Annual Report

CASTNET

2016
Clean Air Status and Trends Network

(CASTNET)

2016 Annual Report

Prepared by:

Wood Environment & Infrastructure Solutions, Inc.

Prepared for:

U.S. Environmental Protection Agency

Office of Air and Radiation

Clean Air Markets Division

Washington, DC

EPA Contract No. EP-W-16-015

August 2018
CASTNET 2016 Annual Report

i Table of Contents

TABLE OF CONT ENTS

Table of Contents

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

Chapter 1 CASTNET Update .......................................................................................................1

Introduction...................................................................................................................1

Related Air Quality Networks ........................................................................................2

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

Measurements Recorded at CASTNET Sites ...............................................................4

Quality Assurance Program..........................................................................................4

Estimating Dry, Wet, and Total Deposition....................................................................5

Chapter 2 Ozone Concentrations................................................................................................6

2015 NAAQS for Ozone................................................................................................7

Eight-hour Ozone Concentrations.................................................................................8

Uinta Basin, Utah Ozone Concentrations....................................................................10

Chapter 3 Nitrogen Pollutant Concentrations..........................................................................16

Total Nitrate Concentrations .......................................................................................16

Particulate Ammonium Concentrations.......................................................................18

Chapter 4 Update on the Ammonia Monitoring Network.........................................................21

Chapter 5 Sulfur Pollutant Concentrations..............................................................................23

Sulfur Dioxide Concentrations ....................................................................................23

Particulate Sulfate Concentrations..............................................................................25

Chapter 6 Continuous Trace-level Gas Concentrations..........................................................27

Continuous Trace-level NOy and Ozone .....................................................................31

Continuous Trace-level NOy and Filter Pack Total Nitrate Concentrations ..................32

Chapter 7 Effects of Wildfires on Air Quality ...........................................................................35

Chapter 8 Atmospheric Deposition of Nitrogen ......................................................................41

Chapter 9 Monitoring on Whiteface Mountain during 2015 and 2016.....................................47

Chapter 10 Atmospheric Deposition of Sulfur, Base Cations, and Chloride...........................56

Sulfur Deposition ........................................................................................................56

Deposition of Base Cations and Chloride....................................................................56

Chapter 11 Critical Loads for Open and Closed Canopy Herbaceous Ecosystems ...............60

References ...................................................................................................................................64

Appendix A Locational and Operational Characteristics of CASTNET Sites

Appendix B Acronyms and Abbreviations
ii Executive Summary

Executive Summary

The EPA Clean Air Status and Trends Network (CASTNET) measures concentrations of atmospheric pollutants across 

the United States. The primary objectives of the network are to determine compliance with ozone National Ambient Air 

Quality Standards and to provide data to evaluate the effectiveness of national and regional air pollution control 

programs. CASTNET data are also used to provide input to the National Atmospheric Deposition Program’s Total 

Deposition Hybrid Method for calculating total deposition and evaluating regional air quality models. This report 

presents maps of 2016 ozone levels, nitrogen and sulfur pollutant concentrations, and deposition fluxes and examines 

trends in air quality over the 27-year period from 1990 through 2016. In 2016, CASTNET measured rural, regionally 

representative concentrations of nitrogen and sulfur species at 95 monitoring stations at 93 locations and ozone levels 

at 81 locations.

Key Results and Highlights through 2016

The median fourth highest daily maximum 8-hour average (DM8A) ozone (O 

3) concentration for 2016 

at the eastern CASTNET reference sites (see Appendix A for designated reference sites) was 

64 parts per billion (ppb). This is a slight increase from the 2015 median of 63.5 ppb. At the western 

CASTNET reference sites, the median was 66 ppb. Three-year averages of fourth highest DM8A O 

3

concentrations exceeded the 2015 8-hour National Ambient Air Quality Standard (NAAQS) of 0.070 

parts per million (ppm) or, equivalently, 70 ppb, at three California CASTNET sites and one site in

New Jersey during the most recent 3 year period (2014–2016). During 2016, 10 eastern, 4 California 

sites, and Dinosaur National Monument (DIN431), UT measured fourth highest DM8A O 

3

concentrations greater than 70 ppb. Three-year averages of fourth highest DM8A O 

3 concentrations 

have been reduced by 24 percent at the eastern reference sites since 1990–1992 and by 10 percent 

at the western reference sites since 1996–1998. Figure E-1 and Table E-1 summarize the long-term 

changes in measured concentrations.

Regional O 

3 concentrations are influenced by 

nitrogen oxides (NOx) emissions. Federal, state, 

and local NOx control programs have resulted in 

substantive reductions in emissions. For example, 

NOx emissions declined by 86 percent over the 27 

year period, 1990 through 2016, at regulated 

electric generating units (EGUs) in the East.

Three-year mean annual concentrations of total 

nitrate (NO3), which is comprised of nitric acid plus 

particulate NO3, declined 48 percent at the eastern 

reference sites over the 27-year period. Three-year 

Figure E-1 Trends in O 

3, Total NO3, and 

SO 

2 at Eastern Reference Sites

50

60

70

80

90

100

0

2

4

6

8

10

12

199019911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013201420152016

Ozone Concentration (ppb)

Filter Pack Concentration (μg/m3)

Total NO3

SO2

Ozone

SO2

Total NO3

-

O3
CASTNET 2016 Annual Report

iii Executive Summary

mean annual total NO3 levels measured at the western reference sites dropped by 34 percent over 

the 21-year period.

Mean annual sulfur dioxide (SO 

2) concentrations measured at the eastern reference sites have 

declined significantly over the 27-year period, 1990 through 2016. Three-year mean annual SO 

2 levels 

at eastern sites decreased 86 percent. SO 

2 concentrations measured at the western reference sites 

declined by 46 percent over the 20 years from 1996 through 2016.

The percent reduction in SO 

2 concentrations at the eastern reference sites is consistent with the 

reduction in regulated eastern EGU SO 

2 emissions (94 percent).

Table E-1 Trends in Aggregated Western and Eastern O 

3, Total NO3, and SO 2

Pollutant Concentrations

Pollutant

Western Reference Sites Eastern Reference Sites Percent Changed

1996–1998 2014–2016 1990–1992 2014–2016 West East

O 

3 (ppb) 74 66 85 64 -10 -24

Total NO3 (μg/m3 ) 1.0 0.7 3.0 1.6 -34 -48

SO 

2 (μg/m3 ) 0.6 0.3 8.8 1.2 -46 -86

The original intent of CASTNET was to measure pollutant concentrations to estimate trends in sulfur 

and nitrogen pollutants. Currently, the focus also includes demonstrating compliance of rural, regional 

O 

3 concentrations with the NAAQS. The network also features measurements of trace-level gases 

and speciated nitrogen pollutants. Additionally, CASTNET supports the National Atmospheric 

Deposition Program’s Ammonia Monitoring Network with operation of ammonia samplers at 69

CASTNET sites. This report provides information on CASTNET pollutant measurements, estimated 

deposition fluxes, and other topics that can be addressed using CASTNET data, such as wintertime 

ozone concentrations in the Uinta Basin, Utah, effects of wildfires on air quality in Wyoming and 

Arizona, and pollutant concentrations measured on Whiteface Mountain, New York.
1 Chapter 1: CASTNET Update

In 2016, ozone monitoring was added to the Nez Perce Tribe’s site in Idaho (NPT006), and the site was 

converted from off grid to normal power. The seasonal small footprint site at the summit of Whiteface 

Mountain, NY (WFM007) was operated by the New York State Department of Environmental Conservation 

(NYSDEC) during the summer of 2016. The site at Coweeta, NC (COW005) was shut down in August 2016

after completion of a special study that utilized solar and wind energy as sources of power for the small 

footprint site.

Chapter 1

CASTNET Update

The Clean Air Status and Trends Network (CASTNET) is a nationwide air quality monitoring network that began 

operating in 1991. The network provides measurements of air pollutant concentrations in rural areas across the United 

States over the long term to determine compliance with ozone National Ambient Air Quality Standards and to evaluate 

the effectiveness of national and regional emission control programs. CASTNET data are used to provide input to 

regional air quality models. CASTNET is managed and operated by the U.S. Environmental Protection Agency in 

cooperation with the National Park Service and other federal, state, tribal, and local partners. In 2016, the network 

operated 95 monitoring stations throughout the contiguous United States, Alaska, and Canada. CASTNET data show a 

27-year decline in ozone concentrations and in nitrogen and sulfur pollutant levels and deposition rates.

Introduction

The Clean Air Status and Trends Network (CASTNET) operated 95 monitoring stations throughout the 

contiguous United States, Alaska, and Canada in 2016. All 95 sites included filter pack systems to 

sample weekly concentrations of acid gases and aerosols. Eighty-one sites included continuous 

ozone (O 

3) analyzers. The U.S. Environmental Protection Agency (EPA) and the National Park 

Service (NPS) are the primary sponsors of CASTNET. NPS began its participation in 1994 and 

operated 25 sites during 2016. The Bureau of Land Management-Wyoming State Office (BLM) 

operated five sites in Wyoming. 

CASTNET depends on contributions from many organizations (EPA, 2015a) including Native 

American tribes, state and federal government agencies, and universities. These participants sponsor 

individual CASTNET sites and provide in-kind services that support the overall performance of the 

network. For example, partners operate and repair site instruments, change weekly filter packs, and 

perform general site maintenance. Many partners provide the land for the CASTNET site. Others, 

such as universities, provide their expertise in air quality monitoring, which is invaluable for improving 

CASTNET monitoring capabilities and ensuring that CASTNET collects data that are valued by the 

scientific research community.
CASTNET 2016 Annual Report

2 Chapter 1: CASTNET Update

The U.S. Congress established the Acid Rain Program (ARP) in 1990 to reduce emissions of sulfur 

dioxide (SO 

2) and nitrogen oxides (NOx) from electric generating units (EGUs). Congress also directed 

EPA to establish CASTNET to assess the effectiveness of the ARP by providing consistent, long-term 

measurements for determining relationships between changes in emissions and changes in air 

quality, atmospheric deposition, and ecological effects. Figure 1-1 shows the locations of the 

CASTNET monitoring sites that were operational during 2016.

Related Air Quality Networks

CASTNET monitors air quality and deposition in cooperation with other national and international 

networks. EPA uses data from CASTNET and the other long-term national networks to assess the 

effectiveness of emission control programs. These networks include the National Atmospheric 

Deposition Program (NADP) (http://nadp.slh.wisc.edu/) and its affiliated networks:

• National Trends Network (NTN)

• Ammonia Monitoring Network (AMoN)

• Mercury Deposition Network (MDN)

• Atmospheric Mercury Network (AMNet).

Other cooperating networks include:

• Canadian Air and Precipitation Monitoring Network (CAPMoN)

(https://www.canada.ca/en/environment-climate-change/services/air-pollution/monitoringnetworks-data/canadian-air-precipitation.html)

• EPA’s National Core Monitoring (NCore)

(https://www3.epa.gov/ttnamti1/ncore.html)

• BLM’s Wyoming Air Resources Monitoring System (WARMS)

(https://www.blmwarms.net/) 

• Interagency Monitoring of Protected Visual Environments (IMPROVE) 

(http://vista.cira.colostate.edu/IMPROVE/)
CASTNET 2016 Annual Report

3 Chapter 1: CASTNET Update

Locations of Monitoring Sites

A map of CASTNET monitoring sites is given in Figure 1-1. Ninety-five monitoring sites were operated 

at 93 distinct locations. To estimate precision across the network, co-located sites were operated at 

Mackville, KY (MCK131/231) and Rocky Mountain National Park, CO (ROM406/206) during 2016. 

The ROM406/206 pair ensures consistency between EPA (ROM206) and NPS (ROM406). Of the two 

Rocky Mountain monitoring sites, ROM406 is specified as the regulatory monitoring site for O 

3. The 

location of each site and information on start date, latitude, longitude, elevation, identification of the 

nearby NADP site, land use, terrain type, operating agency, and if the site is a reference site used for 

trends are given in Appendix A.

Figure 1-1 CASTNET Sites Operational during 2016
CASTNET 2016 Annual Report

4 Chapter 1: CASTNET Update

Measurements Recorded at CASTNET Sites

All CASTNET sites measure weekly ambient concentrations of acidic pollutants, base cations, and 

chloride (Cl-

) using a 3-stage filter pack with a controlled flow rate (Wood, 2015). Gaseous pollutant 

concentrations include nitric acid (HNO 

3) and SO2. Particulate concentrations include nitrate (NO3), 

ammonium (NH+ 

4 ), sulfate (SO2-4 ), magnesium (Mg2+ ), calcium (Ca2+ ), potassium (K+ ), sodium (Na+ ), 

and Cl-

. The filter pack is exchanged each Tuesday and shipped to the analytical chemistry laboratory 

for analysis. Ambient temperature is measured at 9 meters (m) at all sites in part to enable conversion 

of concentrations to local conditions.

Most CASTNET sites also include a temperature-controlled shelter and continuous O 

3 monitoring 

system. O 

3 concentrations were measured at 81 sites. The O 3 inlet and filter pack are located atop a 

10-m tower. Some CASTNET sites also measure trace-level SO 

2, carbon monoxide (CO), and 

nitrogen oxide/total reactive oxides of nitrogen (NO/NOy). In 2016, meteorological parameters were 

measured at 6 EPA-, 25 NPS-, and 5 BLM-sponsored CASTNET sites. Measured meteorological 

parameters include 2-m temperature, wind speed and direction, standard deviation of the wind 

direction, solar radiation, relative humidity, precipitation, and surface wetness (at select sites).

Quality Assurance Program

The CASTNET quality assurance (QA) program was established to ensure that all reported data are 

of known and documented quality in order to meet CASTNET objectives. The QA program also 

ensures intra-network consistency and comparability and the delivery of data that are reproducible 

and comparable with data from other monitoring networks. The 2016 QA program elements are 

documented in the CASTNET Quality Assurance Project Plan (QAPP; Wood, 2015). The QAPP 

includes standards and policies for all components of project operation, from site selection 

through final data reporting, with appendices that provide standard operating procedures for 

CASTNET operations. 

Data quality indicators (DQI) such as precision, accuracy, and completeness are used to assess 

CASTNET measurements and supporting activities. Routine assessment and analysis help guarantee 

the production of high-quality data and information to meet project objectives. Measurements taken 

during 2016 and historical data collected over the period 1990 through 2015 were analyzed relative to 

DQI and their associated metrics. Results from these analyses are available in quarterly and annual 

QA reports posted on the EPA CASTNET website: https://www.epa.gov/castnet/.

The Wood CASTNET laboratory regularly participates in interlaboratory comparison studies and 

proficiency testing (PT) programs such as the Environment Canada (ECAN) PT Program for Inorganic 

Environmental Substances (http://www.ec.gc.ca/inre-nwri/default.asp?lang=En&n=7A20877C-1). The 

ECAN PT program conforms to the requirements of the American Association for Laboratory 

Accreditation (A2LA). The program meets the International Organization for Standardization 
CASTNET 2016 Annual Report

5 Chapter 1: CASTNET Update

(ISO)/International Electrotechnical Commission (IEC) 17043:2010 conformity assessment – general 

requirements for proficiency testing with scope of accreditation 2867.01. The results reported are 

evaluated for systematic bias and precision. Systematic bias is assessed using the Youden (1969) 

non-parametric analysis, while precision is calculated using algorithm A from the ISO standard 13528 

(ISO, 2005). CASTNET laboratory results from the PT studies are summarized in the QA quarterly 

and annual reports posted to the EPA CASTNET website: https://www.epa.gov/castnet/.

Estimating Dry, Wet, and Total Deposition

Total deposition was assessed using the NADP’s Total Deposition Hybrid Method (EPA, 2015d; 

Schwede and Lear, 2014), which is a hybrid approach that combines data from established ambient 

monitoring networks and chemical transport models. To estimate dry deposition, ambient 

measurement data from CASTNET and other networks were merged with dry deposition rates and 

flux output from the Community Multiscale Air Quality (CMAQ) modeling system. Wet deposition 

estimates were derived from precipitation chemistry measurements and precipitation amounts from 

the Parameter-elevation Regressions on Independent Slopes Model (PRISM). Dry and wet deposition 

fluxes were added to obtain the estimates of total deposition that are discussed in Chapters 8 and 10.

This report summarizes CASTNET monitoring and the resulting concentration and deposition data 

collected over the 27-year period from 1990 through 2016. The report covers such topics such as 

wintertime air quality in the Uinta Basin in Utah, trace-level gas concentrations measured at eight 

CASTNET sites, effects of wildfires on air quality, and air quality on Whiteface Mountain in New York. 

Additional information, previous annual reports, descriptions of CASTNET operations, other 

CASTNET documents, and the CASTNET database can be found on the EPA CASTNET website: 

https://www.epa.gov/castnet/.
6 Chapter 2: Ozone Concentrations

Chapter 2

Ozone Concentrations

CASTNET is the principal network for monitoring rural, ground-level ozone concentrations in the United States. The 

network produces ozone data for evaluation of compliance with the National Ambient Air Quality Standards (NAAQS; 

EPA, 2015) plus information on geographic patterns in regional ozone levels. CASTNET ozone data are of the highest 

quality as demonstrated by the results from the CASTNET QA program and its rigorous QA/quality control procedures. 

Ozone data measured at 78 of 81 CASTNET sites from 2014 through 2016 were evaluated with respect to the NAAQS 

and used to calculate design values under Title 40 Code of Federal Regulations Part 50 Appendix U (EPA, 2015b). 

Maps of 3-year averages of fourth highest daily maximum 8-hour average (DM8A) ozone concentrations for 2014 

through 2016 and fourth highest DM8A ozone concentrations for 2016 are presented. Trends in fourth highest DM8A 

ozone concentrations for eastern and western reference sites are shown. For the 2014 through 2016 period, three 

California sites and one eastern site measured concentrations greater than the 0.070 ppm NAAQS.

Hourly average concentrations were measured at 81 CASTNET sites in 2016. These data are 

archived in the CASTNET database and delivered routinely to the EPA Air Quality System (AQS) 

database. Data from these sites, with the exception of Howland, ME (HOW191) and the co-located 

sites at MCK231, KY and ROM206, CO, which are designated as non-regulatory, are used to 

calculate fourth highest DM8A O 

3 concentrations when three years of Title 40 Code of Federal 

Regulations (CFR) Part 58-compliant data become available. CASTNET measurements provide 

information for evaluating rural O 

3 concentrations in the context of the O 3 NAAQS and in terms of 

presenting information on trends and geographic patterns in regional O 

3.

Sample of Heading Three

The information presented in this chapter includes maps of and trends in the annual fourth highest 

DM8A O 

3 concentrations measured at CASTNET sites. Ozone data from Dinosaur National 

Monument (NM) in Utah (DIN431) and from measurements in the Uinta Basin in the northeast corner 

of Utah are also discussed. Additional maps of O 

3 concentrations from the NPS Air Atlas can be 

viewed at https://nature.nps.gov/air/maps/airatlas/ and https://nature.nps.gov/air/data/products/parks/. 

A design value describes the air quality status of a given area with respect to the concentration values 

required by the NAAQS. Design values change as each new 3-year period of monitored ozone 

concentrations becomes available (e.g., 2014–2016). Design values are used to classify nonattainment 

areas, assess progress towards meeting the NAAQS, and develop control strategies to achieve the NAAQS. 

For example, to achieve the 2015 ozone NAAQS, 3-year averages of fourth highest DM8A ozone 

concentrations cannot exceed 0.070 parts per million (ppm). Designated criteria pollutant nonattainment 

areas are provided on the EPA website: https://www.epa.gov/green-book.
CASTNET 2016 Annual Report

7 Chapter 2: Ozone Concentrations

Measurements from 34 eastern and 16 western reference sites (see Appendix A) were analyzed to 

determine trends in O 

3 concentrations. These sites were also used to show trends in ambient nitrogen 

and sulfur concentrations (chapters 3 and 5). The eastern reference sites have been reporting 

CASTNET measurements since at least 1990 and the western reference sites since at least 1996.

2015 National Ambient Air Quality Standards for Ozone

Ozone1

Primary Standard Secondary Standard

Level Averaging Time Level Averaging Time

0.070 ppm1 8-hour2 0.070 ppm1 8-hour2

Note: 1 The NAAQS was revised from 0.075 ppm to 0.070 ppm on October 15, 2015. 

2 To attain this standard, the 3-year average of the fourth highest DM8A O 

3 concentrations measured at each monitor within a 

specified area must not exceed 0.070 ppm or 70 parts per billion (ppb) in practice (effective December 28, 2015). Ozone

concentrations are commonly presented in units of ppb.

The primary O 

3 NAAQS is designed to protect public health. The secondary standard is designed to 

protect public welfare and the environment. Both O 

3 NAAQS are set at a level of 0.070 ppm averaged 

over eight hours for the annual fourth highest value.

To assess compliance with the primary and secondary standards, EPA uses measured O 

3 pollutant 

concentrations, an 8-hour averaging time, and the fourth highest daily maximum averaged across 

three consecutive years. The secondary standard is equivalent, based on the W126 index (Lefohn 

and Runeckles, 1987), to a level of protection of 17 ppm-hour or lower averaged over three years 

(EPA, 2008). The W126 index is a weighted index designed to reflect the cumulative exposures that 

can damage plants and trees during the consecutive three months in the growing season when 

daytime O 

3 concentrations are the highest, and plant growth and production are most affected. 

The EPA and other federal, tribal, state, and local agencies measure O 

3 concentrations on an hourly 

basis through national and local monitoring programs. Wood followed EPA procedures (2015b) to 

estimate O 

3 design values and 2016 fourth highest DM8A O 3 concentrations at CASTNET sites. 

Measurements potentially affected by exceptional events were not removed when calculating these 

estimates. “Exceptional events are unusual or naturally occurring events that can affect air quality but 

are not reasonably controllable using techniques that state, tribal, or local air agencies may implement 

in order to attain and maintain the NAAQS” (EPA, 2016). The Exceptional Events Rule was updated 

on October 3, 2016 (https://www.epa.gov/air-quality-analysis/exceptional-events-rule-and-guidance), 

and provides the requirements for excluding air quality data from regulatory decisions if the data are

affected by events outside an agency’s control, such as a wildfires or stratospheric intrusion. 

CASTNET O 

3 data were used to gauge compliance with the NAAQS at EPA-, NPS- and BLMsponsored sites that were 40 CFR Part 58 compliant for the years 2014 through 2016.
CASTNET 2016 Annual Report

8 Chapter 2: Ozone Concentrations

Eight-hour Ozone Concentrations

All CASTNET sites, with the exception of HOW191, ME; MCK231, KY; and ROM206, CO, are 

regulatory and may be used for NAAQS compliance. HOW191 does not meet regulatory siting criteria. 

MCK231 and ROM206 are co-located sites used solely for QA purposes and are designated as 

“NAAQS excluded.” Three-year averages of the fourth highest DM8A O 

3 concentrations for 2014 

through 2016 are presented in Figure 2-1. Ozone concentrations were not included on the map if the 

3-year average was not available because of incomplete data; these sites are shown as dots with no 

value. Three California CASTNET sites and one eastern site measured fourth highest DM8A O 

3

concentrations above the 2015 NAAQS. The highest 3-year design value of 89 parts per billion (ppb) 

was sampled at the Sequoia and Kings Canyon National Parks, CA (SEK430) site. The highest 3-year 

eastern concentration (73 ppb) was measured at Washington Crossing, NJ (WSP144). Table 2-1 lists 

sites with 2014–2016 O 

3 design values greater than 70 ppb.

Figure 2-1 Three-year Averages of Fourth Highest DM8A O 

3 Concentrations for 

2014–2016
CASTNET 2016 Annual Report

9 Chapter 2: Ozone Concentrations

Table 2-1 Sites with Design Values for 2014–2016 greater than 70 ppb

Site ID State Sponsor 3-year Average

SEK430 California NPS 89

JOT403 California NPS 86

YOS404 California NPS 74

WSP144 New Jersey EPA 73

Figure 2-2 shows 2016 fourth highest DM8A O 

3 concentrations that met percent completeness 

criteria. During 2016, 10 eastern, 4 California sites, and 1 site in Utah measured fourth highest DM8A 

O 

3 concentrations greater than 70 ppb.

Figure 2-2 Fourth Highest DM8A O 

3 Concentrations for 2016

Figure 2-3 provides box plots depicting trends in 1-year mean, median, and annual distributions of 

fourth highest DM8A O 

3 concentrations from the eastern reference sites (right side) for 1990 through 

2016 and for the western reference sites (left side) for 1996 through 2016. The reference sites were 

selected for their long-term data record and consistent performance. The eastern O 

3 data show an 

overall decline since 2002. The 2016 median data point, 64 ppb, was higher than the 2015 value of 

63.5 ppb.

The western O 

3 data show an increase in fourth highest DM8A O 3 concentrations from a 2009 

minimum through 2012, followed by a decline through 2016. The 2016 median of the fourth highest 
CASTNET 2016 Annual Report

10 Chapter 2: Ozone Concentrations

DM8A O 

3 concentrations for the western reference sites was 66 ppb, the lowest value for the western 

reference sites.

Figure 2-3 Trends in Fourth Highest DM8A O 

3 Concentrations

Western Reference Sites Eastern Reference Sites

Uinta Basin, Utah Ozone Concentrations

A network of O 

3 monitors throughout the Uinta Basin has measured elevated DM8A O 3 levels. In fact, 

the Uinta Basin is one of only two places in the United States that measures wintertime O 

3

concentrations in excess of the NAAQS. Wyoming’s Upper Green River Basin is the other (CASTNET 

2010 Annual Report; Wood, 2012). 

The Uinta Basin is an enclosed basin that lies in the northeast corner of Utah and is part of a larger 

area known as the Colorado Plateau. The Basin is bounded on the north by the Uinta Mountain range, 

on the south by the Book and Roan Cliffs, on the west by the Wasatch Range, and on the east by 

elevated terrain separating it from the Piceance Basin in Colorado. The Green River runs through the 

Basin from northeast to southwest, exiting through the Book Cliffs via Desolation Canyon. The floor of 

the Basin is at approximately 1,463 meters above sea level with significant local surrounding 

topography with elevations of tens to hundreds of meters.

Wintertime air quality in the Uinta Basin deteriorates when strong inversion events persist over 

several days (Lyman et al., 2016). These multi-day inversions occur with stagnant, high-pressure 

weather conditions and sufficient snow cover to reflect incoming sunlight, which keeps the ground 

from absorbing sunlight and warming. Snow also provides energy for the chemical reactions that form 

O 

3 by increasing the amount of available solar radiation. Ozone forms in the atmosphere from 

reactions involving NOx and volatile organic compounds (VOC). Inversion conditions trap these 

pollutants near ground level and increase their concentrations and their subsequent ability to generate 

O 

3. Numerous exceedances of the NAAQS have occurred during winters with adequate snow cover 

and sustained high-pressure conditions, and no wintertime exceedances have ever been observed 

without snow cover. During lengthy inversion conditions, high O 

3 concentrations first form in the lowelevation center of the Basin. The O 

3 concentrations increase daily while expanding towards the 
CASTNET 2016 Annual Report

11 Chapter 2: Ozone Concentrations

Basin’s edges. The highest O 

3 concentrations occur primarily in areas at lowest elevation. Longer 

inversion episodes and episodes that occur late in the winter season tend to lead to higher O 

3 levels. 

Figure 2-4 depicts DM8A O 

3 concentrations measured throughout the Basin on February 12, 2016. 

Color shading shows the magnitude of the O 

3 concentration (Lyman et al., 2016). Ozone monitoring 

locations are also shown. The site labeled Dinosaur N.M. is the DIN431 CASTNET site. Table 2-2 lists 

8-hour average O 

3 concentrations measured in the Uinta Basin during the winter of 2015–2016. The 

highest DM8A O 

3 concentration exceeded 100 ppb.

Figure 2-4 DM8A O 

3 Concentrations Measured throughout Uinta Basin on February 12, 2016

Source:Lyman et al., 2016

Esri, DigitalGlobe, i-cubed, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community

Note: Vertical black bar = 70 ppb

Air quality monitoring in the Basin began in 2006 when the Utah Department of Air Quality (UDAQ) 

installed monitors in Vernal to measure fine particulate matter (PM2.5), O 

3, and NOx. EPA added two 

monitoring sites in 2009, and the network further expanded to the number of sites shown in Figure 2-4 

and Table 2-2. The NPS added the DIN431 CASTNET site in November 2013 (Appendix A). The site 

is located in the northeast corner of the Basin east of Vernal (Figure 2-4) at an elevation of 1,463 

meters. Ozone concentrations measured at DIN431 were generally lower than those measured near 

the center of the Basin.
CASTNET 2016 Annual Report

12 Chapter 2: Ozone Concentrations

Table 2-2 8-hour Average O 

3 Concentrations Measured in the Uinta Basin during 

Winter 2015–2016

Location

Site 

Elevation 

(Meters)

Mean 

(ppb)

Maximum 

(ppb)

Minimum 

(ppb)

Fourth

Highest DM8A 

(ppb)

Number of 

Exceedances

Dinosaur NM 1463 37.0 83.6 9.5 75.3 5

Ouray 1464 37.7 120.6 8.8 96.8 11

Fort Duchesne 1559 31.9 96.8 6.8 90.4 9

Horsepool 1569 44.1 115.8 16.4 93.6 11

Roosevelt 1587 35.2 96.0 10.8 84.8 10

Castle Peak 1605 39.0 99.8 16.3 84.0 8

Vernal 1606 34.7 78.4 10.3 73.6 5

Myton 1610 38.7 95.1 16.6 85.5 8

Seven Sisters 1618 39.3 117.5 11.0 100.9 9

Rangely 1648 36.9 67.4 19.8 59.8 0

Red Wash 1689 39.9 96.0 18.6 83.5 7

Rabbit Mountain 1879 32.9 52.9 11.8 48.2 0

Whiterocks 1893 43.4 86.1 25.3 81.3 7

Fruitland 2021 36.4 62.4 9.3 53.1 0

Mountain Home 2234 46.7 72.4 32.6 64.3 1

Flat Rock 2274 44.2 58.2 30.0 54.6 0

Source:Lyman et al., 2016

Figure 2-5 presents a time series of DM8A O 

3 concentrations measured at DIN431 from its inception 

through mid-2017. Several DM8A O 

3 concentrations exceeded 70 ppb. Most of the high 

concentrations were observed during first quarter. However, several high values were measured 

during summer months. Some investigators (Ute Indian Tribe, 2016) have concluded that 

stratospheric O 

3 intrusions and wildfires contribute to elevated spring and summer O 3 levels. No 

concentrations greater than 70 ppb were sampled during the first quarter of 2015 because of a lack of 

snow cover (Neeman et al., 2015).
CASTNET 2016 Annual Report

13 Chapter 2: Ozone Concentrations

Figure 2-5 Time Series of DM8A O 

3 Concentrations Measured at DIN431 from November 2013

through July 2017

Dinosaur National Monument (DIN431), North (full site)

0

10

20

30

40

50

60

70

80

90

100

11/22/13

1/22/143/22/145/22/147/22/149/22/14

11/22/14

1/22/153/22/155/22/157/22/159/22/15

11/22/15

1/22/163/22/165/22/167/22/169/22/16

11/22/16

1/22/173/22/175/22/177/22/17

Concentration (ppb)

Winter

2014

Winter

2015

Winter

2016

Winter

2017
CASTNET 2016 Annual Report

14 Chapter 2: Ozone Concentrations

Table 2-3 summarizes the 10 highest DM8A O 

3 concentrations annually at DIN431 over the four years 

2014 through 2017.

Table 2-3 Ten Highest DM8A O 

3 Concentrations at DIN431 for 2014 through 2017

Date DM8A (ppb) Rank

2014

1/1/14 69 1

1/26/14 65 2

5/18/14 64 3

6/3/14 64 3

6/5/14 64 3

6/4/14 63 6

8/23/14 63 6

1/25/14 62 8

6/28/14 62 8

6/1/14 61 10

6/2/14 61 10

6/13/14 61 10

2015

6/8/15 74 1

6/9/15 72 2

8/20/15 69 3

6/3/15 67 4

6/4/15 67 4

6/7/15 66 6

6/19/15 65 7

8/21/15 65 7

6/20/15 64 9

5/12/15 63 10

6/18/15 63 10

Date DM8A (ppb) Rank

2016

2/13/16 83 1

2/12/16 80 2

2/11/16 77 3

2/10/16 75 4

2/9/16 71 5

8/2/16 69 6

2/8/16 67 7

2/14/16 67 7

1/29/16 65 9

5/6/16 65 9

2017

2/1/17 77 1

2/2/17 75 2

2/4/17 75 2

2/5/17 74 4

1/31/17 72 5

2/3/17 71 6

6/3/17 69 7

1/30/17 68 8

2/6/17 67 9

9/7/17 66 10

3-year Averages

Date DM8A (ppb)

2014–2016 68

2015–2017 72
CASTNET 2016 Annual Report

15 Chapter 2: Ozone Concentrations

Data from DIN431 also provides information on SO 

2 and total NO3 concentrations in micrograms per 

cubic meter (μg/m3 ) of air over the period November 2014 through July 2017. Figure 2-6 presents 

weekly average concentrations. Sulfur dioxide concentrations were low throughout the period while 

total NO3 concentrations showed occasional spikes that were 5 to 10 times higher than average. Two 

periods with high DM8A O 

3 concentrations (Table 2-3) were observed during weeks with high total 

NO3 concentrations.

Figure 2-6 Weekly Average Concentrations of SO 

2 and Total NO3 at DIN431

0

2

4

6

8

10

12

14

11/18/14

1/18/153/18/155/18/157/18/159/18/15

11/18/15

1/18/163/18/165/18/167/18/169/18/16

11/18/16

1/18/173/18/175/18/177/18/17

Concentration (

μg/m3)

SO2

Total NO3 1/31/17

2/9/16 12/1/15 1/6/15

SO 

2

Total NO3
16 Chapter 3: Nitrogen Pollutant Concentrations

Chapter 3

Nitrogen Pollutant Concentrations

During 2016, weekly average concentrations of nitric acid, particulate nitrate, and particulate ammonium were 

measured using 3-stage filter packs at 95 CASTNET monitoring stations. Maps of 2016 annual mean total nitrate (nitric 

acid plus nitrate) and ammonium concentrations show the geographic distribution of the two pollutants measured. Box 

plots provide trends in annual mean total nitrate and ammonium concentrations aggregated over 34 eastern and 16 

western reference sites. The nitrogen pollutants measured at the 34 eastern reference sites declined over the 27-year 

period from 1990 through 2016. Annual mean concentrations of total nitrate were reduced by 48 percent from 1990 

through 2016. Ammonium concentrations declined by 63 percent. Total nitrate and ammonium concentrations 

measured at the 16 western reference sites were reduced by 34 percent and 31 percent, respectively, over the 21-year 

period 1996 through 2016.

Annual mean concentrations of total NO3 (HNO 

3 + NO3) and NH+ 4 for 2016 are presented in two maps 

in this chapter. Additional maps of 2016 quarterly mean concentrations are provided in CASTNET 

quarterly data reports (Wood, 2016a; 2016b; 2017a; 2017b). Trends in annual mean concentrations 

over the 27-year period, 1990 through 2016, were calculated from measurements from the 34 

CASTNET eastern reference sites and for the 21-year period, 1996 through 2016, from data 

measured at the 16 CASTNET western reference sites. See Appendix A for the designated reference 

sites.

Total Nitrate Concentrations

Mean total NO3 concentrations measured in 2016 are presented in the map in Figure 3-1. To illustrate 

trends, Figure 3-2 provides box plots of total NO3 levels for the eastern and western reference sites 

through 2016. Each box presents the mean and median concentrations and the 10th, 25th, 75th, and 

90th percentiles for that year. 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 total NO3

levels began to decline in response to NOx emission controls. Total NO3 levels measured at the 

eastern reference sites were reduced by 53 percent from a mean value of 3.1 μg/m3 in 2000 to a 

mean value of 1.5 μg/m3 in 2016. Over the history of the network, 3-year mean levels declined from 

3.0 μg/m3 for 1990–1992 to 1.6 μg/m3 for 2014–2016, producing a 48 percent reduction in total NO3. 

The left side of Figure 3-2 shows data aggregated from the 16 western sites. Total NO3 levels 

declined from 1.1 μg/m3 to 0.6 μg/m3 from 2000 through 2016, a 43 percent reduction. The 3-year 

mean total NO3 concentration for 2014–2016 was 34 percent lower than the corresponding 1996–

1998 level. The 3-year mean concentration was 1.0 μg/m3 for 1996–1998 and 0.7 μg/m3 for 2014–

2016. 
CASTNET 2016 Annual Report

17 Chapter 3: Nitrogen Pollutant Concentrations

Figure 3-1 Annual Mean Total NO3 Concentrations for 2016

Figure 3-2 Trends in Annual Mean Total NO3 Concentrations

Western Reference Sites Eastern Reference Sites
CASTNET 2016 Annual Report

18 Chapter 3: Nitrogen Pollutant Concentrations

Figure 3-3 illustrates the trend in NOx emissions from regulated EGUs operating in the eastern United 

States from 1990 through 2016. The 27-year decline in aggregated EGU emissions was 86 percent.

Figure 3-3 Trend in Annual Composite NOx Emissions from Regulated EGUs Operating in the 

Eastern United States

Source: EPA (2017)

Particulate Ammonium Concentrations

A map of 2016 mean particulate NH+ 

4 concentrations is provided in Figure 3-4. Figure 3-5 shows box 

plots of NH+ 

4 concentrations. The trend diagram for the eastern sites (right side) shows a reduction in 

mean NH+ 

4 levels from 1990–1992 to 2014–2016. The 1990–1992 mean concentration was 1.8 μg/m3 

, 

and the 2014–2016 value was 0.7 μg/m3 , a 63 percent decline. Similar to total NO3, the eastern NH+ 

4

concentrations began to decline in 2000 and have been reduced from 1.6 μg/m3 in 2000 to 0.5 μg/m3 

in 2016. The western reference sites show a decline from 0.3 μg/m3 in 1996–1998 to 0.2 μg/m3 in 

2014–2016, a 31 percent reduction.

0

1000

2000

3000

4000

5000

1990 1995 2000 2005 2010 2015 2016

Thousand Short Tons
CASTNET 2016 Annual Report

19 Chapter 3: Nitrogen Pollutant Concentrations

QA PROGRAM SUMMARY

Quality Assurance Program Results

Precision of Filter Pack Measurements

Historical (1990 through 2015) mean absolute relative percent difference (MARPD) data for all 11 co-located 

site pairs operated over the history of the network are provided in the bar chart in Figure 3-a. The 2016 data 

for the current co-located sites at MCK131/231 and ROM406/206 are also provided. The precision criterion is 

a MARPD of 20 percent. Historical and 2016 measurements met the criterion for each analyte. The MARPD 

for SO 

2 at ROM406/206 was unusually high because of the imprecision of lower concentrations measured 

during the first two quarters. 

The 2016 analytical precision results for 

10 analytes are also presented in Figure 3-a. 

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 with the original concentration 

results. The laboratory precision data met the 

20 percent measurement criterion.

Data 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 parameter

for each quarter. The historical 

results and the results for 2016 

are given in Figure 3-b. 

Historical results for trace-level 

gas measurements represent 

data from 2013–2015. The 

completeness criterion was met 

for atmospheric (filter pack) and 

O 

3 concentrations, filter pack 

flow, and meteorological 

measurements. Completeness 

of trace-level gas 

measurements (Chapter 6) met 

the completeness requirements 

of 40 CFR Part 50 (EPA, 

2015c).

Figure 3-a Historical and 2016 Precision Results for 

Atmospheric Concentrations and Laboratory Replicate 

Samples

0

5

10

15

20

25

30

Sulfur

Dioxide

Sulfate

Nitric Acid

Nitrate

Ammonium

Calcium

Potassium

Magnesium

Sodium

Chloride

MARPD

Overall - 1990 through 2015

Mackville, KY - 2016

Rocky Mtn, CO - 2016

Laboratory Replicates - 2016

Figure 3-b Historical and 2016 Percent Completeness of 

Measurements (black bars are 1990–2015 for long-term data and 

2013–2015 for trace-level gas data)

65 70 75 80 85 90 95 100

Atmospheric Concentrations

Meteorological Parameters

Filter Pack Flow

CO

NOYDIF

NO

NOY

SO2

Ozone

Percent Completeness

Historical (1990-2015)

2016

Continuous

Parameters

40 CFR Part 50 Requirement DQI Measurement Criterion

SO2

NOy

NOyDIF

O3
CASTNET 2016 Annual Report

20 Chapter 3: Nitrogen Pollutant Concentrations

Figure 3-4 Annual Mean NH+ 

4 Concentrations for 2016

Figure 3-5 Trends in Annual Mean NH+ 

4 Concentrations

Western Reference Sites Eastern Reference Sites
21 Chapter 4: Update on the Ammonia Monitoring Network

Chapter 4

Update on the Ammonia Monitoring Network

The Ammonia Monitoring Network (AMoN) operates passive ammonia samplers at 103 locations, 69 of which are 

located at CASTNET sites. AMoN is managed by the National Atmospheric Deposition Program. The network has 

been in operation since 2007 and provides information on 2-week integrated ammonia concentrations. Like other 

NADP networks, the goal of AMoN is to operate a long-term (i.e., for several decades), spatially diverse network with 

consistent measurements, covering all sensitive ecoregions of the continental United States.

Reduced nitrogen [ammonia (NH 

3) + NH+ 4 ] is an important component to total nitrogen deposition. Wet 

deposition of NH+ 

4 measured by NTN has been increasing in many areas of the United States over the 

past 10 years; however, until 2007, gaseous NH 

3 concentrations were not routinely measured. 

Ammonia is the most prevalent alkaline gas in the atmosphere and is released into the air from a 

variety of agricultural sources (animal waste, fertilizer application, and agricultural burning), biological 

sources, gas and oil production and processing, and combustion. Agriculture is by far the largest 

source, producing approximately 80 percent of gaseous NH 

3 emissions (EPA National Emissions 

Inventory, 2014). Although NH 

3 is beneficial when used as NH 3-based fertilizer, it can have a negative 

effect on the environment when it reacts with acidic ions such as SO2-

4 and NO3 to form PM2.5, which 

contributes to negative impacts on human health and visibility degradation. Atmospheric deposition of 

reduced nitrogen also contributes to eutrophication of sensitive ecosystems, decreases in species 

diversity, and increases in invasive species.

Average annual NH 

3 concentrations for 2016 for the sites that met completeness requirements are 

mapped in Figure 4-1 and show a wide range of concentrations from a low of 0.2 μg/m3 in New 

Hampshire (NH02) to a high of 15.9 μg/m3 in northern Utah (UT01). The Utah monitoring site is 

located on a Utah State University research farm and small quantities of livestock are often present 

(Martin and Baasandorj, 2016). The farm is situated in the Cache Valley, an area with frequent 

stagnant weather. The next highest concentrations ranged from 3.4 to 4.3 μg/m3 at eight sites west of 

the Mississippi River. The highest concentration east of the Mississippi was observed at Cranberry, 

NC (NC02) with a measured concentration of 5.2 μg/m3 . High NH 

3 concentrations can be attributed to 

local emissions from hog and cattle feeding and waste and crop fertilization and production. 
CASTNET 2016 Annual Report

22 Chapter 4: Update on the Ammonia Monitoring Network

Figure 4-1 Annual Mean NH 

3 Concentrations at AMoN sites for 2016
23 Chapter 5: Sulfur Pollutant Concentrations

Chapter 5

Sulfur Pollutant Concentrations

During 2016, weekly average concentrations of sulfur dioxide and particulate sulfate were measured using 3-stage 

filter packs at 95 CASTNET monitoring stations. Maps of 2016 annual mean concentrations show the geographic 

distribution of the two pollutants across the United States. Annual sulfur dioxide and sulfate concentrations were 

aggregated over 34 eastern and 16 western reference sites in order to estimate trends, which are depicted using box 

plots. The sulfur dioxide pollutants measured at the eastern reference sites declined by 86 percent over the 27-year 

period from 1990 through 2016. Particulate sulfate concentrations were reduced by 70 percent. Measured 

concentrations of sulfur dioxide and sulfate have decreased steadily since 2005. Sulfur dioxide and sulfate 

concentrations measured at the 16 western reference sites have decreased by 46 and 31 percent, respectively, over 

the 21-year period 1996 through 2016.

Annual mean concentrations of SO 

2 and SO2-4 for 2016 are presented in this chapter. Additional maps 

of 2016 quarterly mean concentrations are provided in CASTNET quarterly data reports (Wood, 

2016a; 2016b; 2017a; 2017b). Trends in annual mean concentrations over the 27-year period, 1990 

through 2016, were derived from measurements from the 34 CASTNET eastern reference sites and 

for the 21-year period, 1996 through 2016, from data measured at the 16 CASTNET western 

reference sites. See Appendix A for descriptions of the designated reference sites.

Sulfur Dioxide Concentrations

Annual mean SO 

2 concentrations are shown in Figure 5-1 for 2016. Annual mean concentrations were 

highest in the Midwest and East near and downwind of the Ohio River. Box plots of annual mean SO 

2

concentrations aggregated over the 34 eastern reference sites from 1990 through 2016 (right side) 

and the 16 western reference sites from 1996 through 2016 (left side) are depicted in Figure 5-2. The 

y-axes on the western and eastern plots have different scales because concentrations measured at 

the western CASTNET sites were much lower than those measured at the eastern sites. Three-year 

mean concentrations for the CASTNET eastern reference sites for 1990–1992 and 2014–2016 were 

8.8 μg/m3 and 1.2 μg/m3 , respectively. This change constitutes an 86 percent reduction in 3-year 

mean SO 

2 concentrations between the two periods. The 2016 mean level of 0.8 μg/m3 was the lowest 

concentration measured by the eastern reference sites in the history of the network and represents a 

significant decline from the 2005 mean concentration of 6.0 μg/m3 

.

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

2 concentrations 

aggregated over the 16 sites. Three-year mean SO 

2 concentrations for 1996–1998 and 2014–2016 

were 0.6 μg/m3 and 0.3 μg/m3 , respectively. This change constitutes a 46 percent reduction in 3-year 

mean SO 

2 concentrations at the CASTNET western reference sites over the 21 years.
CASTNET 2016 Annual Report

24 Chapter 5: Sulfur Pollutant Concentrations

Figure 5-1 Annual Mean SO 

2 Concentrations for 2016

Figure 5-2 Trends in Annual Mean SO 

2 Concentrations

Western Reference Sites Eastern Reference Sites

The 2016 average sulfur dioxide concentration for the eastern reference sites was 0.8 μg/m3 . The eastern 

sulfur dioxide data show a substantive decline since 1997. The reduction (86 percent) in sulfur dioxide 

concentrations over the period 1990 through 2016 is consistent with the reduction (94 percent) in sulfur 

dioxide emissions from EGUs operating in the eastern United States.
CASTNET 2016 Annual Report

25 Chapter 5: Sulfur Pollutant Concentrations

Figure 5-3 Trend in Annual Composite SO 

2 Emissions from Regulated EGUs Operating in the 

Eastern United States

Source: EPA (2017)

Figure 5-3 illustrates the trend in SO 

2 emissions from regulated EGUs from 1990 through 2016 

aggregated over the eastern United States. The 27-year decline in aggregated emissions was 

94 percent, which is consistent with the 86 percent reduction (Figure 5-2) in annual mean SO 

2

concentrations aggregated over the CASTNET eastern reference sites.

Particulate Sulfate Concentrations

Figure 5-4 shows a map of 2016 annual mean particulate SO2-

4 concentrations. Figure 5-5 provides 

box plots of annual mean SO2-

4 concentrations from the 34 eastern reference sites (right side) and 16 

western reference sites. The figure shows a substantial decline in SO2-

4 over the 27 years for the 

eastern CASTNET reference sites. Of particular interest, concentrations declined rapidly from 2005 

through 2016. The difference between 3-year means from 1990–1992 to 2014–2016 depicts a 70 

percent reduction in SO2-

4 from 5.4 μg/m3 to 1.6 μg/m3 . The 2016 mean SO2-4 level of 1.2 μg/m3 for the 

eastern reference sites 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 5-5. The data show a 31 percent reduction in 

annual mean SO2-

4 concentrations aggregated over the 16 sites with 1996–1998 and 2014–2016 

concentrations of 0.8 μg/m3 

 and 0.5 μg/m3 , respectively.

0

2000

4000

6000

8000

10000

12000

14000

1990 1995 2000 2005 2010 2015 2016

Thousand Short Tons
CASTNET 2016 Annual Report

26 Chapter 5: Sulfur Pollutant Concentrations

Figure 5-4 Annual Mean SO2-

4 Concentrations for 2016

Figure 5-5 Trends in Annual Mean SO2-

4 Concentrations

Western Reference Sites Eastern Reference Sites

The 2016 average sulfate concentration for the eastern reference sites was 1.2 μg/m3 , the lowest level in the 

history of the network. The eastern sulfate data show a substantive decline since 2005. Sulfate 

concentrations declined more slowly than sulfur dioxide concentrations at the eastern reference sites. 

Western sulfate concentrations were lower and decreased at a slower rate than concentrations measured at 

the eastern sites.
27 Chapter 6: Continuous Trace-level Gas Concentrations

Chapter 6

Continuous Trace-level Gas Concentrations

Trace-level, gaseous, air quality monitors were operated continuously at eight CASTNET sites during 2016. EPA 

operated six monitors and NPS operated two. The measurements at these sites were performed to (1) provide data for 

regional model input and evaluation, (2) generate data to elucidate atmospheric processes such as ozone and fine 

particulate matter formation, and (3) support EPA NCore monitoring. Total reactive oxides of nitrogen were measured 

at all eight sites, sulfur dioxide at four sites, and carbon monoxide at two sites. Total reactive oxides of nitrogen 

concentrations were highest at the suburban Beltsville, MD site and lowest at the high-elevation, mountainous sites.

Trace-level gas analyzers were deployed at six EPA and two NPS CASTNET sites during 2016. Other 

federal, tribal, and state agencies also measured NO/NOy at CASTNET or nearby sites in Maine, 

North Dakota, Oklahoma, and South Dakota. Table 6-1 lists the site locations, start dates, and the 

trace-level gas parameters measured at each CASTNET site. These data were sampled continuously 

and archived as 1-hour values.

Table 6-1 Continuous, Trace-level Gas Monitoring Stations Operated at CASTNET Sites 

during 2016

Site Location Start Dates Measurements

Beltsville, MD (BEL116) March 2005 NO/NOy and SO 

2

Mammoth Cave National Park, KY (MAC426)* May 2009 NO/NOy, SO 

2, and CO

Bondville, IL (BVL130) July 2012 NO/NOy, SO 

2, and CO

Huntington Wildlife Forest, NY (HWF187) November 2012 NO/NOy

Pinedale, WY (PND165) May 2013 NO/NOy

Cranberry, NC (PNF126) October 2013 NO/NOy

Rocky Mountain National Park, CO (ROM206) October 2013 NO/NOy

Great Smoky Mountains National Park (GRS420)* November 2014 NO/NOy and SO 

2

Note: *Operated by NPS

NOy is defined as NOx [NO + nitrogen dioxide (NO 

2)] plus NOz [HNO 3, nitrous acid (HONO), 

peroxyacetyl nitrate, peroxyproyl nitrate, other organic nitrates, and nitrite]. It consists of reactive 

gases that are considered precursors of O 

3 and PM2.5. Measurement of NOy begins with conversion to 

NO using a thermal catalytic converter and measurement of the NO by chemiluminescence. 

Continuous SO 

2 is measured using ultraviolet fluorescence, and CO is measured by gas filter 

correlation. 
CASTNET 2016 Annual Report

28 Chapter 6: Continuous Trace-level Gas Concentrations

Figure 6-1 provides a map of the CASTNET continuous trace-level gas monitoring locations. All EPA 

sites were operated according to the CASTNET QAPP Appendix 11, “Procuring, Installing, and 

Operating NCore Air Monitoring Equipment at CASTNET Sites” (Wood, 2015). NPS sites were 

operated according to the NPS QAPP (Air Resource Specialists, 2015). 

Figure 6-1 CASTNET NOy Monitoring Network in 2016

Figures 6-2 through 6-4 and Figure 6-6 present 2016 annual average hourly composite diurnal profiles 

of SO 

2, NOy, and O 3 for BEL116, BVL130, MAC426, and GRS420, respectively. Figures 6-5 and 6-7 

through 6-9 show the 2016 annual average hourly composite diurnal profiles of NOy and O 

3 for 

HWF187, PNF126, PND165, and ROM206. The profiles in Figures 6-2 through 6-9 were constructed 

by averaging all values from the same hour for 2016. Sulfur dioxide and NOy are plotted against the 

left y-axis, and O 

3 is plotted against the right y-axis in the eight diagrams. The figures illustrate that 

differences in geography, terrain, and elevation affect concentrations of photochemically reactive 

pollutants in the boundary layer.
CASTNET 2016 Annual Report

29 Chapter 6: Continuous Trace-level Gas Concentrations

Figure 6-2 BEL116, MD 1-hour Mean Figure 6-3 BVL130, IL 1-hour Mean

Concentrations of SO 

2, NOy, Concentrations of SO 2, NOy, 

and O 

3 for 2016 and O 3 for 2016

Figure 6-4 MAC426, KY 1-hour Mean Figure 6-5 HWF187, NY 1-hour Mean

Concentrations of SO 

2, NOy, Concentrations of NOy

and O 

3 for 2016 and O 3 for 2016

0

10

20

30

40

50

60

0

2

4

6

8

10

12

14

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 - Ozone (ppb)

Concentration - SO2/NOy (ppb)

Hour

SO2

NOY

Ozone

0

10

20

30

40

50

60

0

1

2

3

4

5

6

7

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 - Ozone (ppb)

Concentration - SO2/NOy (ppb)

Hour

SO2

NOY

Ozone

0

10

20

30

40

50

60

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

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 - Ozone (ppb)

Concentration - SO2/NOy (ppb)

Hour

SO2

NOY

Ozone

0

10

20

30

40

50

60

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

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 - Ozone (ppb)

Concentration - NOy (ppb)

Hour

NOY

Ozone

SO 

2

NOy

Ozone

SO 

2

NOy

Ozone

NOy

Ozone

SO 

2

NOy

Ozone
CASTNET 2016 Annual Report

30 Chapter 6: Continuous Trace-level Gas Concentrations

Figure 6-6 GRS420, TN 1-hour Mean Figure 6-7 PNF126, NC 1-hour Mean

Concentrations of SO 

2, NOy, Concentrations of NOy

and O 

3 for 2016 and O 3 for 2016

Figure 6-8 PND165, WY 1-hour Mean Figure 6-9 ROM206, CO 1-hour Mean

Concentrations of NOy Concentrations of NOy

and O 

3 for 2016 and O 3 for 2016

0

10

20

30

40

50

60

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

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 - Ozone (ppb)

Concentration - SO2/NOy (ppb)

Hour

SO2

NOY

Ozone

0

10

20

30

40

50

60

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

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 - Ozone (ppb)

Concentration - NOy (ppb)

Hour

NOY

Ozone

0

10

20

30

40

50

60

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

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 - Ozone (ppb)

Concentration - NOy (ppb)

Hour

NOY

Ozone

0

10

20

30

40

50

60

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

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 - Ozone (ppb)

Concentration - NOy (ppb)

Hour

NOY

Ozone

NOy

Ozone

NOy

Ozone

NOy

Ozone

SO 

2

NOy

Ozone
CASTNET 2016 Annual Report

31 Chapter 6: Continuous Trace-level Gas Concentrations

Table 6-2 Summary of 2016 Minimum and Maximum Values from Diurnal Charts

Site Location

Site Elevation 

(meters)

NOy (ppb) O 

3 (ppb)

Minimum Maximum Minimum Maximum

BEL116, MD 47 4.4 12.0 15 42

BVL130, IL 213 2.5 5.0 20 40

MAC426, KY 243 2.3 3.5 24 41

HWF187, NY 497 0.7 1.0 19 34

GRS420, TN 793 1.3 1.7 36 45

PNF126, NC 1,216 1.0 1.2 38 44

PND165, WY 2,386 0.6 0.8 42 47

ROM206, CO 2,742 0.8 1.5 44 50

Continuous Trace-level NOy and Ozone

The minimum and maximum mean composite NOy and O 

3 concentrations shown in Figures 6-2 

through 6-9 are summarized in Table 6-2. The sites are listed in order of elevation. The highest NOy

concentrations were measured at BEL116, which is situated in an area with numerous mobile-source 

NOx emissions. Low NOy values (less than 2.0 ppb) were recorded at the five rural sites in New York, 

Tennessee, North Carolina, Wyoming, and Colorado. The eight profiles in Figures 6-2 through 6-9 

illustrate the loss of O 

3 during the late afternoon and nighttime hours and its production during daylight 

hours. The diurnal change was less pronounced at the six rural sites. The BEL116 site observed the 

largest nighttime loss and subsequent highest daytime production, an average difference of about 27 

ppb of O 

3 for 2016. The BVL130 data illustrate a typical diurnal relationship between NOy and O 3

concentrations with high NOy concentrations associated with vehicular NOx emissions in the morning 

and evening and elevated O 

3 concentrations in the afternoon. The data from the rural MAC426 site 

also show a diurnal evolution with the highest NOy concentrations in the morning and the evening and 

highest O 

3 concentrations in the afternoon. The MAC426 data appear similar to measurements made 

at an urban site.

Ozone concentrations were also measured at the eight sites listed in Table 6-2 during 2016. The 

highest O 

3 concentration (50 ppb) was recorded at ROM206. The concentrations measured at the four 

sites with the highest elevations show less 24-hour variation than the other four sites because of the 

dearth of nighttime O 

3 loss/depletion mechanisms near the high-elevation monitors (Talbot et al., 

2005). In particular, nighttime dry deposition is small because fresh nitric oxide is not available to 

react with O 

3 and sparse vegetation produces little scavenging. The ROM206 data suggest a 

production or transport of NOy around sunset. There are no significant NOx sources in the immediate 

area. The increase in NOy is likely a result of the transformation of polluted air masses from the Front 

Range Urban Corridor and the frequent late afternoon upslope flow from the east (Baumann et al., 

1997).
CASTNET 2016 Annual Report

32 Chapter 6: Continuous Trace-level Gas Concentrations

Continuous Trace-level NOy and Filter Pack Total Nitrate Concentrations

Nitric acid and particulate NO3 are measured on CASTNET filter packs, and the sum is reported as 

total NO3. Because HNO 

3 and particulate NO3 are measured as components of NOy, NOy

concentrations should always be higher than total NO3 levels (i.e., the ratio of NOy to total NO3 should 

always be greater than 1.0). A comparison of weekly mean continuous NOy concentrations with filter 

pack total NO3 levels at BVL130, PNF126, and PND165 for 2016 was used to evaluate the 

measurements (Figures 6-10 through 6-12). The NOy concentrations were consistently higher than 

the total NO3 levels, as expected. The results are similar for the other five sites. The weekly total NO3

concentrations, the average weekly NOy levels, and their ratios are listed in Table 6-3. These were 

calculated as the average of all valid weekly filter pack concentrations, the average of mean NOy

values matching the run time of the weekly filter packs, and the average of the ratios calculated for 

each week. Weekly NOy levels were higher than the weekly total NO3 concentrations with ratios of 

NOy to total NO3 varying from 2.46 at PNF126 to 10.87 at BEL116. The highest concentration 

(0.98 ppb) of total NO3 was measured at BVL130.

Huntington Wildlife Forest, NY (HWF187)
CASTNET 2016 Annual Report

33 Chapter 6: Continuous Trace-level Gas Concentrations

Figure 6-10 Comparison of BVL130, IL Weekly Mean Continuous Trace-level NOy and Filter 

Pack Total NO3 Concentrations

Figure 6-11 Comparison of PNF126, NC Weekly Mean Continuous Trace-level NOy and Filter 

Pack Total NO3 Concentrations

0.0

2.0

4.0

6.0

8.0

10.0

12.0

12/27/15

1/10/161/24/16

2/7/16

2/21/16

3/6/16

3/20/16

4/3/16

4/17/16

5/1/16

5/15/165/29/166/12/166/26/167/10/167/24/16

8/7/16

8/21/16

9/4/16

9/18/1610/2/16

10/16/1610/30/1611/13/1611/27/1612/11/16

Concentration (ppb)

Filter Pack Total NO3

Mean Trace NOy

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

12/27/15

1/10/161/24/16

2/7/16

2/21/16

3/6/16

3/20/16

4/3/16

4/24/16

5/8/16

5/22/16

6/5/16

6/19/16

7/3/16

7/17/167/31/168/14/168/28/169/11/169/25/1610/9/16

10/23/16

11/6/16

11/20/16

12/4/16

Concentration (ppb)

Filter Pack Total NO3

Mean Trace NOy

Filter Pack Total NO3

Mean Continuous NOy

Filter Pack Total NO3

Mean Continuous NOy
CASTNET 2016 Annual Report

34 Chapter 6: Continuous Trace-level Gas Concentrations

Figure 6-12 Comparison of PND165, WY Weekly Mean Continuous Trace-level NOy and Filter 

Pack Total NO3 Concentrations

Table 6-3 Summary of Total NO3 and NOy Measurements for 2016

Site Location Total NO3 (ppb) NOy (ppb) Ratio

BEL116, MD 0.76 8.01 10.87

BVL130, IL 0.98 4.39 5.03

MAC426, KY 0.70 2.79 4.30

HWF187, NY 0.21 0.94 3.58

GRS420, TN 0.45 1.97 4.93

PNF126, NC 0.33 0.81 2.46

PND165, WY 0.14 0.75 5.27

ROM206, CO 0.20 1.20 5.86

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

12/27/15

1/10/161/24/16

2/7/16

2/28/163/13/163/27/164/10/164/24/16

5/8/16

5/22/16

6/5/16

6/19/16

7/3/16

7/17/167/31/168/14/168/28/169/11/169/25/1610/9/16

10/23/16

11/6/16

11/20/16

12/5/16

Concentration (ppb)

Filter Pack Total NO3

Mean Trace NOy

Filter Pack Total NO3

Mean Continuous NOy
35 Chapter 7: Effects of Wildfires on Air Quality

Chapter 7

Effects of Wildfires on Air Quality

Wildfires produce large amounts of smoke, fine particulate matter, nitrogen oxides, and other trace-level gases. In 

particular, in the western United States, wildfires and prescribed agricultural and forest management burns are large 

sources of aerosols and trace gases. The 2016 western wildfire season was extensive, especially following the winter 

of 2015–2016 drought. The Maple Fire at the western edge of Yellowstone National Park burned over 45,000 acres in 

August 2016. Fine particulate matter concentrations measured at IMPROVE sites in and near the park showed 

elevated concentrations. The Jack Fire in Arizona started on May 29, 2016 and continued to burn until July 1. During 

that period, it burned 33,850 acres in the Coconino National Forest, which is located about 24 kilometers south of 

Flagstaff.

Wildfires occur naturally in the United States. In the West, wildfires and prescribed agricultural and 

forest management burns are a large global source of aerosols and trace-level gases from burning 

vegetation, buildings, and other materials. Smoke from wildfires is a significant source of air pollution 

and can pose potential risks to health, visibility, and safety. According to Liu et al. (2016), open fires 

contributed significantly (about 37 percent) to PM2.5 emitted in the contiguous United States and 

produced substantial amounts of O 

3 precursors. Wildfires usually consume more biomass fuel per unit 

area burned than prescribed fires. Land use changes, wildfire management strategies, and climate 

change have increased wildfire size and frequency and the length of the fire season in the western 

United States. The 2016 western wildfire season was extensive in both area burned and length of the 

season, especially following the drought during the winter of 2015–2016.

Liu et al. (2016) analyzed aircraft air pollutant measurements in three plumes from wildfires in the 

western United States in 2013. The study reported an extensive set of emission factors for about 80 

gases and five components of submicron particulate matter (PM1) from these wildfires. The measured 

emission factors were used to estimate the annual wildfire emissions of CO, NOx, total non-methane 

organic compounds, and PM1 from 11 western states. The wildfires emitted high amounts of PM1 with 

organic aerosol dominating the mass. The results from Liu et al. (2016) indicate that PM1 emissions 

from wildfires are substantially higher than those from prescribed burns and that prescribed burning 

may be an effective method to reduce overall fine particle emissions.

Measurements from CASTNET, IMPROVE, the EPA Chemical Speciation Network (CSN), and other 

federal and state networks provide information to characterize the impacts of wildfires on air quality 

and visibility near critical resources such as national parks. In 2016, fires extended from the northern 

tier states to Arizona, New Mexico, and Texas. Figure 7-1 gives box plots of third quarter mean O 

3

measurements aggregated over the CASTNET western reference sites (Appendix A). The O 

3 box 

plots were constructed by averaging all valid hourly O 

3 concentrations within third quarter by site and 
CASTNET 2016 Annual Report

36 Chapter 7: Effects of Wildfires on Air Quality

then averaging those averages for all western reference sites. The figure shows increased 

aggregated mean concentrations for 2016.

Figure 7-1 Trends in Third Quarter Mean O 

3 Concentrations at CASTNET Western Reference 

Sites

During the 2016 fire season, 22 fires burned in Yellowstone National Park, WY (YEL408). The park is 

required to protect human life as well as the approximately 2 percent of Yellowstone’s 2.2 million 

acres that are considered developed (e.g., roads, buildings, and other infrastructure) from the threat of 

fire, while at the same time letting fire play its ecological role in the landscape as much as possible. 

2016 was the most active fire year since 1988 with 62,000 acres burned. Seven wildfires were the 

result of human activity such as a campfire, vehicle operation, or cigarettes. The remainder of the 

2016 wildfires resulted from natural causes (i.e., lightning). Eleven fires were suppressed because 

infrastructure was threatened. Many fires were managed to allow them to perform their natural role in 

the ecosystem. The largest of these fires, the Maple Fire, burned over 45,000 acres. 

Figure 7-2 is a photograph of the Maple Fire in Wyoming, August 21, 2016, taken by the Visible 

Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the National Oceanic and Atmospheric 

Administration (NOAA)/National Aeronautics and Space Administration (NASA) Suomi National Polarorbiting Partnership satellite. The Maple Fire was detected the evening of August 8, 2016 by an 

aircraft passing over Yellowstone. The fire was located 6 kilometers (km) east of the park’s west 

boundary, 8 km northeast of the community of West Yellowstone, MT, and 4.5 km from Madison 

Junction. Rain accompanied by cool weather at the end of August slowed the spread of the Maple 

Fire that had come within 5 km of West Yellowstone. 
CASTNET 2016 Annual Report

37 Chapter 7: Effects of Wildfires on Air Quality

Figure 7-2 Satellite Photo of Wyoming Maple Fire August 21, 2016

Source: NOAA Environmental Visualization Laboratory/NASA (2016)

Hourly and DM8A O 

3 concentrations measured at three Wyoming CASTNET sites [Basin (BAS601), 

Pinedale (PND165), and YEL408] over the period of August 11, 2016 through September 6, 2016 are 

plotted in Figure 7-3. Time series of PM2.5 concentrations measured over the period July 8, 2016 

through October 6, 2016 at IMPROVE sites in Wyoming [Boulder Lake (BOLA1), Bridger Wilderness 

(BRID1), North Absaroka (NOAB1), and Yellowstone (YELL2)] are shown in Figure 7-4. 

Comparatively high PM2.5 concentrations were measured at YELL2 and NOAB1 after the fire started. 

For example, PM2.5 concentrations were 2.92 times higher at NOAB1 and 2.59 times higher at YELL2 

during the period of the Maple Fire than they were during the remainder of July through August. 

Concentrations were reduced by the end of the month.

Lightning started the Jack Fire in Arizona on May 29, 2016, and it continued to burn until July 1. 

During that period, it burned 33,850 acres in the Coconino National Forest, which is located about 24 

km south of Flagstaff, 113 km south-southeast of the CASTNET site at Grand Canyon National Park 

(GRC474), and 145 km west of the CASTNET site at Petrified National Forest (PET427). Figure 7-5

shows smoke from the Jack Fire streaming eastward. Weekly average O 

3 concentrations shown in 

Figure 7-6 for three CASTNET sites in Arizona [GRC474, PET427, and Chiricahua National 

Monument (CHA467)] and one in Colorado [Mesa Verde National Park (MEV405)] showed no 

significant change after the beginning of the Jack Fire. Time series of PM2.5 concentrations measured 

over the period April 30, 2016 through July 29, 2016 at nearby IMPROVE sites Grand Canyon 

(GRCA2), Petrified National Forest (PEFO1), Chiricahua (CHIR1), and Mesa Verde National Park 
CASTNET 2016 Annual Report

38 Chapter 7: Effects of Wildfires on Air Quality

(MEVE1) are shown in Figure 7-7. Fine particulate matter concentrations measured at PEFO1 and 

CHIR1 were elevated during the fire except for relative minima for two samples on June 14 and June 

17, 2016. Synoptic weather data (NOAA National Centers for Environmental Prediction, 2018) 

suggest the wind direction shifted southeast during those two sampling periods, transporting the fire 

plume away from the samplers at PEFO1 and CHIR1. PM2.5 concentrations were 1.5 times higher at 

CHIR1 and 2.25 times higher at PEFO1 during the period of the Jack Fire than during the remainder 

of April through July.

Figure 7-3 Time Series of Wyoming CASTNET O 

3 Data

Figure 7-4 Time Series of Wyoming IMPROVE PM2.5 Data

Note: Corresponding CASTNET site with the location of the IMPROVE site in relation to the CASTNET site listed in parentheses.

0

10

20

30

40

50

60

70

80

8/11/168/13/168/15/168/17/168/19/168/21/168/23/168/25/168/27/168/29/168/31/16

9/2/169/4/169/6/16

Concentration (ppb)

BAS601 PND165 YEL408

BAS601-DM8A PND165-DM8A YEL408-DM8A

0

2

4

6

8

10

12

14

16

18

7/8/16

7/14/167/20/167/26/16

8/1/168/7/16

8/13/168/19/168/25/168/31/16

9/6/16

9/12/169/18/169/24/169/30/1610/6/16

Concentration (μg/m3)

BOLA1 (14 km S of PND165) BRID1 (11 km S of PND165)

NOAB1 (btwn YEL408 and BAS601) YELL2 (YEL408)
CASTNET 2016 Annual Report

39 Chapter 7: Effects of Wildfires on Air Quality

Figure 7-5 Satellite photo of Arizona Jack Fire June 9, 2016

Source: NASA (2016), LANCE/EOSDIS MODIS Rapid Response Team, GSFC
CASTNET 2016 Annual Report

40 Chapter 7: Effects of Wildfires on Air Quality

Figure 7-6 Time Series of CASTNET O 

3 Data for Sites in Arizona (PET427 GRC474, CHA467) 

and Colorado (MEV405)

Figure 7-7 Time Series of IMPROVE PM2.5 Data for Sites in Arizona (PEF01, GRCA2, CHIR1) 

and Colorado (MEVE1)

Note: IMPROVE sites are approximately co-located with the corresponding CASTNET site listed in parentheses.

0

10

20

30

40

50

60

70

80

5/29/165/31/16

6/2/166/4/166/6/166/8/16

6/10/166/12/166/14/166/16/166/18/166/20/166/22/166/24/16

6/26/166/28/166/30/16

7/2/16

Concentration (ppb)

CHA467 GRC474 MEV405 PET427

CHA467-DM8A GRC474-DM8A MEV405-DM8A PET427-DM8A

0

2

4

6

8

10

12

4/30/16

5/6/16

5/12/165/18/165/24/165/30/16

6/5/16

6/11/166/17/166/23/166/29/16

7/5/16

7/11/167/17/167/23/167/29/16

Concentration (μg/m3)

CHIR1 (CHA467) GRCA2 (GRC474)

MEVE1 (MEV405) PEFO1 (PET427)
41 Chapter 8: Atmospheric Deposition of Nitrogen

Chapter 8

Atmospheric Deposition of Nitrogen

CASTNET was designed to provide estimates of the dry deposition of nitrogen and sulfur pollutants across the United 

States. To assess the status of dry and total deposition for 2016, EPA used NADP’s Total Deposition Science 

Committee Hybrid Method. The hybrid method combines measured pollutant concentrations with output from the 

CMAQ modeling system. Total deposition was calculated as the sum of estimated dry and wet deposition.

Gaseous and particulate nitrogen pollutants are deposited to the environment through dry and wet 

atmospheric processes. A primary goal of CASTNET is to estimate the dry deposition of pollutants 

from the atmosphere to sensitive ecosystems. The NADP Total Deposition Science Committee 

(TDep) Hybrid Method (EPA, 2015d; Schwede and Lear, 2014) combines CASTNET monitoring data 

with output from the CMAQ modeling system (Byun and Schere, 2006) to estimate dry deposition. 

The TDep method gives priority to using measurement data from air quality monitoring sites when 

available and to CMAQ output in areas where monitoring data are not available. In addition, CMAQ 

provides modeled data for species that are not routinely measured. The TDep method and its recent 

updates are discussed on the TDep web page (http://nadp.slh.wisc.edu/committees/tdep/). See also 

the NADP Fact Sheet, “Hybrid Approach to Mapping Total Deposition,” 

(http://nadp.slh.wisc.edu/lib/brochures/tdepsheet.pdf).

The TDep method estimates wet deposition using PRISM to develop a continuous grid of precipitation 

data. PRISM uses terrain elevation, slope, and aspect and climatic measurements to estimate 

precipitation. Pollutant concentrations in precipitation, which were estimated for the PRISM grid, were 

provided by NADP/NTN. The concentration and precipitation grids were merged in order to estimate 

pollutant wet deposition rates. Dry and wet deposition fluxes were added to obtain estimates of 

total deposition, which are presented on the maps in this chapter as kilograms per hectare per year 

(kg ha-1

 yr-1 ).

Figure 8-1 illustrates TDep method estimates of dry fluxes of nitrogen (N) for 2016. The magnitude of 

the deposition fluxes is illustrated by the shading in the figure legend. A map of total deposition of N 

for 2016 is given in Figure 8-2. The percentage of total deposition of N due to dry deposition is shown 

in Figure 8-3. A map of TDep method estimates of total deposition of reduced N species for 2016 is 

given in Figure 8-4. Figure 8-5 gives the percentage of reduced N species from dry deposition. Dry 

deposition of N species that are not routinely measured but are estimated by the TDep method is 

shown in the map in Figure 8-6. The percentage of total deposition of N that is not measured directly 

but is calculated by the TDep method is shown in Figure 8-7. Annual gross dry deposition of NH 

3 for 

2016 is shown in Figure 8-8, and the net dry deposition of NH 

3 is given in Figure 8-9.
CASTNET 2016 Annual Report

42 Chapter 8: Atmospheric Deposition of Nitrogen

Figure 8-1 TDep Dry Deposition Estimates of N (kg ha-1

 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN

Figure 8-2 TDep Total Deposition Estimates of N (kg ha-1

 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN
CASTNET 2016 Annual Report

43 Chapter 8: Atmospheric Deposition of Nitrogen

Figure 8-3 TDep Percent of Total Deposition of N from Dry Deposition for 2016

Source: CASTNET|CMAQ|NADP/NTN

Figure 8-4 TDep Total Deposition Estimates of Reduced N Species (kg ha-1

 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN
CASTNET 2016 Annual Report

44 Chapter 8: Atmospheric Deposition of Nitrogen

Figure 8-5 TDep Percent of Total Deposition of Reduced N Species from Dry Deposition 

for 2016

Source: CASTNET|CMAQ|NADP/NTN

Figure 8-6 TDep Dry Deposition Estimates of Unmonitored N Species (kg ha-1

 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN
CASTNET 2016 Annual Report

45 Chapter 8: Atmospheric Deposition of Nitrogen

Figure 8-7 TDep Percent of Total Deposition of N from Dry Deposition of Unmonitored Species 

for 2016

Source: CASTNET|CMAQ|NADP/NTN

Figure 8-8 TDep Gross Dry Deposition of NH 

3 as N (kg ha-1 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN
CASTNET 2016 Annual Report

46 Chapter 8: Atmospheric Deposition of Nitrogen

Figure 8-9 TDep Net Dry Deposition of NH 

3 as N (kg ha-1 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN
47 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Chapter 9

Monitoring on Whiteface Mountain during 2015 and 2016

Continuous, trace-level, gaseous air quality monitors and filter pack samplers were run at two CASTNET sites on 

Whiteface Mountain during 2015 and 2016. The measurements at these sites were performed to (1) analyze 

differences in air quality resulting from variance in elevation and exposure and to (2) provide data to understand 

atmospheric processes such as ozone formation.

Whiteface Mountain in the Adirondack Mountains in upstate New York has been the site of many 

research studies over the decades and has a long history of atmospheric chemistry measurements. A 

CASTNET small footprint filter pack site (WFM105) was installed near an NTN precipitation collector 

in 2012. This location is also known as the Marble Mountain Lodge site and sits on the eastern 

shoulder of the Whiteface massif at an elevation of 604 meters. A seasonal CASTNET small footprint 

site, WFM007, was installed at the Summit Observatory location in 2015 and usually operates from 

May or June through September or October, as conditions allow. The Summit Observatory is at the 

peak of the mountain at 1,483 meters. Continuous O 

3, NO 2, NO, and SO 2 have been measured at 

both locations since the late 1980s. The continuous data used in this chapter were provided by the 

Atmospheric Sciences Research Center (ASRC) of the State University of New York and the New 

York State Energy Research and Development Authority (NYSERDA).

Weekly filter pack concentrations of SO2-

4 , SO 2, NO3, NH+ 4 , HNO3, and Ca2+ from WFM105 and WFM007, 

the lodge and summit sites, respectively, were compared for 2015 and 2016 during the warm season 

from the onset of sampling at the summit location in the spring until the site was closed for the season 

in the fall. Additionally, continuous SO 

2 and filter pack SO 2 data from both locations were analyzed 

during the period of operation for the summit location. Continuous O 

3, NO, and NO 2 data, which are 

available year-round from both sites, were compared for 2015 and 2016 (ASRC, 2017).

Figures 9-1 and 9-2 depict seasonal average filter pack concentrations of SO2-

4 , SO 2, NO3, NH+ 4 , HNO3, 

and Ca2+

 for 2015 and 2016 at both WFM105 and WFM007. Sulfate, SO 2, and NH+ 4 seasonal 

concentrations were higher at WFM105 than WFM007 for both years, with the 2015 concentrations 

being higher than the 2016 concentrations. The WFM007 summit site had higher concentrations of 

NO3, HNO3, and Ca2+

 than WFM105 in 2015. Comparisons were similar in 2016 with the exception

that HNO3 concentrations were higher at WFM105. 

Concentrations were higher in 2015 than 2016 at WFM105 with the exceptions of HNO3 and Ca2+

 ,

which had similar concentrations (0.5 μg/m3 versus 0.512 μg/m3 for HNO3 and 0.119 μg/m3 

versus

0.12 μg/m3 for Ca2+

 ) for both years. The 2015 concentrations were greater than 2016 concentrations 

at WFM007 for all analytes.
CASTNET 2016 Annual Report

48 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Figure 9-1 Warm Season Filter Pack Concentrations for WFM105 and WFM007 for 2015

Figure 9-2 Warm Season Filter Pack Concentrations for WFM105 and WFM007 for 2016

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Sulfate Sulfur

Dioxide

Nitrate Ammonium Nitric Acid Calcium

Concentration (

μg/m3)

WFM105

WFM007

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Sulfate Sulfur

Dioxide

Nitrate Ammonium Nitric Acid Calcium

Concentration (

μg/m3)

WFM105

WFM007
CASTNET 2016 Annual Report

49 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Sulfur dioxide and SO2-

4 are both produced by SO 2 emissions. The ratio of SO2-4 to SO 2 is a measure of 

the age of the polluted air mass. Higher SO2-

4 concentrations relative to SO 2 levels measured at both 

sites suggest that air pollution measured at Whiteface Mountain was produced during transport from 

distant pollutant sources.

Figure 9-3 shows seasonal filter pack and continuous SO 

2 concentrations from both locations for 2015 

and 2016. The filter pack SO 

2 concentrations were higher than the continuous concentrations at both 

sites during both years. The 2015 seasonal concentrations for filter pack and continuous SO 

2 were 

higher than the 2016 seasonal concentrations. 

Figure 9-3 Warm Season Filter Pack and Continuous SO 

2 Concentrations at WFM105 and 

WFM007 for 2015 and 2016

0.00

0.05

0.10

0.15

0.20

0.25

0.30

WFM105 WFM007 WFM105 WFM007

Concentration (

μg/m3)

Continuous Sulfur Dioxide

FP Sulfur Dioxide

2015 2016
CASTNET 2016 Annual Report

50 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Quarterly averages of O 

3 for both years and both sites are presented in Figure 9-4. WFM007 generally 

had higher quarterly averages than WFM105 with exception of third quarter 2015. Quarterly O 

3

averages were greater in 2016 than 2015 at both sites with the exception of the first quarter for 

WFM007. Ozone values were not available for fourth quarter 2015 for WFM105.

Figure 9-4 Quarterly Average O 

3 Concentrations for WFM105 and WFM007 for 

2015 and 2016

Continuous NO and NO 

2 quarterly average concentrations for both sites for 2015 and 2016 are plotted 

in Figure 9-5. WFM105 measured higher quarterly averages of NO and NO 

2 than WFM007 for both 

years. Data were not available for fourth quarter 2015 from WFM105. 

Nitrogen dioxide concentration values for 2015 at WFM105 were greater with respect to the 2016 

values. However, the 2015 NO concentration values at WFM105 were lower than 2016 for the first 

and second quarters and equal for the third quarter. Concentrations of both analytes were greater at 

WFM007 in 2015 than 2016. 

10

15

20

25

30

35

40

45

50

1 2 3 4

ppb

WFM105 2015

WFM007 2015

WFM105 2016

WFM007 2016

Quarter
CASTNET 2016 Annual Report

51 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Figure 9-5 NO and NO 

2 Continuous Data for WFM105 and WFM007 for 2015 and 2016

Diurnal plots of O 

3, NO, and NO 2 for both locations for the 2007 and 2016 warm seasons are shown in 

Figures 9-6 through 9-9. Data from 2007 were selected to illustrate the changes in air quality over a 

10-year period. The O 

3 and NO 2 concentrations were higher at WFM007 in 2007 than at WFM105. 

While NO values were about equivalent at the two sites, WFM105 had a higher diurnal peak. There 

was no discernible diurnal pattern for O 

3 in 2007 at WFM007, but both locations showed a midday 

minimum for NO 

2 due to conversion to O 3 by daytime photochemical processes. 

Ozone values were again greater at WFM007 than WFM105 in 2016. However, the NO 

2 values were 

lower at WFM007 with respect to the WFM105 site. The NO concentrations were also lower at the 

WFM007 site. The 2016 NO 

2 concentrations at WFM105 again showed a midday peak for ozone and 

a dip for NO 

2; WFM007 showed a slight midday decline for both parameters.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

NO NO2 NO NO2 NO NO2 NO NO2

1 2 3 4

Concentration (

μg/m3)

WFM105 2015

WFM007 2015

WFM105 2016

WFM007 2016

Quarter

NO2 NO2 NO2 NO2
CASTNET 2016 Annual Report

52 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Figure 9-6 WFM105 O 

3, NO, and NO 2 Concentrations for Warm Season 2007

Figure 9-7 WFM007 O 

3, NO, and NO 2 Concentrations for Warm Season 2007

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10

15

20

25

30

35

40

45

50

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

NO, NO2 Concentrations (ppb)

O3 Concentration (ppb)

Hour of Day

WFM105 O3O3 WFM105 NONO WFM105 NO2 NO2

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10

15

20

25

30

35

40

45

50

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

NO, NO2 Concentrations (ppb)

O3 Concentration (ppb)

Hour of Day

WFM007 O3O3 WFM007 NONO WFM007 NO2 NO2
CASTNET 2016 Annual Report

53 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Figure 9-8 WFM105 O 

3, NO, NO 2 Concentrations for Warm Season 2016

Figure 9-9 WFM007 O 

3, NO, and NO 2 Concentrations for Warm Season 2016

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10

15

20

25

30

35

40

45

50

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

NO, NO2 Concentrations (ppb)

O3 Concentration (ppb)

Hour of Day

WFM105 O3O3 WFM105 NONO WFM105 NO2 NO2

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10

15

20

25

30

35

40

45

50

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

NO, NO2 Concentrations (ppb)

O3 Concentration (ppb)

Hour of Day

WFM007 O3O3 WFM007 NONO WFM007 NO2 NO2
CASTNET 2016 Annual Report

54 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

The 2016 average warm season NO and NO 

2 concentrations were higher than the 2007 warm season 

averages at WFM105, while the 2016 O 

3 average was slightly lower (37 ppb in 2007 versus 35 ppb in 

2016). This pattern was reversed at the summit, WFM007, where the 2016 warm season averages of 

all three analytes were lower than the 2007 averages.

Figures 9-10 and 9-11 show O 

3 concentrations for both Whiteface Mountain locations for 2015 and 

2016 and for the nearby, lower elevation CASTNET site at Huntington Wildlife Forest, NY (HWF187) 

to provide a more detailed analysis of the diurnal pattern for O 

3 and to illustrate the significant diurnal 

change of O 

3 at lower elevations. 

Figure 9-10 Ozone Concentrations for Warm Season 2015

10

15

20

25

30

35

40

45

50

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)

Hour of Day

WFM105 WFM007 HWF187
CASTNET 2016 Annual Report

55 Chapter 9: Monitoring on Whiteface Mountain

during 2015 and 2016

Figure 9-11 Ozone Concentrations for Warm Season 2016

Ozone levels were are highest at WFM007, the summit, and showed little diurnal variation, most likely 

due to a lack of depletion mechanisms, e.g., little vegetation to produce dry deposition and no fresh 

NO to scavenge O 

3. WFM105 ozone values were greater than those at HWF187. A slight diurnal 

pattern was discernible at WFM105, but it was not as pronounced as the diurnal patterns seen at 

HWF187, which exhibited a diurnal change of around 20 ppb daily.

10

15

20

25

30

35

40

45

50

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)

Hour of Day

WFM105 WFM007 HWF187
56 Chapter 10: Atmospheric Deposition of Sulfur, 

Base Cations, and Chloride

Chapter 10

Atmospheric Deposition of Sulfur, Base Cations, and Chloride

CASTNET was designed to provide estimates of the dry deposition of nitrogen and sulfur pollutants, base cations, and 

chloride across the United States. EPA used the NADP TDep method to assess the status of dry and wet deposition 

for 2016. Total deposition was calculated as the sum of estimated dry and wet deposition.

Gaseous and particulate sulfur pollutants, base cations, and chloride are deposited to the 

environment through dry and wet atmospheric processes. A principal goal of CASTNET is to estimate 

the rate of dry deposition of these compounds from the atmosphere to sensitive ecosystems. The 

NADP TDep method (EPA, 2015d; Schwede and Lear, 2014) was used to estimate dry and wet 

deposition. Dry and wet deposition rates were summed to obtain total deposition across the United 

States.

Sulfur Deposition

Figure 10-1 shows a map of TDep method estimates of dry deposition rates of sulfur (S) for 2016. 

Estimated rates of total deposition of sulfur for 2016 are given in Figure 10-2. The magnitude of the 

deposition fluxes is illustrated by the shading in the figure legends. The percentage of total deposition 

of S due to dry deposition is shown in Figure 10-3.

Deposition of Base Cations and Chloride

A map of 2016 estimated total deposition of base cations (Ca2+

 , K+ , Mg2+ , and Na+ ) is given in 

Figure 10-4. Figure 10-5 provides estimated rates for 2016 for total deposition of Cl-

.

Scenic View from PNF126, NC
CASTNET 2016 Annual Report

57 Chapter 10: Atmospheric Deposition of Sulfur, 

Base Cations, and Chloride

Figure 10-1 TDep Dry Deposition Estimates of S (kg ha-1

 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN

Figure 10-2 TDep Total Deposition Estimates of S (kg ha-1

 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN
CASTNET 2016 Annual Report

58 Chapter 10: Atmospheric Deposition of Sulfur, 

Base Cations, and Chloride

Figure 10-3 TDep Percent of Total Deposition of S from Dry Deposition for 2016

Source: CASTNET|CMAQ|NADP/NTN

Figure 10-4 TDep Total Deposition Estimates of the Base Cations Ca2+

 , K+ , Mg2+ , Na+  

(kiloequivalents per hectare per year) for 2016

Source: CASTNET|CMAQ|NADP/NTN
CASTNET 2016 Annual Report

59 Chapter 10: Atmospheric Deposition of Sulfur, 

Base Cations, and Chloride

Figure 10-5 TDep Total Deposition Estimates of Total Cl-(kg ha-1

 yr-1 ) for 2016

Source: CASTNET|CMAQ|NADP/NTN
60 Chapter 11: Critical Loads for Open and Closed

Canopy Herbaceous Ecosystems

Chapter 11

Critical Loads for Open and Closed Canopy Herbaceous Ecosystems

Critical loads were estimated for biodiverse open and closed canopy herbaceous ecosystems based on TDep

estimates of wet and dry deposition of nitrogen across the United States. Three-year averages for 2013–2015 were 

compared for the open and closed ecosystems. Open canopy systems had more extensive critical load exceedance 

rates than the closed systems. The analysis suggests that, for the majority of regions where data were available, the 

loss of herbaceous biodiversity due to air pollutant deposition is unlikely. However, areas in Minnesota and North 

Carolina are likely experiencing loss of herbaceous biodiversity because of elevated levels of nitrogen deposition.

Critical loads describe the threshold at which a natural system is impacted by deposition of nitrogen 

(N) and/or sulfur (S) air pollutants. Critical loads provide tools that allow the evaluation of the 

sensitivity and the potential impact of air pollution on terrestrial and aquatic ecosystems. This chapter 

focuses on critical loads for herbaceous biodiversity and their potential exceedances. A critical load 

exceedance is the case when deposition is greater than the critical load (e.g., total deposition of N > 

critical load). Critical load exceedances indicate (1) a risk of negative impacts to natural resources as 

a result of air pollutant deposition, (2) whether pollutant deposition might be impacting natural 

systems, and (3) where impacts to the landscape might be occurring. For ecosystems impacted by 

deposition of pollutants, changes in critical load exceedances provide information to indicate if 

deposition has improved enough to allow ecosystem recovery, to judge the effectiveness of emission 

reduction policies and strategies, and to inform land management decisions.

The critical loads for herbaceous biodiversity were determined by Simkin et al. (2016) and were based 

on total deposition of N (wet and dry). The critical loads describe the level of deposition of N above 

which decreases in herbaceous plant species richness (i.e., total number of unique species per plot of 

land) were observed. They are expressed in terms of kg ha-1

 yr-1 of N deposition. The analysis by 

Simkin et al. (2016) used a nationwide statistical analysis of 15,136 forest, woodland, shrubland, and 

grassland sites assembled from 12 distinct data sets.

The critical loads from Simkin et al. (2016) were calculated separately for open canopy and closed 

canopy systems based on Level 1 of the U. S. National Vegetation Classification (USNVC, 2016). A 

total of 11,819 plots were located in closed canopy systems while 3,317 were in open canopy 

systems. An open system includes grasslands, shrublands, and woodlands. A closed system includes

those herbaceous species growing in the forest understories. This distinction was made because 

reduced sunlight limits the growth, reproduction, and other biological factors that in turn reduce the 

richness of the herbaceous community growing in the understory of forests (Neufeld and Young, 

2014). 
CASTNET 2016 Annual Report

61 Chapter 11: Critical Loads for Open and Closed

Canopy Herbaceous Ecosystems

Critical loads were derived statistically using multiple regression models relating the species richness 

of a plot to environmental factors that included deposition of N, temperature, precipitation, soil pH, and 

others. A critical load was then estimated using a two-step process whereby the partial derivative of 

the best statistical model was selected, which yielded an equation for the critical load based on 

temperature, precipitation, and soil pH. Using that equation, the critical load was calculated at a given 

plot using local environmental data.

Critical load exceedances were evaluated using total N deposition values derived from TDep

simulations (Chapter 8). A three-year average from 2013–2015 was compared to each plot for 

both open and closed systems. The range of the critical loads for closed canopy forest was 7.3 to 19.6 

kg ha-1

 yr-1 of N deposition, while open canopy environments were lower with a range of 7.4 to 9.0 

kg ha-1

 yr-1 of N deposition (Figure 11-1). Open canopy sites are designated as triangles while closed 

canopy systems are noted as circles. Figure 11-2 shows the spatial extent of critical load 

exceedances where data were available. Green triangles/circles show sites where the critical load 

was not exceeded while red triangles/circles indicate deposition greater than the critical load. Yellow 

triangles/circles show the sites where deposition of N was within 1 kg ha-1

 yr-1 of the critical load. The 

open canopy systems had a higher exceedance rate (red triangles) of 22.7 percent than the closed 

canopy systems of 1.6 percent (red circles). The regions with the higher exceedances are in 

Minnesota and North Carolina. There were also many examples where deposition was near (i.e., 

within 1 kg ha-1

 yr-1 ) the critical load (yellow circles/triangles) for closed and open systems. Sites that 

did not exceed the critical load were far more common. Open canopy sites did not exceed their critical 

load 69 percent of the time (green triangles) while forested systems did not exceed their critical load 

at 94 percent of the sites (green circles). This analysis suggests that, for the majority of regions where 

data were available, the loss of herbaceous biodiversity due to air pollution is unlikely. However, areas 

in Minnesota and North Carolina are likely experiencing loss of herbaceous biodiversity because of 

the deposition of elevated levels of N to these systems.
CASTNET 2016 Annual Report

62 Chapter 11: Critical Loads for Open and Closed

Canopy Herbaceous Ecosystems

Figure 11-1 Critical Loads of Nitrogen Deposition for Herbaceous Biodiverse Ecosystems 

Determined by Simkin et al. (2016)
CASTNET 2016 Annual Report

63 Chapter 11: Critical Loads for Open and Closed

Canopy Herbaceous Ecosystems

Figure 11-2 Critical Loads Exceedance for Herbaceous Biodiverse Ecosystems from TDep

Deposition Estimates
64 References

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CASTNET 2016 Annual Report

Appendix A

Appendix A

Locational and Operational Characteristics of CASTNET Sites
CASTNET 2016 Annual Report

A-1 Appendix A

Table A-1 Locational and Operational Characteristics of CASTNET Sites (1 of 3)

Site ID Site Name Start date Latitude Longitude Elevation

Nearby

NADP

Land 

Use Terrain Agency Reference

ABT147, CT Abington 12/28/1993 41.8405 -72.0104 202 CT15 Urban/A

gric

Rolling EPA

ACA416, ME Acadia NP 12/1/1998 44.3771 -68.2608 158 ME98 Forest Rolling NPS

ALC188, TX AlabamaCoushatta4/6/2004 30.7016 -94.674 105 TX10 Prairie Rolling EPA

ALH157, IL Alhambra 6/28/1988 38.869 -89.6228 164 IL46 Agric Flat EPA E

ANA115, MI Ann Arbor 6/28/1988 42.4166 -83.9022 266 MI52 Forest Flat EPA E

ARE128, PA Arendtsville 6/28/1988 39.9232 -77.3079 266 PA00 Agric Rolling EPA E

ASH135, ME Ashland 12/20/1988 46.6038 -68.4132 231 ME00 Agric Flat EPA E

BAS601, WY Basin 11/6/2012 44.28 -108.0411 1242 MT00 Prairie Rolling BLM

BBE401, TX Big Bend NP 7/18/1995 29.3027 -103.1778 1052 TX04 Forest Complex NPS W

BEL116, MD Beltsville 11/1/1988 39.0282 -76.8171 47 MD99 Range Flat EPA E

BFT142, NC Beaufort 12/28/1993 34.8847 -76.6207 5 NC06 Agric Flat EPA

BUF603, WY Buffalo 11/6/2012 44.1442 -106.1089 1324 WY99 Prairie Rolling BLM

BVL130, IL Bondville 2/9/1988 40.052 -88.3725 213 IL11 Agric Flat EPA E

BWR139, MD Blackwater NWR 7/4/1995 38.445 -76.1113 1 MD15 Forest/

Marsh

Coastal EPA

CAD150, AR Caddo Valley 10/4/1988 34.1793 -93.0988 78 AR03 Forest Complex EPA E

CAN407, UT Canyonlands NP 1/24/1995 38.4583 -109.8213 1809 UT09 Desert Complex NPS W

CAT175, NY Claryville 5/10/1994 41.9423 -74.552 754 NY68 Forest Complex EPA

CDR119, WV Cedar Creek 11/10/1987 38.8795 -80.8477 240 WV05 Forest Complex EPA E

CDZ171, KY Cadiz 1/5/1999 36.7841 -87.8502 190 KY99 Agric Rolling EPA

CHA467, AZ Chiricahua NM 4/25/1989 32.0094 -109.3891 1570 AZ98 Range Complex NPS W

CHE185, OK Cherokee Nation 4/2/2002 35.7508 -94.6698 305 AR27 Agric Rolling EPA

CKT136, KY Crockett 8/24/1993 37.9215 -83.0663 376 KY35 Agric Rolling EPA

CND125, NC Candor 9/25/1990 35.2633 -79.8375 172 NC36 Forest Rolling EPA E

CNT169, WY Centennial 5/9/1989 41.3645 -106.24 3175 WY95 Forest Complex EPA W

COW005, NC Coweeta 

Screwdriver 

Knob

11/18/2014 35.0469 -83.4531 960 NC25 Forest Complex EPA

COW137, NC Coweeta 11/4/1987 35.0605 -83.4303 683 NC25 Forest Complex EPA E

CTH110, NY Connecticut Hill 9/29/1987 42.4009 -76.6535 511 NY67 Forest Rolling EPA E

CVL151, MS Coffeeville 12/27/1988 34.0027 -89.7992 138 MS30 Forest Rolling EPA

DCP114, OH Deer Creek 9/28/1988 39.6359 -83.2606 264 OH54 Agric Rolling EPA E

DEN417, AK Denali NP 10/6/1998 63.7232 -148.9676 661 AK03 Forest Complex NPS

DIN431, UT Dinosaur NM 11/20/2013 40.4373 -109.3046 1463 CO15 Desert Complex NPS

EGB181, ON Egbert 12/27/1994 44.2311 -79.7831 227 NY10 Agric Rolling EPA

ESP127, TN Edgar Evins 3/22/1988 36.0389 -85.7331 302 KY10 Forest Rolling EPA E

EVE419, FL Everglades NP 10/6/1998 25.3912 -80.6808 2 FL11 Forest/

Marsh

Flat NPS

FOR605, WY Fortification 

Creek

5/21/2013 44.3395 -105.9198 1408 WY99 Prairie Rolling BLM

GAS153, GA Georgia Station 6/28/1988 33.1812 -84.4101 265 GA41 Agric Rolling EPA E

GLR468, MT Glacier NP 12/27/1988 48.5103 -113.9968 976 MT05 Forest Complex NPS W

GRB411, NV Great Basin NP 5/16/1995 39.0051 -114.2159 2060 NV05 Forest Complex NPS W

GRC474, AZ Grand Canyon 

NP

5/16/1989 36.0586 -112.1836 2073 AZ03 Forest Rolling NPS W

GRS420, TN Great Smoky 

NP- Look Rock

10/16/1998 35.6335 -83.9416 793 TN11 Forest Complex NPS
CASTNET 2016 Annual Report

A-2 Appendix A

Table A-1 Locational and Operational Characteristics of CASTNET Sites (2 of 3)

Site ID Site Name Start date Latitude Longitude Elevation

Nearby 

NADP

Land 

Use Terrain Agency Reference

GTH161, CO Gothic 5/16/1989 38.9563 -106.9859 2915 CO10 Range Complex EPA W

HOW191, ME Howland 

Ameriflux

9/27/2011 45.204 -68.74 68 ME09 Forest Rolling EPA

HOX148, MI Hoxeyville 10/31/2000 44.1809 -85.739 297 MI53 Forest Flat EPA

HWF187, NY Huntington 

Wildlife Forest

5/28/2002 43.973 -74.2233 497 NY20 Forest Complex EPA

IRL141, FL Indian River 

Lagoon

7/9/2001 27.8492 -80.4556 2 FL99 Coastal/

Marsh

Flat/

Water

EPA

JOT403, CA Joshua Tree NP 2/16/1995 34.0696 -116.3889 1244 CA67 Desert Complex NPS W

KEF112, PA Kane 

Experimental 

Forest

1/3/1989 41.5981 -78.7679 618 PA29 Forest Rolling EPA E

KIC003, KS Kickapoo Tribe 2/18/2014 39.8539 -95.6578 367 KS97 Prairie Rolling EPA

KNZ184, KS Konza Prairie 3/26/2002 39.1022 -96.6096 346 KS31 Prairie Flat EPA

LAV410, CA Lassen Volcanic 

NP

7/25/1995 40.54 -121.5765 1756 CA96 Forest Complex NPS W

LRL117, PA Laurel Hill 12/15/1987 39.9883 -79.2516 609 PA83 Forest Complex EPA E

MAC426, KY Mammoth Cave 

NP

7/24/2002 37.1314 -86.1481 243 KY10 Agric Rolling NPS

MCK131, KY Mackville 7/31/1990 37.7047 -85.0487 293 KY03 Agric Rolling EPA E

MCK231, KY Mackville 

Co-located

12/29/1992 37.7047 -85.0487 293 KY03 Agric Rolling EPA

MEV405, CO Mesa Verde NP 1/10/1995 37.1984 -108.4905 2165 CO99 Forest Complex NPS W

MKG113, PA M.K. Goddard 1/12/1988 41.4268 -80.1452 377 NY10 Forest Rolling EPA E

NEC602, WY Newcastle 11/7/2012 43.873 -104.1919 1468 WY99 Prairie Rolling BLM

NIC001, NY Nicks Lake 11/20/2012 43.6805 -74.9891 525 NY29 Forest Rolling NYSDEC

NPT006, ID Nez Perce Tribe 12/15/2015 46.2756 -116.0216 945 Forest Rolling EPA

OXF122, OH Oxford 8/18/1987 39.5311 -84.7235 284 OH09 Agric Rolling EPA E

PAL190, TX Palo Duro SP 4/24/2007 34.8806 -101.6647 1053 TX02 Prairie Complex EPA

PAR107, WV Parsons 1/19/1988 39.0904 -79.6617 510 WV18 Forest Complex EPA E

PED108, VA Prince Edward 11/3/1987 37.1652 -78.3071 149 VA24 Forest Rolling EPA E

PET427, AZ Petrified Forest 9/12/2002 34.8225 -109.8925 1723 AZ97 Desert Flat NPS

PIN414, CA Pinnacles NM 5/16/1995 36.4832 -121.1569 335 CA66 Forest Complex NPS W

PND165, WY Pinedale 12/27/1988 42.929 -109.7878 2386 WY06 Forest Rolling EPA W

PNF126, NC Cranberry 12/27/1988 36.1054 -82.045 1216 NC45 Forest MountaintopEPA E

PRK134, WI Perkinstown 9/27/1988 45.2065 -90.5972 462 WI35 Agric Rolling EPA E

PSU106, PA Penn State 1/6/1987 40.7209 -77.9318 364 PA42 Agric Rolling EPA E

QAK172, OH Quaker City 1/5/1999 39.9427 -81.3379 371 OH49 Agric Rolling EPA

RED004, MN Red Lake Nation 8/26/2014 47.8638 -94.8352 372 MN16 Forest Flat EPA

ROM206, CO Rocky Mountain 

NP Co-located

7/3/2001 40.2781 -105.5456 2742 CO19 Forest Complex EPA

ROM406, CO Rocky Mountain 

NP

12/20/1994 40.2781 -105.5456 2743 CO19 Forest Complex NPS W

SAL133, IN Salamonie 

Reservoir

6/28/1988 40.816 -85.6614 250 IN20 Agric Flat EPA E

SAN189, NE Santee Sioux 7/5/2006 42.8292 -97.8541 434 SD99 Range Rolling EPA

SEK430, CA Sequoia & Kings 

Canyon NP - Ash

Mountain

4/7/2005 36.4895 -118.8292 510 CA75 Forest MountaintopNPS
CASTNET 2016 Annual Report

A-3 Appendix A

Table A-1 Locational and Operational Characteristics of CASTNET Sites (3 of 3)

Site ID Site Name Start date Latitude Longitude Elevation

Nearby 

NADP

Land 

Use Terrain Agency Reference

SHE604, WY Sheridan 11/6/2012 44.93 -106.85 1115 MT00 Prairie Rolling BLM

SHN418, VA Shenandoah NP 

- Big Meadows

6/28/1988 38.5231 -78.4347 1073 VA28 Forest MountaintopNPS E

SND152, AL Sand Mountain 12/27/1988 34.289 -85.9701 349 AL99 Agric Rolling EPA E

SPD111, TN Speedwell 6/12/1989 36.4698 -83.8265 361 TN04 Agric Rolling EPA E

STK138, IL Stockton 12/28/1993 42.2872 -90 281 IL18 Agric Rolling EPA

SUM156, FL Sumatra 12/27/1988 30.1102 -84.9904 16 FL23 Forest Flat EPA E

THR422, ND Theodore 

Roosevelt NP

10/6/1998 46.8948 -103.3777 850 ND00 Forest Rolling NPS

UND002, VT Underhill 11/13/2012 44.5283 -72.8688 399 VT99 Forest Complex EPA

UVL124, MI Unionville 6/28/1988 43.6136 -83.3599 202 MI51 Agric Flat EPA E

VIN140, IN Vincennes 8/4/1987 38.7408 -87.4849 136 IN22 Agric Rolling EPA E

VOY413, MN Voyageurs NP 6/13/1996 48.4125 -92.8292 429 MN32 Forest Rolling NPS

VPI120, VA Horton Station 6/2/1987 37.3298 -80.5575 920 VA13 Agric MountaintopEPA E

WFM007, NY Whiteface 

Mountain Summit

6/4/2015 44.36608 -73.90312 1415 NY98 Forest Complex EPA

WFM105, NY Whiteface 

Mountain

11/20/2012 44.39 -73.86 570 NY98 Forest Complex NYSDEC

WNC429, SD Wind Cave NP 11/20/2003 43.5576 -103.4839 1292 SD04 Prairie Rolling NPS

WSP144, NJ Washington

Crossing

12/27/1988 40.3123 -74.8727 59 NJ99 Range Rolling EPA E

WST109, NH Woodstock 12/27/1988 43.9445 -71.7008 255 NH02 Forest Complex EPA E

YEL408, WY Yellowstone NP 6/26/1996 44.5654 -110.4003 2400 WY08 Agric Rolling NPS W

YOS404, CA Yosemite NP -

Turtleback Dome

9/25/1995 37.7133 -119.7062 1605 CA99 Forest Complex NPS W

Note: NM = National Monument

NP = National Park

NWR = National Wildlife Reserve

SP = State Park

E = eastern reference site

W = western reference site
CASTNET 2016 Annual Report

Appendix B

Appendix B

Acronyms and Abbreviations
CASTNET 2016 Annual Report

B-1 Appendix B

List of Acronyms and Abbreviations

A2LA American Association for Laboratory Accreditation

AMNet Atmospheric Mercury Network

AMoN Ammonia Monitoring Network 

AQS EPA’s Air Quality System

ARP Acid Rain Program

ASRC Atmospheric Sciences Research Center

BLM Bureau of Land Management

BOLA1 IMPROVE site at Boulder Lake, WY

BRID1 IMPROVE site at Bridger Wilderness, WY

Ca2+ particulate calcium 

CAPMoN Canadian Air and Precipitation Monitoring Network

CASTNET Clean Air Status and Trends Network

CFR Code of Federal Regulations

CHIR1 IMPROVE site at Chiricahua National Monument, AZ

Cl- particulate chloride 

CMAQ Community Multiscale Air Quality Modeling System

CO carbon monoxide

CSN Chemical Speciation Network

DM8A daily maximum 8-hour average

DQI data quality indicator

ECAN Environment Canada

EGUs electric generating units

EPA U. S. Environmental Protection Agency

GRCA2 IMPROVE site at Grand Canyon National Park

HNO 

3 nitric acid

HONO nitrous acid

IEC International Electrotechnical Commission

IMPROVE Interagency Monitoring of Protected Visual Environments

ISO International Organization for Standardization

K+ particulate potassium

kg ha-1 yr-1 kilograms per hectare per year

km kilometer

m meter

MARPD mean absolute relative percent difference

MDN Mercury Deposition Network

MEVE1 IMPROVE site at Mesa Verde National Park

Mg2+

 particulate magnesium 

N nitrogen

Na+ particulate sodium 
CASTNET 2016 Annual Report

B-2 Appendix B

List of Acronyms and Abbreviations (continued)

NAAQS National Ambient Air Quality Standards

NADP National Atmospheric Deposition Program

NASA National Aeronautics and Space Administration

NCore EPA’s National Core Monitoring

NH 

3 ammonia

NH +

4 particulate ammonium

NM National Monument

NO nitrogen oxide

NO 

2 nitrogen dioxide

NO -

3 particulate nitrate 

NOx nitrogen oxides (NO + NO 

2)

NOy total reactive oxides of nitrogen

NOz HNO 

3, nitrous oxide, peroxyacetyl nitrate, peroxyproyl nitrate, other organic 

nitrates, and nitrite

NOAA National Oceanic and Atmospheric Administration

NOAB1 IMPROVE site at North Absaroka, WY

NPS National Park Service

NTN National Trends Network

NYSDEC New York State Department of Environmental Conservation

NYSERDA New York State Energy Research and Development Authority

O 

3 ozone

PEFO1 IMPROVE site at Petrified Forest National Park, AZ

PM1 submicron particulate matter

PM2.5 fine particulate matter

ppb parts per billion

ppm parts per million

PRISM Parameter-elevation Regressions on Independent Slopes Model

PT proficiency testing

QA quality assurance

QAPP Quality Assurance Project Plan

S sulfur

SO 

2 sulfur dioxide

SO2-

4 particulate sulfate

TDEP NADP Total Deposition Science Committee

total NO3 gaseous HNO 

3 + particulate NO3

μg/m3 micrograms per cubic meter

UDAQ Utah Department of Air Quality

USNVC United States National Vegetation Classification

VIIRS Visible Infrared Imaging Radiometer Suite
CASTNET 2016 Annual Report

B-3 Appendix B

List of Acronyms and Abbreviations (continued)

VOC volatile organic compounds

WARMS Wyoming Air Resources Monitoring System

YELL2 IMPROVE site at Yellowstone National Park