# T he NO x 

### Budget Trading Program (NBP) was a mar

ket-based cap and trade program created to reduce the regional transport of emissions of nitrogen ox

ides (NO x 

### ) from power plants and other large combustion
sources that contribute to ozone nonattainment in the east

ern United States. NO x 

### is a major precursor to the formation of ground-level ozone, a pervasive air pollution problem in many areas in the eastern United States. The NBP was de

signed to reduce NO x 

### emissions during the warm summer months, referred to as the ozone season, when ground-lev

el ozone concentrations are highest. In 2009, the NBP was replaced by the Clean Air Interstate Rule (CAIR) NO x 

### ozone season program, which started requiring emission reduc

tions from affected sources in an expanded geographic area on May 1, 2009.

Throughout the summer, the U.S. EPA is releasing a series of reports summarizing progress under the NBP. This is the third report in the series and it contains 2008 data on environmental results as well as analyses of the effects of
reduced NO x 

### emissions on ozone and nitrate levels.

For more information on the NBP, visit: < www.epa.gov/ airmarkets/progsregs/nox/sip.html >. Detailed emission results and other facility and allowance data are also publicly available on EPA’s Data and Maps Web site at

< camddataandmaps.epa.gov/gdm >. To view emission and other facility information in an interactive format using Google Earth or a similar three-dimensional platform, go to

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



# The NBP and Ozone

EPA has developed more than a dozen programs to reduce

NO x 

### and volatile organic compounds (VOCs) from mobile, industrial, and power sector sources since 1990. Between 1999 and 2002, states in the Northeast reduced NO x 

### emis

sions from electric generating units (EGUs) and industrial boilers through the OTC NO x 

### Budget Program. In addition, mobile source programs such as the Tier 2 Vehicle and Gasoline Sulfur Program, the Clean Air Diesel Trucks and 

# At a Glance: NBP Results in 2008

**Ozone:** Ground-level ozone has decreased since imple

mentation of the NBP in 2003

• Analyses of ozone trends using various metrics show

regionwide ozone reductions ranging from 10-14 percent in the NBP region

• There is a strong association between areas with the

greatest reductions in NO x 

### emissions and downwind sites exhibiting the greatest improvements in ozone

**Nonattainment Areas:** Based on 2006-2008 air monitor

ing data, ozone air quality improved in almost all of the 104 areas in the eastern U.S. designated to be in nonat

tainment for the 1997 8-hour National Ambient Air Qual

ity Standards (NAAQS)

• 88 areas (85 percent) now have ozone air quality that

is better than the level of the 1997 standard

• 13 areas continue to exceed the standard but have

experienced an average of 10 percent improvement

in ozone

• In total, over 103 million Americans in the East are

living with cleaner air

**Human Health Benefits:** NO x 

### reductions due to the NBP have led to improvements in ozone and PM 2.5 

### , saving an estimated 580-1,800 lives in 2008

**Ecosystem Protection:** Changes in ozone and nitrate con

centrations due to the NBP have contributed to improve

ments in ecosystems in the East

• Decrease in areas with significant ozone damage to

seven ozone-sensitive tree species

• 33 percent reduction in total nitrate concentrations



### Buses Program (also known as the Heavy-Duty Highway Diesel Program), the Clean Air Nonroad Diesel program,
and the recently finalized Locomotive and Marine Vessel Compression-Engine Standards have started to reduce NO x 

### emissions from a variety of mobile source categories and will continue to do so into the future. These programs com



# The NO x 

# Budget Trading Program: 2008 Environmental Results

September 2009

### plement state and local efforts to improve ozone air quality
and meet national standards.

While these programs, particularly the mobile source pro

grams, have achieved dramatic decreases in NO x 

### emissions in recent years, the majority of NO x 

### reductions since 2003 were achieved under the NBP. Accordingly, the NBP is the

most significant contributor to the improvements in ozone concentrations in the East.

To better understand how the NBP affected ozone formation in the atmosphere, this report examines changes in ozone concentrations before and after implementation of the NBP in the eastern United States. The report compares regional and geographic trends in ozone levels to changes in meteoro

logical conditions (such as temperature) and NO x 

### emissions from NBP sources. This report also explores changes in hu

man health and forest ecosystems due to ground-level ozone effects as well as changes in nitrate concentration.



# Measuring and Evaluating Changes in Ozone

Two long-term monitoring networks measure ozone lev

els as well as meteorological and other air quality data throughout the United States. Monitoring sites used for regulatory compliance are located mainly in urban areas and report data to EPA’s Air Quality System (AQS). Sites in EPA’s Clean Air Status and Trends Network (CASTNET) measure trends in ozone at rural sites. The changes in eastern ozone concentrations presented in this report de

pict data from AQS and CASTNET monitoring sites located within both NBP and adjacent states. These analyses show a range of ozone reductions based on the metric used and the years examined.



### Metrics for Assessing Ozone Concentrations

Two types of metrics are used to evaluate trends in ozone levels in this report. Both metrics indicate that ozone has decreased since implementation of the NBP. The two met

rics are:

• Meteorologically-adjusted daily maximum 8-hour ozone

concentrations: This metric is the maximum 8-hour rolling average for each day. It shows progress toward meeting the primary (health-based) ozone National Ambient Air Quality Standards (NAAQS). The seasonal average indicates general changes in daily maximum8-hour concentrations in the NBP region. The threeyear average of the fourth highest daily maximum 8-hour ozone concentration is used to designate non

attainment status in the United States. The Clean Air Status and Trends Network (CASTNET) is a long-term monitoring network designed to assess trends in regional (rural) ozone levels and acidic dry deposition. Sites areequipped with an ozone analyzer and a threestage filter pack to collect total weekly gaseous (i.e., nitric acid) and particulate (i.e., nitrate) concentrations. Many of the monitoring sites have been running continuously for over 15 years, making the network ideal for long-term trends analyses. Regional trends in ozone lev

els from CASTNET sites have been used to as

sess emission reduction programs, such as the NBP and the Acid Rain Program (ARP). Figure 1 shows the 43 CASTNET sites used in this report’s analysis of trends in rural ozone and nitrate con

centrations. These sites met data completeness
criteria and are located in NBP states or within 200 kilometers (km) of an NBP state’s border.

Note: States in the NBP region are shaded.

Source: EPA, 2009 

## Figure 1: Location of CASTNET Sites 

# CASTNET

CASTNET Sites 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

2

## Figure 2: Percent Change in 1-Hour Ozone Concentrations during the Ozone Season, 2000-2002 versus 2006-2008

Note: AQS and CASTNET monitoring sites used for this analysis are shown as black dots on this map.

Source: EPA, 2009



# Changes in Rural Ozone Concentrations

Rural ozone measurements are useful in assessing the im

pacts on air quality resulting from regional NO x 

### emission reductions because these monitoring sites are typically less affected by local sources of NO x 

### (e.g., industrial, automo

tive, and power generation sources) than urban measure

ments. Consequently, the formation of ozone in these areas is particularly sensitive to changes in levels of regional NO x 

### emissions. The majority of reductions in rural ozone con

centrations can therefore be attributed to reductions in re

gional NO x 

### emissions and transported ozone.

While ozone levels vary by season and location, regional trends reveal notable drops in ambient ozone levels since the NBP began in 2003. EPA investigated trends in both roll

ing 8-hour and 1-hour ozone concentrations as measured at CASTNET monitoring sites within the NBP region and in adjacent states (states within 200 km of an NBP state’s borders). • Unadjusted 99 th 

### percentile of 1-hour and 8-hour ozone

concentrations: This metric shows changes in the highest concentrations of ozone and provides a broad picture of ozone in the eastern United States. The 99 th 

### percentile is used in this report because it is statisti

cally similar to the 4 th 

### highest daily maximum 8-hour ozone concentration—the ozone NAAQS. This metric is representative of true, measured ozone concentra

tions without meteorological adjustments.

Although they differ in the amount of ozone reduced, all of the analyses presented in this report show substantial overall improvements in the NBP region since implementa

tion of the program in 2003. These results are further sup

ported by several studies investigating the impact of NO x 

### emission reductions from NBP sources on ozone in the re

gion. 1



### Weather

Weather plays an important role in determining ozone
levels. EPA often uses a statistical model to account for the weather-related variability in seasonal ozone concen

trations to provide a trend that is more representative of changes in emissions. Averaging ozone concentrations across multi-year periods is another way to account for the
effects of weather on ozone formation. Both methods are used in the analyses that follow.



# Changes in 1-Hour Ozone Concentrations in the East

EPA examined changes in regional 1-hour ozone concen

trations, as measured at urban (AQS) and rural (CASTNET)
sites. Results demonstrate how NO x 

### emission reduction policies have affected ozone concentrations in the eastern United States. Figure 2 shows changes in the 99 th 

### percentile of 1-hour ozone concentrations between 2000–2002 (be

fore implementation of the NBP) and 2006-2008 (under the NBP). Using this metric, an overall regional reduction in ozone levels was observed between these two time peri

ods, with an average reduction in ozone concentrations in NBP states of 11 percent. 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

3

### Site-Specific Changes in Ozone

Similar trends in rural ozone concentrations were ob

served at individual CASTNET monitoring sites. As ex

pected, there was variation across the region. The largest
and most significant decreases in ozone were observed at sites downwind of the Ohio River Valley (Ohio, West Vir



## Figure 4: Percent Reduction in Rural 1-Hour Ozone during the Ozone Season, 2000-2002 versus 2006-2008

Notes:

•	 States in the NBP region are shaded.

•	 The change in ozone concentration is the percent change of the

average of the 99th percentile of 1-hour ozone concentrations between each three-year period.

•	 Ozone data are from CASTNET sites that met completeness cri

teria and are located in or adjacent to the NBP region.

Source: EPA, 2009 Percent Change in the 99th Percentile Ozone Concentration

Between -20% and -23%

Between -15% and -20%

Between -10% and -15%

Between -5% and -10%

Between -1% and -5%

Statistically Significant Reductions 

### Regional Trends in Ozone

An Autoregressive Integrated Moving Average (ARIMA)
model was used to determine the trend in ozone concen

trations since the inception of the NBP. The ARIMA model is an advanced statistical analysis tool that can evaluate trends over time (time series analysis). The average of the

99 th 

### percentile of the 8-hour daily maximum ozone con

centrations (the highest daily levels of ozone) measured at CASTNET sites during the NBP ozone season were mod

eled (Figure 3). The ARIMA model shows that between 1990 and 2003, the average of the 99 th 

### percentile of ozone concentration was 91 parts per billion (ppb). After 2004, a statistically significant shift occurred and a new trend was established, with an average ozone level of 79 ppb. The

ARIMA model shows a statistically significant, 13 percent (12 ppb) decrease in ozone concentrations beginning at the start of the NBP, suggesting that this program is a major contributor to these regional improvements in ozone.



## Figure 3: Shift in 8-Hour Seasonal Ozone Concentrations in the NBP Region, 1990-2008

70 80 90 100Ozone Concentration (ppb)

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 60

50

40

30

20

10

0 110

Actual 95% Confidence Band Model Estimate

Notes: Total ozone concentration data are from CASTNET sites that met completeness criteria and are located in and adjacent to the NBP region.

Source: EPA, 2009 

### ginia, and Pennsylvania), where NBP sources reduced NO x 

### emissions most dramatically. Figure 4 displays the average percent reduction in the 99 th 

### percentile of 1-hour ozone
concentrations at individual rural CASTNET sites between 2000–2002 and 2006–2008. Between the two time peri

ods, ozone levels fell by an average of 14 percent in the NBP region. A total of four CASTNET sites (in Connecticut, New York, Pennsylvania, and North Carolina) measured ozone reductions greater than 20 percent. The largest reduction 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

4

### in ozone (23 percent) was measured at the Abington site (ABT147) in Connecticut. Furthermore, at many sites in the NBP region, the decrease in ozone between the two

time periods was significant and statistically different.



### Changes in the Monthly Distribution of Ozone

An additional statistical analysis shows that the monthly distribution of 8-hour daily maximum ozone concentra

tions has shifted to lower concentrations. This shift has occurred in the NBP region during the ozone season since implementation of the program. Figure 5 depicts every 8-hour daily maximum value measured in January and June (where January represents months outside the ozone season and June represents months within the ozone sea

son) for two time periods. The blue lines represent ozone concentrations before implementation of the NPB (2000- 2002), while the red lines represents ozone concentrations after implementation of the NBP (2006-2008). The y-axis represents the percent of the total number of days in a
month with measurements at a specific ozone ppb level.

As the right-hand graph in Figure 5 shows, there is a no

ticeable shift toward lower ozone concentration during the ozone season (represented by the red arrow). As NO x 

### emis

sion controls were turned on at sources subject to the NBP, there have been fewer days with high levels of ozone dur

ing the ozone season. In months outside the ozone season (represented by the month of January), there is little to no
shift.

As Table 1 shows, the 99 th 

### percentile of 8-hour ozone dropped by 3-10 ppb during the ozone season, while there



## Figure 5: Monthly Distribution of 8-Hour Ozone Concentrations, 2000-2002 versus 2006-2008

Note: Ozone data are from CASTNET sites that met completeness criteria and are located in or adjacent to the NBP region.

Source: EPA, 2009 

## Outside of the Ozone Season (January) During the Ozone Season (June)

10 60 70 80Percent

0 10 20 30 40 50 60 70 80 90 0 20 50

40

30

100
Ozone (ppb) 10 60 70 80Percent

0 10 20 30 40 50 60 70 80 90 0 20 50

40

30

100
Ozone (ppb)

Ozone concentration 2006–2008 Ozone concentration 2000–2002 

## Table 1: Shift in 8-Hour Ozone Concentration by Month,
2000-2002 versus 2006-2008

Month Change i n 99th Percentile 8-Hour Ozone Concentration

January No statistically significant shift

February No statistically significant shift

March No statistically significant shift

April No statistically significant shift

May Down 3 ppb

June Down 10 ppb

July Down 9 ppb

August Down 8 ppb

September Down 8 ppb

October Down 10 ppb

November No statistically significant shift

December No statistically significant shift

Note: Month s within the ozone season are shaded.

Source: EPA, 2009



### were no significant changes in the months outside of the ozone season (except for October).

The downward shift in the monthly distribution of ozone levels in the NBP region is indicative of broader, substantial change in ozone concentrations due in significant part to the program. 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

5

### Ozone Changes after Adjusting for Meteorology

As noted earlier, weather plays an important role in deter

mining ozone levels. Accordingly, EPA uses a generalized linear model to describe the relationship between daily ozone and several meteorological parameters. 2 

### The model
also accounts for the variation in seasonal ozone across dif

ferent years by correcting for meteorological fluctuations. The most important meteorological parameters considered in this model are daily maximum 1-hour temperature and midday (10 a.m. to 4 p.m.) relative humidity. This method

ology and the subsequent ozone estimates are provided by
EPA’s Office of Air Quality Planning and Standards (OAQPS), Air Quality Assessment Division < www.epa.gov/airtrends/
weather.html >.
Figure 7 shows trends in the seasonal average 8-hour ozone concentrations in the NBP region with and without consid

ering the influence of weather. 3 

### It is important to account for meteorological variations when comparing two years with notably different weather conditions and ozone-forming potential (e.g., 2004 versus 2007). In general, lower tem

peratures in the NBP region during the 2004 ozone season dampened ozone formation, while higher temperatures in
the 2007 ozone season increased ozone formation. Remov

ing the effects of weather results in a higher-than-observed
ozone estimate for 2004 and a lower-than-observed ozone estimate for 2007. Consequently, despite weather condi



# Changes in 8-Hour Ozone Concentrations

Daily maximum 8-hour ozone concentration data were as

sessed from 52 urban AQS areas and 28 rural CASTNET sites located in the NBP region. For a monitor or area to be included in this trend analysis, it had to provide complete and valid data for 50 percent of the ozone season days for each of the years from 1997–2008. In addition, urban AQS areas often include more than one monitoring site. In these cases, the site with the highest observed ozone con

centration for each day was used. Figure 6 shows the AQS and CASTNET monitoring sites in the NBP region that met these completeness criteria.



## Figure 6: Location of Urban and Rural Ozone Monitoring Sites

Notes:



## • States in the NBP region are shaded.



## • Urban areas are represented by multiple monitoring sites. Ru

ral areas are represented by a single monitoring site. For more information on AQS, visit < www.epa.gov/ttn/airs/airsaqs >. For more information about CASTNET, visit < www.epa.gov/

CASTNET >. Source: EPA, 2009 

## Figure 7: Seasonal Average 8-Hour Ozone Concentrations in the NBP Region, 1997-2008

Note: Data presented in this figure are averages of 8-hour daily maximum ozone concentrations during the ozone season for AQS and CASTNET sites within the NBP region.

Source: EPA, 2009Ozone Concentration (ppb)

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Adjusted for Weather Unadjusted for Weather 0 10 20 30 40 50 60 70

Rural site (CASTNET)
Urban area (AQS) 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

6

### tions conducive to ozone formation in 2008, average ozone concentrations in the NBP region were lower than in 2002, before implementation of the NBP.

A closer look at the meteorologically-adjusted ozone
trends since the start of the NBP in 2003 indicates that
these reductions are substantive and sustainable. The av

erage reduction in seasonal 8-hour ozone concentrations measured in the NBP region in the 2000-2002 and 2006- 2008 time periods was about 6 percent. After considering
the influence of weather, the improvement in 8-hour ozone concentrations between these three-year periods was 11percent. A comparison of single year meteorologicallyadjusted ozone reveals a 14 percent reduction between
2002 and 2008.



## Figure 8: Reductions in Seasonal NO
x 

## Emissions from NBP Sources and Changes in 8-Hour Ozone, 2002 versus 2008

Notes:



## • F rom 1999 to 2002, states in the Northeast reduced emissions from EGUs and industrial boilers under the OTC NO

x Budget Program. OTC

states include Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Virginia.



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



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

ing unit-level emissions and controls, visit the Clean Air Market Division’s interactive mapping site at < www.epa.gov/airmarkt/progress/ interactivemapping.html >. Source: EPA, 2009 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

7

### Furthermore, the pace of these reductions has increased since implementation of the NBP. Between 1997 and 2002, ozone fell by 3 percent, while between 2002 and 2008, ozone dropped by 14 percent. On average, across the NBP region, meteorologically-adjusted ozone levels have been fairly stable since 2004, indicating that the majority of the progress made in reducing ozone levels since 2003 is be

ing maintained. This is also consistent with the downward
trend in NO x 

### emissions.


# Linking Ozone and NO x Emissions

Figure 8 on the previous page is a Google Earth snapshot depicting the relationship between reductions in NO x 

### emis

sions from NBP sources and reductions in 8-hour average ozone after implementation of the NBP. As indicated previ

ously, between 2002 and 2008, ozone decreased across all NBP states (after adjusting for meteorology) by an average of 14 percent. The largest reductions occurred in New York, Ohio, Virginia, North Carolina, and Pennsylvania.

Generally, there is a strong association between areas with the greatest NO x 

### emission reductions from NBP sources and downwind monitoring sites measuring the greatest improvements in ozone. This suggests that, as a result of the NBP, transported NO x 

### emissions have been reduced in the East, contributing to ozone reductions that have oc

curred after 2002. 4



### Changes in Ozone Nonattainment Areas

In April 2004, EPA designated 126 areas as nonattainment for the 8-hour ozone standard adopted in 1997. 5 

### These designations were made using data from 2001-2003. Of those areas, 104 are in the East (as shown in Figure 9) and are home to about 108 million people. 6 

### Based on data gath

ered from 2006-2008, 88 of these original nonattainment
areas show concentrations below the level of the 1997 ozone standard (0.08 ppm), indicating improvements in ozone. Improvements in these 88 areas mean that 85 per

cent of the original nonattainment areas in the East now have ozone air quality that is better than the standard un

der which they were originally designated nonattainment. These improvements bring cleaner air to over 57 million people. The majority of these areas have officially been re

designated to attainment or maintenance, as described in
Section 107 of the Clean Air Act.

Fifteen of the original 104 areas in the East continue to ex

ceed the level of the standard. In 13 of these areas, how

ever, ozone concentrations have fallen by an average of 10 percent. Because of these reductions in ozone, over 46 mil

lion Americans living in these areas are experiencing bet

ter air quality. Given that the majority of relevant NO x 

### emission reduc

tions occurring after 2003 are attributable to the NBP, it

is clear that the NBP is the most significant contributor to these improvements in ozone air quality.



# Human Health Benefits from NBP Implementation

Epidemiological studies 7 

### continue to show a significant link between exposure to air pollution, particularly PM 2.5 

### and ozone, and adverse health effects, including respira

tory and cardiovascular effects as well as incidences of pre

mature mortality. The analysis presented here is a screen

ing-level estimate of the annual human health benefits (the number of premature deaths avoided annually) from NO x 

### emission reductions achieved under the NBP. 

## Figure 9: Changes in Ozone Nonattainment Areas in the East, 2001-2003 (Original Designations) versus 2006-2008

Note: States in the NBP region are shown inside the black bound

ary line.

Source: EPA, 2009 Areas Improved to be below the NAAQS (88 areas)
Areas above the NAAQS that Show Improvement (13 areas)

Areas above the NAAQS that Show No Change (1 area)

Areas above the NAAQS that Are Increasing (1 area)
Areas with Incomplete NAAQS Data (1 area) 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

8

### In order to calculate the amount of NO x 

### emissions reduced as a result of NBP implementation, EPA compared NO x 

### emission levels under the program with estimates of what emissions would have been without the program. In this analysis, actual monitored NO x 

### emission data were used for most years to represent NO x 

### emissions as a result of the

program. 8 

### The amount of NO x 

### emitted from affected units in the absence of the NBP was estimated using historical,
unit-level NO x 

### rates (from 2000, where available) and year

ly measured heat input from 2003 through 2008.

EPA’s Response Surface Model (RSM) and Benefits Map

ping and Analysis Program (BenMAP) were used to esti

mate the human health benefits per ton of NO x 

### emissions
reduced for both ozone 9 

### and PM 2.5 10 

### . RSM scenarios were

run to develop “benefit per ton” estimates, specifically for

NO x 

### emission reductions in the power sector.

Figure 10 illustrates how many lives were estimated to be saved annually because of air quality improvements in
ozone and PM 2.5 

### as a result of the NBP. The results of this
health benefits assessment are influenced by the amount of

NO x 

### emissions reduced by NBP sources in a given year, the pollutant affected (ozone or PM 2.5 

### ), and the health function that relates exposure to that pollutant with incidences of premature mortality. In addition, results are presented as a range in order to capture the variation across the 8 studies used in this analysis.

This analysis shows that improvements in ozone air quality have led to fewer premature deaths annually. For example, in 2008 alone, between 130 and 600 lives were estimated
to be saved because of decreases in ozone. In addition to
these ozone benefits, improvements in PM 2.5 

### protected an additional 450 to 1,200 lives in 2008. Therefore, as a result
of reductions in NO x 

### emissions due to the NBP, total human
health benefits (for ozone and PM 2.5 

### ) range from 580 to 1,800 incidences of premature deaths avoided in 2008.


# Changes in Ozone and Nitrate Impacts on Ecosystems

Ozone Impacts on Forests

Air pollution can impact the environment and affect eco

logical systems, leading to changes in the ecological com

munity and influencing the diversity, health, and vigor of individual species. Ozone has been shown in numerous studies to have a strong effect on the health of many plants, including a variety of commercial and ecologically impor

tant forest tree species throughout the United States. 13



### When ozone is present in the air, it can enter a plant through

pores in its leaves and cause significant cellular damage. This damage can compromise the ability of the plant to pro

duce energy during photosynthesis. The remaining energy resources of the plant are then depleted as leaves attempt to repair or replace damaged tissue. This loss of energy re

sources can lead to reduced growth and/or reproduction of plants. Ozone stress also increases the susceptibility of plants to disease, insects, fungus, and other environmental stresses (e.g., harsh weather). Because ozone damage can also cause visible injury to leaves, it can reduce the aesthet

ic value of ornamental vegetation and trees, and negatively affect scenic vistas in protected natural areas.

Assessing the impact of ozone on forests in the eastern United States involves understanding the risk to tree spe

cies from ambient ozone concentrations and accounting for the prevalence of those species within the forest. As a way to quantify the risk to particular trees, scientists have developed concentration-response (C-R) functions which relate ozone exposure to tree response. Tree C-R functions are determined by exposing tree seedlings to different ozone levels and measuring reductions in growth as “bio

mass loss.” In areas where certain species dominate the forest community, the biomass loss from ozone can be sig

nificant. In this analysis, biomass loss is used as an indica

tor for the effects of ozone on the forest ecosystem.

Some of the common tree species in the eastern United States that are sensitive to ozone are black cherry ( Prunus

serotina ), yellow-poplar ( Liriodendron tulipifera ), sugar maple ( Acer saccharum ), eastern white pine ( Pinus strobus ), Virginia pine ( Pinus virginiana ), red maple ( Acer rubrum ), and quaking aspen ( Populus trenuloides ). To estimate the 

## Figure 10: Annual Incidences of Premature Mortality Avoided,
2003-2008Deaths Avoided

2 0 0 3 2 0 0 4 2 0 0 5 2 0 0 6 2 0 0 7 2 0 0 8 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0

Range of Ozone Benefits Range of PM 2.5 Benefits

Notes:



## • Ozone benefits were calculated using Ito, Schwartz, Bell 2004,

Bell 2005, Levy, and Huang. 11



## • PM 2.5 benefits were calculated using Laden and Pope. 12

Source: EPA, 2009 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

9

### biomass loss for forest ecosystems across the eastern Unit

ed States, the biomass loss for each of the seven tree spe

cies was calculated using the three-month, 12-hour W126 exposure metric 15 

### at each location, along with each tree’s individual C-R functions. The W126 exposure metric was calculated using monitored ozone data from CASTNET and AQS sites, and a three-year average was used to mitigate the effect of variations in meteorological and soil moisture conditions. The biomass loss estimate for each species was then multiplied by its prevalence in the forest community using the U.S. Department of Agriculture (USDA) Forest
Service IV index of tree abundance calculated from Forest Inventory and Analysis (FIA) measurements. 16 

### This analy

sis compared two time periods: 2000-2002 (before the NBP) and 2006-2008 (under the NBP) and demonstrates
the benefit to forest ecosystems from decreasing ozone
concentrations. Since implementation of the NBP, the number of areas with significant biomass loss 17 

### due to ozone has decreased for all seven tree species across their range in the East (see Figure 11). Of these seven species, the black cherry and yellow poplar are the most sensitive to ozone. Compar

ing data from 2000-2002 versus 2006-2008, EPA found
that the total land area in the Eastern U.S. with significant biomass loss has decreased by 5 percent for black cherry and by 4 percent for yellow poplar. In addition, areas with significant biomass loss for the remaining five species (red maple, sugar maple, quaking aspen, Virginia pine, and east

ern white pine) now make up less than 1 percent of their total range. While this change in biomass loss cannot be exclusively attributed to the implementation of the NBP, it is likely that NO x 

### emission reductions achieved under the NBP and the corresponding decreases in ozone concentra

tion contributed to this environmental improvement. Note: Sources of uncertainty include the ozone-exposure/plant-response functions, the tree abundance index, and other factors (e.g., soil moisture). Although these factors were not considered, they can affect ozone damage. 14

Source: EPA, 2009 

## Figure 11: Estimated Black Cherry, Yellow Poplar, Sugar Maple, Eastern White Pine, Virginia Pine, Red Maple, and Quaking Aspen Biomass Loss due to Ozone Exposure, 2000-2002 versus 2006-2008

Pre-NBP Implementation Average Biomass Loss, 2000-2002 Post-NBP Implementation Average Biomass Loss, 2006-2008 

## Pre-NBP Implementation Average Biomass Loss, 2000-2002 Post-NBP Implementation Average Biomass Loss, 2006-2008 Pre-NBP Implementation Average Biomass Loss, 2000-2002 Post-NBP Implementation Average Biomass Loss, 2006-2008 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

10

## Figure 12: Shift in Seasonal Nitrate Concentrations in the NBP Region, 1990-2008

Notes: Total nitrate concentration data are from CASTNET sites that met completeness criteria and are located in and adjacent to the NBP region.

Source: EPA, 2009

1.5 2.5 3.0 3.5Nitrate Concentration (μg/m3)

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2.0

1.0

0.5

0.0

Actual 95% Confidence Band Model Estimate 

### Changes In Nitrate

NO x 

### is emitted from a source as nitric oxide (NO) and ni

trogen dioxide (NO 2 

### ). Once in the air, several chemical re

actions occur, depending on meteorological conditions and concentrations of other pollutants in the atmosphere. NO x 

### contributes to the formation of many secondary pollutants, including particulate nitrate (NO 3 

### ), nitric acid (HNO 3 

### ), ozone, and organic compounds. For example, ozone is pro

duced when NO 2 

### , volatile organic compounds (VOCs), and sunlight are present.

Generally, NO x 

### is removed directly from the atmosphere by dry deposition of nitric acid and particulate nitrates, and wet deposition of dissolved nitrates. Nitrate deposition can be harmful to sensitive ecosystems, vegetation, and water bodies by causing eutrophication, changes in biological communities, and an increased sensitivity to changes in the environment. Because the majority of NO x 

### in the NBP region is removed from the atmosphere over a period of four to nine days, nitrogen deposition from transported

NO x 

### emissions may still affect areas that are considerable
distances from NO x 

### emission sources. 18



### As facilities install and use control technologies, reducing
the amount of NO x 

### emitted in the NBP region, the amount of

NO x 

### secondary pollutants also decreases. To determine the trend in total nitrate since the start of the NBP, an ARIMA model was used to assess changes in the average of median
total nitrate concentrations as measured at CASTNET sites located in the NBP region during the ozone season (Figure 12). The ARIMA model illustrates that between 1990 and 2003, total nitrate concentrations averaged about 3 μg/m 3



### . After 2004, a statistically significant shift occurred and a new trend was established with an average concentration of 2 μg/m 3 

### . Similar to the shift observed for ozone concen

trations, the ARIMA model shows a statistically significant, 33 percent (1 μg/m 3 

### ) decrease in total nitrate since the

start of the NBP, suggesting that the NBP was a significant contributor to these improvements in total nitrate.



# Endnotes

1 Gilliland, A.B., Hogrefe, C., Pinder, R.W., Godowitch, J.M., Foley, K.L., & Rao, S.T. 2008. Dynamic evaluation of regional air quality models: As

sessing changes in O 3 stemming from changes in emissions and meteorology. Atmospheric Environment . 42:20, 5110-5123.

Godowitch, J., Gilliland, A.B., Draxter, R.R., & Rao, S.T. 2008. Modeling assessment of point source NO
x emission reduction on ozone air qual

ity in the eastern United States. Atmospheric Environment . 42:1, 87-100.

Kim, S.W., Heckel, A., McKeen, S.A., Frost, G.J., Hsie, E.Y., Trainer, M.K., Richtec, A., Burrows, J.P., Peckham, S.E., & Grell, G.A. 2006. Satelliteobserved U.S. power plant NO

x emission reductions and their impact on air quality. Geophysical Research Letters

, 33, L22812.

2 Cox, W. M. & Chu, S.H. 1996. Assessment of interannual ozone variation in urban areas from a climatological perspective. Atmospheric Envi

ronment . 30:16, 2615-2625.

Camalier, L., Cox, W.M. & Dolwick, P. 2007. The effects of meteorology on ozone in urban areas and their use in assessing ozone trends. At

mospheric Environment. 41:33, 7127-7137.

3 The seasonal average ozone concentration is calculated as the average of the daily maximum 8-hour ozone levels during the ozone season.
These results provide a combined seasonal average for NBP states and do not show variations in ozone concentrations for specific urban or rural areas.

4 Gégo, E.P., P.S. Porter, A. Gilliland, & S.T. Rao. 2007. Observation-based assessment of the impact of nitrogen oxides emissions reductions on ozone air quality over the eastern United States. Journal of Applied Meteorology and Climatology , special issue on the NOAA-EPA Golden Jubilee Symposium. 46(7):994-1008.

Gégo, E., et al. 2008. Modeling analyses of the effects of changes in nitrogen oxides emissions from the electric power sector on ozone air quality in the eastern United States. Journal of the Air & Waste Management Association , 58: 580-588. 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

11Godowitch, J., A.B. Gilliland, R.R. Draxler, & S.T. Rao. 2008. Modeling assessment of point source NO
x emission reductions on ozone air quality
in the eastern United States. Atmospheric Environment , 42: 87-100.

Godowitch, J.M., C. Hogfrefe, & S.T. Rao. 2008. Diagnostic analyses of a regional air quality model: Changes in modeled processes affecting ozone and chemical-transport indicators from NO point source emission reductions. Journal of Geophysical Research , 113, D19303.

5 40 CFR Part 81. Air quality designations and classification for the 8-hour ozone national ambient air quality standards (NAAQS).

6 U.S. Census. 2000.

7 **PM 2.5**  **Mortality, All Cause**

Pope, C.A., III, Burnett, R.T., Thun, M.J., Calle, E.E., Krewski, D., Ito, K., and Thurston, G.D. 2002. Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution. JAMA 287 (9): 1132-41.

Laden, F., Schwartz, J., Speizer, F.E., and Dockery, D.W. 2006. Reduction in Fine Particulate Air Pollution and Mortality: Extended follow-up of the Harvard Six Cities Study. American Journal of Respiratory and Critical Care Medicine 173: 667-672.

**O 3**  **Mortality, Non-Accidental**

Ito, K., De Leon, S.F., and Lippmann, M. 2005. Associations between ozone and daily mortality: analysis and meta-analysis. Epidemiology 16(4): 446-57.

Schwartz, J. 2005. How sensitive is the association between ozone and daily deaths to control for temperature? American Journal of Respira

tory and Critical Care Medicine 171 (6): 627-31.

Bell, M.L., McDermott, A., Zeger, S.L., Samet, J.M., and Dominici, F. 2004. Ozone and short-term mortality in 95 US urban communities, 1987-
2000. JAMA 292(19): 2372-8.

**O 3**  **Mortality, All Cause**

Levy, J.I., Chemerynski, S.M., and Sarnat, J.A. 2005. Ozone exposure and mortality: an empiric bayes metaregression analysis. Epidemiology 16(4): 458-68.

Bell, M.L., Dominici, F., and Samet, J.M. 2005. A meta-analysis of time-series studies of ozone and mortality with comparison to the national morbidity, mortality, and air pollution study. Epidemiology 16 (4): 436-45.

**O 3**  **Mortality, Cardiopulmonary**

Huang, Y., Dominici, F., and Bell, M. L. 2005. Bayesian hierarchical distributed lag models for summer ozone exposure and cardio-respiratory mortality. Environmetrics 16: 547–562.

8 The NBP regional cap was used to represent emissions for 2007 and 2008 in order to reduce the influence of early reductions from CAIR.

9 Hubbell, B., Dolwick, P., Mooney, D., and Morara, M. 2005. Evaluating the Relative Effectiveness of Ozone Precursor Controls: Design of Com

puter Experiments Applied to the Comprehensive Air Quality Method with Extensions (CAMX). Proceedings of the Air Quality V Conference, Arlington, VA.

Abt Associates Inc. 2008. Environmental Benefits Mapping and Analysis Program (Version 3.0). Bethesda, MD. Prepared for Environmental
Protection Agency, Office of Air Quality Planning and Standards, Innovative Strategies and Economic Group. Research Triangle Park, NC.

10 Fann, N., Fulcher, C.M., and Hubbell, B.J. 2009. The influence of location, source, and emission type in estimates of the human health benefits of reducing a ton of air pollution. Air Quality, Atmosphere & Health . ISSN 1873-9318.

11 Ito et al., Schwartz, Bell et al. 2004, Bell et al. 2005, Levy et al., and Huang.

12 Laden et al. and Pope et al.

13 U.S. EPA. 2007. Review of the National Ambient Air Quality Standards for Ozone, Policy Assessment of Scientific and Technical Information. OAQPS Staff Paper. EPA-452/R-07-003. This document is available in Docket EPA-HQ-OAR-2003-0190 and online at < http://www.epa.gov/ ttn/naaqs/standards/ozone/s_o3_cr_sp.htm l>.

14 Chappelka, A.H. and Samuelson, L.J. 1998. Ambient ozone effects on forest trees of the eastern United States: A review. New Phytologist 139:
91-108.

15 The W126 exposure metric is a cumulative (not average) exposure index that is biologically based and places a greater weight on the higher hourly ozone concentrations.

16 Prasad, A.M. and Iverson, L.R. 2003. Little’s range and FIA importance value database for 135 eastern U.S. tree species. < http://www.fs.fed. us/ne/delaware/4153/global/littlefia/index.html >, Northeastern Research Station, USDA Forest Service.

17 Areas with more than 2 percent biomass loss are defined here as significant based on a consensus workshop on ozone effects, which re

ported that a 2 percent annual biomass loss causes harm because of the potential for compounding effects over multiple years as short-term negative effects on seedlings affect long-term forest health. See:

Heck, W.W. &Cowling E.B. 1997. The need for a long term cumulative secondary ozone standard

– an ecological perspective. Environmental Management , January, 23-33.

18 Seinfeld, J.H. & Pandis, S.N. 1998. Atmospheric Chemistry and Physics . John Wiley and Sons, Inc. New York. 

# The NO x 

# Budget Trading Program: 2008 Environmental Results

12