmospheric deposition, and ecological effects. 

The ARP has produced significant reductions in SO2 and NOx emissions from EGUs since 1995. 

More recent NOx emission control programs also produced substantive declines in NOx

emissions in the eastern United States. These programs include the Ozone Transport 

Commission (OTC) NOx Budget (1999–2002) and the NOx State Implementation Plan (SIP) 

Call/NOx Budget Trading Program (NBP), which operated from 2003 through 2008. The NBP 

placed a cap on total NOx emissions from EGUs in the eastern United States during the ozone 

season (May 1 through September 30) when the potential for ozone formation is high. The 

Clean Air Interstate Rule (CAIR), which was issued in March 2005, aimed to permanently lower 

SO2 and NOx emissions in the eastern United States. CAIR, as promulgated, established three 

compliance programs: an annual NOx program, an ozone season NOx program, and an annual 
CASTNET Annual Report – 2008 ~ 2 ~ Chapter 1: CASTNET Overview 

SO2 program. Although CAIR was remanded back to EPA in 2008, these programs remain in 

effect while EPA works to develop a replacement rule. The first phase of the annual and ozone 

season NOx requirements began in 2009. The SO2 requirements will begin in 2010. EPA relies 

on CASTNET and other long-term monitoring networks to provide the air quality 

measurements used to assess the effectiveness of emission control programs. 

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

in 1987. The 50 NDDN sites were transferred to CASTNET in 1991. The network, as of 

December 2008, included 84 monitoring stations at 82 site locations throughout the contiguous 

United States, Alaska, and Canada. CASTNET is sponsored by EPA and the National Park 

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

With the participation of NPS, the network became a national, rather than a primarily eastern, 

network. NPS is responsible for the protection and enhancement of air quality and related 

values in national parks and wilderness areas. The CASTNET sites sponsored by NPS as of 

December 2008 numbered 25. Additional information on the NPS Air Monitoring program can 

be found on the Web site: http://www.nature.nps.gov/air/monitoring/. 

CASTNET stations measure rural, regionally representative concentrations of sulfur and 

nitrogen pollutants and ozone in order to detect and quantify trends, define the geographic 

distribution of rural pollutants, and estimate dry deposition of pollutants. Dry deposition is 

calculated from CASTNET concentration measurements and modeled deposition velocities 

using the Multi-Layer Model (MLM). The model requires several meteorological parameters and 

information on vegetation and land use specific to each site. CASTNET data are also used for 

atmospheric model evaluation, e.g., the Community Multiscale Air Quality (CMAQ) modeling 

system, and to provide input to ecological models. 

This report summarizes CASTNET/NDDN monitoring activities and the resulting 

concentration and deposition data collected over the 19-year period from 1990 through 

2008. Additional information, previous annual reports, and other CASTNET documents can 

be found on the EPA Web site, http://www.epa.gov/castnet/. The CASTNET database is also 

available to the public by accessing the “Download Data” link on EPA’s CASTNET Web page. 

The Web site provides a complete archive of concentration and deposition data for all EPA and 

NPS-sponsored CASTNET sites. Fully validated data are available approximately 10 months 

following collection. NPS data collected during 2008 from the NPS-sponsored CASTNET sites 

and the NPS Gaseous Pollutant Monitoring Program are available in the NPS 2008 Annual Data 

Summary Report (Ray, 2009) and the NPS 2008 Data Quality Assurance Report (ARS, 2009). 
CASTNET Annual Report – 2008 ~ 3 ~ Chapter 1: CASTNET Overview 

Cooperating Networks 

In addition to EPA and NPS, the principal sponsors, CASTNET monitors air quality and 

deposition in cooperation with other national networks. 

 National Atmospheric Deposition Program (NADP) operates the National 

Trends Network (NTN), which includes monitoring stations with wet deposition 

samplers to measure the concentrations and deposition rates of air pollutants removed 

from the atmosphere by precipitation. NADP/NTN operates wet deposition samplers at 

or near virtually every CASTNET site. NADP operates the Mercury Deposition

Network (MDN), which operates samplers to measure mercury in precipitation. 

MDN samplers are operated at several CASTNET sites. Additionally, NADP operates 

the Ammonia Monitoring Network (AMoN), which operates triplicate passive 

ammonia (NH 

3) samplers at about 20 NTN locations. AMoN has been operating for 

two years as a NADP initiative. AMoN provides information on 2-week average NH 

3 

concentrations. Additional information on NADP can be found on its Web site: 

http://nadp.sws.uiuc.edu/. 

 Canadian Air and Precipitation Monitoring Network (CAPMoN) operates 28 

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

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

Pennsylvania State University. 

 Interagency Monitoring of Protected Visual Environments (IMPROVE)

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

particulate air pollutants that affect visibility. 

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

needed to assess the effectiveness of promulgated emission control programs under several 

different mandates including the Government Performance and Results Act, the National Acid 

Precipitation Assessment Program (NAPAP), Title IX of the CAAA, and the United States – 

Canada Air Quality Agreement. 

Although EPA and NPS are the primary sponsors of CASTNET, other organizations, Native 

American tribes, universities, and government agencies play a role in sponsoring individual 

CASTNET sites. These co-sponsors provide in-kind services that support the overall operation 

of a site, including site operation, land use, or both. All of the sites added during recent 

expansion of the network (since 2001) have an associated co-sponsor. Three CASTNET 

monitoring sites are located on tribal lands: Cherokee Nation in eastern Oklahoma (CHE185), 
CASTNET Annual Report – 2008 ~ 4 ~ Chapter 1: CASTNET Overview 

Alabama-Coushatta in eastern Texas (ALC188), and Santee Sioux in northern Nebraska 

(SAN189). State agencies also operate special purpose air pollutant measurement devices at 

some CASTNET sites. 

Locations of Monitoring Sites 

Figure 1-1 shows the locations of CASTNET monitoring sites as of December 2008. Eighty-four 

sites were operational at 82 distinct locations. Most CASTNET sites are located in rural or 

remote locations away from pollutant emission sources and heavily populated areas. 

Appendix A provides the location of each site by state and includes information on start date, 

latitude, longitude, elevation, and the parameters measured. 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. In general, sample flow rates are set to 1.5 liters per minute 

(lpm) in the east and at a higher rate of 3.0 lpm in the west due to the lower pollutant 

concentrations generally found in the western United States. 

Figure 1-1 CASTNET Sites as of December 2008 
CASTNET Annual Report – 2008 ~ 5 ~ Chapter 1: CASTNET Overview 

CASTNET Reference Sites 

Chapters 2 through 4 present maps 

illustrating the magnitude of pollutant 

concentrations and deposition fluxes across 

the United States. In addition, 

measurements from 34 CASTNET eastern 

reference sites (Figure 1-2) were analyzed 

for each pollutant in order to determine 

trends in concentrations and trends in rates 

of dry, wet, and total deposition. These 34 

sites have been reporting CASTNET 

measurements since at least 1990. The 

reference sites were selected using criteria 

similar to those used by EPA in its National 

Air Quality and Emissions Trends Report 

(2000). The criteria include site longevity 

and data completeness. EPA’s procedures 

to interpolate and extrapolate quarterly 

mean data were also used to replace 

missing or invalid data. Trends in pollutant 

concentrations measured at CASTNET 

western reference sites (Figure 1-3) are also 

presented. The 17 western reference sites 

have been operating since at least 1996. 

In chapters 2 through 4, the data from the 

34 eastern reference sites were aggregated 

and then presented using box plots for the 

period 1990 through 2008. Data from the 

17 western reference sites were aggregated 

and then presented using box plots for the 

period 1996 through 2008. 

Figure 1-2 CASTNET Eastern Reference Sites 

Figure 1-3 CASTNET Western Reference Sites
CASTNET Annual Report – 2008 ~ 6 ~ Chapter 1: CASTNET Overview 

Quick Disconnect

Two

Whatman Nylon Teflon

Filters Filter Filter Shipping Cap 

(removed during sampling)

Teflon Spacers

Direction of Air Flow

Quick Disconnect

Two

Whatman Nylon Teflon

Filters Filter Filter Shipping Cap 

(removed during sampling)

Teflon Spacers

Direction of Air Flow

Quick Disconnect

Two

Whatman Nylon Teflon

Filters Filter Filter Shipping Cap 

(removed during sampling)

Teflon Spacers

Direction of Air Flow

Two 

Cellulose Nylon Teflon

Filters Filter Filter 

 Teflon Spacers 

Measurements Collected at CASTNET Sites 

CASTNET was designed primarily to measure trends in 

seasonal and annual average concentrations and to 

model depositions over many years. Consequently, 

measurement of weekly average (Tuesday to Tuesday) 

concentrations was selected as the basic sampling 

strategy. Over the course of the week, air is drawn at a 

controlled flow rate through an open-face 3-stage filter 

pack (Figure 1-4) mounted atop a 10-meter tower to 

collect air pollutants in the form of gases and particles. 

The first stage of the filter pack encloses a Teflon filter, 

the second a nylon filter, and the third holds two 

potassium carbonate (K2CO3)-impregnated cellulose 

filters. The filter pack is changed out each Tuesday and 

shipped to the analytical chemistry laboratory 

for analysis. 

The filter packs are prepared, loaded, shipped, received, extracted, and analyzed at the 

MACTEC Gainesville, FL laboratory. Following receipt from the field, exposed Teflon filters and 

blanks are extracted and then analyzed for sulfate (SO2-

4 ), nitrate (NO3), and concentrations of 

chloride (Cl-

) by micromembrane-suppressed ion chromatography (IC). Teflon filter extracts 

are also analyzed for ammonium (NH+ 

4 ) by the automated indephenol method with the 

Cellulose (2) 

Gaseous 

• SO 

2

Nylon 

Gaseous 

• HNO 

3 • SO 2 

Teflon

Particulate 

• SO2-

4 • NO3 • NH+ 4 • K +

• Ca2+ • Mg2+ • Na + • Cl-

 Figure 1-4 Three-Stage Filter Pack

CASTNET Ambient 

Measurements 

 Sulfur dioxide (SO2) 

 Particulate sulfate (SO2-

4 ) 

 Particulate nitrate (NO3) 

 Nitric acid (HNO3) 

 Particulate ammonium (NH+ 

4 ) 

 Particulate calcium (Ca2+) 

 Particulate sodium (Na+ ) 

 Particulate magnesium (Mg2+) 

 Particulate potassium (K+ ) 

 Particulate chloride (Cl-) 

 Ozone (O3) 

 Meteorological variables and 

information on land use and 

vegetation 
CASTNET Annual Report – 2008 ~ 7 ~ Chapter 1: CASTNET Overview 

Bran+Luebbe AutoAnalyzer 3. The Teflon filter extracts are additionally analyzed for calcium 

(Ca2+), sodium (Na+ ), magnesium (Mg2+), and potassium (K+ ) by inductively coupled plasmaatomic emission spectrometry (ICP-AES) using a Perkin Elmer Optima 3000 Dual View 

spectrometer. The cellulose filter extracts are analyzed for SO2 as sulfate using IC. In 

November 2008, the analytical laboratory began using the Dionex AS22 analytical column/AG22 

guard column for the impregnated cellulose filter analyses. The nylon filter extracts are analyzed 

via IC for nitric acid (HNO3) and for SO2. The SO2 concentrations from the cellulose and nylon 

filters are summed to obtain total SO2. 

CASTNET also measures hourly ozone (O3) concentrations, one of the major components of 

smog. In addition to the air pollutants, CASTNET sites collect hourly measurements of 

temperature, solar radiation, relative humidity, precipitation, wind speed and direction, standard 

deviation of wind direction (sigma theta), and surface wetness. These meteorological 

measurements are used to gauge the transport of air pollutants and as input to the MLM, a 

numerical model used for estimating dry deposition to ecosystems in the atmospheric boundary 

layer. The ozone and meteorological measurements are recorded continuously and archived as 

hourly averages. 

Delivery of CASTNET Ozone Measurements to 

the EPA Air Quality System 

CASTNET was not designed to operate as a network for demonstration of compliance 

with National Ambient Air Quality Standards (NAAQS) for O 

3. Instead, CASTNET was 

designed to provide information on geographic patterns in regional, rural O3 levels. 

However, because of interest in rural O3 concentrations by the regulatory and scientific 

communities, EPA has directed MACTEC to prepare EPA-sponsored sites to meet 

40 CFR Part 58 monitoring requirements and to ultimately deliver CASTNET O3

measurements to the EPA Air Quality System (AQS). AQS is EPA’s repository of ambient 

air quality monitoring data from more than 10,000 monitors. State, local, and tribal 

agencies and other organizations collect data and submit them to AQS on a periodic 

basis. AQS data are flagged with status codes to indicate the type of data (e.g., regulatory 

or non-regulatory) submitted. 

CASTNET monitoring equipment has been upgraded as one step toward meeting Part 58 

criteria. Upgrades include new ozone analyzers, data loggers with improved data 

communication, long-term manufacturer support for analyzers and loggers, and internal 

shelter temperature sensors. These instrument upgrades support conversion to 

regulatory-compliant operating and reporting procedures. The new data loggers and 
CASTNET Annual Report – 2008 ~ 8 ~ Chapter 1: CASTNET Overview 

analyzers allow more efficient tracking and recording of shelter temperature and 

provide system monitoring data that enable remote troubleshooting and optimization 

of operations. 

The data logger is programmed to control daily zero/span/precision (z/s/p) checks for the 

O3 analyzer. The O3 concentration needed for the precision (90 parts per billion [ppb]) 

and span (400 ppb) checks is produced internally by the onboard ozonator. Zero air is 

used for all quality control (QC) checks, including daily zero checks, and as the dilution 

medium for the ozonator precision and span checks. Instrument span and precision 

checks must be within ± 7 percent of reference value and zero checks must be ± 15 ppb 

for O3 data to be considered valid. 

All CASTNET continuous measurements, including the O3 data and supporting 

parameters, are collected via the data logger, polled remotely, archived at the CASTNET 

Data Management Center (DMC), and uploaded to AIRNow every hour. For sites to 

meet Part 58 monitoring criteria, data will be collected in accordance with EPA Quality 

Assurance (QA) Handbook Volume II (EPA, 2008b). Multi-point calibrations, which will be 

performed every six months, will also be in compliance with the EPA QA handbook. 

Ozone transfer standards will be used in accordance with EPA Technical Assistance 

Document, “Transfer Standards for the Calibration of Ambient Air Monitoring Analyzers 

for Ozone” (EPA, 2009d). 

Data will be uploaded to the AQS data submittal Web application in batch format using 

text files of raw ozone data and measurement accuracy and precision data. The AQS data 

submittal Web application is accessed at http://www.epa.gov/ttn/airs/airsaqs/aqsweb/.

AQS is divided into two parts: 

1. CDX – Central Data Exchange: A “Windows Explorer” for AQS. This 

component transfers and manages files to and from AQS. Batch data files are 

uploaded here and become available in the AQS application for processing. 

2. AQS Application: This application is used to interact with, process, and 

create reports of data.

Calculating Dry Deposition 

Dry deposition processes are modeled as resistances to deposition. The original network 

design was based on the assumption that dry deposition or flux could be estimated as the linear 

product of measured pollutant concentration (C) and modeled deposition velocity (Vd). The 

equation to estimate flux is shown in Figure 1-5. Measured atmospheric concentrations are 

calculated based on the mass of each analyte in each filter extract and the volume of air 
CASTNET Annual Report – 2008 ~ 9 ~ Chapter 1: CASTNET Overview 

ra = turbulence

ra, soil = turbulence near soil

rb = thin layer at surface

rcut = cuticular

rs = stomatal

rsoil = soil rb

ra

rsoil

Temp, RH, 

SR, LAI

Wind Speed, 

Sigma Theta

Wetness,

Precip

ra, soil

rb

rcut

rs

 1 1 1

sampled. The rate of deposition of a pollutant, also known as deposition velocity, is influenced 

by meteorological conditions, vegetation, and atmospheric and plant chemistry. The deposition 

velocity values for each site are calculated for each hour of each year using the MLM. The MLM 

is described by Meyers et al. (1998) and Finkelstein et al. (2000). 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 1-5 shows the relationships among the various resistances 

and illustrates the meteorological and other data that are required as model input. An 

improved version of the MLM (Schwede, 2006) includes changes to the soil moisture factor, 

which affects the stomatal and soil resistances, and to the radiation algorithm, which also affects 

the stomatal resistance. The deposition velocities and fluxes presented in Chapter 3 were 

calculated using the updated model. 

Figure 1-5 Multi-Layer Model 

Flux = C x Vd

1/Vd = + ra

 rs + rb 

+

 rcut + rb 

+

 ra, soil + rsoil

Resistances 

ra = aerodynamic 

ra, soil = aerodynamic near soil 

rb = boundary layer in thin layer at surface 

rcut = cuticular 

rs = stomatal 

rsoil = soil 

Sulfur Dioxide and Nitrogen Oxides Emissions 

The ARP, established under Title IV of the 1990 CAAA, was designed to reduce the adverse 

effects of acid deposition by requiring major reductions of SO2 and NOx emissions from the 

electric power industry. EPA recently assessed the effects of the ARP and related programs in 

1 
CASTNET Annual Report – 2008 ~ 10 ~ Chapter 1: CASTNET Overview 

its 2008 progress report (EPA, 2009a). The report summarizes 2008 compliance with the ARP 

and reported progress toward achieving environmental goals. 

Under the ARP, SO2 reductions are achieved using a cap and trade program that sets a 

permanent cap on the total amount of SO2 that may be emitted by all regulated EGUs in the 

contiguous United States. The program began in 1995 and is underway with the final 2010 SO2

cap set at 8.95 million tons, a level equal to about one-half of the emissions from the power 

sector in 1980. Use of a market-based cap and trade mechanism to reduce SO2 emissions 

allows flexibility for individual combustion units to select their own methods of compliance. 

Currently, one allowance provides a regulated unit limited authorization to emit one ton of 

SO2. The CAAA allocated allowances to regulated units based on historic fuel consumption and 

specific emission rates prior to the start of the program. The total allowances allocated for 

each year equal the SO2 emission cap. The program encourages early reductions by allowing 

sources to bank unused allowances in one year and use them in a later year. 

The ARP uses a more traditional approach to achieve NOx emission reductions. Rate-based 

limits apply to most of the coal-fired electric utility boilers subject to the SO2 emission 

reductions, and no nationwide cap has been placed on NOx emissions. Other NOx emission 

control programs have resulted in significant reductions in NOx emissions during the ozone 

season (see Chapter 4). Two prominent control programs are the OTC NOx Budget (1999–

2002) and the NOx SIP Call/NBP, which began in 2003 and continued through 2008. The NBP 

placed a cap on total NOx emissions from EGUs during the ozone season (May 1 through 

September 30) when the potential for ozone formation is high. The CAIR NOx ozone season 

trading program replaced the NBP in 2009. Although CAIR was remanded back to EPA in 2008, 

the CAIR programs remain in effect while EPA works to develop a replacement rule. 

The ARP is comprised of two phases for the reduction of SO2 and NOx. Phase I applied 

primarily to the largest coal-fired EGUs from 1995 through 1999 for SO2 and from 1996 

through 1999 for NOx. Phase II for both pollutants began in 2000. In 2008, the SO2

Phase II requirements affected 3,572 operating units. The Phase II NOx requirements applied to 

969 of those operating units that exceed 25 megawatts and burned coal between 1990 and 

1995 (EPA, 2009a). Under the ARP’s emission reduction requirements, total SO2 emissions 

from ARP sources were 7.6 million tons in 2008; total NOx emissions from ARP sources were 

3.0 million tons. 

 

Figure 1-6 presents state-by-state total annual SO2 emissions for Phase I and Phase II electric 

utility plants for four years (1990, 1995, 2000, and 2008). The most significant reduction in SO2

emissions occurred in and near the Ohio River Valley where many coal-fired power plants are 

located. Many of the states with the highest SO2 emissions realized the largest reductions. The 

seven states with the greatest annual reductions include Ohio, which decreased emissions by 
CASTNET Annual Report – 2008 ~ 11 ~ Chapter 1: CASTNET Overview 

Annual Emissions of Sulfur Dioxide

Scale: Largest bar equals 

2,212 thousand short 

tons (Ohio, 1990).

1990

1995

2000

2008

1.5 million tons since 1990, and Illinois, Indiana, Kentucky, Missouri, Tennessee, and West 

Virginia. Annual NOx emissions by state are depicted in Figure 1-7 for the same four years. 

States with the highest NOx emissions also produced the most significant declines. Every state 

east of the Mississippi River experienced a significant decline in annual NOx emissions from 

2000 to 2008. For example, NOx emissions from Illinois power plants declined by 47 percent 

from 2000 to 2008. 

Figure 1-6 Annual Utility SO2 Emissions (Phase I and Phase II Plants only) 

Figure 1-7 Annual Utility NOx Emissions (Phase I and Phase II Plants only) 

Annual Emissions of Nitrogen Oxides

Scale: Largest bar equals 

534 thousand short 

tons (Ohio, 1990).

1990

1995

2000

2008
CASTNET Annual Report – 2008 ~ 12 ~ Chapter 1: CASTNET Overview 

2008 Significant Events 

January

The first Campbell Scientific CR3000 data logger was installed at Palo Duro Canyon State Park, TX.

February

Analog cellular service ended. First installations of the AirLink Raven X cellular Ethernet modems 

were completed to provide access and communication to sites without landlines.

May

Due to budget constraints, it was decided that cloud water sampling would not be conducted at 

CLD303, TN for the 2008 sampling season under the Mountain Acid Deposition Program 

(MADPro). This is the first season without sampling since MADPro began sampling in 1994.

July

MACTEC determined the date and time when model runs initialized with drought and saturated 

model runs coalesced for each site for the entire record of MLM simulations. This point of 

coalescence is now the starting point for each site’s dry deposition record.

September

MACTEC’s CASTNET analytical laboratory tied for first place out of 39 participating laboratories in 

Environment Canada’s laboratory intercomparison Proficiency Test 0092.

October

Yagi directional antennae were installed at select remote sites to boost the cellular signal at each site 

and allow use of Raven X Cellular Ethernet modems for Internet Protocol (IP) connections.

Supplemental CASTNET training videos became accessible through a dedicated MACTEC Web site. 

Operators can access videos from the sites.

November

MACTEC’s CASTNET analytical laboratory began using the Dionex AS22 analytical column/AG22 

guard column for the impregnated cellulose filter analyses, replacing the Dionex AS4A analytical 

column /AG4A guard column. The new column provides improved peak separation and is less 

susceptible to matrix interferences.

NPS produces a biannual CASTNET newsletter called The Monitor that contains information 

about some of the changes and important events affecting CASTNET operations. For an 

electronic library of current and previous newsletters, go to: 

http://www.nature.nps.gov/air/Pubs/theMonitor.cfm.
CASTNET Annual Report – 2008 ~ 13 ~ Chapter 2: Atmospheric Concentrations 

Chapter 2: Atmospheric Concentrations 

Three-stage filter packs are used to measure 7-day average concentrations of SO2, 

SO2-

4 , HNO3, NO3, NH+ 4 , Cl-

, and four earth metals at 84 CASTNET monitoring 

stations. Measured annual mean concentrations of sulfur species have decreased 

steadily since 1990. Concentrations of nitrogen species remained relatively steady 

from 1990 until 2000 when they began to decline as NOx emission reduction 

programs were implemented. Trends in mean annual SO2, SO2-

4 , total NO3, and NH+ 4

concentrations aggregated over the 34 eastern reference sites are shown over the 

period 1990 through 2008 and for the 17 western sites for the period 1996 through 

2008 using box plots for each year. All four parameters declined over the 19-year 

period. SO2 and SO2-

4 concentrations declined significantly since 2005. SO2

concentrations measured at the 17 western reference sites also declined. 

Concentrations of the other three pollutants measured at the western sites did not 

change significantly. 

Separate maps depicting the annual mean concentrations of SO 

2, SO2-4 , total nitrate (HNO 3 + 

NO3), and NH+ 

4 are presented in this chapter. Additional maps are provided in CASTNET 

quarterly reports (MACTEC 2008a, 2008d, 2009c, 2009a). The concentration shading used in 

the maps in this chapter was prepared using an algorithm based on inverse distance weighting 

and the scales specified on each map. In addition, trends in concentrations over the 19-year 

period (1990 through 2008) were derived from the 34 eastern CASTNET reference sites 

(Figure 1-2) and are presented using box plots. Trends in annual mean concentrations were also 

estimated from measurements aggregated over the 17 western CASTNET reference sites 

(Figure 1-3) for the period 1996 through 2008. 

Sulfur Dioxide 

Sulfur dioxide is a gaseous pollutant emitted during the combustion of coal, oil, and other fossil 

fuels that contain sulfur. EGUs constitute the largest source of SO 

2 in the United States. SO 2 is 

a criteria pollutant regulated by the NAAQS, which are designed to protect human health and 

welfare. To be compliant under the SO 

2 NAAQS, the annual average concentration must be 

below 80 micrograms per cubic meter (μg/m3

) of air. SO 

2 gas reacts in the atmosphere to form 

various acidic compounds including sulfuric acid (H 

2SO 4), a significant contributor to acid rain, 

and ammonium sulfate [(NH 

4)

 

2SO 4], a major component of fine particle matter (PM2.5). Fine 

particles are regulated by the NAAQS since PM2.5 contributes to negative health effects and also 

to degradation of atmospheric visibility, including range and detail. The NAAQS for an annual 

average PM2.5 concentration is 15 μg/m3

. 

Annual mean SO 

2 concentrations measured in 2008 are presented in Figure 2-1. Six states 

centered on and downwind of the Ohio River Valley in the eastern United States recorded 
CASTNET Annual Report – 2008 ~ 14 ~ Chapter 2: Atmospheric Concentrations 

mean concentrations greater than or equal to 5.0 g/m3 of air. The region covers Indiana, Ohio, 

Pennsylvania, New Jersey, Maryland, and western Virginia. Quaker City, OH (QAK172) 

measured the highest concentration in the network with a value of 11.4 g/m3

. Only two 

western sites (Figure 1-1) measured an annual mean SO 

2 concentration greater than or equal to 

1.0 g/m3

. The western sites are Palo Duro Canyon State Park, TX (PAL190) and Theodore 

Roosevelt National Park, ND (THR422). 

Figure 2-1 Annual Mean SO2 Concentrations (g/m3

) for 2008 

Figure 2-2 shows box plots of annual mean SO 

2 concentrations aggregated over the 34 eastern 

reference sites from 1990 through 2008 (right side) and the 17 western reference sites from 

1996 through 2008 (left side). The y-axes on the western and eastern plots have different 

scales. The box plots for the eastern sites show a downward trend. The most substantial 

reduction in ambient SO 

2 was recorded in 1995 at the beginning of the ARP. A noteworthy 

decline was also recorded from 2005 through 2008. Three-year mean concentrations for 1990–

1992 and 2006–2008 were 8.9 g/m3 and 4.6 g/m3, respectively. This change constitutes a 

48 percent reduction in 3-year mean SO 

2 concentrations between the two time periods. The 

2008 mean level of 4.1 g/m3

 was the lowest mean value measured by the eastern reference 

sites in the history of the network. 

The box plots for the western reference sites indicate a decline in annual mean SO 

2

concentrations aggregated over the 17 sites. Three-year mean SO 

2 concentrations for 1990–

1992 and 2006–2008 were 0.6 g/m3

 and 0.4 g/m3, respectively. This change constitutes a 

37 percent reduction in 3-year mean SO 

2 concentrations over the 13 years. The aggregated 

mean SO 

2 concentrations from the western reference sites were more than 10 times lower 

than mean concentrations measured at the eastern reference sites. 

 
CASTNET Annual Report – 2008 ~ 15 ~ Chapter 2: Atmospheric Concentrations 

Figure 2-2 Trend in Annual Mean SO2 Concentrations (g/m3) 

 Western Reference Sites Eastern Reference Sites 

Ammonia Monitoring Network (AMoN) 

Gaseous NH  

3 affects chemical deposition and biogeochemical processes in ecosystems. NH  3

reacts with sulfur (S), nitrogen (N), and other acidic species to form (NH4)2SO4 and 

ammonium nitrate (NH4NO3) particles, which exist in the atmosphere as PM2.5. These 

aerosols, along with carbon aerosols, constitute the major fraction of PM2.5 pollution in the 

atmosphere. PM2.5 affects human health, visibility, and visual quality. PM2.5 is subject to longrange transport and contributes to international transboundary air pollutant issues. 

Domesticated animals and fertilizer are the largest global source of anthropogenic 

atmospheric NH3 emissions. Current estimates of NH3 emissions are uncertain because of 

the diverse nature of agricultural and feedlot operations. Figure 2a illustrates modeled NH3

emissions for 2002. 

A 2007 United States-Canada 

workshop on NH3 (NADP, 2009) 

called for the creation of an 

extensive long-term network of 

passive NH3 samplers with NADP 

serving as the coordinating 

organization. The participants 

also recommended the use of 

Radiello diffusive passive samplers 

throughout the network because 

of low detection limits and high 

reproducibility. 

 

0.0

0.5

1.0

1.5

1996199719981999200020012002200320042005200620072008

Concentration (g/m3)

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

1990199119921993199419951996199719981999200020012002200320042005200620072008

Concentration (g/m3)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

Figure 2a Ammonia Emissions: All Sources but Soil 

(2002) 

Source: Carnegie Mellon University emissions model described in 

http://www.cmu.edu/ammonia. 
CASTNET Annual Report – 2008 ~ 16 ~ Chapter 2: Atmospheric Concentrations 

Table 2a AMoN Sampling Locations 

Site Name 

Latitude (N) Longitude (W) 

Site Name 

Latitude (N) Longitude (W) 

CO13 Fort Collins, CO 40.5592 105.0781 NM99 Farmington, NM 36.7358 108.2380 

IL11 Bondville (QAQC), IL 40.0520 88.3725 NY16 Millbrook, NY 41.7858 73.7414

IN99 Indianapolis, IN 39.7333 86.2833 NY67 Ithaca, NY 42.4014 76.6589

KS24 Glen Elder State Park, KS 37.0378 95.6264 OH02 Athens Super Site, OH 39.3167 82.1000

MI96 Detroit, MI 42.2500 83.2000 OH27 Cincinnati, OH 39.1500 84.5167

MN18 Fernberg, MN 48.0500 91.8166 OK99 Stilwell, OK 35.7514 94.6717

MN29 Blue Mounds, MN 43.6667 96.2333 ON07 Egbert, ON 44.2333 79.7833 

MN42 Great River Bluffs, MN 44.0500 91.6333 PA00 Arendtsville, PA 39.9231 77.3078

NC30 Duke Forest, NC 35.7789 78.8003 SC05 Cape Romain Refuge, SC 32.9419 79.6591

NC35 Clinton Research Station, NC 35.0258 78.2783 TX43 Canonceta, TX 34.8803 101.6649

NC99 Durham, NC 35.8106 76.8978 WI07 Mayville, WI 43.4833 88.5300

NM98 Navajo Lake, NM 36.8097 107.6520 

Note: Collocated CASTNET sites are highlighted in yellow. 

In response, NADP initiated AMoN near the end of 2007 as a network of passive NH3

samplers across the United States with a site also operating in Egbert, ON. Table 2a lists the 

AMoN locations. In addition to providing data that describe atmospheric NH3 concentrations 

over space and time, NADP is evaluating the Radiello passive NH3 sampler against other 

passive sampler types and denuder-based measurement systems to record the accuracy, 

precision, and repeatability of the passive NH3 samplers in order to determine the best 

sampler for the lowest cost. 

Information about AMoN can be 

found on NADP NH3 Web site 

(http://nadp.sws.uiuc.edu/nh3Net/). 

The Web site discusses the 

sampling system and related 

information. Each site 

operates triplicate Radiello 

samplers over 2-week periods.

The samplers are removed at the 

end of the two weeks and sent to 

the NADP Central Analytical 

Laboratory at the Illinois 

State Water Survey for chemical 

analysis. The site also maintains a 

database of NH 

3 measurements. 

Figure 2b was constructed from the triplicate 2-week data and shows spring 2008 mean 

seasonal NH3 concentrations. The highest concentrations for 2008 were observed during the 

spring, perhaps associated with fertilizer application. Nine sites measured NH3 values greater 

than 2.5 g/m3. 

Figure 2b Average Spring 2008 NH3 Concentrations 
CASTNET Annual Report – 2008 ~ 17 ~ Chapter 2: Atmospheric Concentrations 

Particulate Sulfate 

Particulate sulfate is formed in the atmosphere through the transformation of SO 

2 via both gas 

and aqueous (cloud) phase reactions. It typically exists in the atmosphere as (NH4)2SO4, a major 

component of PM2.5. Figure 2-3 provides a map of annual mean particulate SO2-

4 concentrations 

measured during 2008. Pennsylvania State University, PA (PSU106) and QAK172, OH each 

measured a concentration of 4.0 g/m3

. The map shows significant geographic gradients in SO2-

4

levels from the monitors in the vicinity of the Ohio River Valley northeastward to sites in 

New England and northwestward to sites in Wisconsin and northern Minnesota. Sulfate 

concentrations greater than or equal to 1.0 g/m3 in the western region were measured at four 

sites in California, two in Texas, and the monitoring station at THR422, ND. 

Figure 2-3 Annual Mean SO2-

4 Concentrations (g/m3

) for 2008 

Box plots of annual mean SO2-

4 concentrations from the 34 eastern reference sites from 1990 

through 2008 are presented in the right half of Figure 2-4. The plots illustrate the trend in 

atmospheric SO2-

4 over the 19-year period. The figure shows a substantial decline in SO2-4 with 

some interannual variability. The difference between 3-year means from 1990–1992 to 2006–

2008 represents a 26 percent reduction in SO2-

4 from 5.4 g/m3

 to 3.6 g/m3, respectively. The 

2008 mean SO2-

4 level of 3.2 g/m3

 was the lowest in the history of the network. 

The box plots for the western reference sites are provided on the left side of Figure 2-4. The 

boxes show no real change in annual mean SO2-

4 concentrations aggregated over the 17 sites. 

Mean sulfate concentrations measured at the western sites were lower than mean values 

measured at eastern sites. 

 
CASTNET Annual Report – 2008 ~ 18 ~ Chapter 2: Atmospheric Concentrations 

Figure 2-4 Trend in Annual Mean SO2-

4 Concentrations (g/m3

) 

 Western Reference Sites Eastern Reference Sites 

Total Nitrate 

Total nitrate is the sum of HNO 

3 and NO3, which are formed from emissions of NOx produced 

through the combustion of fossil fuels. Transportation sources are the largest contributors of 

NOx emissions in the United States. Nitric acid exists as a gas and contributes to acid 

deposition. Nitrate is a component of PM2.5 in the form of NH 

4NO 3 and as larger particles, e.g., 

sodium nitrate (NaNO 

3) or calcium nitrate [Ca(NO 3)

 

2]. A map of annual mean total nitrate 

concentrations for 2008 is shown in Figure 2-5. This chapter discusses data on total nitrate 

levels because of the uncertainty in individual species measurements and because total nitrate is 

more representative of a response to changes in NOx emissions than either of its constituents 

alone. The map of 2008 total nitrate concentrations shows three regions with mean 

concentrations greater than or equal to 2.5 g/m3. The largest region extends from eastern 

Kansas to Ontario. CASTNET monitors in six states in the Midwest, including Kansas, Illinois, 

Indiana, Kentucky, Ohio, and Michigan, measured concentrations greater than or equal to 2.5 

g/m3. The monitor at Egbert, ON (EGB181) also measured an annual mean concentration of 

2.5 g/m3

. The second, smaller region covers sites in eastern Pennsylvania, New Jersey, and 

Maryland. Three sites in California constitute the third region. Three sites, including Stockton, IL 

(STK138); Salamonie Reservoir, IN (SAL133); and Lykens, OH (LYK123), measured the highest 

concentration (3.7 g/m3

) in the network. 

Box plots of total nitrate levels for 1990 through 2008 are given in Figure 2-6. The data shown 

on the right side of the figure were aggregated from the 34 eastern reference sites. The data 

show no trend in mean concentrations until 2000 when nitrate levels began to decline in 

response to NOx emission control programs. Three-year mean levels declined from 3.0 g/m3

to 2.3 g/m3

 from 1990–1992 to 2006–2008, producing a 25 percent reduction in total nitrate. 

Total nitrate levels measured at the eastern reference sites declined from a 2000 mean value of 

3.2 g/m3

 to a 2008 level of 2.1 g/m3, the lowest in the history of CASTNET. 

0.0

0.5

1.0

1.5

2.0

1996199719981999200020012002200320042005200620072008

Concentration (g/m3)

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

1990199119921993199419951996199719981999200020012002200320042005200620072008

Concentration (g/m3)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2008 ~ 19 ~ Chapter 2: Atmospheric Concentrations 

Figure 2-5 Annual Mean Total Nitrate (NO3 + HNO3) Concentrations (g/m3) for 2008 

Data aggregated from the 17 western sites are shown on the left side of Figure 2-6. The 3-year 

mean total nitrate concentration for 2006–2008 was lower than the corresponding 1990–1992 

level. However, this change is not considered substantive. 

Figure 2-6 Trend in Annual Total Nitrate (NO3 + HNO3) Concentrations (g/m3) 

 Western Reference Sites Eastern Reference Sites 

Particulate Ammonium 

Particulate ammonium is formed when NH 

3, HNO 3, SO2-4 , and NO3 particles interact in the 

atmosphere. NH 

3 is formed through volatilization of farm animal wastes and fertilizers and 

some combustion processes. Annual mean NH+ 

4 concentrations for 2008 are depicted in 

Figure 2-7. No monitors measured concentrations above 2.0 g/m3

. The data show a flat 

geographic distribution across the eastern United States with most sites reporting values 

greater than or equal to 1.0 g/m3

. Higher concentrations were measured in the agricultural 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1996199719981999200020012002200320042005200620072008

Concentration (g/m3)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0

1

2

3

4

5

6

7

8

1990199119921993199419951996199719981999200020012002200320042005200620072008

Concentration (g/m3)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2008 ~ 20 ~ Chapter 2: Atmospheric Concentrations 

Midwest, Pennsylvania, and northern Alabama. The NH+ 

4 concentrations measured at western 

sites were low with all sites measuring concentrations less than 1.0 g/m3. 

Figure 2-7 Annual Mean NH+ 

4 Concentrations (g/m3

) for 2008 

Box plots of NH+ 

4 concentrations are provided in Figure 2-8. The trend diagram for the eastern 

sites shows a reduction in mean NH+ 

4 levels from 1990–1992 to 2006–2008. The 1990–1992 

mean concentration was 1.8 g/m3 and the 2006–2008 value was 1.3 g/m3. The box plots 

characterizing the western sites show no change. 

Figure 2-8 Trend in Annual Mean NH+ 

4 Concentrations (g/m3

) 

 Western Reference Sites Eastern Reference Sites 

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1996199719981999200020012002200320042005200620072008

Concentration (g/m3)

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

1990199119921993199419951996199719981999200020012002200320042005200620072008

Concentration (g/m3)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2008 ~ 21 ~ Chapter 2: Atmospheric Concentrations 

Trends in Air Quality at CASTNET Western Reference Sites

Trends in concentrations over the 13-year 

period (1996–2008) were derived from the 

17 CASTNET western reference sites 

(Figure 1-3). Box plots constructed from 

data aggregated from the 17 sites are given in 

Figures 2-2, 2-4, 2-6, and 2-8. Additional 

trend plots are shown in this discussion. 

Figure 2c presents mean SO 

2 trend lines for 

eight western sites selected to depict a range 

of results. Declines in annual mean SO 

2 levels 

were observed at six of the sites. Noticeable 

reductions were measured at Chiricahua 

National Monument, AZ (CHA467) and 

Mesa Verde National Park, CO (MEV405). 

The box plots (Figure 2-2) derived from 

aggregated data show a 37 percent decline. 

Trend lines for annual mean total nitrate 

concentrations measured at four California 

CASTNET sites are shown in Figure 2d. A 

significant decline was measured at Joshua 

Tree National Park, CA (JOT403) with about 

a 17 percent reduction between 3-year 

averages at the beginning and end of the 

13-year period. Concentrations measured at 

JOT403, which is downwind of the Los 

Angeles Basin, were about three times higher 

than concentrations measured at Yosemite 

National Park, CA (YOS404). 

Figure 2e depicts trends in all four annual 

mean pollutants measured at Mount Rainier 

National Park, WA (MOR409). The figure 

shows that all four pollutants declined with 

especially noticeable declines in SO 

2 and SO2-4

levels during 2000 to 2002. The decline in 

sulfur pollutants is attributed to the 

installation of SO 

2 scrubbers at the Centralia 

Power Plant and a corresponding reduction 

in emissions. 

Figure 2c Trends in Mean SO 

2

Concentrations (g/m3) at Eight 

Western Sites 

Figure 2d Trend in Annual Mean Total 

Nitrate Concentrations (g/m3

) at Four 

California Sites 

Figure 2e Trends in Annual Mean Pollutant 

Concentrations (g/m3

) at Mount Rainier 

National Park, WA 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1996199719981999200020012002200320042005200620072008

Concentration (g/m3)

SO2 SO4

Total NO3 NH4

SO2

Total NO3

SO4

2-

NH4

+

0

1

2

3

4

5

1996199719981999200020012002200320042005200620072008

Concentration (g/m3)

JOT403 LAV410

PIN414 YOS404

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1996199719981999200020012002200320042005200620072008

Concentration (g/m3)

CAN407 CHA467

GLR468 GRB411

GRC474 MEV405

ROM406 YEL408
CASTNET Annual Report – 2008 ~ 22 ~ Chapter 3: Atmospheric Deposition 

Chapter 3: Atmospheric Deposition 

CASTNET was designed to provide estimates of the dry deposition of sulfur and 

nitrogen pollutants across the United States. CASTNET uses a hybrid approach to 

estimate dry deposition by combining measured pollutant concentrations and modeled 

deposition velocities. The Multi-Layer Model is used to calculate hourly deposition 

velocities for each monitoring site based on meteorological measurements and 

information on the vegetation within 1 km of each site. Total deposition is the sum of 

estimated dry deposition and measured wet deposition. Total sulfur deposition estimated 

for eastern reference sites has declined since 1990. The data show a 38 percent 

reduction in 3-year mean sulfur fluxes over the period from 1990–1992 to 2006–2008. 

Dry and total sulfur deposition estimated for 17 western sites declined over the period 

1996 through 2008. Total nitrogen deposition estimated for the eastern reference sites 

declined by 19 percent. Total nitrogen deposition did not change at the western 

reference sites over the 13 years. Dry deposition is responsible for a significant 

percentage of total deposition, especially in major emission source regions. 

 

Gaseous and particulate sulfur and nitrogen pollutants are deposited through dry and wet 

atmospheric processes. A critical objective of CASTNET is to estimate the rate, or flux, of dry 

deposition from the atmosphere to sensitive ecosystems based on measured meteorological 

and other environmental conditions. Flux values are estimated as the product of measured 

concentration data and MLM-modeled dry deposition velocities. Wet deposition measurements 

were obtained from NADP/NTN and combined with CASTNET dry deposition data to 

estimate total deposition. Dry sulfur, total sulfur, dry nitrogen, and total nitrogen deposition 

decreased during 2008. Precipitation-weighted mean concentrations of atmospheric sulfur 

declined over the past 19 years. Nitrogen concentrations in precipitation have declined slowly 

since 1998. 

Dry deposition processes were simulated using the MLM (Figure 1-5) as described by 

Meyers et al. (1998) and Finkelstein et al. (2000). The most recent version of the MLM 

(Schwede, 2006) was used for this report. The MLM was run using CASTNET filter pack 

concentrations and meteorological measurements with information on land use, vegetation, and 

surface conditions, to calculate deposition velocities for SO 

2, HNO 3, O 3, and the particles, SO2-4 , 

NO3, and NH+ 

4 . The deposition velocities were assumed to be identical for all particle species. 

Deposition velocity values were calculated for each of the pollutant species for each hour with 

valid meteorological data for each CASTNET site for the entire period 1990 through 2008. For 

a deposition velocity to be estimated, measurements of temperature, solar radiation, relative 

humidity, wind speed, and standard deviation of the wind direction (sigma theta) must all be 
CASTNET Annual Report – 2008 ~ 23 ~ Chapter 3: Atmospheric Deposition 

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

calculation of an annual value. If an annual value was not available for a specific site, the results 

were not included on the maps presented in this chapter. Sites with no deposition estimates 

are shown as dots with no value. For trends analyses, missing values were replaced by 

interpolation or extrapolation using valid annual estimates. For example, if an intermediate year 

was missing, the value for that year was interpolated from adjacent years. If a 2008 value was 

missing, the 2008 value was assumed equal to the value for 2007. 

Sulfur Deposition 

MLM runs were made separately for SO 

2 and SO2-4 . The model calculations were summed to 

obtain estimates of dry sulfur deposition (as S). A map of dry sulfur deposition fluxes for 2008 is 

provided in Figure 3-1. The magnitude of a deposition rate is illustrated by the size of the circle. 

The map depicts three CASTNET sites with estimated fluxes greater than 5.0 kilograms per 

hectare per year (kg/ha/yr). These sites are located in Ohio at Quaker City (QAK172) and in 

Pennsylvania at Pennsylvania State University (PSU106) and Arendtsville (ARE128). The highest 

deposition rate was estimated for QAK172, OH with a flux of 8.9 kg/ha/yr. The highest dry 

sulfur deposition rates coincided with the major SO 

2 source region (Figure 1-6) and declined 

sharply with distance. The dry deposition rates for the western sites were all less than 

1.0 kg/ha/yr with the majority of sites less than 0.5 kg/ha/yr. 

Figure 3-1 Dry Sulfur (SO2 + SO2-

4 ) Deposition (kg/ha/yr) for 2008 

 

4.3

8.9

2.2

3.8

2.1

1.7

2.8

0.2

0.2 2.5

1.5

0.3

1.1

0.3

1.2

0.5

1.3

2.7

1.7

5.1

0.6

0.5

2.6

1.9

3.2 3.0

0.6

0.2

0.3

0.9

2.4

1.6

0.2

0.6

2.1

0.8

1.2

1.1

0.6

2.7

1.0

0.3

0.9

0.3

0.8

0.1

3.7

3.2

4.6

0.8

2.6

1.6

0.6

1.6

0.6

7.9

0.2

0.7

2.3

0.6

0.3

2.6

4.3

0.4

2.8

3.4

0.2

0.3

0.2

Site not pictured:

DEN417, AK 0.1

Deposition

10

5

1
CASTNET Annual Report – 2008 ~ 24 ~ Chapter 3: Atmospheric Deposition 

Wet deposition values used to estimate total deposition were based on a combination of 

historical CASTNET wet deposition data and NADP/NTN wet deposition data. For CASTNET 

sites where wet concentrations were measured prior to January 1999, 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 diameters of 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 the percent wet deposition, and the light shading 

(tan) shows the percent dry deposition. Seven CASTNET sites in Indiana, Ohio, and 

Pennsylvania had total (dry + wet) sulfur deposition fluxes greater than 10.0 kg/ha/yr. The 

highest total sulfur deposition rate was estimated for QAK172, OH with a value of 

17.2 kg/ha/yr. Total sulfur deposition at western sites was less than or equal to 2.0 kg/ha/yr. 

Centennial, WY (CNT169) had the highest estimated flux for the western sites with a value of 

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

source regions. For example, the contribution of dry sulfur deposition ranged from about half 

of total sulfur deposition at Horton Station, VA (VPI120) to less than 20 percent at sites 

in New England. 

Figure 3-3 presents box plots that show the trend in dry sulfur deposition (as S) for the eastern 

(right side) and western (left side) reference sites. Figure 3-4 shows the trend in annual total 

(dry + wet) sulfur deposition (as S). The box plots were based on data obtained from the 34 

CASTNET eastern reference sites (Figure 1-2) for the period 1990 through 2008 and from the 

17 western reference sites (Figure 1-3) for 1996 through 2008. The y-axes on the two figures 

have different scales. Aggregated sulfur deposition declined considerably at the eastern and 

western reference sites over their respective periods. Figure 3-5 presents estimates of trends 

in dry, wet, and total deposition of sulfur (as S) on the same diagram for the eastern reference 

sites only. The trend line for precipitation-weighted mean sulfur concentrations in precipitation 

shows a decline in 2008 after small increases during the previous three years. 
CASTNET Annual Report – 2008 ~ 25 ~ Chapter 3: Atmospheric Deposition 

Figure 3-2 Total (Dry + Wet) Sulfur Deposition (kg/ha/yr) for 2008 

Figure 3-3 Trend in Dry Sulfur Deposition (kg/ha/yr) 

Western Reference Sites Eastern Reference Sites 

 

0.0

0.2

0.4

0.6

0.8

1996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

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

1990199119921993199419951996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

7.9 6.5

6.8

6.5

6.4

7.8 8.1

0.8

6.2

5.1

4.8

9.6

6.0

11.4

2.7

1.0

6.3

8.8

4.5

0.6

0.8

4.5

7.3

6.0

2.0

4.5

6.9

5.2

10.3

6.0

4.6

5.4

0.8

4.0

5.1

4.8

0.4

4.0

0.5

10.1

8.7

8.3 1.0

11.0

1.9

8.8

5.4

0.8

0.5

5.9

3.2

13.9

1.1 17.2

2.7

6.6

6.6

5.7

4.2

1.0

5.7

12.1

1.9

6.6

9.1

4.4

0.6

0.3

Site not pictured:

DEN417, AK 0.2

Total Deposition

16

8

1.6

Dry Deposition

Wet Deposition
CASTNET Annual Report – 2008 ~ 26 ~ Chapter 3: Atmospheric Deposition 

Figure 3-4 Trend in Total Sulfur Deposition (kg/ha/yr) 

Western Reference Sites Eastern Reference Sites 

The influence of precipitation on total sulfur deposition is illustrated by comparing the solid 

(top) line to the dotted blue line in Figure 3-5. The solid line shows total deposition, which 

depends on sulfur concentrations in precipitation and precipitation amounts. The dotted line 

shows concentrations in precipitation, which are more representative of changes in SO 

2

emissions. The relatively wet year 2003 experienced high total sulfur deposition even though 

the sulfur concentration in precipitation was relatively low. Overall, total sulfur deposition 

declined at the eastern reference sites from a 1990–1992 mean of 13.2 kg/ha/yr to a 2006–2008 

mean of 8.2 kg/ha/yr, a 38 percent reduction. Total sulfur deposition declined at the western 

reference sites from a 1996–1998 mean of 1.17 kg/ha/yr to a 2006–2008 mean of 0.83 kg/ha/yr, 

a 29 percent reduction. 

Figure 3-5 Trend in Sulfur Deposition (kg/ha/yr) with Concentrations in Precipitation (mg/l): 

Eastern Reference Sites 

 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

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

1990199119921993199419951996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

2

4

6

8

10

12

14

16

1990199119921993199419951996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

Concentration (mg/l)

Wet Deposition

Dry Deposition

Total Deposition

Concentration in Precipitation
CASTNET Annual Report – 2008 ~ 27 ~ Chapter 3: Atmospheric Deposition 

Rocky Mountain National Park, CO (ROM406/206)

Using CASTNET Data to Assess Quantity of Atmospheric Deposition 

Compared with Critical Loads 

A critical load is a measure of the exposure to one or more pollutants found in an 

ecosystem, below which significant harmful effects on sensitive members of the ecosystem 

do not occur (Nilsson and Grennfelt, 1988). Measures of critical load have been most often 

applied to atmospheric deposition of sulfur and nitrogen pollutants. The critical load of 

pollutants provides a measure to gauge the extent to which the ecosystem has recovered 

from past deposition or is potentially at risk due to current or future deposition loads. For 

this reason, the critical load approach has become an important assessment tool for 

examining the environmental benefits that result from emission reduction programs. For 

example, NPS has specified a goal for a critical load of 1.5 kg/ha/yr of wet nitrogen 

deposition (Baron, 2006) for Rocky Mountain National Park. In other words, annual wet 

deposition fluxes less than the specified goal will not have harmful effects on the highelevation ecosystems in the park. 

Two EPA-administered monitoring networks, the Temporally Integrated Monitoring of 

Ecosystems (TIME) and the Long-Term Monitoring (LTM) programs, provide surface water 

chemistry measurements in four regions known to be sensitive to acid precipitation 

(EPA, 2009b): New England, the Adirondack Mountains, the Appalachian Plateau, and the 

Blue Ridge Mountains (Figure 3a). Sulfate and NO3 ion concentrations, base cation (Ca2+

, 

Mg2+, K+ , Na+ ) concentrations, acid neutralizing capacity (ANC), and other parameters are 

monitored in the TIME/LTM networks in order to track changes in surface water chemistry 

and the level of acidification produced in response to changes in acidic deposition. Surface 

water chemistry data from TIME/LTM and other programs and deposition loadings from 

NADP and CASTNET can be used to determine whether a critical load is exceeded, i.e., 

whether the amount of deposition is greater than the critical level needed to reach and/or 

maintain a healthy ecosystem. 

 
CASTNET Annual Report – 2008 ~ 28 ~ Chapter 3: Atmospheric Deposition 

Figure 3a Trends in Lake and Stream ANC Concentrations at LTM Sites, 1990-2006 

Source: EPA 

CASTNET provides weekly concentration data for acidic pollutants and base cations, which 

could be utilized to estimate dry deposition fluxes and gauge exceedances of critical loads. 

Figure 3b shows 2008 annual mean Ca2+ concentrations. These data and other CASTNET 

ion concentration measurements can be used to model dry deposition loading of base 

cations to an ecosystem. This information is typically missing from critical load and 

biogeochemical hydrological models. The benefits of using CASTNET data for input to these 

models are that CASTNET (1) provides long-term trends of pollutants measured near 

sensitive ecosystems and (2) provides a more complete estimate of the ions that contribute 

to depositional loading to an ecosystem. 

Figure 3b CASTNET 2008 Annual Mean Ca2+ Concentrations (g/m3) 
CASTNET Annual Report – 2008 ~ 29 ~ Chapter 3: Atmospheric Deposition 

Nitrogen Deposition 

Dry fluxes of nitrogen (as N) for 2008 are shown in Figure 3-6. These fluxes are the sum of 

fluxes of HNO 

3 + NO3 + NH+ 4 , based on the individual MLM simulations for the three species. 

A majority of CASTNET sites in the eastern United States had estimated dry nitrogen 

deposition rates greater than 1.0 kg/ha/yr. Deposition rates greater than 2.0 kg/ha/yr were 

calculated for sites in Ohio, Pennsylvania, New Jersey, Kentucky, and at Great Smoky 

Mountains National Park (GRS420) in Tennessee. Two monitoring sites in California had fluxes 

greater than or equal to 2.0 kg/ha/yr. Locations on the map with no value had insufficient data 

to calculate fluxes. 

Figure 3-6 Dry Nitrogen (HNO3 + NO3 + NH+ 

4 ) Deposition (kg/ha/yr) for 2008 

Figure 3-7 presents a map of total nitrogen deposition (as N) for 2008. The map was 

constructed by summing the estimates of dry (light shading) and wet (dark shading) deposition. 

The figure shows that a majority of the eastern sites recorded deposition rates greater than 

5.0 kg/ha/yr. No values above 10.0 kg/ha/yr were estimated for 2008. The highest total nitrogen 

flux (9.6 kg/ha/yr) was estimated for Vincennes, IN (VIN140). The values at the western sites 

ranged from 1.0 kg/ha/yr at Yosemite National Park, CA (YOS404) to 3.8 kg/ha/yr in southern 

California at Converse Station (CON186). The contributions of dry nitrogen deposition to 

total nitrogen were lower than the corresponding contributions of dry sulfur deposition. Dry 

nitrogen deposition contributed less than 50 percent of total deposition in the East. On the 

1.4

2.8

2.6

2.3

1.8

2.3

1.5

1.0 2.0

1.6

0.4

2.3

0.5

1.1

1.3

0.6

1.3

1.1

1.6

2.3

0.4

0.8

1.9

1.1

1.5 1.9

0.8

0.8

0.7

1.5

1.8

1.6

0.7

0.6

1.3

1.1

1.3

1.0

0.6

1.9

1.1

0.3

0.5

2.3

1.5

0.4

1.0

2.2

1.7

1.7

1.2

1.3

1.3

1.5

0.9

1.7

0.7

1.6

1.8

0.6

0.7

1.4

1.8

0.5

1.7

2.2

0.2

0.3

0.7

Site not pictured:

DEN417, AK 0.1

Deposition Deposition Deposition

3.0

1.5

0.3
CASTNET Annual Report – 2008 ~ 30 ~ Chapter 3: Atmospheric Deposition 

other hand, dry nitrogen deposition contributed more than half of total nitrogen deposition at 

four of five monitoring sites in California, a region with elevated concentrations of nitrogen 

species and limited rainfall. 

Figure 3-7 Total (Dry + Wet) Nitrogen Deposition (kg/ha/yr) for 2008 

Figure 3-8 presents box plots that were constructed using data from the 34 eastern reference 

sites over the period 1990 through 2008 (right side) and 17 western reference sites for 1996 

through 2008 (left side). The box plots show the trends in dry nitrogen deposition (as N). The 

box plots for the eastern sites in Figure 3-8 show a reduction in dry nitrogen deposition 

beginning in 1999. Three-year mean fluxes declined from 2.2 kg/ha/yr in 1990–1992 to 

1.6 kg/ha/yr in 2006–2008, a 27 percent reduction over the 19 years. The box plots for the 

western sites show a smaller 15 percent decline, a change from 0.90 kg/ha/yr in 1996–1998 to a 

mean of 0.76 kg/ha/yr in 2006–2008. 

 

Total Deposition

10

5

1

Dry Deposition

Wet Deposition

5.5 5.8

6.0

6.0

4.4

5.7 6.7

3.8

5.8

3.8

4.5

7.8

6.5

7.8

2.6

1.5

4.3

7.1

4.5

1.8

2.0

5.9

6.1

5.8

3.7

3.8

6.1

6.1

7.6

4.8

3.5

4.2

1.5

5.5

4.4

3.3

2.7

7.1

1.2

5.4

8.0

6.5 2.3

6.9

3.5

6.0

4.6

1.8

1.4

5.1

6.0

6.8

2.9 8.8

6.8

5.8

4.6

7.4

3.0

2.3

5.4

9.6

3.7

4.6

7.1

4.3

1.1

1.0

Site not pictured:

DEN417, AK 0.2
CASTNET Annual Report – 2008 ~ 31 ~ Chapter 3: Atmospheric Deposition 

Figure 3-8 Trend in Dry Nitrogen Deposition (kg/ha/yr) 

Western Reference Sites Eastern Reference Sites 

Figure 3-9 shows the trends in annual total (dry + wet) nitrogen deposition for the eastern 

(right side) and western (left side) reference sites. Total nitrogen deposition aggregated over 

the eastern sites is more variable because the annual wet and total fluxes depend on the 

amount of precipitation. The figure suggests that total flux has decreased since 1996 with a 

substantial decline over the last five years. Total nitrogen flux for the western sites shows a 

relatively flat distribution. Estimates of trends in wet, dry, and total deposition of atmospheric 

nitrogen (as N) are presented in Figure 3-10 for the eastern reference sites only. The trend line 

(dotted) for precipitation-weighted mean nitrogen concentrations in precipitation shows a slow 

downward trend since 1998 with a drop in 2008. This trend line is reasonably representative of 

the effect of changes in NOx emissions because it does not depend on precipitation amounts. 

Total nitrogen deposition declined 19 percent in the East over the 19 years. 

Figure 3-9 Trend in Total Nitrogen Deposition (kg/ha/yr) 

Western Reference Sites Eastern Reference Sites 

 

0.0

0.5

1.0

1.5

2.0

1996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

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

1990199119921993199419951996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

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

1996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

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

1990199119921993199419951996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2008 ~ 32 ~ Chapter 3: Atmospheric Deposition 

Figure 3-10 Trend in Nitrogen Deposition (kg/ha/yr) with Concentrations in Precipitation 

(mg/l): Eastern Reference Sites 

Uncertainties in NO3 and HNO 

3 Concentrations 

and Their Effect on Dry Nitrogen Deposition 

The uncertainties of NO3 and HNO 

3 concentrations were estimated using results of the 

Maryland Aerosol Research and Characterization (MARCH)/CASTNET data 

intercomparison (Lavery et al., 2009). MARCH data were collected at Fort Meade, MD, 

and the CASTNET measurements were taken at Beltsville, MD (BEL116). The CASTNET 

filter pack technology causes uncertainty in the measured nitrogen species. The effects of 

these uncertainties on weekly and annual dry deposition fluxes of NO3, HNO 

3, and total 

nitrogen deposition (NO3+HNO 

3+NH+ 4 , as N) were analyzed by adjusting the HNO 3 and 

NO3 concentration values for BEL116, MD based on the MARCH/CASTNET 

intercomparison results and then recalculating the total nitrogen flux. 

NO3 concentrations were decreased by a factor of 3.5 to characterize the fact that filtersampled NO3 was comprised primarily of larger particles. HNO 

3 concentrations were 

increased by a factor of 1.15 based on the MARCH/CASTNET intercomparison results. 

Total nitrogen deposition values were then remodeled using the MLM based on 

measurements collected at BEL116, MD for the years 1998 through 2007.

As Table 3a shows, differences from the recalculated concentrations are relatively small 

(approximately 10 percent or less) reflecting the fact that the HNO3 component 

dominates the total nitrogen dry deposition. Dry deposition of particulate NO3 has a 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

2

4

6

8

10

12

1990199119921993199419951996199719981999200020012002200320042005200620072008

Deposition (kg/ha/yr)

Concentration (mg/l)

Wet Deposition

Dry Deposition

Total Deposition

Concentration in Precipitation
CASTNET Annual Report – 2008 ~ 33 ~ Chapter 3: Atmospheric Deposition 

relatively small contribution to the total nitrogen flux, and thus, the large decrease in 

NO3 concentrations does not have a significant effect on total deposition. 

Table 3a Changes to Dry Deposition of Total Measured Nitrogen after Adjustments to 

NO3 and HNO3 Fluxes 

Beltsville, MD (BEL116) 

Site ID Year

Total 

Measured N

NO3

Adjustment Only

HNO3

Adjustment Only 

Both 

Adjustments

BEL116 1998 2.62 2.58 2.93 2.89

BEL116 1999 3.00 2.94 3.35 3.29

BEL116 2000 1.85 1.77 2.05 1.97

BEL116 2001 2.41 2.36 2.68 2.64

BEL116 2002 2.57 2.53 2.87 2.84

BEL116 2003 2.23 2.18 2.49 2.44

BEL116 2004 2.56 2.50 2.85 2.79

BEL116 2005 2.25 2.18 2.51 2.44

BEL116 2006 2.63 2.59 2.94 2.90

BEL116 2007 2.40 2.38 2.69 2.66
CASTNET Annual Report – 2008 ~ 34 ~ Chapter 4: Ozone Concentrations 

Chapter 4: Ozone Concentrations 

Almost all CASTNET sites operate an O 

3 analyzer that measures hourly concentrations. While 

CASTNET is not a compliance network, the data collected provide useful information on 

geographic patterns in regional O 

3 and the extent to which rural areas potentially exceed 

concentration values mandated by the NAAQS. The 8-hour O 

3 standard is a useful measure for 

assessing the status and trends in rural O 

3 levels in order to gauge the success of EPA emission 

reduction programs such as the NOx SIP Call/NBP and CAIR. The analyses presented in this 

section provide maps and examine trends in the fourth highest daily maximum 8-hour average 

O 

3 concentrations measured annually. 

Ground-level O 

3 is an air pollutant that can cause harmful effects to the human respiratory 

system and damage to vegetation and ecosystems. Ground-level O 

3 is formed in the lower 

atmosphere when volatile organic compounds (VOCs) and NOx react in the presence of 

sunlight. Emissions from motor vehicle exhaust, industrial facilities, chemical solvents, gasoline 

vapors, and power plants are the major anthropogenic sources of NOx and VOCs. Also, 

biogenic VOC emissions from trees and other vegetation contribute to O 

3 formation in rural 

areas. VOC emission reduction strategies have been successful in reducing higher, short-term 

O 

3 concentrations in and downwind of urban areas. However, as discussed in this chapter, 

implementation of the NOx emission reductions that were mandated by the ARP and other 

NOx emission control programs contributed to reductions in O 

3 concentrations, especially in 

CASTNET provides the primary platform for monitoring rural, ground-level ozone 

(O 

3) concentrations in the United States and for providing information on geographic 

patterns in rural O3 levels. CASTNET was not designed to operate as a network for 

demonstration of compliance with O 

3 NAAQS. However, the network provides data 

on the extent to which rural areas potentially exceed concentration values mandated 

by NAAQS. Ozone measurements collected during 2006–2008 were used evaluate 

both the 1997 (EPA, 1997) and 2008 (EPA, 2008a) O 

3 standards. To attain the 1997 

standard, the 3-year average of the fourth-highest daily maximum 8-hour average O 

3

concentrations measured at each monitor within a specified area over each year must 

not exceed 0.08 parts per million (ppm) or be greater than or equal to 85 ppb in 

practice. The 2008 standard is achieved when the 3-year average of the fourth-highest 

daily maximum 8-hour average O 

3 concentrations measured at each monitor within a 

specified area over each year do not exceed 0.075 ppm (75 ppb in practice). The year 

2008 is the first year when no eastern CASTNET sites measured 8-hour average O 

3

concentrations greater than or equal to 85 ppb.
CASTNET Annual Report – 2008 ~ 35 ~ Chapter 4: Ozone Concentrations 

rural areas with elevated 8-hour average levels, because regional transport of pollutants 

contributes to ozone formation. 

Meteorological conditions play a significant role in O 

3 formation. Dry, hot, and sunny days are 

most conducive to O 

3 production. Ozone concentrations typically increase during daylight and 

peak in the late afternoon after peak temperature and sunlight intensity. Concentrations then 

drop in the evening. The warm months in spring, summer, and fall typically define the O 

3

season. EPA has defined a specific ozone season for each state and has proposed recently that 

the ozone season be designated as year round in most locations. 

On May 1, 2009, the CAIR NOx ozone season trading program began, replacing the NBP in 

states covered under the CAIR NOx ozone season program, requiring further NOx emission 

reductions from the power sector. 

National Ambient Air Quality Standards for Ozone 

Primary Standards Secondary Standards

Level Averaging Time Level Averaging Time

Ozone

0.075 ppm 8-hour 1

Same as Primary 0.08 ppm 8-hour 2

Notes: 1 (a) On September 5, 2009, EPA announced that it is reconsidering the current levels of the ozone 

primary and secondary standards. 

 (b) To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average O 

3

concentrations measured at each monitor within a specified area over each year must not exceed 

0.075 ppm (effective May 27, 2008). 

2 (a) To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average O 

3

concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm 

(effective 1997). 

 (b) The 1997 standard—and the implementation rules for that standard—will remain in place for 

implementation purposes as EPA undertakes rulemaking to address the transition from the 1997 O 

3

standard to the 2008 O 

3 standard. 

The concentration shading for the figures used in this chapter was prepared using the scales 

shown on each map. Additional maps of ozone concentrations can be viewed on the Web 

site for the NPS Air Atlas (http://science.nature.nps.gov/AirAtlas/AirAtlas0105/viewer.htm). 

The Air Atlas incorporates all ozone monitoring reporting to AQS plus the CASTNET 

ozone measurements. 

Eight-Hour Ozone Concentrations 

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

3

concentrations for 2006–2008. During this period, 3-year averages of the fourth highest daily 
CASTNET Annual Report – 2008 ~ 36 ~ Chapter 4: Ozone Concentrations 

maximum 8-hour average O 

3 concentrations were greater than or equal to 85 ppb at Beltsville, 

MD (BEL116), Great Smoky Mountains National Park, TN (GRS420), and four sites in 

California. Figure 4-1 also shows the geographic distribution of fourth highest daily maximum 

8-hour average O 

3 concentrations greater than 75 ppb, which exceed the revised NAAQS 

(0.075 ppm). The number of CASTNET sites with 8-hour average O 

3 levels greater than the 

new standard is much larger than for values greater than or equal to 85 ppb. Eleven eastern and 

eight western CASTNET sites exceeded the new standard. These 3-year average O 

3

concentrations constitute the current design values for achieving the 8-hour O 

3 NAAQS. For 

example, the value of 107 ppb at Converse Station, CA (CON186) would have to be reduced 

to 84 ppb to achieve the old standard and to 75 ppb to achieve the new standard. A design 

value is a statistic that describes the air quality status of a given area relative to the level of the 

NAAQS. Design values are typically used to classify nonattainment areas, assess progress 

towards meeting the NAAQS, and develop control strategies to achieve the NAAQS. Design 

values change as a new 3-year database of monitored O 

3 concentrations becomes available. 

Figure 4-1 Three-Year Average of Fourth Highest Daily Maximum 8-Hour Average Ozone 

Concentrations (ppb) for 2006–2008 

For comparison to current design values, 3-year averages of the fourth highest daily maximum 

8-hour average O 

3 concentrations for 2000–2002 are presented in Figure 4-2. This period was 

selected for comparison because the NOx SIP Call/NBP began in 2003 for the eastern United 

States. A comparison of O 

3 data for these two 3-year periods (2000–2002 and 2006–2008) 

illustrates the effectiveness of the emission reduction programs. Using the 84 ppb standard, 

19 eastern and 3 California sites recorded 3-year averages greater than or equal to 85 ppb 

during 2000–2002. The regions with elevated concentrations were located along the East Coast 
CASTNET Annual Report – 2008 ~ 37 ~ Chapter 4: Ozone Concentrations 

from northern Virginia to Connecticut, extending almost to Maine, and in the central states of 

Pennsylvania, Ohio, Michigan, Indiana, and Illinois. Exceedances were also recorded in Kentucky, 

Tennessee, and greater Atlanta. Using the 75 ppb standard, the map in Figure 4-2 shows that 

most of the eastern sites measured O 

3 concentrations greater than 75 ppb, as well as five 

monitors in California and the site at Rocky Mountain National Park (ROM406). The period 

2006–2008 represents a significant improvement in air quality and is one of the best periods of 

air quality since the inception of CASTNET in terms of having the fewest sites with 

exceedances of the 8-hour O 

3 NAAQS. However, sites in California, Maryland, and at 

GRS420, TN continued to measure elevated ozone levels. 

Figure 4-2 Three-Year Average of Fourth Highest Daily Maximum 8-Hour Average Ozone 

Concentrations (ppb) for 2000–2002 

Measurements of 8-hour average O 

3 concentrations during 2008 (Figure 4-3) were lower than 

2007 and considerably lower than concentrations measured over the period 2000–2002. Five 

sites in California measured O 

3 concentrations greater than or equal to 85 ppb. The five 

California sites include Yosemite National Park (YOS404), Pinnacles National Monument 

(PIN414), Sequoia National Park (SEK430), Converse Station (CON186), and Joshua Tree 

National Park (JOT403). The monitor at SEK430, CA measured the highest value (112 ppb) in 

the network during 2008. The year 2008 is the first year when no eastern CASTNET sites 

measured 8-hour average O 

3 concentrations greater than or equal to 85 ppb. 

Figure 4-3 also depicts the geographic distribution of fourth highest daily maximum 8-hour 

average O 

3 concentrations greater than 75 ppb. Eleven eastern sites in eight states and six 

California monitors measured ozone concentrations above 75 ppb. The monitor at 
CASTNET Annual Report – 2008 ~ 38 ~ Chapter 4: Ozone Concentrations 

ROM406, CO measured a concentration of 76 ppb. The eastern states include Pennsylvania, 

New Jersey, Maryland, Virginia, North Carolina, Tennessee, Georgia, and Texas. In addition to 

the five California sites already mentioned, Lassen Volcanic National Park (LAV410) measured a 

fourth highest daily maximum 8-hour average O3 concentration of 83 ppb. 

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

for 2008 

Figure 4-4 provides box plots depicting trends in fourth highest daily maximum 8-hour average 

O 

3 concentrations from the 34 CASTNET eastern reference sites (right side) and 17 western 

reference sites (left side). The eastern ozone data show a decline since 2002. The mean 

aggregated value (69 ppb) for 2008 was the lowest in the history of the network. It represents 

an improvement over the mean value of 90 ppb measured in 1998. The box plots constructed 

from the aggregated western O 

3 concentrations show no trend. The 2006–2008 average of the 

fourth highest daily maximum 8-hour average O 

3 concentrations for the western reference sites 

was 72 ppb. 

 
CASTNET Annual Report – 2008 ~ 39 ~ Chapter 4: Ozone Concentrations 

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

Western Reference Sites Eastern Reference Sites 

Impacts of NOx Budget Program and Clean Air Interstate Rule 

on Rural and Urban Ozone Levels in the 

Eastern United States 

Researchers at Cornell University and 

the Cary Institute of Ecosystem Studies 

used random coefficient models to 

assess the impact of reduced NOx

emissions during the O 

3 season on daily 

maximum 8-hour average O 

3

concentrations for various regions of the 

eastern United States for the period 

1997 through 2007. This assessment 

extended previous analyses by Butler et 

al. (2003, 2005) that investigated the 

impact of reduced NOx emissions on 

NO3 concentrations in precipitation and 

ambient concentrations of HNO3. 

Random coefficient models were used 

because O 

3 concentration values are not 

independent but clustered for each site. 

In addition, the models can examine 

monitoring sites on a regional basis (e.g., 

the Northeast) or in other combinations 

(e.g., urban versus rural sites). In this 

Figure 4a Locations of Ozone 

Monitoring Sites 

Note: Four sites in eastern Texas were included in the analysis 

for Eastern United States but are not shown on map. 

Source: T. J. Butler 

50

70

90

110

1996199719981999200020012002200320042005200620072008

Concentration (ppb)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

50

70

90

110

1990199119921993199419951996199719981999200020012002200320042005200620072008

Concentration (ppb)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile
CASTNET Annual Report – 2008 ~ 40 ~ Chapter 4: Ozone Concentrations 

analysis, O 

3 data from 95 CASTNET and AQS sites were evaluated for the 11-year time 

period for (a) the Eastern United States as a whole, (b) by region (Northeast, MidAtlantic, Southeast, and Midwest), and (c) by rural CASTNET sites (32 sites) versus urban 

AQS sites (63 sites). Figure 4a shows the locations of the sites and the defined regions 

used in this analysis, as well as the NBP regulated states/areas. 

Source regions for NOx emissions were derived from multiyear 24-hour air mass back 

trajectories at 500 meters above ground level (AGL) and 1,000 meters AGL. The Hybrid 

Single-Particle Lagrangian Integrated Trajectory (HYSPLIT)-4 model was applied to 

generate the trajectories. State-level emissions for stationary sources, which were 

derived from the EPA ARP emissions database, provided the most complete record of O 

3

season emissions for the period 1997 through 2007 and are considered the best estimate 

of NOx emission changes from stationary sources before and after NBP implementation. 

CAIR, as promulgated, was designed to further reduce power plant pollutant emissions, 

including a 2 million ton (61 percent) reduction in NOx emissions, from 2003 levels. The 

models were used to estimate the impact of CAIR in terms of reducing O 

3 concentrations 

in the eastern United States in 2015. 

Ozone season O3 concentrations were meteorologically-adjusted to account for year-toyear variations in humidity and temperature, which influence the production of O 

3. 

Statistical model results were generated by dividing each region into rural and urban sites. 

The models were used to evaluate how reduced NOx emissions would impact the sites. 

Figure 4b illustrates the declines in daily maximum 8-hour average O 

3 concentrations for 

the different regions and for rural and urban sites for pre-NBP (1997–2000) and 

post-NBP (2004–2007) implementation, as well as for projected 2015 NOx emissions. 

Figure 4b Declines (ppb) in Daily Maximum 8-Hour Average O 

3 Concentrations for 

Urban (red) and Rural (blue) Sites 

Source: T. J. Butler Decline in Ozone Urban after NBP Rural after NBP Urban 2015 

Rural 2015 

Urban after NBP 

Rural after NBP 

Urban 2015 

Rural 2015 

Urban after NBP 

Rural after NBP 

Urban 2015 

Rural 2015 

Urban after NBP 

Rural after NBP 

Urban 2015 

Rural 2015 

Urban after NBP 

Rural after NBP 

Urban 2015 

Rural 2015 

Decline in Ozone 
CASTNET Annual Report – 2008 ~ 41 ~ Chapter 4: Ozone Concentrations 

The double asterisk (**) indicates the urban and rural site differences for a region are 

statistically significant at p < 0.05. Similarly, a single asterisk (*) indicates statistically 

significant differences between rural and urban sites in a region at p < 0.10. Error bars are 

based on the standard error of the slope of the model regression lines. For the eastern 

United States as a whole, O 

3 data from rural and urban sites are statistically different 

(p < 0.05). Greater declines in ozone concentrations occurred at the rural sites, which 

show a 7 ppb (12 percent) decline, while urban sites show a 5 ppb (8 percent) decline. 

The Northeast region also shows statistically different (p < 0.05) daily maximum 8-hour 

average O 

3 concentrations between rural and urban sites and the greatest difference 

between declines in O 

3 levels at these sites. Urban sites show a post-NBP decline of 

4 ppb (9 percent) while the rural sites show a decline of 9 ppb (18 percent). Modeled 

differences between rural and urban sites for the Southeast and the Midwest regions 

were less statistically significant (p < 0.10), with urban declines of 9 percent and 8 percent 

for the two regions and rural declines of 12 percent and 11 percent. The difference 

between urban and rural sites in the Mid-Atlantic region was not statistically significant. 

Rural monitoring sites are typically affected little by local emissions. They are likely more 

affected by transported emissions such as those from large stationary sources (EGUs). 

The greater declines at rural sites, except for the Mid-Atlantic region, may be explained 

by the fact that stationary source emissions have been controlled to a larger extent than 

comparable urban and transportation NOx sources. Urban sites are more affected by a 

variety of local sources such as vehicular NOx emissions, which are more difficult to 

regulate and control. The Northeast had the greatest decline in rural O 

3 concentrations. 

The Northeast rural monitoring sites are “downwind” of a large number of stationary 

sources that are now being regulated. Further ozone reductions at urban locations may 

require a greater emphasis on controlling local NOx and VOC emissions. 

Nitrogen Oxides and Ozone 

In May 2009, EPA published The NOx Budget Trading Program: 2008 Emission, Compliance, and 

Market Analyses. The report analyzed changes in NOx emissions from 1990 through 2008. 

Figure 4-5, which was taken from the EPA report, depicts O 

3 season NOx emissions from all 

NBP sources in the eastern United States from 1990 through 2008. The NBP was in effect from 

2003 through 2008. The CAIR NOx ozone season program began on May 1, 2009 and replaced 

the NBP in affected states. The OTC NOx Budget was in effect from 1999 through 2002. Other 

emission control programs such as mobile source controls, VOC Reasonably Available Control 

Technology (RACT) and Maximum Available Control Technology (MACT), new source review, 

and the ARP contributed to NOx and VOC emission reductions. 
CASTNET Annual Report – 2008 ~ 42 ~ Chapter 4: Ozone Concentrations 

NBP sources emitted 481,420 tons of NOx in the 2008 O 

3 season (EPA, 2009c). Emissions in 

2008 decreased 24,880 tons from 2007 and were 62 percent below 2000 levels and 75 percent 

below 1990 emissions. NBP regulated 2,568 units in 2008. EGUs constituted 88 percent of the 

regulated units; industrial sources constituted most of the remaining 12 percent. 

Figure 4-5 Ozone Season NOx Emissions from All NBP Sources 

Notes: Data reflect full ozone season emissions in all years for all states. The year 2000 baseline value has been adjusted to correct a 

misprint in Figure 5 of the 2007 NBP report. 

 The 2008 total state trading budgets include opt-in allowances, where applicable (New York, Ohio, and West Virginia). 

Source: EPA (2009c) 

Trends in CASTNET measurements of total nitrate concentrations (Figure 4-6) measured 

during the ozone season (May through September) at the 34 eastern reference sites show 

almost no change from 1990 through 1999 followed by a decline as the emission reductions 

from the OTC and NBP became effective. Three-year median concentrations before (2000–

2002) and after (2003–2005) the implementation of the NBP were 2.43 g/m3

 and 1.87 g/m3, 

respectively. The most recent three-year (2006–2008) median value was 1.67 g/m3

. Figure 4-7, 

which was taken from the EPA report on NBP compliance (EPA, 2009c), shows the relationship 

between NOx emission reductions from power industry sources and changes in O 

3 levels at 

CASTNET and EPA AQS-compliant sites in the eastern United States over the period 2002–

2008. The figures show declines in concentrations in all NBP states. The figure also shows a 

strong association between regions with the greatest emission reductions and downwind 

monitoring sites showing the greatest improvement in O 

3 levels. 
CASTNET Annual Report – 2008 ~ 43 ~ Chapter 4: Ozone Concentrations 

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Concentration (g/m3)

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

90th Percentile

75th Percentile

Median

Mean

25th Percentile

10th Percentile

Figure 4-6 Trend in Ozone Season (May through September) Mean Total Nitrate 

 (NO3 + HNO3) Concentrations (g/m3) – Eastern Reference Sites 

Figure 4-7 Reductions in Ozone Season Power Industry NOx Emissions and Changes in 

8-Hour Average Ozone, (2002 versus 2008) 

Notes: 

 From 1999 to 2002, states in the Northeast reduced emissions from EGUs and industrial boilers under the OTC NOx Budget 

Program. OTC states include Connecticut, Delaware, the District of Columbia, Main, Maryland, Massachusetts, New Hampshire, 

New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Virginia. 

 Meteorologically-adjusted ozone data are from AQS and CASTNET sites that met completeness criteria. 

 Google Earth was used to display the information shown in this figure. To access the data layers shown here as well as other data, 

including unite-level emissions and controls, visit the Clean Air Market Division’s interactive mapping site at 

<www.epa.gov/airmarkt/progress/interactivemapping.html>. 

Source: EPA (2009c) 
CASTNET Annual Report – 2008 ~ 44 ~ Chapter 4: Ozone Concentrations 

Ozone Episode in the Great Smoky Mountains, TN 

(GRS420) in July 2008 

Periods with extended high ozone 

concentrations have occurred 

occasionally over the last 10 years at the 

Look Rock site in Great Smoky Mountains 

National Park, TN (GRS420). Measured 

fourth highest daily maximum 8-hour 

average O 

3 concentrations have exceeded 

85 ppb causing potential contravention of 

both the 1997 0.08 ppm and 2008 0.075 

ppm NAAQS. A four-day O 

3 episode was 

observed at the park during July 17–20, 

2008. Surface weather conditions are 

illustrated in Figure 4c, which shows a 

Bermuda High off the East Coast and 

Tropical Storm Cristobal off the coast of 

North Carolina. The circulation around 

the tropical storm was sufficiently 

developed to produce northeasterly 

winds along the East Coast from New 

Jersey to the park. However, the cloud 

pattern produced by the storm was 

limited and did not inhibit O 

3 formation. 

A time series of hourly O 

3 concentrations 

observed at GRS420, TN during 

July 13–24, 2008 is provided in Figure 4d. 

Daily maximum 8-hour O 

3 average 

concentrations are also shown. The 

8-hour levels are plotted at 0000 local 

time for each day. Figure 4d shows the 

gradual buildup of O 

3 beginning on 

July 15th with a subsequent peak hourly 

value of 90 ppb on the 19th and a peak 

daily 8-hour value of 87 ppb, shown at 

0000 on July 19th. The episode was 

terminated by a shift to westerly winds on 

July 20th. 

20

30

40

50

60

70

80

90

100

110

7/137/147/157/167/177/187/197/207/217/227/237/24

Concentration (ppb)

HourlyOzone

DailyMax 8‐Hr Avg Ozone

85 ppb

75 ppb

Figure 4c Surface Weather Map for 

July 20, 2008

Figure 4d Time Series of Ozone 

Concentrations

Great Smoky Mountains National Park, TN 

Source: NPS
CASTNET Annual Report – 2008 ~ 45 ~ Chapter 4: Ozone Concentrations 

Figure 4d shows a fairly steady increase in peak hourly O 

3 values during the ozone 

buildup. The peak 1-hour concentration during the episode was not much higher than the 

peak 8-hour value. The figure also shows a diurnal cycle daily with lower O 

3

concentrations observed around 0900. Figure 4e shows two plots of composite O 

3

concentrations. The top curve was 

constructed by averaging all hours for 

each hour of the day for the four-day 

episode. The bottom curve was created 

from a composite of the remaining hours in 

July. The two daytime O 

3 peaks in the top 

curve might have been produced by 

pollutants from two different source regions 

or by recirculated pollutants. The minimum 

concentrations around 0900 to 1000 can be 

explained by the end of nighttime dry 

deposition or by fresh NOx emissions that 

scavenge O 

3 around that time. 

 

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Concentration (ppb)

Ozone Event (7/17‐20)

Remainderof July

Figure 4e Composite Diurnal Ozone 

Concentrations

Figure 4f Backward Trajectories Ending 

at 1000 EDT July 19, 2008 

Figure 4g Backward Trajectories Ending at 

1000 EDT July 20, 2008 
CASTNET Annual Report – 2008 ~ 46 ~ Chapter 4: Ozone Concentrations 

Backward trajectories from the National Oceanic and Atmospheric Administration 

(NOAA) HYSPLIT Model for July 19, 2008 at 1400 UTC (1000 EDT) and for July 20, 2008 

at 1400 UTC are provided in Figures 4f and 4g, respectively. Trajectories ending at 

GRS420, TN are given for 100 m, 200 m, and 500 m AGL. The three trajectories ending 

at GRS420, TN at 1000 EDT on July 19th show similar origins. The 100 m and 200 m 

trajectories originated in Maryland. The 500 m trajectory originated in New Jersey. All 

three trajectories show significant subsidence and recirculation of air near their endpoint 

at the park. The 100 m trajectory originated at an altitude of approximately 500 m three 

days earlier. Hourly ozone concentrations reached 90 ppb during the afternoon of 

July 19th, and the highest 8-hour average daily maximum level was recorded at 0000 on 

the 19th. The recording of high concentrations in the afternoon suggests the transport of 

ozone and its precursors along the trajectory pathways. The episode ended on July 20, 

2008 when the winds switched to westerly as shown by the trajectories in Figure 4g. 

The occurrence of northeasterly winds with significant atmospheric subsidence is 

somewhat unusual during the summer in eastern Tennessee. Evidently, the northeasterly 

winds transported precursor pollutants to the park from the Mid-Atlantic states, and the 

pollutants were trapped under a subsidence inversion. These pollutants produced 

relatively high ozone concentrations over the 4-day period, which ended with the 

wind shift. 

Views from the Look Rock (GRS420, TN) air quality monitoring station. 

Photo on left shows a day with 83 mile visual range. Haziness (16 mile visual range) in 

the photo on right is caused primarily by tiny sulfate particles. 

July 14, 2008 – 83 mile visual range July 19, 2008 – 16 mile visual range 

Source: NPS 
CASTNET Annual Report – 2008 ~ 47 ~ Chapter 5: Data Quality 

Chapter 5: Data Quality 

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 2008 QA 

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

Revision 4.1 (MACTEC, 2008c). The QAPP is comprehensive and includes standards and 

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

It includes major sections on field measurements, chemical analysis of field samples, data 

management, and assessments and response actions. Standard operating procedures are 

included as appendices. 

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

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

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

accuracy, and completeness for CASTNET 2008 data were analyzed and compared with 

historical data collected during the period 1990 through 2007. The information in this report is 

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

(MACTEC, 2008b; 2008e; 2008f; 2009b). These QA reports are produced four times per year 

with the fourth quarter report including an annual summary. 

Precision 

Exposed Filter Concentrations 

Figure 5-1 provides a bar chart in which the bars represent precision estimates for five 

CASTNET analytes. Table 5-1 lists the precision and accuracy criteria for laboratory filter pack 

measurements. Precision is defined as the mean absolute relative percent difference (MARPD). 

 

CASTNET measurements and supporting activities are assessed routinely in order to 

provide high-quality information to meet project objectives. The CASTNET Quality 

Assurance program is based on specific data quality objectives that are evaluated using 

data quality indicators (DQI) such as precision, accuracy, and completeness. 

Measurements taken during 2008 and historical data collected over the period 1990–

2007 were analyzed relative to DQI and their associated metrics. These analyses 

demonstrate that CASTNET data can be used with confidence and that CASTNET 

continues to produce information of the highest quality.
CASTNET Annual Report – 2008 ~ 48 ~ Chapter 5: Data Quality 

Figure 5-1 Historical and 2008 Precision Data for Atmospheric Concentrations 

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

Precision1 Accuracy2 Nominal 

Analyte Method (MARPD) (%) Reporting Limits 

Ammonium (NH +

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

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

Potassium (K +) ICP-AES 5 95 - 105 0.006* mg/L

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

Calcium (Ca2+) ICP-AES 5 95 - 105 0.006* mg/L

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

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

Sulfate (SO2-

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

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

on replicate samples. The goal for the ICP-AES precision relative percent difference (RPD) criterion changed from 10 percent to 5 

percent at the onset of the CASTNET III contract beginning on July 30, 2003. The precision criterion is applied as described below: 

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

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

 Condition 2: if (v1 – v2)  RL and v1  5 x RL) = OK 

 Condition 3: if (v1  5*RL and RPD  5%) = OK 

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

2

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

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

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

 * Effective September 26, 2007, changed to 0.006 mg/L from 0.003 mg/L for calcium and 0.005 mg/L for potassium 

 MARPD = Equation 5-1 

 Where: 

S1 = The value for the primary sampler 

S2 = The value for the collocated sampler 

k = The number of pairs of valid data 

 

 Percent recovery = Equation 5-2 

 

 RPD = Equation 5-3 

 

 For more information on the analytical methods and associated precision and accuracy criteria used for 2007, see the CASTNET QAPP 

Revision 4.1 (MACTEC, 2008c). 

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MARPD

Overall - 1990 through 2007

Mackville, KY - 2008

Rocky Mtn, CO - 2008

SO2 SO4

2- HNO3 NO3- NH4+

100

2

1 x SS

200

1 2

1 2 x S SS S





















200

1 2

1 1 2

1

x S S

S S

k j

k

j 

















 
CASTNET Annual Report – 2008 ~ 49 ~ Chapter 5: Data Quality 

Historical (1990 through 2007) data for all 11 collocated site pairs operated over the history of 

the network and the 2008 data for the current collocated sites at Mackville, KY (MCK131/231) 

and Rocky Mountain National Park, CO (ROM406/206) are provided. The two sites at Rocky 

Mountain National Park are operated independently. ROM206 is operated on behalf of EPA and 

ROM406 on behalf of NPS. Trace cations and chloride are excluded from this figure but are 

shown later in Figure 5-2. The historical results vary from just over 4 percent for particulate 

SO2-

4 to more than 12 percent for particulate NO3. The historical MARPD for SO2-4 met the 

criterion for the CASTNET filter pack measurements shown in Table 5-1. The historical results 

for SO2 and HNO3 were above the 5 percent criterion but are considered reasonable. The 

results for NH+ 

4 met the goal of 10 percent. 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 (Lavery et al., 2009). 

The 2008 precision results shown in Figure 5-1 indicate that the MARPD data for MCK131/231 

were lower than (i.e., more precise than) the historical results for all five parameters. Four 

parameters (SO2, SO2-

4 , HNO3, and NH+ 4 ) met precision criteria. The 2008 results for 

ROM406/206 showed better precision than historical results for HNO3, and the result for NH+ 

4

met the DQI criteria. The precision criterion for NO3 was not met at either site during 2008. 

The precision results were worse for ROM406/206 because of lower concentrations measured 

at this site. Overall, the filter pack precision results for 2008 were about the same as the 

2007 results. 

Historical and 2008 precision statistics for four cations and chloride (Cl-) 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. As discussed in earlier CASTNET annual reports 

(e.g., MACTEC, 2004 and MACTEC, 2003), the very high historical MARPD for Na + was the 

result of sample bottle contamination. These bottles are no longer purchased. Also, acceptance 

testing of the Teflon filters was instituted for the trace cations and Cl-

 in 2003. The 2008 

precision results show that Cl-

 met the precision criterion at MCK131/231, and the results for 

the four cations were reasonable. The 2008 precision results for MCK131/231 showed some 

improvement over the 2007 results. The 2008 precision data for ROM406/206 are somewhat 

worse than 2007. 

Table 5-2 summarizes 2008 precision results by quarter for the two sets of collocated sites. See 

the 2008 Quarterly Data Reports (MACTEC, 2008a; 2008d; 2009a; 2009c) and QA Quarterly 

Reports (MACTEC, 2008b; 2008e; 2008f; 2009b) for discussions of quarterly precision data. 

 
CASTNET Annual Report – 2008 ~ 50 ~ Chapter 5: Data Quality 

Figure 5-2 Historical and 2008 Precision Data for Cation and Cl- Concentrations 

Table 5-2 Collocated Precision Results (MARPD) for 2008 Filter Pack Data by Quarter 

Site Pairs SO2-

4 NO3 NH+ 

4 Ca2+ Mg2+ Na + K + HNO3 SO2

Total 

NO3 Cl-

 MCK131/231, KY 

Quarter 1 1.78 4.68 2.00 7.67 4.66 2.39 2.45 2.66 1.89 2.17 5.04

Quarter 2 2.01 13.16 1.65 12.21 11.67 8.88 6.94 3.18 2.86 4.26 5.04

Quarter 3 2.36 9.40 2.38 3.78 3.73 4.10 4.39 3.91 1.94 3.25 4.63

Quarter 4 2.64 4.80 2.69 5.97 3.82 4.86 17.11 4.99 4.40 3.31 4.79

2008 2.20 8.01 2.18 7.41 5.97 5.06 7.72 3.68 2.77 3.25 4.87

 ROM406/206, CO 

Quarter 1 7.03 10.22 5.82 9.08 11.34 9.05 14.60 6.45 5.14 6.73 4.38

Quarter 2 6.74 12.77 6.67 8.22 11.46 8.13 11.20 4.18 8.04 6.13 5.28

Quarter 3 7.76 17.79 7.74 11.55 10.26 10.82 7.29 8.63 9.25 8.06 6.70

Quarter 4 4.84 15.66 4.40 12.88 14.00 16.72 29.56 6.77 7.59 4.65 6.46

2008 6.59 14.11 6.16 10.43 11.76 11.18 15.66 6.51 7.50 6.39 5.71

The 2008 analytical precision results for five analytes and the three filter types are presented in 

Figure 5-3. The results were based on analysis of 5 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. 

 

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Overall - 2000 through 2007

Mackville, KY - 2008

Rocky Mtn, CO - 2008

MARPD

Ca2+ K+ Mg2+ Na+ Cl-
CASTNET Annual Report – 2008 ~ 51 ~ Chapter 5: Data Quality 

Figure 5-3 Precision Results for Laboratory Replicate Samples (2008) 

Ozone Concentrations 

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

requirements for State and Local Monitoring Stations (SLAMS) monitoring (EPA, 1998). 

However, as discussed in Chapter 1, MACTEC is preparing CASTNET monitoring shelters to 

meet the 40 CFR Part 58 monitoring requirements. The QA procedures for the O3 analyzers at 

the NPS-sponsored CASTNET sites also do not meet the SLAMS requirements, but the NPS 

sites utilize the appropriate procedures and equipment, including an on-site O 

3 transfer 

standard. In any event, the operation of the collocated EPA and NPS O3 analyzers at 

ROM406/206, CO provides an opportunity to evaluate the precision of the independent 

systems. Table 5-3 provides the DQI criteria for the CASTNET continuous measurements 

including O3. The precision criterion for the collocated O3 data is 10 percent. 

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

sites MCK131/231, KY and ROM406/206, CO during 2008. In addition, quarterly historical 

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

summarized in Figure 5-4. Table 5-4 provides precision results for O3 concentrations by quarter 

for 2008. The data show the historical and 2008 results met the 10 percent criterion. The 

historical data are based on the operation of 11 collocated site pairs over the history of the 

network. The 2008 O 

3 precision data for ROM406/206 were excellent and demonstrate the 

comparability of the two independent O3 sampling systems. 

 

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1 2 3 4 5 6 7 8 9 10 11

contribute to SO2

MARPD

for In-Run Replicates

Teflon

SO4

2-

Nylon

SO4

2-

Nylon

NO3

-

Teflon

NH4

+

Cellulose 

SO4

2-

Teflon

NO3

-

Teflon

Na+

Teflon

K+

Teflon

Mg2+

Teflon

Ca2+

Teflon

ClHNO3
CASTNET Annual Report – 2008 ~ 52 ~ Chapter 5: Data Quality 

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

Measurement Criteria* 

Parameter Method Precision Accuracy 

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

5 m/s or  5% for winds  5 m/s 

Wind Direction Wind Vane  5°  5°

Sigma Theta Wind Vane Undefined Undefined

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

 20%, relative humidity  85% 

Solar Radiation Pyranometer  10% (of reading taken 

at local noon) 

 10%

Precipitation Tipping Bucket Rain 

Gauge 

 10% (of reading)  0.05 inch† 

Ambient 

Temperature 

Platinum RTD  1.0°C  0.5°C

Delta Temperature Platinum RTD  0.5°C  0.5°C

Surface Wetness Conductivity Bridge Undefined Undefined

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

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

Note: Mean Absolute Difference (MAD) is the precision measure for difference criteria such as for wind speed. 

 MARPD is the precision measure for percentage criteria such as for relative humidity. 

 °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. 

Figure 5-4 Historical and 2008 Precision Data by Quarter for Ozone Concentrations 

 

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Quarter

Second

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Third

Quarter

Fourth

Quarter

Overall - 1990 through 2007

Mackville, KY - 2008

Rocky Mtn, CO - 2008

MARPD
CASTNET Annual Report – 2008 ~ 53 ~ Chapter 5: Data Quality 

Table 5-4 Collocated Precision Results (MARPD) for 2008 Ozone Concentrations by Quarter 

Sampling 

Period MCK131/231, KY ROM406/206, CO 

Quarter 1 8.57 1.71

Quarter 2 6.49 1.16

Quarter 3 3.91 2.90

Quarter 4 6.19 1.51

2008 6.29 1.82

Continuous Measurements 

Precision criteria for the continuous measurements are listed in Table 5-3. Precision was 

calculated in terms of the MARPD or mean absolute difference (MAD) of hourly measurements 

collected at all collocated pairs operated over the history of the network and also for 

MCK131/231, KY and ROM406/206, CO for 2008. Figure 5-5 provides precision results for 

historical data through 2007 and precision statistics for the two collocated sites for 2008. All 

historical precision results met the DQI criteria. Table 5-5 gives precision data by quarter for 

2008 for the two collocated sites. The results show excellent instrument precision. All 2008 

annual and quarterly precision data met the DQI criteria. The first quarter MAD value for wind 

direction at ROM 406/206, CO was not available because of invalid data from ROM206, CO 

during that quarter. Precipitation measurements were invalid from MCK231, KY during the 

second and third quarters and delta temperature data were invalid for the second quarter from 

ROM406, CO. 

Figure 5-5 Historical and 2008 Precision Data for Continuous Measurements 

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0.6

0.7

0.8

0

1

2

3

4

5

6

7

8

9

10

Flow Rate

Relative

Humidity

Sigma

Theta

Solar

Radiation

Delta

Temperature

Precipitation

Scalar

Wind Speed

Temperature

Wetness

Wind

Direction

Wind Speed

MAD

MARPD / MAD for Wind Direction

MARPD: Overall - 1990 through 2007

MARPD: Mackville, KY - 2008

MARPD: Rocky Mtn, CO - 2008

MAD: Overall - 1990 through 2007

MAD: Mackville, KY - 2008

MAD: Rocky Mtn, CO - 2008

Flow RateRelativeHumiditySigmaThetaSolarRadiationDeltaTemperaturePrecipitationScalarWind SpeedTemperatureWetnessWindDirectionWind Speed
CASTNET Annual Report – 2008 ~ 54 ~ Chapter 5: Data Quality 

Table 5-5 Collocated Precision Results for 2008 Continuous Measurements by Quarter Site Pairs 

MARPD MAD 

Flow Rate Relative Humidity Sigma Theta Solar Radiation Delta Temperature Precipitation Scalar Wind Speed Temperature Wetness Wind Direction Wind Speed 

MCK131/231, KY 

Quarter 1 1.31 2.87 2.21 1.96 0.34 0.04 0.10 0.12 0.05 1.32 0.09 

Quarter 2 9.66 2.47 2.97 3.03 0.08 na 0.09 0.09 0.07 1.01 0.08 

Quarter 3 2.22 0.83 4.21 4.33 0.08 na 0.08 0.04 0.05 1.36 0.07 

Quarter 4 4.46 2.03 2.29 2.96 0.26 0.02 0.05 0.18 0.03 2.60 0.05 

2008 4.41 2.05 2.92 3.07 0.19 0.03 0.08 0.11 0.05 1.57 0.07 

ROM406/206, CO 

Quarter 1 0.90 8.19 4.53 4.59 0.11 0.02 0.28 0.49 0.23 na 0.19 

Quarter 2 0.91 7.51 4.49 5.56 na 0.04 0.23 0.35 0.05 2.96 0.15 

Quarter 3 1.28 4.86 4.74 3.58 0.23 0.01 0.17 0.36 0.09 4.82 0.11 

Quarter 4 5.33 9.18 3.88 2.65 0.28 0.01 0.20 0.36 0.06 1.66 0.14 

2008 2.11 7.44 4.41 4.10 0.21 0.02 0.22 0.39 0.11 3.14 0.15 

Accuracy 

Laboratory Filter Concentrations 

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

continuing calibration verification (CCV) samples. Reference samples and CCV are procured 

from independent suppliers and are traceable to the National Institute of Standards and 

Technology (NIST). 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 CCV 

solution is set to the midrange of the calibration curve. In 2008, the CCV were analyzed every 

tenth sample to verify that instrument calibration had not drifted beyond established limits. 

Table 5-6 presents the percent recoveries and standard deviations for reference samples and 

CCV relative to target concentrations. The table shows that the DQI goals (see Table 5-1) 

were met in 2008. Table 5-6 corroborates the precision results that were shown in Figure 5-3. 

 
CASTNET Annual Report – 2008 ~ 55 ~ Chapter 5: Data Quality 

Table 5-6 Filter Pack Quality Control Summary for 2008 Filter Type Parameter

Reference 

Sample1 Recovery 

(%R) 

Continuing Calibration 

Verification Samples 

(%R) 

In-Run Replicate2

(RPD) 

Mean Standard Deviation Count3Mean Standard Deviation Count3Mean Standard Deviation Count3

Teflon SO2-

4 98.62 1.69 153 99.57 1.39 717 0.71 1.29 331

 NO3 100.02 1.33 153 99.57 1.28 717 1.18 1.87 331

 NH+ 

4 101.72 1.88 144 99.61 1.22 696 0.63 0.71 326

 Ca2+ 104.42 2.87 146 100.83 1.21 710 1.84 2.90 332

 Mg2+ 102.66 1.50 146 100.05 0.80 710 1.58 1.97 332

 Na+ 98.21 2.32 146 100.17 1.12 710 1.21 2.31 332

 K+ 97.83 2.46 146 100.05 0.96 710 1.73 1.90 332

 Cl- 99.80 1.53 153 100.01 1.24 717 1.67 3.11 327

Nylon SO2-

4 99.83 1.77 144 99.88 1.54 692 1.58 1.99 317

 NO3 99.60 1.38 144 100.27 1.43 692 0.87 1.07 317

Cellulose SO2-

4 100.23 1.17 173 99.48 0.96 686 2.31 3.04 318

 Note: % R = percent recovery (see Equation 5-2) 

 RPD = relative percent difference (see Equation 5-3) 

1

 Results of reference sample analyses provide accuracy estimates 

2

 Results of replicate analyses provide precision estimates 3

 Number of QC Samples 

Continuous Measurements 

Table 5-7 presents field accuracy results for 2008 based on instrument challenges performed 

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

calibrated every six months with NIST-traceable standards. The calibration results were 

evaluated using the accuracy criteria listed in Table 5-3. Each parameter was within its criterion 

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

at 87.3 percent and solar radiation at 85.0 percent. However, these results did not adversely 

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

more than two times the criterion. Using the two times standard, the two parameters passed 

with 98.2 and 98.1 percent frequency, respectively. 

 
CASTNET Annual Report – 2008 ~ 56 ~ Chapter 5: Data Quality 

Table 5-7 Accuracy Results for 2008 Field Measurements 

Parameter

Percent Within 

Criterion

Temperature (0C) 98.3 percent

Temperature (ambient) 99.1 percent

Delta Temperature (0C) 98.3 percent

Delta Temperature (ambient) 96.6 percent

*Relative Humidity > 85% 87.3 percent

Relative Humidity  50% 99.1 percent

*Solar Radiation 85.0 percent

Wind Direction North 92.2 percent

Wind Direction South 92.2 percent

Wind Speed < 5 m/s 98.2 percent

Wind Speed  5 m/s 98.2 percent

Precipitation 100.0 percent

Wetness (w/in 0.5 volts) 99.1 percent

Ozone Slope 97.2 percent

Ozone Intercept 98.2 percent

Flow Rate 100.0 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 these parameters was about 

98 percent. 

Completeness 

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

system relative to total possible data points. The CASTNET measurement criterion for 

completeness requires a minimum completeness of 90 percent for every measurement for each 

quarter. In addition, data aggregation procedures require approximately 70 percent 

completeness for hourly fluxes and weekly concentrations/fluxes. Figure 5-6 presents historical 

(black) and 2008 completeness data for all sites for measured filter concentrations and 

continuous measurements and calculated parameters. The figure shows that the 2008 direct 

measurements met the 90 percent completeness goal, and five continuous measurements 

exceeded 95 percent, including filter pack flow. Atmospheric concentrations also exceeded 95 

percent. The four parameters derived from model results exceeded 89 percent completeness 

for 2008. Completeness results for 2008 are better than historical results for all parameters 

except delta temperature and precipitation. 

 
CASTNET Annual Report – 2008 ~ 57 ~ Chapter 5: Data Quality 

Figure 5-6 Historical and 2008 Percent Completeness of Measurements and Modeled 

Estimates (black bars are 1990–2007) 

65 70 75 80 85 90 95 100

Annually Aggregated Flux Estimates

Annual Mean Deposition Velocities

Annual Mean Atm. Concentrations

Hourly Flux Estimates

Surface Wetness

Filter Pack Flow

Ozone

Delta Temperature

Ambient Temperature

Precipitation

Solar Radiation

Relative Humidity

Sigma Theta

Wind Direction

Scalar Wind Speed

Vector Wind Speed

Atmospheric Concentrations

Percent Completeness

Meteorological

Parameters

DQI Measurement Criterion

Model

Results
CASTNET Annual Report – 2008 ~ 58 ~ Chapter 5: Data Quality 

Interlaboratory Comparison Results 

The MACTEC laboratory is one of eight laboratories that participate in the US Geological 

Survey (USGS) interlaboratory comparison program. The laboratory receives four 

samples for chemical analysis from USGS every two weeks. The samples are a mix of 44 

synthetically prepared samples, 8 deionized water samples, and 52 natural wet deposition 

samples. The laboratory reported the eight CASTNET parameters for a total of 104 

samples during 2008. Results for the 44 synthetically prepared samples are depicted in the 

figure below, which presents results as percent recoveries of the median value for 

all laboratories. 

 

As shown below, only 3 of 352 reported values were more than 10 percent from their 

corresponding median. All values shown are within two standard deviations of their 

corresponding median. 

Figure 5a Results from Intercomparison of Synthetic and Natural Samples 

Additionally, precision results for the 52 natural wet deposition samples were reported as 

absolute percent differences for replicate analyses. None of the paired natural wet 

deposition sample data points exceeded 10 percent difference. These results are 

presented in the USGS report (USGS, 2008). 

The laboratory generally participates in two to three studies each year through 

Environment Canada’s National Water Research Institute (NWRI) Proficiency Testing 

QA Program in addition to interlaboratory comparison studies for the USGS. MACTEC’s 

laboratory was rated free of systemic bias for all eight parameters for the two NWRI 

2008 studies and was tied for first place out of 39 participating laboratories at the end of 

2008 (Environment Canada, 2008). 

85

90

95

100

105

110

115

0 10 20 30 40 50

% Recovery

CA

MG

NA

K

NH4

CL

NO3

SO4

Ca2+

Mg2+

Na+

K+

NH4

+

ClNO3

-

SO4

2-

Ca2+

Mg2+

Na+ 

K+ 

NH+ 

4 

ClNO3 

SO2-

4 
CASTNET Annual Report – 2008 ~ 59 ~ Chapter 5: Data Quality 

Summary of Data Quality Results 

DQI results demonstrate that field and laboratory processes were adequately monitored 

through QA/QC procedures and were generally free of systemic bias during 2008. Accuracy 

data met the established criteria for field and laboratory parameters with the exception of 

relative humidity > 85 percent and solar radiation. However, since the criterion was 

exceeded by a value less than its own magnitude, the associated continuous data collected are 

considered valid. 

Precision data for SO 

2, SO2-4 , HNO 3, and NH+ 4 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 uncertain nature of the 

gas-particle equilibrium of the nitrate species. 

The 2008 precision data for O 

3 concentrations met the 10 percent DQI criterion. The 2008 

precision data for ROM406/206 were excellent and demonstrate the comparability of the two 

independent O 

3 sampling systems. Completeness criteria were met for all parameters in 2008. 

Completeness results for 2008 were better than historical results for all but two parameters. 

The precision of continuous measurements for 2008 was excellent. Quarterly and annual 

precision results for 2008 met the DQI criteria. 

The laboratory intercomparison results show the CASTNET analytical chemistry laboratory 

was rated free of systematic bias and was tied for first place out of 39 participating laboratories 

at the end of 2008 in Environment Canada’s NWRI Proficiency Testing QA Program. 
CASTNET Annual Report – 2008 ~ 1 ~ References 

References 

Air Resource Specialists, Inc. (ARS). 2009. 2008 Data Quality Assurance Report. Prepared for 

National Park Service, Denver, CO. 

http://www.nature.nps.gov/air/Pubs/pdf/ads/2008DataQualityAssurance.pdf (accessed 

November 2009). 

Baron, J. S. 2006. Hindcasting Nitrogen Deposition to Determine an Ecological Critical Load. 

Ecological Applications, 16(2), 433-439. 

Butler, T. J., Likens, G. E., Vermeylen, F. M., and Stunder, B. J. B. 2005. The Impact of Changing 

Nitrogen Oxide Emissions on Wet and Dry Nitrogen Deposition in the Northeastern 

USA. Atmospheric Environment 39(27):4851-4862. 

Butler, T. J., Likens, G. E., Vermeylen, F. M., and Stunder, B. J. B. 2003. The Relation Between 

NOx Emissions and Precipitation NO3 in the Eastern USA. Atmospheric Environment 

37(15):2093-2104. 

Environment Canada. 2008. Water Science and Technology Directorate. Proficiency Testing 

Program. Rain and Soft Waters PT Studies 0092 and 0093 Report. Prepared for 

MACTEC Engineering and Consulting, Inc. 

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. 

Lavery, T.F., Rogers, C.M., Baumgardner, R., and Mishoe, K.P. 2009. Intercomparison of 

CASTNET Nitrate and Nitric Acid Measurements with Data from Other Monitoring 

Programs. Journal of Air & Waste Management Association (JAWMA) ISSN: 1047-3289, 

59:214-226. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2009a. Clean Air Status and Trends 

Network (CASTNET) Fourth Quarter 2008 Data Report. Prepared for U.S. Environmental 

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

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

 
CASTNET Annual Report – 2008 ~ 2 ~ References 

References (continued) 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2009b. Clean Air Status and Trends 

Network (CASTNET) Fourth Quarter 2008 Quality Assurance Report with 2008 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). 2009c. Clean Air Status and Trends 

Network (CASTNET) Third Quarter 2008 Data Report. Prepared for U.S. Environmental 

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

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

MACTEC Engineering and Consulting, Inc. (MACTEC). 2008a. Clean Air Status and Trends 

Network (CASTNET) First Quarter 2008 Data Report. Prepared for U.S. Environmental 

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

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

MACTEC Engineering and Consulting, Inc. (MACTEC). 2008b. Clean Air Status and Trends 

Network (CASTNET) First Quarter 2008 Quality Assurance Report. Prepared for U.S. 

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

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

MACTEC Engineering and Consulting, Inc. (MACTEC). 2008c. Clean Air Status and Trends 

Network (CASTNET) Quality Assurance Project Plan (QAPP), Revision 4.1. Prepared for U.S. 

Environmental Protection Agency (EPA), Research Triangle Park, NC, Contract No. 

68-D-98-112. Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2008d. Clean Air Status and Trends 

Network (CASTNET) Second Quarter 2008 Data Report. Prepared for U.S. Environmental 

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

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

MACTEC Engineering and Consulting, Inc. (MACTEC). 2008e. Clean Air Status and Trends 

Network (CASTNET) Second Quarter 2008 Quality Assurance Report. Prepared for U.S. 

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

Division, Washington, D.C. Contract No. 68-D-03-052. Gainesville, FL. 
CASTNET Annual Report – 2008 ~ 3 ~ References 

References (continued) 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2008f. Clean Air Status and Trends 

Network (CASTNET) Third Quarter 2008 Quality Assurance Report. Prepared for U.S. 

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

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

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

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

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

Gainesville, FL. 

MACTEC Engineering and Consulting, Inc. (MACTEC). 2003. 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. 

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. 

National Atmospheric Deposition Program (NADP). 2009. Ammonia Monitoring Network 

(AMoN). Passive Ammonia Monitoring Network, http://nadp.sws.uiuc.edu/nh3net/ 

(accessed July 2009). 

Nilsson, J. and Grennfelt, P. (Eds). 1988. Critical Loads for Sulphur and Nitrogen. Report from a 

workshop held at Skokloster, Sweden, 19-24 March 1988. NORD Miljørapport 1988: 

15, Nordic Council of Ministers, Copenhagen, pp. 225-268. 

Ray, J.D. 2009. Annual Data Summary 2008: Gaseous Pollutant Monitoring Program. Natural 

Resource Data Series, NPS/NRPC/ARD/NRDS – 2009/011. National Park Service, 

Denver, CO. 

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

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

U.S. Environmental Protection Agency (EPA). 2009a. Acid Rain and Related Programs: 

2008 Emission, Compliance, and Market Data.

http://www.epa.gov/airmarkets/progress/ARP_2008_ECM_Data.pdf (accessed 

August 14, 2009). 
CASTNET Annual Report – 2008 ~ 4 ~ References 

References (continued) 

U.S. Environmental Protection Agency (EPA). 2009b. Acid Rain and Related Programs: 2007 

Progress Report. EPA-430-K-08-010, Washington, DC. 

http://www.epa.gov/airmarkt/progress/docs/2007ARPReport.pdf (accessed 

August 2009). 

U.S. Environmental Protection Agency (EPA). 2009c. NOx Budget Trading Program: 2008 

Emission, Compliance, and Market Analyses.

http://www.epa.gov/airmarkets/progress/NBP_2/NBP_2008_ECM_Analyses.pdf 

(accessed August 14, 2009). 

U.S. Environmental Protection Agency (EPA). 2009d. “Transfer Standards for the Calibration 

of Ambient Air Monitoring Analyzers for Ozone.” Draft Technical Assistance 

Document, EPA-OAQPS, Research Triangle Park, NC. 

U.S. Environmental Protection Agency (EPA). 2008a. National Ambient Air Quality Standards 

for Ozone; Final Rule, Federal Register 73, no. 60 (March 2008). EPA-HQ-OAR-2005-

0172. 

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Pollution Measurement Systems, Volume II, Ambient Air Quality Monitoring Program. 

EPA-454/B-08-003. 

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

Trends Report, 1998. EPA-454-R-00-003. OAQPS, RTP, NC 27711. 

 

U.S. Environmental Protection Agency (EPA). 1998. Quality Assurance Requirements for State 

and Local Air Monitoring Stations (SLAMS). 40 CFR 50, Appendix L. 

U.S. Environmental Protection Agency (EPA). 1997. National Ambient Air Quality Standards 

for Ozone. 40 CFR 50. 

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Interlaboratory Comparison Program 

http://bqs.usgs.gov/precip/new/frontpage_home.htm (accessed July 28, 2008). 
 CASTNET Annual Report – 2008 Appendix A 

Appendix A 

Locational and Operational Characteristics of CASTNET Sites
 CASTNET Annual Report – 2008 ~ 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 

Ozone and 

Meteorology2 

Primary Land Use 

Terrain 

Alabama SND152 Sand Mountain 12/27/88 34.2894 85.9704 352 • • Agri. RolAlaska DEN417 Denali National Park and Preserve 10/06/98 63.7258 148.9633 661 • • Forested ComArizona CHA467 Chiricahua National Monument 04/25/89 32.0092 109.3892 1570 • • Range ComGRC474 Grand Canyon National Park 05/16/89 36.0597 112.1822 2073 • • Forested ComPET427 Petrified Forest National Park 09/24/02 34.8225 109.8919 1723 • • Desert FlaArkansas CAD150 Caddo Valley 10/04/88 34.1792 93.0989 71 • • Forested RolCalifornia CON186 Converse Station 06/17/03 34.1941 116.9130 1837 • • Agri./Forested ComJOT403 Joshua Tree National Park 02/16/95 34.0714 116.3906 1244 • • Desert ComLAV410 Lassen Volcanic National Park 07/25/95 40.5403 121.5764 1756 • • Forested ComPIN414 Pinnacles National Monument 05/16/95 36.4850 121.1556 335 • • Forested ComSEK430 Sequoia National Park 04/07/05 36.4894 118.8269 457 • • Forested MoYOS404 Yosemite National Park 09/25/95 37.7133 119.7061 1605 • • Forested Com
 CASTNET Annual Report – 2008 ~ 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 

Ozone and 

Meteorology2 

Primary Land Use 

Terrain 

Colorado GTH161 Gothic 05/16/89 38.9573 106.9854 2926 • • Range ComMEV405 Mesa Verde National Park 01/10/95 37.1983 108.4903 2165 • • Forested ComROM206 Rocky Mountain National Park 07/03/01 40.2778 105.5453 2743 • • Forested ComROM406 Rocky Mountain National Park 12/20/94 40.2778 105.5453 2743 • • Forested ComConnecticut ABT147 Abington 12/28/93 41.8402 72.0111 209 • • Urban-Agri. RolFlorida EVE419 Everglades National Park 10/06/98 25.3911 80.6806 2 • •4 Swamp Flat IRL141 Indian River Lagoon 07/09/01 30.1065 80.4554 2 • • Beach Flat SUM156 Sumatra 12/28/88 30.1065 84.9938 14 • • Forested Flat Georgia GAS153 Georgia Station 06/28/88 33.1812 84.4100 270 • • Agri. RolIllinois ALH157 Alhambra 06/28/88 38.8690 89.6229 164 • • Agri. Flat BVL130 Bondville 02/09/88 40.0520 88.3725 212 • • Agri. Flat STK138 Stockton 12/28/93 42.2872 89.9998 274 • • Agri. Rol
 CASTNET Annual Report – 2008 ~ 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 

Ozone and 

Meteorology2 

Primary Land Use 

Terrain 

Indiana SAL133 Salamonie Reservoir 06/28/88 40.8164 85.6608 250 • • Agri. Flat VIN140 Vincennes 08/04/87 38.7406 87.4844 134 • • Agri. RollKansas KNZ184 Konza Prairie 03/26/02 39.1021 96.6096 348 • • Prairie Flat Kentucky CDZ171 Cadiz 10/01/93 36.7841 87.8500 189 • • Agri. RollCKT136 Crockett 08/24/93 37.9211 83.0658 455 • • Agri. RollMAC426 Mammoth Cave National Park 07/24/02 37.1319 86.1478 243 • • Agri./Forested RollMCK131 Mackville 07/31/90 37.7044 85.0483 353 • • Agri. RollMaine ACA416 Acadia National Park 12/01/98 44.3769 68.2608 158 • • Forested ComASH135 Ashland 12/20/88 46.6039 68.4142 235 • • Agri. Flat HOW132 Howland 11/24/92 45.2158 68.7085 69 • • Forested RollMaryland BEL116 Beltsville 11/01/88 39.0283 76.8175 46 • • Urban-Agri. Flat BWR139 Blackwater National Wildlife Refuge 07/04/95 38.4448 76.1115 4 • • Forest-Marsh Coa
 CASTNET Annual Report – 2008 ~ 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 

Ozone and 

Meteorology2 

Primary Land Use 

Terrain 

Michigan ANA115 Ann Arbor 06/28/88 42.4164 83.9019 267 • • Forested Flat HOX148 Hoxeyville 10/31/00 44.1809 85.7390 298 • • Forested Flat UVL124 Unionville 06/28/88 43.6139 83.3597 201 • • Agri. Flat Minnesota VOY413 Voyageurs National Park 06/13/96 48.4128 92.8292 429 • • Forested RollMississippi CVL151 Coffeeville 12/27/88 34.0028 89.7989 134 • • Forested RollMontana GLR468 Glacier National Park 12/27/88 48.5103 113.9956 976 • • Forested ComNebraska SAN189 Santee Sioux 07/05/06 42.8292 97.8541 429 • • Agri. RollNevada GRB411 Great Basin National Park 05/16/95 39.0053 114.2158 2060 • • Forested ComNew Hampshire WST109 Woodstock 12/27/88 43.9446 71.7008 258 • • Forested ComNew Jersey WSP144 Washington’s Crossing 12/27/88 40.3133 74.8726 61 • • Urban-Agri. Roll
 CASTNET Annual Report – 2008 ~ 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 

Ozone and 

Meteorology2 

Primary Land Use 

Terrain 

New York CAT175 Claryville 05/10/94 41.9423 74.5519 765 • •4, 5 Forested ComCTH110 Connecticut Hill 09/28/87 42.4010 76.6535 515 • • Forested RollHWF187 Huntington Wildlife Forest 05/28/02 43.9732 74.2232 502 • • Forested ComNorth Carolina BFT142 Beaufort 12/28/93 34.8843 76.6213 2 • • Agri. Flat CND125 Candor 09/25/90 35.2643 79.8382 198 • • Forested RollCOW137 Coweeta 11/04/87 35.0605 83.4302 686 • • Forested ComPNF126 Cranberry 12/27/88 36.1040 82.0448 1250 • • Forested MouNorth Dakota THR422 Theodore Roosevelt National Park 10/06/98 46.8947 103.3778 850 • • Range RollOhio DCP114 Deer Creek State Park 09/28/88 39.6358 83.2600 267 • • Agri. RollLYK123 Lykens 01/10/89 40.9169 82.9981 303 • • Agri. Flat OXF122 Oxford 08/18/87 39.5314 84.7231 284 • • Agri. RollQAK172 Quaker City 09/28/93 39.9431 81.3378 372 • • Agri. RollOklahoma CHE185 Cherokee Nation 04/02/02 35.7507 94.6700 299 • • Agri. RollOntario EGB181 Egbert, Ontario 12/27/94 44.2317 79.7840 251 • •

4 Agri. Roll
 CASTNET Annual Report – 2008 ~ 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 

Ozone and 

Meteorology2 

Primary Land Use 

Terrain 

PennsylvaniaARE128 Arendtsville 06/28/88 39.9231 77.3078 269 • • Agri. RollKEF112 Kane Experimental Forest 01/03/89 41.5981 78.7683 622 • • Forested RollLRL117 Laurel Hill State Park 12/15/87 39.9883 79.2522 615 • • Forested ComMKG113 M.K. Goddard State Park 01/12/88 41.4250 80.1447 384 • • Forested RollPSU106 Penn. State University 01/06/87 40.7209 77.9316 376 • • Agri. RollSouth Dakota WNC429 Wind Cave National Park 11/18/03 43.5578 103.4839 1292 • • Prairie RollTennessee ESP127 Edgar Evins State Park 03/22/88 36.0389 85.7330 302 • • Forested RollGRS420 Great Smoky Mountains National Park 10/06/98 35.6331 83.9422 793 • • Forested ComSPD111 Speedwell 06/12/89 36.4698 83.8265 361 • • Agri. RollTexas ALC188 Alabama-Coushatta 04/02/04 30.4210 94.4045 101 • • Forested RollBBE401 Big Bend National Park 07/18/95 29.3022 103.1772 1052 • • Forested ComPAL190 Palo Duro Canyon State Park 04/24/07 34.8803 101.6649 1050 • • Prairie ComUtah CAN407 Canyonlands National Park 01/24/95 38.4586 109.8211 1809 • • Desert Com
 CASTNET Annual Report – 2008 ~ 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 

Ozone and 

Meteorology2 

Primary Land Use 

Terrain 

Virginia PED108 Prince Edward 11/03/87 37.1653 78.3070 150 • • Forested RollSHN418 Shenandoah National Park 06/28/88 38.5231 78.4347 1073 • • Forested MouVPI120 Horton Station 06/02/87 37.3300 80.5573 920 • • Forested MouWashington MOR409 Mount Rainier National Park 08/29/95 46.7583 122.1244 415 • • Forested ComWest Virginia CDR119 Cedar Creek State Park 11/10/87 38.8794 80.8478 234 • • Forested ComPAR107 Parsons 01/19/88 39.0906 79.6614 510 • • Forested ComWisconsin PRK134 Perkinstown 09/27/88 45.2066 90.5972 472 • • Agri. RollWyoming CNT169 Centennial 08/19/91 41.3722 106.2422 3178 • • Range ComPND165 Pinedale 12/27/88 42.9214 109.7900 2388 • • Range RollYEL408 Yellowstone National Park 06/26/96 44.5597 110.4006 2400 • • Forested Roll

1. The dry deposition filters are analyzed for the following constituents: 

Teflon = SO2-

4 , NO3, NH+ 

4 , Cl -, K +, Na +, Mg2+, Ca2+

Nylon = SO2-

4 , NO3 (reported as HNO3)

Cellulose = SO2-

4 (reported as SO2)

2. Meteorological sensors: temperature, delta temperature, relative humidity, solar 

radiation, vector wind speed, scalar wind speed, wind direction, sigma theta, surface wetness, and precipitation via tipping bucket rain gauge. 

3. N = No; Y = Yes; M = Marginal. 

4. O3 not measured. 5. Solar-powered site.  Indicates current monitoring. 

100 and 200 series = EPA – Operated S400 series = NPS – Operated S
 CASTNET Annual Report – 2008 Appendix B 

Appendix B 

Acronyms and Abbreviations
 CASTNET Annual Report – 2008 ~ 1 ~ Appendix B 

List of Acronyms and Abbreviations

AGL above ground level

AMoN Ammonia Monitoring Network  

ANC acid neutralizing capacity

AQS EPA’s Air Quality System

ARP Acid Rain Program

Ca2+

   particulate calcium ion

CAAA Clean Air Act Amendments

Ca(NO  

3)

  

2 calcium nitrate

CAIR Clean Air Interstate Rule

CMAQ Community Multiscale Air Quality

CAPMoN Canadian Air and Precipitation Monitoring Network

CASTNET Clean Air Status and Trends Network

CCV continuing calibration verification samples

CDX   AQS Central Data Exchange

Cl‐ particulate chloride ion

CO carbon monoxide  

DMC Data Management Center  

DQI data quality indicator

EAC Early Action Compact areas

EGU electric generating unit

EPA U.S. Environmental Protection Agency

EDT Eastern Daylight Time

H  

2SO  4 sulfuric acid

HNO  

3 nitric acid

HYSPLIT Hybrid Single‐Particle Lagrangian Integrated Trajectory

IC ion chromatography

ICP‐AES inductively coupled plasma‐atomic emission spectrometry

IMPROVE Interagency Monitoring of Protected Visual Environments

IP Internet protocol  

K+particulate potassium ion

K  

2CO  3 potassium carbonate

kg/ha/yr kilograms per hectare per year

km kilometer

LAI leaf area index

lpm    liters per minute

LTM Long‐Term Monitoring program

m meters

MACTEC MACTEC Engineering and Consulting, Inc.

MACT Maximum Available Control Technology  

MAD mean absolute difference
 CASTNET Annual Report – 2008 ~ 2 ~ Appendix B 

List of Acronyms and Abbreviations (continued)

MADPro Mountain Acid Deposition Program

MARCH Maryland Aerosol Research and Characterization  

MARPD mean absolute relative percent difference

MDN Mercury Deposition Network

Mg2+

   particulate magnesium ion

mg/l milligrams per liter

MLM Multi‐Layer Model

N nitrogen

Na+

particulate sodium ion

NAAQS National Ambient Air Quality Standards

NADP National Atmospheric Deposition Program

NaNO  

3 sodium nitrate  

NAPAP National Acid Precipitation Assessment Program

NBP NOx Budget Trading Program

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 ‐

3 particulate nitrate

NOx nitrogen oxides  

NOAA    National Oceanic and Atmospheric Administration

NPS National Park Service

NTN   National Trends Network

NWRI Environment Canada’s National Water Research Institute

O  

3 ozone

OTC Ozone Transport Commission

PM2.5 fine particle matter

ppb parts per billion

ppm parts per million

QA quality assurance

QAPP Quality Assurance Project Plan

QC quality control

RACT Reasonably Available Control Technology  

RPD relative percent difference

S sulfur

SIP State Implementation Plan
 CASTNET Annual Report – 2008 ~ 3 ~ Appendix B 

List of Acronyms and Abbreviations (continued)

SLAMS State and Local Monitoring Stations

SO  

2 sulfur dioxide

SO2‐

4 particulate sulfate

TIME Temporally Integrated Monitoring of Ecosystems

total NO‐ 

3 gaseous nitric acid (HNO  3) + particulate nitrate (NO‐ 3)

g/m3micrograms per cubic meter

USGS U.S. Geological Survey

V  

d deposition velocity

VOCs volatile organic compounds

z/s/p zero/span/precision  
For More Information:

U.S. Environmental Environmental Protection Protection Agency

Office of Air and Radiation Radiation

Clean Air M kt ar e s Di i i v s on

Washington, DC

On the Web:

CASTNET CASTNET Home Page: Cl Ai M kt EPA H P

www.epa.gov/castnet

Clean Air Markets

Division Home Page:

www.epa.gov/airmarkets

EPA Home Page:

www.epa.gov