MARAMA Mid-Atlantic Regional Air

Management Association

A Guide to Mid-Atlantic

Regional Air Quality

October 2005
.
A Guide to Mid-Atlantic

Regional Air Quality

Mid-Atlantic Regional

Air Management Association

October 2005
About MARAMA

The Mid-Atlantic Regional Air Management Association is a voluntary, non-profit

association of ten state and local air pollution control agencies. MARAMA’s mission

is to strengthen the skills and capabilities of member agencies and to help them work

together to prevent and reduce air pollution impacts in the Mid-Atlantic Region.

MARAMA provides cost-effective approaches to regional collaboration by pooling

resources to develop and analyze data, share ideas, and train staff to implement

common requirements.

The following State and Local governments are MARAMA members: Delaware,

the District of Columbia, Maryland, New Jersey, North Carolina, Pennsylvania, Virginia, West Virginia, Philadelphia, and Allegheny County, Pennsylvania.

For copies of this report contact:

MARAMA

Mid-Atlantic Regional Air Management Association

711 West 40th Street, Suite 312

Baltimore, Maryland 21211

phone 410.467.0170

fax 410.467.1737

www.marama.org

Cover Photos: (clockwise from lower left)

Lidar from the Northeast Oxidant and Particle Study (NE-OPS) in Philadelphia --

Photo, Russell Philbrick. (See page 6 for more about this project.)

Research aircraft from the University of Maryland -- Photo, Bruce Doddridge.

Rehoboth Beach, Delaware -- Photo, Alice Lutrey
Principal Author

Jeff Stehr, Ph.D.

Assistant Research Scientist, Department of Atmospheric and Oceanic Science

University of Maryland at College Park

Contributing Editor

Susan S.G.Wierman

Executive Director, Mid-Atlantic Regional Air Management Association

Project Manager, Layout, and Design

Susan Stephenson

Air Quality Planner, Mid-Atlantic Regional Air Management Association

Acknowledgments

The Mid-Atlantic Regional Air Management Association (MARAMA) recognizes

the significant contributions made by the lead author, Dr. Jeff Stehr, from the University of Maryland in making this report possible. His insight into the role geography and meteorology each play in the Region’s air quality have made the report an

excellent resource for the area’s air quality managers.

In addition, MARAMA would also like to thank the review committee comprised of

the following state and local staff:

Roger Westman and Jayme Graham, Allegheny County, Pennsylvania

Ray Malenfant, Delaware

Tad Aburn and Brian Hug, Maryland

Chris Salmi and Charles Pietarinen, New Jersey

Sheila Holman and Laura Boothe, North Carolina

Wick Havens, Pennsylvania

Dan Salkovitz, Virginia

The MARAMA members mentioned above met numerous times via conference

call and pored through a number of report drafts. At each stage they offered careful

criticism and intuitive insight into the substance of the report. Pooling their regional

knowledge significantly added to the quality of the final report.

We would also like to thank Serpil Kayin, Bill Gillespie, Katie Sheen Abbott, Pat

Davis, and Ningqi Hou of the MARAMA staff for their contributions to this report.

Without their efforts, many of the charts and maps would not have been possible.

Finally, MARAMA would like to thank U.S. Environmental Protection Agency Region III, which provided maps and charts as well as the funding for the development

of this report. (Grant Number XA-983865-01)
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 Mid-Atlantic Regional Air Management Association

Table of Contents

List of Figures....................................................................................................................vii

List of Features..................................................................................................................ix

Introduction........................................................................................................................xi

Setting the Stage.............................................................................................................xii

Part I The Nature of Air Pollutants................................................................................1

Introduction to Terms and Concepts

Ground-Level Ozone

Fine Particles (PM2.5)

Haze

Interconnections

Pollutant Fate

Part II How’s the Air Out There?..................................................................................15

Nonattainment Areas

How Many Days of Unhealthful Air Quality?

Design Values

PM2.5 Composition

Seasonal Variation in Total PM2.5

An Ozone Episode

Part III Meteorology and Transport in Air Pollution Episodes.............................31

The Basics: Mixing, Temperatures, and Daily Cycles

Meteorological Transport Mechanisms

The Airshed and the Range of Transport

The Whole Picture: Everything at Once

Part IV Pollution Sources...............................................................................................47

Anthropogenic Sources

Analysis of the 2002 Emissions Inventory

Part V Measurements, Data Analysis, and Modeling............................................59

Measurement

Data Analysis

Air Quality Modeling

Combining Techniques

Part VI Closing Thoughts..............................................................................................67

Understanding A Diverse Region

Pollutant Interactions are Important

Emissions Must be Reduced

Transport and Local Sources are Both Important

A Commitment to Improving Air Quality
Mid-Atlantic Regional Air Management Association

-viAppendices...........................................................................................................................71

A. Health Effects of Air Pollutants

B. Air Pollution Effects on Ecosystems and the Environment

C. Air Quality Standards and Goals

D. MARAMA Region Data Tables

E. Measuring and Calculating Visibility Impairment

F. Bibliography and Suggested Readings
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 Mid-Atlantic Regional Air Management Association

List of Figures

Part I The Nature of Air Pollutants

Figure 1 Ozone molecule (O3)............................................................................................................2

Figure 2 Diurnal pattern, PM.........................................................................................................5

Figure 3 Electron microscope comparison of human hair and particle.......................................7

Figure 4 Class I Federal areas in the East and Southeast..........................................................10

Figure 5 Comparison of hazy vs. clear day at Shenandoah National Park...................................11

Figure 6 Types of particles that impaired visibility on the 20% of days

with the poorest visibility................................................................................................13

Part II How’s The Air Out There?

Figure 7 Eight-hour ozone attainment/nonattainment in the MARAMA Region.........................16

Figure 8 PM2.5 nonattainment/attainment areas in the MARAMA Region..........................................17

Figure 9 MARAMA Region 2000-2002 8-hour ozone design values by site...............................19

Figure 10 MARAMA Region PM2.5 design values 2001-2003.........................................................20

Figure 11 Annual average composition of fine particles at urban sites

 throughout the United States............................................ ........................................22

Figure 12 Annual average composition of fine particles at rural sites

 throughout the United States....................................................................................22

Figure 13 Ambient urban excess PM concentrations for 13 example areas...................................24

Figure 14 PM2.5 time series for the northeastern MARAMA Region,

summer 2002.................................................................................................................27

Figure 15 PM2.5 time series for the southeastern MARAMA Region,

summer 2002.................................................................................................................27

Figure 16 Average FRM Values for 2002, Baltimore, MD.............................................................28

Figure 17 Average FRM Values for 2002, Richmond, VA............................................................28

Figure 18 Average FRM Values for 2002, Wilmington, DE..........................................................29

Figure 19 Average FRM Values for 2002, Pittsburgh, PA............................................................29

Part III Meteorology and Transport in Air Pollution Episodes

Figure 20 Temperature inversion................................................................................................32

Figure 21 Daily cycle of inversions and mixing..................................................................................33

Figure 22 Bermuda High.............................................................................................................36

Figure 23 Satellite picture of smoke from 2002 Quebec wildfires..............................................38

Figure 24 Time and altitude profile of a low level jet...................................................................41

Figure 25 Appalachian lee side trough......................................................................................42
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Figure 26 2002 Annual anthropogenic sources (MARAMA and Northeast)..................................47

Figure 27 Sulfur dioxide concentrations in the eastern United States.......................................49

Figure 28 Sulfate concentrations in the eastern United States...................................................49

Figure 29 Trends in sulfur dioxide emissions from utilities 1980-1997......................................50

Figure 30 Annual sulfur dioxide emissions by state -- 2002.........................................................53

Figure 31 Annual point source sulfur dioxide emissions density map -- 2002 ................................53

Figure 32 Annual nitrogen oxide emissions by state -- 2002............................................................54

Figure 33 Annual on road nitrogen oxide emissions density map -- 2002 .......................................54

Figure 34 Annual volatile organic compound emissions by state -- 2002 ........................................55

Figure 35 Annual area source volatile organic compound emissions density map -- 2002 ..............55

Figure 36 Annual ammonia emissions by state -- 2002.................................................................56

Figure 37 Annual area source ammonia emissions density map -- 2002 ...........................................56

Figure 38 Annual fine particle (PM 2.5) emissions by state -- 2002.................................................57

Part V Measurement, Data Analysis, and Modeling

Figure 39 Monitors used for nonattainment designations in the MARAMA Region..................60

Figure 40 Air quality monitoring sites measuring additional pollutants........................................61
List of Features

Northeast Oxidant and Particle Study (NE-OPS).......................................................6

Pittsburgh Air Quality Study.......................................................................................26

Maryland Aerosol Research and Characterization (MARCH Atlantic)................39

Air Quality Monitoring Sites Measuring Additional Pollutants...........................62

Southern Appalachian Mountain Initiative (SAMI).................................................65

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Introduction

A Guide to Mid-Atlantic Regional Air Quality

Understanding the causes of the Region’s air quality problems and taking steps to prevent air pollution

are two of the most important duties of state and local air pollution control agencies. The information in

this report is intended as a basic resource for explaining and describing air quality issues to air quality

managers, officials, and the public. For more in-depth explanations and discussions about topics in the

report, please investigate the bibliography.

This report’s main focus is on ozone, fine particle pollution, and pollutant interactions. It reviews the

current status of air quality, pollution and its sources, and the roles geography and weather play in the

Region’s air quality. Key points are highlighted in text boxes.

Throughout this report, short “Features” highlight important studies, results, or activities that help understand air quality in the Mid-Atlantic Region. The Features demonstrate much of the new and important work in the air quality arena since the mid-1990s, laying the groundwork for improved air quality

management.

In the Mid-Atlantic Region, areas surrounding New York City, Philadelphia, Baltimore, and Washington, D.C. record the highest number of days with unhealthy ozone pollution. The highest concentrations are often found downwind from the central cities and are affected by a combination of local

emissions and transport from outside the area. Driving and electricity generation are the major human

activities contributing to ozone pollution.

High levels of fine particulate matter are also found in the metropolitan areas between Washington and

New York. The greater Pittsburgh region, the Huntington-Ashland region, and several counties in

Pennsylvania, West Virginia, and North Carolina also suffer from elevated levels of fine particle pollution. High levels of fine particulate matter may be experienced in industrial, urban, or rural areas due

to the diversity of particulate matter sources.

This report explains how weather patterns play a major role in defining the nature and extent of air

pollution episodes in the Mid-Atlantic Region. Summertime air pollution episodes are typically hazy,

hot, and humid, with light winds and few clouds. Polluted air from outside the region, carrying high

concentrations of both ozone and fine particles, nearly always contributes to these episodes. Wintertime air pollution episodes, in contrast, have high levels of particulate matter (not ozone), are typically

cool, with light winds, and are more dominated by local stagnation and local emissions. While longrange pollution transport and local pollution stagnation are important throughout the Region, the relevant range of transport is generally shorter in the south than in the north. There are many variations

on these themes, giving each pollution episode unique characteristics.

The Region’s air pollution problems will not be solved by local controls alone, nor by upwind controls

alone; not by controlling only power plants, nor by just reducing emissions from transportation. Effective air pollution control requires a partnership of local, state, and federal authorities as well as private

citizens, businesses, and industries, and a commitment in all areas to continuing improvement.

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 Mid-Atlantic Regional Air Management Association
Setting the Stage

An Air Pollution Episode in the Mid-Atlantic Region

The sun rises through a warm haze as the Mid-Atlantic

Region begins to dry out from storms that left the area

the previous night. The forecast calls for clearing skies

and rising temperatures over the next few days and mentions that the Bermuda High is backing in over the area.

Forecasters warn that this is the beginning of a heat wave;

we are advised to check on the elderly and be sure our

pets have plenty of water when they are outside. Tucked

into the weather forecast is a “code orange” air quality

forecast that many mistake for a heat alert. Light winds

wander from one direction to the other and seem only to

push the heat around. The sun beats down from a hazy,

cloudless sky, baking the ground beneath.

By the second day, the air quality forecast shifts to “code

red” and warns the public to stay indoors in the afternoons and evening and limit their driving. Hospitals notice that more people are complaining of the heat and of

difficulty breathing. The skies above have given up their

natural blue and turned a bright, milky white color. A few

clouds turn up in the late afternoon, but show no inclination to rain and never seem to offer any

shade. Power company officials come on the radio and the local news to discuss capacity, overtaxed power lines, and the heat wave. They mention that some home air conditioners have been shut

down to conserve energy when power demand peaks. Spotty power outages are reported, but with

no storms and no winds, those who return home to find the power off are puzzled. Those lucky

enough to have planned a beach vacation enjoy strong breezes off the ocean during the

day. However, air quality monitors, a short

distance inland indicate that the air just a few

miles away from the ocean is particularly dirty.

Finally, the forecast contains some good news.

Relief, promised in the form of showers and

thunderstorms, should arrive the next day.

Nature explodes in a fury of rain, wind, and

cooler air. Weather forecasters announce

that a burst of clean, cool Canadian air has

entered the Region, and air quality forecasts

return to their more normal code green or

yellow. Areas in the northern part of the ReMid-Atlantic Regional Air Management Association

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gion get the quickest relief from both the heat and the cleansing rain, while areas farther south must

be content with the cleansing action of a few thunderstorms. At area hospitals, individuals treated

for heat exhaustion disappear from the waiting rooms, while those suffering from respiratory illness

continue to come in for a few days.

The Mid-Atlantic Region has just suffered through one of

its worst air pollution episodes in years. What causes

these episodes? How do they start? Why do they persist? Where does our pollution come from, and why does

the weather seem to play such a critical role in producing

these events? These are the questions we seek to answer in this document.

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A Guide to Mid-Atlantic Regional Air Quality

The Nature of Air Pollutants

Part I

Primary pollutants such as sulfur dioxide are

emitted directly from their sources. Secondary

pollutants such as ozone are the products of

reactions in the atmosphere.

This report focuses on outdoor (also called ambient) air quality and the emissions of various substances

that cause outdoor air pollution. Indoor air quality is also very important to health, but is beyond the

scope of this report. This section introduces terms and concepts, describes the nature of ozone and

particulate matter, and explains their relationships. For more information about the health effects of air

pollution, see Appendix A. Appendix B summarizes air quality impacts on ecosystems and the environment.

Introduction to Terms and Concepts

Smog

The term “smog,” coined in London, refers to the thick, soupy combination of smoke and fog so vividly

described in Sir Arthur Conan Doyle’s Sherlock Holmes books. The term’s use has since broadened to

include two varieties: the London-type smog, and the hot-weather Los Angeles-type smog. Los Angeles’ smog is created when a mixture of auto exhaust, industrial emissions, and other pollutants react in

sunlight. In general use today, smog refers to the whole mixture of air

pollution in an area, and may include ozone, a whole host of other gases,

and fine particles and the hazy conditions they cause. Fog is no longer a

necessary component of smog, though humidity certainly plays a role, as

will be described later.

Primary and Secondary Pollutants

Scientists distinguish between primary and secondary pollutants. These terms do not refer to their

relative importance, but to how pollutants come to exist in the atmosphere. Primary pollutants are

compounds such as sulfur dioxide that come directly from their sources. Particles such as soil and soot

are also primary pollutants. Secondary pollutants are not emitted directly, but are either formed or modified

in the atmosphere. Ozone, for example, is a secondary pollutant that forms as a result of reactions

involving primary pollutants. Essentially no ozone is emitted directly into the atmosphere. Sulfate is a

secondary particulate pollutant; it is the product of the transformation of a primary pollutant, sulfur dioxide, in the atmosphere. Ozone and fine particles, two of the most troublesome air pollutants for the Mid-Atlantic Region, are described

in more detail in the following sections.

Ground-Level Ozone

High concentrations of ground-level ozone pose a particularly nettlesome problem for the Mid-Atlantic

Region. The western and northern parts of the Region are routinely saddled with a large burden of

ozone entering from the industrialized Midwest. In the southern part of the Region, ozone episodes tend

to have stronger local influences, so episodes in North Carolina are different from those in Maryland

and Pennsylvania. In some areas the burden of transported pollution may be enough to push ozone

concentrations above the health standard even before winds have reached the urbanized areas of the

Mid-Atlantic Region.

Smog is a general term referring to

the entire mixture of air pollution in

an area.
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Ozone is a highly reactive form of oxygen. High

above, in the ozone layer, it protects the health

of nearly every living thing on Earth by absorbing harmful ultraviolet light. Near the surface,

where it reacts readily with anything it comes into

contact with, it is a health hazard and can be

harmful to the environment.

Figure 1 Ozone molecule (O3)

Unlike the oxygen that we breathe, which has

only two atoms of oxygen (O2 ), ozone has an

additional oxygen atom, making it very reactive.

This is why ozone is said to burn or irritate the

lungs.

Ozone is a colorless highly reactive gas, composed of three oxygen atoms instead of the usual, breathable two. The three oxygen

atoms are not held very tightly in the molecule, making it very

reactive. The smell that is often attributed to ozone is likely not

due to the molecule itself, but to the hydrocarbon fragments created when the molecule burns the inside of one’s nose.

In any discussion of ozone, it is important to distinguish between

the effects of ozone at the ground and ozone high in the atmosphere, several miles above our heads. An

advertisement might use the slogan “good up high, bad nearby,” to describe ozone. Regardless of

where it is, no one would want to breathe it. However, up high in what’s called the ozone layer, ozone

is essential to the health of nearly every living thing, since it protects the Earth from harmful ultraviolet

(UV) light. If not for this natural layer, UV light would

sterilize the Earth’s surface, and life as we know it would

cease to exist. Near the ground, ozone reacts with buildings, plants, animals, and people, and is one of the most

irritating, harmful components of smog.

Ozone Precursors and Ozone Formation

Near the ground, ozone is formed when volatile organic

compounds (VOCs) and oxides of nitrogen (NOx

) react

in the presence of sunlight. VOCs are organic compounds that evaporate readily, such as gasoline vapors

and paint fumes. NOx

 stands for two compounds, nitric

oxide (NO) and nitrogen dioxide (NO2

). Nitric oxide

forms in high temperature burning processes when nitrogen (N2

) and oxygen (O2) each split. The free nitrogen and oxygen atoms largely recombine with themselves

to return to N2

 and O2, but some link up with each other

to form NO. NO2

 forms in subsequent atmospheric processes.

Ozone, NOx

, and VOCs are all present naturally in the

atmosphere, though their concentrations are substantially smaller under normal natural conditions than

under smoggy ones. NOx

 is emitted naturally by soil microbes and formed in lightning and forest

fires. Nitric oxide is found naturally in the human body, where it is an important neurotransmitter.

In developed areas, natural sources have minimal impact; here human activities, such as fuel burning,

emit much more NOx

 than do natural sources.

In contrast to natural NOx

 emissions, which are normally

insignificant in urban air pollution, natural VOC emissions

are highly significant in smog chemistry. VOCs are naturally emitted by vegetation, soils, and animals. Some of the

most reactive VOCs are emitted by trees: terpenes from

pine trees and isoprene from oaks and aspens. VOC emissions from trees typically increase with temperature, though

In some areas the burden of transported

pollution may be enough to push ozone

concentrations above the health standard

even before winds have reached the

urbanized areas of the Mid-Atlantic

Region.

Part I The Nature of Pollutants
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A Guide to Mid-Atlantic Regional Air Quality

extremely high temperatures hinder their release as tree stomata

(pores) close to reduce water loss, consequently limiting VOC

emissions.

VOCs that come from human activities are called anthropogenic

VOCs. Anthropogenic VOCs are important and may dominate the

emissions by mass (weight) in an urban area, even though natural

sources dominate in the overall region. Some anthropogenic VOCs,

such as benzene, are themselves toxic and may increase risks of cancer or lead to other adverse health effects in addition to helping form

ozone.

VOC emissions are typically measured or estimated by the mass

of the pollutants emitted, but, particularly where ozone production is concerned, not all VOCs are equal.

Some VOCs are considerably more reactive in the atmosphere than others. The reactivity of a VOC

influences how quickly ozone forms. A compound that reacts in a few minutes to produce ozone will

have a much greater impact near its source than one that reacts more slowly. Thus, ozone can form

nearer or farther downwind of a VOC source due to faster or slower chemical reactions.

Ozone is formed when a mixture of VOCs and NOx

 is exposed to sunlight. Ozone is merely an undesirable intermediary generated as the Sun’s energy gradually breaks down VOCs into water vapor and

carbon dioxide. Essentially, the process is a low-temperature VOC burning process. Unlike normal

burning, in this process, NOx

 is not produced, but is turned into nitric acid and other compounds, which

are ultimately deposited to the Earth’s surface.

Why are the Highest Ozone Levels found Downwind of Cities and Large

Industrial Sources?

It is tempting to think of compounds in the atmosphere as sitting in neat little boxes that only interact with

a few other compounds through one or two pathways. While such a simple view might make it easier

to learn basic atmospheric chemistry, the atmosphere recognizes no such boundaries. This is particularly true when considering VOCs, NOx

, and ozone. Eventually, VOCs are broken down by the process

that produces ozone. However, this big picture masks the intermediate reactions of all three with one

another. Certain VOCs react with both NOx

 and ozone, while NOx and ozone react readily with each

other.

The reaction of NOx

 with ozone, called “NOx titration,” is particularly important in the plume from a city

or a large industrial source of highly concentrated NOx

. This reaction can temporarily eliminate nearly

all the ozone in a plume. Later, as the plume disperses and the NOx

 concentration drops, ozone will form

in the same plume. Eventually the ozone concentration downwind of the city will be higher than it was

when entering the city. Ozone disappears near the city as NOx

 titration takes its toll, and then reappears

at even higher concentrations as NOx

 and VOCs react in sunlight downwind. The highest ozone concentrations in the Washington, DC, Baltimore, and Philadelphia metropolitan areas are not in the urban

centers, but are downwind of the cities and their suburbs.

VOCs are also necessary for ozone formation, and they are abundant in any city. If VOCs are less

abundant, less ozone is formed in the short term. The plume from a coal-fired boiler or power plant

represents just such a case. Near the plant, the plume has abundant NOx but only low levels of VOCs,

Ozone is generated when volatile organic

compounds (VOCs) react with oxides of

nitrogen (particularly NO and NO2, known

together as NOx) in sunlight. VOCs are

emitted by trees, plants, animals, soils,

and by human activities such as solvent

use and driving. NOx is mostly formed in

high temperature burning processes.

Ozone forms as VOCs are broken down

into simpler compounds in the presence
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NOx limited conditions occur when

there is an overabundance of VOCs,

and relatively little NOx, so reducing

NOx emissions will reduce ozone

concentrations, while changes in VOC

emissions will have relatively little

impact. When VOCs are scarce, and

NOx

 is overabundant, conditions are

then VOC limited, and VOC controls

will have a greater impact.

so little ozone is produced initially. Later, as the plume mixes with its

surroundings, VOCs from other sources mix into the plume and more

ozone will be produced. The mix of VOCs and NOx

 in the plume will

affect how much ozone is produced in the plume and how quickly.

Eventually, VOCs will mix into the plume and react with the existing

NOx

 to produce ozone.

NOx Limited and VOC Limited Ozone Production

The concentrations of VOCs and NOx are usually not optimal for producing as much ozone as possible. The concentration of one is typically too low when compared with the other. When the concentration

of NOx

 is too low, ozone production is NOx limited. Additional NOx will

increase ozone, but additional VOCs will not. Conversely, when the

concentration of VOCs is too low, ozone production is VOC limited.

These conditions have implications for ozone control. When ozone

production is VOC limited, VOC controls will be more effective, while NOx

 controls are more effective

when conditions are NOx

 limited. This assumes that all sources of NOx and VOC can be controlled.

Given the abundance of highly reactive natural VOCs, this is often not the case in the Mid-Atlantic

Region.

Distinctions between whether an area is NOx

 or VOC limited do not hold for all parts of a Region or

even for all parts of a plume. Because cars and other combustion sources produce a large amount of

NOx

, conditions in a city center may well be VOC limited, while conditions downwind, where the NOx

has aged and fresh natural VOCs are available, are often NOx limited. An area may be NOx limited

during some parts of the a day and VOC limited during other times of

the day.

Fine Particles (PM2.5)

Gases such as ozone are not the only air pollutants that cause environmental and health problems. Solid and liquid particles can stay in the

air and, if small enough, can make their way far into the lungs. Particles come in a wide variety of shapes and sizes, which affect their

impacts on the environment and human health. Bigger particles, such

as dust, are easier to see and can cause problems, but smaller particles are probably worse for our health.

Fine particles, those 2.5 micrometers (μm) in diameter or less, called

PM2.5, can be inhaled deeply into the lungs. A diameter of 2.5 μm corresponds to 1/100th of an inch,

which is about 40 times smaller than the diameter of a human hair. Three additional terms related to

particle size are also useful: PM10, Total Suspended Particles (TSP), and PM-coarse. PM10 represents

the fraction of particles below 10 micrometers. PM-coarse represents all the particles between 2.5

micrometers and 10 micrometers in diameter. PM10 includes both PM2.5 and PM-coarse. Particles

below 10 micrometers in diameter can make their way into the lungs, though not as deeply as those

below 2.5 micrometers. TSP represents all particles that can stay suspended in the atmosphere, which

NOx titration is just one example of

an interaction between cycles and

families of compounds. When NOx

is very abundant, as is the case in

the plume from a major city or power

plant, it reacts with ozone directly,

destroying the molecule, and

reducing ozone concentrations. As

the plume disperses and more

VOCs mix into the plume, conditions become more favorable for

ozone production, and ozone will be

produced inside the same plume.

Part I The Nature of Pollutants
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A Guide to Mid-Atlantic Regional Air Quality

loosely corresponds to those with diameters below roughly 50 micrometers. Particles larger than 50

micrometers will settle quickly out of the atmosphere.

The General Composition of Particulate Matter (PM)

Fine particles are treated as though they are a single pollutant, but fine particles come from many

different sources and are composed of thousands of different compounds. Fortunately, these compounds fall into a few dominant categories: sulfates, nitrates, ammonium

compounds, soil, organic carbon compounds, and elemental carbon. Water

is nearly always an important and variable part of PM, and sea salt is often

significant near the coast. Specifics of Mid-Atlantic Region particle composition are described later in this document.

Given the complex composition of PM, it is no surprise that its chemistry is also complex. Particles may

be liquid, dry or wet. An important distinction is between primary and secondary particles. Primary

particles are emitted directly into the atmosphere as particles, while secondary particles are produced

when gases or other particles coalesce. Many particles are collections of smaller particles that have

collided and stuck together, and particles are often collections of both primary and secondary particles.

Figure 2 Diurnal pattern, PM

This graph shows the average hourly concentrations, giving a diurnal pattern for PM2.5 from January 1, 2003 -

April 10, 2003 at the Oldtown monitoring site in Baltimore, Maryland. The hour by hour fluctuations seem to

track traffic patterns, which is a reasonable finding for an inner city monitor.

An aerosol is a suspension of

fine solid or liquid particles in

gas.
Northeast Oxidant and

Particle Study (NE-OPS)

This project contributed to the understanding of how pollutant transport in the upper levels of the atmosphere contribute to high levels of air pollution. Located in Philadelphia, the

Northeast Oxidant and Particle Study (NE-OPS) conducted

intensive air quality measurements in the summers of 1999,

2001, and 2002. Seven universities, three national laboratories, six agencies, and private industry collaborated on the

project.

Objectives

• Investigate the urban polluted environment to find the relationships among conditions leading

to concentrations of ozone and fine particles

• Determine the contributions from local and distant pollution sources.

• Examine the role that meteorological properties play in the build-up and distribution of pollutant concentrations over urban and regional scales and interpret these results within the context of past measurement programs to extend the knowledge gained to other applicable locations and atmospheric conditions.

Research Conclusions

• Meteorology is the primary driver and leading factor controlling high ozone and particulate

matter episodes in the northern U.S.

• Essentially all of the major air pollution events involve regional scale circulations and are

associated with transport from the Midwest.

• Vertical mixing of pollutants and precursors from the storage/transport reservoir above the

nocturnal boundary layer provide major input to pollution episodes.

• Vertical profiles of atmospheric properties are essential for understanding the processes and

evolution of air pollution episodes.

• Successful application of simpler modeling options has been validated using the NE-OPS

ground and upper air data. The NE-OPS data base will provide opportunities for critical

testing and evaluation of models.

Funding for this project was provided by the U.S. EPA and the state of Pennsylvania. The

principal investigator was Russell Philbrick of the Pennsylvania State University.

For more information see: http://lidar1.ee.psu.edu/narsto-neops/index.htm

A tethered weather balloon used

during NE-OPS research to gather

data.

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Part I The Nature of Pollutants

photo: Russell Philbrick
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Mid-Atlantic Regional Air Management Association

Primary particles are the simplest. Soil and other

crustal materials are fairly straightforward primary

particles. When the wind blows hard enough, soil,

silt, and sand can be lifted from the surface. Human

activities such as mining, construction, plowing, and

driving on unpaved roads, also lift particles into the

air. Soil particles that are sufficiently small will remain airborne for long periods. Larger particles are

not typically transported as far as smaller ones. This

was overlooked in many early estimates of the impact of soil emissions, resulting in overestimates of

the importance of these particles. The bulk of these

particles are either too heavy to stay suspended in

the atmosphere or too large to be inhaled deeply into

the lungs.

Soot, also referred to as black carbon or elemental carbon, is emitted directly by diesel engines and

forest fires, among other sources. When fresh, soot does not take on water. However, as soot ages in

the atmosphere, it will take on water and combine with other aerosols.

On an annual basis, sulfates comprise the largest portion of the fine

particulate matter in the Mid-Atlantic Region. Sulfate particles are

secondary particles, which are almost entirely formed from sulfur

dioxide emitted from the combustion of coal and other fossil fuels.

Both coal and crude oil naturally contain some (typically a few

percent) sulfur, with the exact composition varying dramatically depending on the source. Natural sources of atmospheric sulfur include emissions from volcanoes and a few sulfurous compounds,

but these sources are ordinarily insignificant contributors to urban

air pollution.

Sulfur dioxide is transformed into sulfate, and thereby sulfuric

acid, via numerous pathways, though two are considered dominant. Sulfur dioxide is slowly turned into sulfate as a gas in the air,

but a much more rapid reaction takes place in cloud particles to

turn sulfur dioxide into sulfate. Sulfate has a very high affinity for

water—so high that it almost immediately acquires an ensemble of six surrounding water molecules.

Sulfate dissolved in such a particle is sulfuric acid, a strong acid, which makes the particle very acidic.

The acidity draws in some atmospheric ammonia, making the particle highly attractive to water. These

particles then grow rapidly into larger particles that scatter light efficiently, reducing visibility. Seldom is

there enough ammonia to fully neutralize the sulfuric acid in these particles, so they end up as a significant component of acid rain.

Nitrate (NO3

), represents the fate of NOx once it has been fully oxidized from NO to NO2 to NO3.

Though the formation process is less complex than that of sulfate, nitrates are formed in a process

similar to the gas-phase process that forms sulfate. Nitrates also form aerosol particles readily, though

Figure 3 Electron microscope

comparison of human hair and a fine

particle

Particulate pollutants are characterized

by the sizes of the particles. TSP

stands for Total Suspended Particles—

all those particles with diameters less

than 50 micrometers. PM10 and PM2.5

stand for all particles with diameters

less than 10 micrometers and 2.5

micrometers, respectively. Particles

smaller than 2.5 micrometers in

diameter can be inhaled deeply into the

lungs, making them more likely to

cause health problems than larger

particles.
Mid-Atlantic Regional Air Management Association

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Nitrate and sulfate particles tend to be

acidic, while ammonia, the only significant

atmospheric base tends to neutralize

those acids. Both nitrate and sulfate are

important components of acid rain. Nitrate

has other impacts on the environment,

since it is also a fertilizer. Sulfate is the

principal component of regional haze.

not as quickly as sulfate. And once nitrates are incorporated into an

aerosol, they too form an acid—nitric acid, a significant component of

acid rain. Nitrates are also fertilizers. As such, they contribute to

nutrient loading in bodies of water such as the Chesapeake Bay and

Pamlico Sound. Roughly a third of the nitrogen entering the Chesapeake Bay comes from the air. For other bodies of water, somewhere

between 10 and 45 percent of the nitrogen comes from the air.

In contrast to the two acids just discussed, ammonia is the only significant atmospheric base. As such, it

reacts readily with sulfuric acid and nitric acid to form ammonium sulfate and ammonium nitrate. Both

of these gases take on water readily to form aerosols. Ammonium sulfate is fairly stable, but ammonium

nitrate decomposes promptly as temperatures rise. When ammonia deposits to the ground, it is quickly

converted to nitrate by soil microbes, so one is faced with the conundrum of an atmospheric base that

increases soil acidity. Ammonia comes from a variety of sources, some of which are not well quantified.

Its main sources are thought to be agricultural, particularly from the excreta of livestock. Ammonia

emissions from human activities result in elevated ammonia levels in cities as well. Some emission

control processes in power plants add ammonia to the stack to remove NOx

; the result is considerably

less NOx

 with a small amount of ammonia slipping out the stack.

Organic carbon aerosols form when gaseous organic compounds, such as VOCs, condense to form

particles. In contrast to elemental carbon, which is a primary particle, a significant fraction of organic

carbon particles are secondary pollutants. Organic carbon (OC) aerosols are typically mixtures of a

wide variety of compounds. Natural compounds such as terpenes are a significant source of OC.

Terpenes come from pine trees, and will swiftly form aerosols, producing some of the famous blue haze

of the Blue Ridge Mountains in the southern Mid-Atlantic Region.

Physical Properties

Particles in different size ranges tend to have different physical properties, so, for example, those particles which most affect visibility may not necessarily be the same as those which most affect human

health.

Particles larger than 2.5 micrometers in diameter contribute the majority of particle mass, but the most

numerous particles are the very smallest, below 0.1 micrometers. Most of the surface area of particles

occurs on particles with diameters somewhere between these

extremes. Sheer numbers are important for some physical processes, such as cloud formation, while surface area is more important in haze, visibility, and certain processes in atmospheric

chemistry.

Particle sizes differ according to how they are emitted, grow,

and are removed from the atmosphere. The particles remaining

in the atmosphere reflect the result of a balance between growth

and removal processes. Aerosols usually come in three size

groups, called modes. The names of the modes, and the boundaries between the modes, may shift slightly depending on the preference of the author or the nature of

regulations in a country, but a loose guide is given here.

As with gases, fine particles are also

classified as primary and secondary.

Sulfate particles, most organic

particles, and nitrates are secondary

particles.

Part I The Nature of Pollutants
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A Guide to Mid-Atlantic Regional Air Quality

Fine particles are composed of thousands of different

compounds that can be lumped into a few categories:

organic carbon compounds, sulfates, nitrates, elemental

carbon or soot, ammonium compounds, soils and crustal

materials. Water is generally a significant part of most

particles. Sulfates are the largest single category.

The group containing the smallest particles is

the Aitken mode, containing ultrafine particles

and nuclei—the beginnings of fine particles.

These tiny particles occur in the greatest number, though their small size means that they make

up only a tiny fraction of the mass. Nuclei may

be only a few molecules held together. These

particles tend to grow rapidly by coalescing with

other particles and by taking on gases directly from the atmosphere. Certain nuclei are particularly

suited to taking on water, giving them the name condensation nuclei. These nuclei are essential to life as

we know it, because they start raindrop growth long before it would otherwise start. Without them, the

atmosphere would have to absorb considerably more moisture before rainfall would start.

The next larger mode is the accumulation mode. Particles of this size can grow by taking on gases and

smaller particles. If they do grow larger, accumulation mode particles are efficiently removed by

rain, snow, and other precipitation processes. The result is a mode of very fine particles that tend to

remain about the same size, products of the growth of nuclei and the removal of larger particles. Whereas

the Aitken mode or nuclei were greatest in number, the accumulation mode is greatest in surface area.

A large surface area is important for producing haze and for accommodating reactions that take place

on surfaces. A significant portion of the mass of fine particles typically resides in this mode.

The third mode is the coarse mode. Coarse particles come from different sources than do the Aitken

and accumulation mode particles. Such particles are partly the result of soils and crustal materials being

lofted into the atmosphere. Sea salt particles are typically coarse aerosols. Most of the mass of

atmospheric particles is located in the coarse mode. Particles larger than these tend to settle out of the

atmosphere quickly, having minimal effects on atmospheric chemistry and public health.

Most particles are likely mixtures of different substances, the product of growing by collisions with other

particles and by taking on gases. The composition of particles varies with their size. The smallest

particles tend to be made up of metals and organics. Larger ones grow by adding water, acids, and

organics, so metals are a relatively small fraction of their mass. The largest particles are quite different,

owing to their different sources, and are usually made up of soils and other crustal materials. Most

individual particles are likely mixtures of different substances, the products of growing by collisions with

other particles and by taking on gases.

Haze

Fine particles and haze are inextricably linked, since fine particles scatter and absorb light, which is the

very nature of haze. Haze is simply the visibility obstruction caused by fine particles. In the United

States, under natural conditions, a visual range is roughly 120 miles in the West and 90 miles in the East.

Currently, the EPA estimates that typical visibility in

the West is only 1/2 to 2/3 of what it would naturally

be, while visibility in the eastern U.S. is roughly 20

percent as good as natural conditions.

Haze should not be confused with fog or mist, which

are largely composed of water and are essentially lowlying clouds. In weather reports, conditions are called

Haze and fine particles are inextricably linked, since

fine particles cause the scattering and absorption

that lead to visibility reduction. Some amount of

haze is natural, caused by aerosols and gases in the

atmosphere.
Mid-Atlantic Regional Air Management Association

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Figure 4 Class I Federal areas in the East and Southeast

There are 10 Class I Federal Areas in the MARAMA Region. MARAMA member agencies participate in two

regional planning efforts to improve visibility. States in the northern MARAMA Region are part of the MidAtlantic / Northeast Visibility Union (MANE-VU, www.mane-vu.org). MARAMA members to the south are part of

the Visibility Improvement State and Tribal Association of the Southeast (VISTAS, www.vistas-sesarm.org).

Class I Areas in VISTAS

Class I Areas in MANE-VU

Part I The Nature of Pollutants
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A Guide to Mid-Atlantic Regional Air Quality

Figure 5 Comparison of hazy

vs. clear day at Shenandoah

National Park

hazy when the air is dry, and foggy or misty otherwise. The term

fog applies when visibility is 5/8 of a mile or less, and mist applies

when visibility is between 5/8 of a mile and 7 miles (about 1 km to

11 km).

There are three components to visibility obstruction: scattering by

the atmosphere, scattering by natural particles, and scattering by

human generated particles. Through a process known as Rayleigh scattering, atoms and molecules in the air scatter light in

all directions, so even if the atmosphere were entirely free of

particles, visibility would be somewhat limited. Rayleigh scattering

limits visibility to roughly 180 miles (300 km) at sea level. Nitrogen

is the most notable molecule in this regard, since it preferentially

scatters blue light, giving the Earth’s sky its brilliant blue color.

Visibility is measured in three ways: as a visual range in meters, as

extinction in inverse megameters, and in deciviews. Visibility

disruption is fundamentally the same, regardless of which measure

is used. Instead of traveling directly from a target to your eye, light

is absorbed or scattered away from your line of sight and light

from other objects is also scattered into your line of sight. The

combination of increased light from other sources and decreased

light from the desired source produces a reduction in visibility.

The term visual range is straightforward, since it just refers to how

far away an average observer can still discern an object from its

surroundings. Haze scatters and absorbs light. An average human can generally distinguish a two percent contrast between a

black object and its surroundings if that object sits in broad daylight. This assumption leads to the 180 mile visibility limit due to

Rayleigh scattering mentioned previously.

The visual range can be related to an intrinsic property of the

particles in the atmosphere, namely light extinction. Since particles

affect visibility both by scattering and by absorbing light, we have to consider the two processes together to estimate a visual range. If our goal is to see a mountain, and particles are in the way, it does

not matter much whether those particles are scattering or absorbing light—less light reaches our

eyes, reducing our ability to see the mountain. Extinction represents the combined effects of both scattering and absorption, which reduce our ability to see. As extinction goes up, visibility goes down. The

term extinction links particle properties and visual range.

Extinction can be calculated from the properties of the

particles in the atmosphere, since each particle contributes a little bit to extinction. Extinction is measured in

inverse megameters or inverse kilometers, which appear

to be clumsy units, but really just show that increased

extinction results in decreased visibility. The daytime

Visibility is measured in meters, deciviews, and

inverse megameters. Each scale has its own

purpose. Visibility may be measured directly, but

is often reconstructed from mass and composition

measurements of fine particles.

Clear Day View 43 Miles

View 12 Miles

Hazy Day View 6 Miles
Mid-Atlantic Regional Air Management Association

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formula for visual range is a constant (determined by the two percent assumption mentioned above)

divided by the extinction. Taking that constant and dividing it by the extinction in inverse kilometers

gives the visual range in kilometers. So, the units of extinction are set up so that the visual range comes

out as a distance.

Visibility is also measured in deciviews. The deciview scale was designed in hopes of doing for visibility

what the decibel scale did for sound. Decibels relate changes in sound energy in a way that makes

sense for the human ear. Likewise, deciviews represent changes in extinction and visibility in a way that

makes sense for the human eye. The deciview scale was also designed to increase as visibility gets

worse in much the same way that air quality gets worse when ozone and fine particle concentrations

increase.

Mathematically, deciviews are defined as ten times the natural log of extinction divided by 10, or 10 x ln

(extinction/10), where ln is the natural logarithm (to base e) and the extinction is measured in inverse

megameters. Logarithms appear in the definitions of both deciviews and decibels because that is how

human eyes and ears respond to light and sound. A speaker that produces twice as much sound energy

does not sound to us like it is twice as loud. Likewise, a light source that produces twice the energy does

not appear to us to be twice as bright. Instead, it takes far more sound energy and far more light to

produce a response in our ears and eyes that is twice as large. The result is a far larger range of

detectable sights and sounds. An ear that hears the roar of an ocean

can also hear the squeak of a mouse, while eyes that let us see in broad

daylight can also see by the light of the crescent moon.

Deciviews are convenient in that they correlate well with human

perceptions of visibility changes, regardless of what the visibility may

be. A change of one deciview is perceived as being the same if

visibility goes from 10 to 11 deciviews or from 30 to 31 deciviews.

Visibility differs between night and day. In daytime, one wants to be

able to discern an object from its surroundings, all of which are typically

well-lit by the sun. At night, one is typically concerned with being able

to see bright objects such as runway lights, stars, and car taillights.

These two needs are fundamentally different. Methods for calculating visibility at night and in the

daytime are different because picking out bright lights against a dark sky is different from picking

out an object from its well-lit surroundings. As a concrete example, lights from distant radio towers

may be visible at night, even though those towers are not visible in the day. This change is not due

to a change in the particles in the atmosphere, but because distinguishing a light from the black sky is

typically much easier than picking out a distant object in the daytime.

Some instruments measure the scattering or absorption of light by particles directly, either in the

ambient atmosphere or by drawing outdoor air into an instrument. On the other hand, visibility is often

not measured directly, but is instead calculated or “reconstructed” from measurements of the mass and

composition of fine particles. This helps us figure out the major sources causing poor visibility, since

different kinds of particles come from different sources. (See Appendix E for a discussion on

calculating visibility.)

A change of one deciview is

perceived as the same amount of

change whether the visibility goes

from 10 to 11 deciviews or from 30

to 31 deciviews. In contrast, a

change of visual range from 5 miles

to 10 miles is perceived as a much

larger change than a change from

100 miles to 105 miles.

Part I The Nature of Pollutants
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A Guide to Mid-Atlantic Regional Air Quality

Soil

1%

Crustal 

M atter

4%

NO3

10%

SO4

67%

Elemental

Carbon

5%

OC

13%

Interconnections

While it may be useful to break down

atmospheric chemistry compound by

compound, the atmosphere recognizes no such divisions. Pollutants

interact, and the result of those interactions can be to accelerate,

slow down, or alter the production

of other pollutants. Haze and ozone may appear at

first to be unrelated, but haze increases the scattering of light, which in turn increases ozone production

under certain conditions. So particles may accelerate the production of certain gases. Conversely,

gases also form particles. The same VOCs and NOx

that lead to ozone production also form organic and

nitrate particles. Sulfate is commonly formed in

cloud droplets when sulfur dioxide reacts with

hydrogen peroxide. Hydrogen peroxide is formed

as a result of the same cycles that form ozone.

These interactions have led to the concept of “oneatmosphere modeling,” which recognizes that

changes in emissions of one pollutant will necessarily affect others.

Pollutant Fate

What happens to all these pollutants? Ultimately,

most compounds end up on the Earth’s surface.

Exactly how these pollutants get to the surface

affects their concentrations in the atmosphere.

Gases

Ozone reacts with surfaces and other compounds

directly, forming a chemical product plus oxygen.

It will also react with itself, returning breathable

molecular oxygen. Nitrogen oxides form nitrates,

nitric acid, and nitrogenated hydrocarbons, all of

which ultimately deposit to the Earth’s surface.

Sulfur dioxide is deposited on the surface through

various mechanisms involving both wet and dry

deposition. Volatile organic species are broken

down in the atmosphere into carbon dioxide and

water unless they deposit first to the surface. Carbon monoxide has a more interesting fortune, since

it eventually turns into carbon dioxide, which is

Figure 6 Types of particles that

impaired visibility on the 20% of days

with the poorest visibility

The pie charts above show the relative composition

of visibility reducing pollutants at various sites.

Note the increasing importance of sulfates (SO4)

in the southern part of the Region. Organic carbon

(OC), nitrates (NO3), and elemental carbon are

all important contributors to haze.

 “Tools and Techniques for Identifying Contributions to Regional Haze in the Northeast and Mid-Atlantic United States.” NESCAUM, January 2005. p. 3-2.

Pollutants interact,

and the result of

those interactions can

be to accelerate, slow

down, or alter the

production of other

pollutants.

Brigantine Wilderness Area

Acadia National Park

Shenandoah National Park

OC

12%

Elemental 

Carbon

5%

SO4

71%

NO3

9%

Soil

1%

Crustal 

Matter

2%

SO4

82%

OC

8%

NO3

4%

Elemental 

Carbon

4%

Soil

0% Crustal 

M atter

2%
Mid-Atlantic Regional Air Management Association

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associated with global warming. Carbon dioxide is taken up by plants,

which can release that carbon in forest fires or when they decay. The

only way to truly sequester carbon is by burial, where the carbon may

eventually form coal and oil deposits. Carbon dioxide may also be

turned into carbonate shells by microorganisms in the ocean which die

and settle to the bottom where they are turned into deposits of limestone and chalk.

Particles

Fine particles are affected by a variety of loss processes, depending on

their solubility and size. If particles grow too large, gravity will ensure

that they settle quickly out of the air. Rain storms, fog, snow, clouds, and all other precipitation phenomena will also remove fine particles from the atmosphere.

The Big Picture: Geological Cycles

Atmospheric pollutants all participate in various cycles. Their time as air pollutants is typically very

limited, and they spend most of their time in other parts of the cycle. One such example is the carbon

cycle, where carbon-containing compounds eventually turn into coal, oil, and limestone. Coal and oil

deposits may burn, releasing carbon back into the atmosphere. Limestone rock might seem like a fairly

permanent fate, but rocks of all kinds continuously return to the Earth’s mantle, where they are melted

down to be reborn later in a volcano or a new mountain range. The carbon that was tied up in limestone

can then return to the atmosphere as carbon dioxide when a volcano erupts.

Other cycles form important links between different parts of the biosphere. The nitrogen cycle and the

sulfur cycle have parts in both the air and the water, as does the carbon cycle. Therefore, an air

pollution problem will likely have impacts on a water pollution problem and vice versa.

Part I The Nature of Pollutants

Each pollutant suffers its own

particular fate. Most participate in

global cycles that take place on

time scales much longer than the

atmospheric lifetimes of these

pollutants. All, at some point, end

up back on the ground or in the

water.
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A Guide to Mid-Atlantic Regional Air Quality

Part II

How’s the Air Out There?

This section presents a brief snapshot of air pollution conditions in the Mid-Atlantic Region. The purpose

here is to give a broad overview, not to discuss particular areas at particular times. Since PM2.5 and

ozone are the two pollutants that violate health standards in the Mid-Atlantic Region, they are the focus

of this section. Maps and charts of pollutant concentrations across the Region are also included. The

maps of nonattainment areas highlight the places with the highest concentrations, though emissions from

other areas also contribute to air pollution in nonattainment areas.

Trends in pollutant concentrations do indicate a region’s progress toward healthful air quality. Ozone

trend data available in Appendix D have not been adjusted to account for differences in meteorology, and

weather patterns do significantly affect ozone concentrations. The PM2.5 record is not yet long enough

for discussion of trends.

Nonattainment Areas

Areas where air quality does not meet national health standards for several years are designated as

nonattainment areas. Figures 7 and 8 show the designated ozone and PM2.5 nonattainment areas in the

Mid-Atlantic Region.

High ozone and PM2.5 episodes occur in broad, multi-state regions, though the highest levels occur in

smaller areas. Many nonattainment areas include an entire metropolitan area, and nonattainment areas

often cross state boundaries. Rural areas can also be designated nonattainment.

Ozone nonattainment areas are classified according to the severity of the air quality problem as marginal,

moderate, serious, or severe nonattainment areas. There are also basic nonattainment areas that

generally experience less frequent or less severe air

quality problems. PM2.5 nonattainment areas are not

classified.

EPA revised ozone nonattainment areas in the MidAtlantic Region in 2003 to reflect the shift from

the 1-hour ozone standard to the newer and stricter

8-hour ozone standard. Some areas that had

complied with the 1-hour ozone standard exceed

the 8-hour standard because it is a stricter standard. Larger areas are designated nonattainment

than before, but the severity classification of the

violations is often less. For example, several areas

that were classified as severe ozone nonattainment

areas under the 1-hour standard are now classified

as moderate nonattainment areas under the 8-hour

ozone standard.

In the Mid-Atlantic Region, the areas surrounding

New York City, Philadelphia, Baltimore, Washington,

Communities that are close to exceeding, or exceed

the 8-hour ozone standard may choose to enter into an

Early Action Compact (EAC) with EPA. The goal of

the compact is to take actions to clean the air as soon

as possible, rather than waiting for the 2007 deadline.

In 2004, communities participating in the EACs

submitted plans for meeting the 8-hour ozone standard

by December 31, 2007. EAC requirements include:

developing and implementing air pollution control

strategies, accounting for emissions growth, and

achieving and maintaining the 8-hour standard.

As long as EAC areas meet agreed upon goals, an

8-hour ozone nonattainment designation will be

deferred.

Source: http://www.epa.gov/ttn/naaqs/ozone/eac/

Early Action Compacts
Mid-Atlantic Regional Air Management Association

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Figure 7 Eight-hour ozone attainment/nonattainment areas in the MARAMA Region

Part II How’s the Air Out There?
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A Guide to Mid-Atlantic Regional Air Quality

Figure 8 PM2.5 nonattainment/attainment areas in the MARAMA Region
Mid-Atlantic Regional Air Management Association

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D.C., and Charlotte, N.C. usually record the highest number of days with unhealthy air quality for

ozone. These areas also usually experience the highest levels of ozone in the Region.

PM2.5 nonattainment areas range from small parts of counties to entire metropolitan areas. High levels

of PM2.5 may be experienced in industrial, urban, or rural areas due to the diversity of sources affecting

PM concentrations.

How Many Days of Unhealthful Air Quality?

The number of days on which monitored air quality exceeds the federal health standard for ozone is one

measure of how serious the air pollution problem is in an area. (The 24-hour PM2.5 standard is met

throughout the Region.) Tables D-4 through D-7 in Appendix D record the number of days exceeding

the 1-hour and 8-hour ozone standards for each state in the Region, and for each current or former

ozone nonattainment area in the Region.

An ozone exceedance day occurs when air quality surpasses the level of the National Ambient Air

Quality Standard (NAAQS) at a particular monitoring site. A day with widespread high ozone levels

can result in multiple ozone exceedances. As shown in Tables D-4 through

D-7 in Appendix D, the Region had fewer ozone exceedances in 2003

than in 2002. During 2002 the weather conditions (drought, clear skies,

and high temperatures) were conducive to ozone formation. In contrast,

2003 weather conditions made ozone production more difficult. These

conditions were characterized by lower temperatures and increased rainfall. For example, Table D-5 shows that from 2002 to 2003 Pennsylvania

dropped from 50 days with exceedances to 19 days, New Jersey fell from

44 days to 19, and Maryland went from 39 days to just nine days with exceedances of the 8-hour

standard.

Table D-6 in Appendix D demonstrates that, for the most part, 1-hour ozone exceedances have

decreased since the late 1980s. Table D-4 lists the number of days above the 8-hour standard since

1998. Year-to-year variations reflect both efforts to control pollution and the impact of the weather.

Design Values

Another way to judge the severity of an area’s air pollution problem is to consider its “design value.”

The design value is the average concentration that is compared to the air quality standard to determine

whether air quality has violated the standard. (See Appendix C for more information about the National

Ambient Air Quality Standards.) Design values for both the PM2.5 and the 8-hour ozone standards are

calculated for a 3-year period to remove some of the year-to-year variability caused by the weather. If

the design value is below the standard, then the area meets the standard. In areas with multiple

monitors, the design value for a nonattainment area is determined by the monitoring site in the

nonattainment area with the highest design value.

For the 8-hour ozone standard, the design value is a three-year average of each year’s fourth-highest

daily maximum 8-hour ozone concentration. For PM2.5 the design value is also a three-year average.

The daily average PM2.5 levels are first combined into quarterly averages, then the those averages are

combined into an annual average. Finally, three consecutive annual averages are combined to

determine a 3-year PM2.5 design value.

An ozone exceedance is a day

at a particular monitoring site

when air quality surpasses the

level of the National Ambient Air

Quality Standard (NAAQS).

Part II How’s the Air Out There?
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A Guide to Mid-Atlantic Regional Air Quality

Figure 9 MARAMA Region 2000-2002 8-hour ozone design values by site

Data obtained from MARAMA member agencies. Design values have been grouped according to the

classifications used in the Air Quality Index (AQI), although the AQI is meant for use with 8-hour concentrations,

not averages such as the design value.

Ozone Design Values

The 8-hour design value standard is 0.08 ppm averaged over eight hours (0.085 rounds up). Ozone data

are usually listed in parts per billion (ppb), so a design value of 85 ppb violates the standard. Many

counties in the Region are classified as nonattainment for the 8-hour standard. Tables D-2a and 2b in

Appendix D list 8-hour ozone design values for 2001 through 2003 by county. They are grouped into

counties in attainment and those designated nonattainment. (Counties without monitors are not listed.)

Design values for the previous three-year period are mapped in Figure 9.

In counties with monitors that are classified attainment, 11 design values were 80 ppb or less, and 10

were between 81 and 84 ppb, just below the standard. In counties classified as nonattainment, 43

slightly exceeded the standard, with design values of 85-90 ppb, 50 counties had design values of

between 91 and 100 ppb, and three counties exceeded 100 ppb (Ocean and Camden Counties in New

Jersey and Harford County in Maryland).
Mid-Atlantic Regional Air Management Association

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The county with the highest ozone design value in the Region (109 ppb) was Ocean County, New

Jersey. This county borders New Jersey’s Atlantic Coast and is characterized by the commercial

activities associated with seasonal resorts. Ocean County’s air quality is affected by sources in

Philadelphia and New York City. The county with the lowest ozone design value (74 ppb) is Swain

County, North Carolina. Located in the western part of the state, Swain County is 93 percent forestland

and is home to most of the Great Smoky Mountains National Park.

Table D-3 in Appendix D lists 8-hour design values for 2001-2003 by nonattainment area rather than by

county. The nonattainment area with the highest design value (106 ppb) is the Philadelphia-WilmingtonAtlantic City area, which includes portions of Pennsylvania, New Jersey, Maryland, and Delaware.

Particulate Matter Design Values

For the annual PM2.5 standard, design values greater than or equal to 15.1 micrograms per cubic meter

(μg/m3

) indicate a violation of the annual standard. Most of the PM2.5 design values in the Region show

Part II How’s the Air Out There?

Figure 10 MARAMA Region PM2.5 design values 2001-2003

Data obtained from EPA’s AIRS website
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A Guide to Mid-Atlantic Regional Air Quality

compliance with the annual standard of 15 μg/m3. Table D-1 in Appendix D lists PM2.5 design values for

2001 through 2003 for each monitoring site in the Mid-Atlantic Region. These values are mapped in

Figure 10.

The highest PM2.5 design value in the Region (21.2 μg/m3 for 2001 to 2003) is located near Pittsburgh

(Liberty), and is influenced both by regional transport of fine particle pollution and by local sources,

including a large coke plant. The site with the lowest design value in the region for 2001-2003 was at

Keeney Knob in Summers County in southwestern West Virginia.

Most of the PM2.5 design values in the Mid-Atlantic Region are relatively close to the annual standard of

15 μg/m3

. Table D-1 in Appendix D shows that 25 monitors recorded design values between 15 and 16

μg/m3

, and another 25 were between 14 and 15 μg/m3. Monitors with design values of 16 μg/m3 or

greater were limited to one monitor in the Baltimore area, eight sites in Pennsylvania, seven sites in

West Virginia, and one in Delaware.

PM2.5 Composition

Data from the urban speciation network run by state and local air quality agencies, and data from

the National Park Service’s more rural Interagency Monitoring of Protected Visual Environments

(IMPROVE) network show that, on average, particulate matter across the Mid-Atlantic Region is

dominated by sulfates, and that organics are generally higher in cities than in rural areas. (See Figures 11

and 12.) The sizes of the pie charts in Figures 11 and 12 represent the overall PM mass present at each

site. Figure 12 shows very similar rural concentrations across much of the Eastern U.S. Concentrations of particulate matter at Mid-Atlantic urban sites are all near the annual standard of 15 μg/m3

, while

rural sites are consistently somewhat lower.

Sulfate is a large fraction of the fine particles and haze in the Mid-Atlantic Region throughout the year,

though its role is considerably larger in summer than in winter. In winter, the chemical reactions that

turn sulfur dioxide into sulfate are much slower, so most of the atmospheric sulfur is present as sulfur

dioxide instead of sulfate. In summer, the opposite is true, and most atmospheric sulfur is present as

sulfate. This leaves the significant, but nowhere near as dominant, annual contribution from sulfate

shown in Figures 11 and 12. Ammonia is also quite significant, since it is generally found as ammonium

sulfate in the summertime.

When PM2.5 is broken down in terms of contributions to haze on the 20% worst days, sulfate is also the

dominant component of haze throughout the Mid-Atlantic Region. This is partly because sulfate

aerosols take on water readily, growing rapidly, and scattering light efficiently, and partly because of

their greater concentration. (See Figure 6 in Part I.)

Comparing nearby urban and rural sites can help determine the fraction of particulate matter due to a

particular city’s emissions and the fraction that is due to sources affecting the entire region. Rural

IMPROVE sites are taken to represent the regional load entering a city, while urban sites are taken to

represent the sum of both the regional load and the local contribution. Subtracting the IMPROVE

concentrations from their paired urban site counterparts provides an estimate of the mass and speciation

of aerosols from the urban area. This analysis reveals that over a year, roughly two thirds of the fine

particle mass in Mid-Atlantic cities is the result of a widespread regional load. The other third has been

termed the “urban excess” PM 2.5 concentrations, as shown in Figure 13.
Mid-Atlantic Regional Air Management Association

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Figure 12 Annual average composition of fine particles at rural sites throughout the

United States

This map was developed using annual average data from the IMPROVE network (March 2001- February 2002).

In the eastern U.S., sulfate is highly significant both at urban sites shown in figure 11 and at these rural sites.

Figure 11 Annual average composition of fine particles at urban sites throughout the

United States

This map was developed using data from the Speciation Trends Network (March 2001- February 2002).

Concentrations at these urban sites are higher than at the rural sites shown below, especially in the western U.S.Figures provided by EPA

Part II How’s the Air Out There?

Figures provided by EPA
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A Guide to Mid-Atlantic Regional Air Quality

EPA’s data analysis represented in Figure 13 shows that the excess

mass in urban areas is largely organic carbon and soot. Of that

excess, organic carbon is by far the largest constituent.

A similar analysis of preliminary results from the Pittsburgh “super

site” (see page 26) indicates that the city’s haze has a strong

regional component for both sulfate and organics. This field project

used a network of nearby stations outside the Pittsburgh metropolitan area to determine the regional load. Monitors closer to the city center measured the urban

contribution. Conceptually, the experiment worked the same as the comparisons between urban and

IMPROVE data, though the monitors outside Pittsburgh were closer to the city than most of the

IMPROVE sites were to their urban counterparts. High aerosol loads were present at both the satellite

site and the urban site, with somewhat higher loads of carbon compounds in the city.

The importance of different species shifts from summer to winter in the Mid-Atlantic Region. In

summer, sulfate and organic carbon dominate fine particulate matter mass, with sulfate most important

in the north and nearly equal contributions from both organic carbon and sulfate in the southern part of

the Region. In winter, sulfate is still significant, but not as dominant as in the

summer. Nitrates become far more prominent in winter, since they are more

stable in cold weather and break up readily in the heat of summer. Organic

carbon remains constant throughout the year.

Seasonal Variation in Total PM2.5

PM concentrations can be high at any time of the year, though the highest

values usually occur in the summer. Summertime PM2.5 concentrations often

show patterns similar to those shown by ozone, since the meteorology that

generates PM2.5, haze, and ozone events is often identical. Notable exceptions are found when, for

example, a humid, cloudy summer day with no rain may show high levels of PM2.5, but low levels of

ozone. Winter is another matter entirely, since PM2.5 is often high in winter, when ozone is not.

Figures 16-19 demonstrate that PM2.5 levels are at their highest levels in the summertime. Figures 14 and

15 show that peak values tend to occur throughout the eastern part of the Region on the same days.

(Note that Figures 14 and 15 do not include sites in West Virginia and western Pennsylvania.) The broad

consistency shown on these charts reflects data showing that the highest PM2.5 levels consist primarily

of sulfate, which is a secondary pollutant formed downwind of large sources of sulfur dioxide. The

MARAMA report, The Development of PM2.5 Forecasting Tools for Selected Cities in the

MARAMA Region concluded that there are several types of high PM2.5 events, but that many days with

high PM2.5 levels are influenced by a slow-moving or stationary high pressure system that results in

suppressed vertical mixing of emissions and low wind speed or stagnation.

As explained in Appendix C, the daily PM2.5 standard is 65 μg/m3

, and the Mid-Atlantic Region complies

with this level. However, the Air Quality Index (AQI), described in Appendix A, provides a stricter level

for reporting potential adverse health impacts. Concentrations of 40 μg/m3

 or more for 24 hours triggers

an AQI of “unhealthy for sensitive groups.” At these levels, people with heart or lung disease, older

adults and children are advised to reduced prolonged or heavy exertion.

Much of the fine particle and haze

problem throughout the Mid-Atlantic is

regional in nature, especially in summer.

In winter, the problem becomes much

more localized.

Sulfate is a large fraction of

the fine particles and haze in

the Mid-Atlantic Region

throughout the year, though

its role is considerably larger

in summer than in winter.
Mid-Atlantic Regional Air Management Association

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Part II How’s the Air Out There?

Figure 13 Ambient urban excess PM concentration for 13 example areas

EPA mapped the difference between urban and rural PM2.5 levels in the 13 areas examined. For this map, the

difference was calculated for five categories of particles: sulfates, ammonium, nitrate, total carbon mass (TCM),

and crustal matter. For each category, the height of the bar represents the amount by which the urban

concentration exceeds the nearby rural concentration. In the Eastern U.S., sulfate, nitrate, and ammonia

concentrations are very similar in urban and rural areas, so the differences are small. Most of the “urban excess”

that causes higher concentrations in urban areas is total carbon mass. (Total carbon mass is the sum of elemental

and organic carbon.) Two assumptions about how to calculate total carbon mass are represented, one by the

light gray part of the bar, and the other by the taller, darker gray. The biggest difference in PM concentrations

between the eastern rural and urban areas is that urban areas have higher levels of total carbon.

see http://www.epa.gov/airtrends/aqtrnd03/pdfs/2_chemspecofpm25.pdf page 22

Figure provided by EPA

Figures 14 and 15 show that on about 10 days during the summer of 2002, PM2.5 levels were unhealthy

for sensitive groups at one monitor, at least once in the Region. These were all summer days, occurring

between late June and August and were associated with high pollution episodes.

Figures 14 and 15 show that the first of these four 2002 episodes affected only the northern part of the

Region. These charts also show that the more southern parts of the Region tended to have lower

concentrations in 2002.

Figures 16-19 show data for the entire year for selected areas. The data for 2002 are not necessarily

representative of long-term averages, since weather and emissions can vary from year to year, but
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A Guide to Mid-Atlantic Regional Air Quality

The importance of some species shifts

throughout the year. Organic carbon is

significant throughout the year; sulfate is

dominant in summer and important in winter,

while nitrate is only significant in winter.

these charts illustrate the regional, episodic nature of many high

pollution events.

An Ozone Episode

Day-to-day 8-hour ozone levels show a substantial influence

from short-term changes in the weather. An episode of high

ozone days invariably shows a pattern of high ozone that moves

as weather patterns move across the Mid-Atlantic Region. Episodes involving a particularly large

weather feature such as the Bermuda High may last weeks, as high ozone moves from Texas and

Louisiana, up through the industrialized Midwest, over the Appalachians, and into the Mid-Atlantic Region.

The mid-August 2002 episode is a good example of a lengthy episode. The pattern started as early as

August 5, 2002, when a cold front pushed deep into the South, bringing clean air with it. As the cold

front pushed on, the Bermuda High pushed westward, first over the southern U.S., and then farther

north. High ozone was observed on the 6th in Texas, around Houston. Before long, North Carolina

started experiencing high ozone. High ozone then began the push to the north and east, ending up in the

Mid-Atlantic Region around the 10th of August. Different parts of the region showed the influence of a

myriad of transport patterns in this episode, with recirculation, localized stagnation, a low-level jet, and

long-range transport driven by the Bermuda High all showing up before the episode finally came to an

end with thunderstorms and instability in the Midwest. Ozone along the Eastern Seaboard cleared out

from south to north, and the influence of transport along the populated I-95 corridor was seen clearly as

pollutants pushed from the southwest to the northeast. Some parts of the region experienced their worst

air quality in this end phase.

Since meteorology drives air quality episodes, the pattern of poor air quality in Mid-Atlantic ozone

episodes tends to take on the scale and character of the weather that drives them. The next part of this

report explains more about the influence of weather patterns on air quality.
Mid-Atlantic Regional Air Management Association

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Part II How’s the Air Out There?

Pittsburgh Air Quality Study (PAQS)

The Pittsburgh Air Quality Study (PAQS) was a comprehensive multi-disciplinary set of projects

designed to improve our understanding of airborne PM in the Pittsburgh region. PAQS was led by

Carnegie Mellon University (Professors Spyros Pandis (ChE/EPP), Cliff Davidson (CEE/EPP),

and Allen Robinson (ME/EPP)) and included investigators from twelve universities, two national

laboratories, two private companies, and state and local air pollution agencies. PAQS was supported by the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy

National Energy Technology Laboratory (NETL).

Objectives

• Characterize PM (size, surface, and volume distribution; chemical composition as a

function of size and on a single particle basis; morphology; and temporal and spatial

variability) in the Pittsburgh region.

• Quantify the impact of various sources (transportation,

power plants, biogenic, etc.) on the PM concentrations

in the area.

• Develop and evaluate the next generation of atmospheric aerosol monitoring techniques (single

particle measurements, continuous composition

measurements, ultrafine aerosol measurements,

improved organic component characterization,

etc.).

Lessons Learned

• Regionality of pollution does not imply the same

concentration everywhere. There are gradients,

and pollution moves around.

• Concentrations of both sulfate and organics in Pittsburgh are influenced by large regional

contributions.

• For Pittsburgh, modeling indicates reducing SO2 emissions will reduce sulfate and PM2.5 ,

but nitrate will also increase in all seasons. Modeling also indicates ammonia reductions

can prevent nitrate increases, and NOx emission reductions can help in winter.

• Biogenic (natural) sources, transportation, and biomass burning are important sources of

organics. In summer, about 30-40% of organic PM is secondary, and around 10% in

winter.

• New monitoring technologies (single particle mass spectrometry, semi-continuous metal

measurements) allow fingerprinting of point sources.

For more information see

http:homer.cheme.cmu.edu

USX Tower

USX Tower

Top: July 2,2001, PM2.5 =4 μg/m3

Bottom: July 18, 2001, PM2.5 =45 μg/m3

Photo: Carnegie Mellon University
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A Guide to Mid-Atlantic Regional Air Quality

Figure 15 PM2.5 time series for the southeastern MARAMA Region, summer 2002

Based on data from Federal Reference Method Monitors, four cities in the southeastern part of the Region

experienced many similar and some different patterns of PM2.5 concentrations. During most of this season

concentrations tended to be lower than in the northern cities shown in Figure 14.

Figure 14 PM2.5 time series for the northeastern MARAMA Region, summer 2002

Based on data from Federal Reference Method (FRM) monitors, five cities in the northeastern part of the Region

experienced very similar PM2.5 levels in the summer of 2002.

0

10

20

30

40

50

60

70

6/1/02

6/5/02

6/9/02

6/13/026/17/026/21/026/25/026/29/02

7/3/02

7/7/02

7/11/02

7/15/027/19/027/23/027/27/027/31/02

8/4/02

8/8/02

8/12/028/16/028/20/02

8/24/028/28/02

Concentration (ug/m 3

)

B altim ore, M D

Newark, NJ

Philadelphia, PA

W ashington, DC

W ilm ington, DE

0

10

20

30

40

50

60

70

6/1/026/5/02

6/9/02

6/13/02

6/17/02

6/21/026/25/026/29/02

7/3/02

7/7/02

7/11/02

7/15/02

7/19/027/23/027/27/02

7/31/02

8/4/02

8/8/02

8/12/02

8/16/02

8/20/02

8/24/02

8/28/02

Concentration (ug/m 3

)

B ristol, V A

Charlotte, NC

Richm ond, VA

Roanoke, VA

Figure provided by Bill Gillespie, MARAMA Figure provided by Bill Gillespie, MARAMA

Date

Date
Mid-Atlantic Regional Air Management Association

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0

10

20

30

40

50

60

70

1/1/022/1/023/1/02

4/1/025/1/026/1/02

7/1/02

8/1/029/1/02

10/1/0211/1/02

12/1/02

Concentration (ug/m 3

)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

1/1/20022/1/2002

3/1/20024/1/20025/1/20026/1/20027/1/20028/1/2002

9/1/2002

10/1/200211/1/200212/1/2002

Concentration (ug/m 3

)

Part II How’s the Air Out There?

Figure provided by Bill Gillespie, MARAMA Figure provided by Bill Gillespie, MARAMA

Figure 17 Average FRM values for 2002, Richmond, VA

Richmond’s average daily PM2.5 values in 2002 were somewhat lower than Baltimore, but high values occurred

in both cities on many of the same days.

Figure 16 Average FRM values for 2002, Baltimore, MD

Average daily PM2.5 values exceeding 40 μg/m3 occurred on only six days in 2002 in Baltimore. Daily values

above 40 trigger public health notices that air quality conditions are unhealthy for sensitive groups.

Date

Date
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A Guide to Mid-Atlantic Regional Air Quality

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

1/1/2002

2/1/2002

3/1/2002

4/1/2002

5/1/20026/1/20027/1/20028/1/2002

9/1/2002

10/1/2002

11/1/2002

12/1/2002

Concentration (ug/m 3

)

Figure 18 Average FRM values for 2002, Wilmington, DE

Average PM2.5 daily values for Wilmington for 2002 show a similar pattern to Baltimore and Richmond, with five

summer days exceeding 40 μg/m3 and many days exceeding 15 μg/m3 throughout the year.

Figure 19 Average FRM values for 2002, Pittsburgh, PA.

Data for the Liberty monitor were not included in this chart. The pattern of high daily values is similar to the

other cities in the Region.

Figure provided by Bill Gillespie, MARAMA Figure provided by Bill Gillespie, MARAMA

0

10

20

30

40

50

60

70

200201012002013120020303

20020402

20020502

20020601

20020701

20020731

20020830

20020929

20021029

2002112820021228

Concentration (ug/m3)

Date

Date
Mid-Atlantic Regional Air Management Association

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A Guide to Mid-Atlantic Regional Air Quality

Meteorology and Transport in Air

Pollution Episodes

The Basics: Mixing, Temperatures, and Daily Cycles

What makes a day in an air pollution episode different from any other day? Among other things,

pollution is typically confined to a shallow layer near the surface, either in winter or summer. On cleaner

days, pollution typically mixes more freely to a greater depth, or it might be blown away by strong winds.

The cap that confines pollution near the surface is known as a temperature inversion. A temperature

inversion occurs when warmer, more buoyant air sits over colder, denser air.

Anyone who has hiked in the mountains knows that air usually cools with increasing altitude. Where

there are no mountains, the temperature decreases even more rapidly. This is the natural result of two

facts: air cools as it expands to a lower pressure, and the source of most of the atmosphere’s heat is at

the surface of the Earth. In general, when the atmosphere is well mixed, the temperature drops

uniformly as one rises in altitude. The temperature decrease with distance from the surface sets the

stage for considering what happens to a small, polluted parcel of air near the surface.

Let us start with the common saying “hot air rises,” which should also be paired with “cold air sinks.”

This simple phenomenon is very important in air quality. In the atmosphere, this should be extended to

“hotter air rises, cooler air sinks.” So if a parcel of air is warmer than its surroundings, it will tend to rise.

Now consider stability. If we grab an air parcel near the surface, and give it a nudge upwards, what will

happen to it? If the atmosphere is well mixed, then the air parcel will expand and cool at the same

rate as the rest of the air around it. This parcel has no reason to keep moving up or down because

it is always cooling at the same rate as

the rest of the atmosphere, and is never

hotter or cooler than its surroundings.

If the atmosphere’s temperature does

not decrease uniformly with altitude,

but increases in a temperature inversion, then, when an air parcel is pushed

Summertime air pollution episodes in the Mid-Atlantic Region are typically hazy, hot, and humid, with

light winds and few clouds. Throughout the Mid-Atlantic Region, polluted air from elsewhere, often the

industrialized Midwest, nearly always brings elevated pollution levels into the Region before any

pollution from the Mid-Atlantic Region joins the mix. Wintertime air pollution episodes, in contrast,

are typically cool, with light winds, and are more dominated by local stagnation and local emissions.

Conditions favorable to pollution are produced by a combination of meteorological features of all sizes,

though the largest features typically receive the most attention. This section begins with a description of

the local meteorological conditions generally present during pollution episodes, and then takes a step

back to examine their large-scale causes, before revisiting the small scale to look at the local breezes

that also play a role in air quality. At the end of this section, the meteorological phenomena are brought

together to see how they influence pollutants in an air pollution episode.

Part III

Ordinarily, temperature decreases uniformly with altitude, and

the atmosphere is free to mix vertically. A temperature inversion

occurs when warmer air sits atop cooler air. Temperature

inversions prevent mixing, dividing the atmosphere into two

parts: that above the inversion and that below it.
Mid-Atlantic Regional Air Management Association

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Part III Meteorology

Temperature

Temperature 

Inversion

Altitude

Pollution trapped 

below inversion

Temperature

Temperature 

Inversion

Altitude

Pollution trapped 

below inversion

Figure 20 Temperature inversion

This is a simplified picture of a temperature inversion, where warmer air aloft inhibits vertical mixing,

concentrating pollution in a smaller volume of air near the ground.

upwards, it suddenly encounters warmer air above it. Since the air parcel is now cooler than its

surroundings, it tends to sink. The temperature inversion acts as a cap, inhibiting mixing. Pollutants

emitted from the surface cannot move through the inversion and are trapped near the surface. Likewise, any air above the temperature inversion will be hotter than its surroundings if it tries to move down

through the inversion. The temperature inversion therefore caps air near the surface and divides the

atmosphere into two parts.

Temperature Inversions: Origins

Though they might not know it, most people have direct experience with the effects of a temperature

inversion. On a warm summer night, winds at the surface are generally quite weak because a nighttime

or nocturnal temperature inversion has formed overhead. This inversion forms as the sun sets, and the

Earth’s surface cools. Land surfaces are far more efficient at radiating heat than the atmosphere

above, so the Earth’s surface cools more rapidly than the air. That temperature drop is then conveyed

to the lowest few hundred feet of the atmosphere. The air above cools more slowly, and a temperature

inversion forms only a few hundred feet (sometimes only a few feet) above the ground. The inversion

divides the atmosphere into two sections, above and below the inversion, which do not mix. In the

surface section, winds are weak, and any pollutants emitted overnight accumulate beneath the

inversion. Above the inversion, winds continue unabated through the night and can even become

stronger as the inversion isolates the winds from the friction of the rough surface. The inversion is

similar to an air hockey table, letting the winds aloft blow freely by eliminating surface friction.

In the morning, the nocturnal inversion breaks down as the heating of the day gets into full swing.

Eventually, the sun warms the Earth’s surface, which in turn warms the cool air near the surface,
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A Guide to Mid-Atlantic Regional Air Quality

Temperature

Altitude

←Subsidence

Temperature

Altitude

←Subsidence

← Nocturnal

replacing the heat that radiated away the night before. When the air near the surface warms enough, it

rises and breaks through the former nocturnal inversion, so the atmosphere may once again mix freely.

Air from above then mixes down to the surface, and air that was near the surface is free to mix with the

air above. (Depending on whether the air above the inversion is cleaner or more polluted than the air at

the surface, this mixing can either lower or increase air pollution levels.)

A second inversion is often present during an air pollution episode, well above the nocturnal inversion,

but with a very different cause. This is a subsidence inversion, caused by subsiding (sinking) air (Figure

21). Air cools as it rises and expands, and warms as it sinks or is forced downward and compressed.

This warming leads to a subsidence inversion—a phenomenon associated with the sinking motion that

occurs in a high pressure system. (High pressure systems are discussed later in this document.) This

kind of inversion is particularly strong, since it is associated with a large scale downward motion of the

atmosphere. The subsidence inversion typically caps pollution at a higher altitude in the atmosphere,

and it is far more difficult to break than the nocturnal inversion’s cap. The subsidence inversion limits

vertical mixing in the middle of the day during an air pollution episode.

Daily Cycles

As temperature inversions build and break down with heating from the sun, they produce daily cycles of

winds and air pollution. Consider a typical day, starting at sunrise when the air is at its coolest. At this

time, the nocturnal inversion is in full force overhead, and winds at the surface are typically quite calm,

Figure 21 Daily cycle of inversions and mixing

A temperature inversion effectively traps pollutants near the surface and allows pollutants above the inversion

to travel freely over considerable distances. There are two kinds: a low level “nighttime” or “nocturnal”

inversion; and an elevated “subsidence” inversion. The low level inversion typically breaks down in the mid- to

late-morning, while the elevated inversion is more difficult to breach and limits vertical mixing at mid-day during

air pollution episodes.
Mid-Atlantic Regional Air Management Association

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Part III Meteorology

while winds above the nocturnal inversion continue unabated. As the temperature increases through the

morning, the nocturnal inversion eventually breaks down, and the atmosphere mixes up to the height of

the subsidence inversion. If the day is particularly hot, the subsidence inversion may also be punctured.

In the late afternoon, temperatures are at their hottest, and the atmosphere mixes to its greatest height.

As afternoon passes into evening, temperatures cool, and mixing subsides. The following night, the

nocturnal inversion forms, once again isolating the surface from stronger winds only a few hundred feet

overhead. This process continues uninterrupted until the large-scale weather pattern changes.

The daily cycle of mixing is partially responsible for the daily cycle of air pollutants such as ozone. At

night, ozone near the surface cannot mix with ozone above. Instead, ozone below the nocturnal

inversion is destroyed as it reacts with the Earth’s surface

and everything on it. In a city, fresh nitrogen oxide (NOx

)

emissions react with ozone, further reducing its concentration,

so that by morning, very little ozone is left below the nocturnal

inversion.

Above the nocturnal inversion, the story is entirely different.

Ozone from the previous day’s emissions remains largely

intact. There are no surfaces to react with the ozone and

destroy it, so a large reservoir of ozone remains above the

inversion. In the morning, when the nocturnal inversion breaks

down, all the ozone that remained above the inversion comes

mixing back down. Likewise, the air near the surface, laden

with the emissions of the night before, mixes up away from the

surface. The result of all this mixing is a sudden surge in ozone levels in the middle of the morning.

This surge is almost entirely due to mixing. Readings from elevated monitors and measurements with

instrumented aircraft have confirmed this large reservoir of ozone aloft. Those measurements also

show ozone mixing down to the surface.

This mixing mechanism will also be important in explaining the significance of long-range transport,

because the ozone above the nighttime inversion usually comes from far away and is not local.

Pollutants such as particles that do not react with the surface as readily as ozone do not show such a

marked diurnal cycle, but the same mixing mechanism also affects their concentrations. Nighttime

emissions of particles can build up under the nocturnal inversion, leading to higher levels in the early

morning. In the summertime, regional sulfate levels above the inversion can combine with local

emissions as the inversion breaks up. In the winter, with less sunshine, it’s harder to break the inversion,

and local emissions can continue to build unless washed out by rain or dispersed by winds.

Meteorological Transport Mechanisms

Large-scale Transport: Global Circulation, High Pressure, Low Pressure,

and Fronts

All weather systems on Earth, from the global circulation pattern to the smallest sea breeze, are driven

by differences in temperature. Globally, the largest circulations (such as the trade winds in the tropics

and mid-latitude storms) are driven by temperature differences between the steamy tropics and the icy

poles. Storm systems serve to even out these differences in temperature by mixing cold and warm air.

The Sun’s daily cycle of heating results in a

daily cycle of mixing. Mixing is driven by the

warm surface, which heats the air above it.

That warm air rises, causing colder air to fall

down to replace it. Temperature inversions

inhibit mixing, so the air below an inversion

may have completely different characteristics

from that above the inversion. Air below the

nighttime inversion is rather still, while air

above that inversion may be moving quite

rapidly.
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A Guide to Mid-Atlantic Regional Air Quality

As the position of the Sun in the sky shifts from its northernmost point at the summer solstice to its

southernmost point at the winter solstice, storm tracks shift, too. Over the Mid-Atlantic Region, this

shift produces winter weather with frequent storms, which periodically clean out the Region’s air. In

summer, the storm track shifts far to the north, so summer cold fronts typically pass through the northern

Mid-Atlantic Region, occasionally reach the central part, and only rarely push into the far southern

parts.

Because the storm track shifts, most of the Mid-Atlantic Region’s worst pollution events occur in the

summer—wintertime weather is not conducive to the large, regional episodes seen in summer. Wintertime episodes can be locally intense, but they generally do not share the regional nature of their summertime counterparts.

Other seasonal factors also combine to influence pollution events: temperatures, mixing, and strong

winds all shift with the seasons. The next sections discuss the large-scale impacts of global circulation,

high and low pressure systems, and fronts.

Global Circulation

The global circulation of the atmosphere is driven by the enormous heat engine of the tropics. When the

Sun’s rays are directly overhead, the surface heats rapidly, pushing copious amounts of moisture

skyward. This lift eventually results in the downpours for which the tropics are deservedly famous.

Just outside the tropics, the air that was lifted aloft by the strong tropical heat now sinks, creating large

areas—the subtropics—where the upward motion of air is strongly discouraged. This large belt of

sinking air lies between 20 and 30 degrees north, where many of the world’s great deserts are found.

Land masses and oceans pinch this belt in places, so, for example, the Southeastern United States is

relatively moist, while the Southwestern United States is quite dry. These large areas of sinking air form

semi-permanent, high pressure systems that strongly influence weather throughout the subtropics.

For the Mid-Atlantic Region, the most relevant feature of this global chain of subtropical high pressure

systems typically lies offshore to our east: the Western Atlantic Ridge, also known as the Bermuda

High. In the summer, it occasionally pushes westward, bringing a

heat wave to the Eastern United States. In winter, it retreats to

the Azores in the eastern Atlantic.

Winds circulating clockwise around the Bermuda High are also

responsible for steering hurricanes as they travel across the

Atlantic Ocean toward the Leeward Islands and the Eastern United

States. Depending on its position, form, and orientation, the

Bermuda High can steer clean, moist air to the Mid-Atlantic

Region or it can bring a prolonged pollution episode. Air quality

becomes particularly foul when the Bermuda High links up with a

polluted continental high pressure system.

In contrast to the conditions in the middle of the Bermuda High, where rainfall is suppressed, at its outer

fringes, one often finds numerous strong thunderstorms. These thunderstorms occur partly because the

far western edges of these systems tend to be unstable, but circulation around the Bermuda High also

brings with it considerable moisture from the Gulf of Mexico. In areas where the suppressing influence

of the Bermuda High is weak, this moisture leads to numerous thunderstorms. The Bermuda High is

Because the storm track shifts, most of

the Mid-Atlantic Region’s worst pollution

events occur in the summer—wintertime

weather is usually not conducive to the

large, regional episodes seen in summer.

Wintertime episodes can be locally

intense, but they generally do not share

the broad regional nature of their summertime counterparts.
Mid-Atlantic Regional Air Management Association

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Part III Meteorology

Storms too far north and 

too weak to bring relief

Hot humid air from 

the Gulf of MexicoClockwise circulation 

around high pressure

H

therefore often referred to in weather forecasts as a “ring of fire,” where a parched, polluted center is

surrounded by a ring of hefty thunderstorms with relatively good air quality.

In winter, the tropics remain hot, but the region of peak heating shifts south of the Equator. This allows

cold air from the Arctic to push farther south. The clashes between this cold Arctic air and the warmer

air to the south produce the strong winter storms so common to mid-latitudes such as the Mid-Atlantic

Region. These clashes bring frequent storms with strong winds, which in turn limit the extent of wintertime pollution episodes. Instead, wintertime air pollution episodes tend to arise from local stagnation and

nearby sources.

Just as the tropics force air upwards, cold air sinks over the poles, completing a hemisphere-wide

circuit. The interaction of cold air from the poles and warm air from the tropics, when combined with

a steering effect resulting from the rotation of the Earth, leads to the west-to-east motion of winds and

storm systems in the mid-latitudes. Near the equator and near the poles this is not the case—the

prevailing winds at those latitudes blow from the east to the west. Two things drive all of these

prevailing winds: the temperature difference between the equator and the poles, and the rotation of the

earth.

Figure 22 Bermuda High

A semi-permanent area of high pressure, commonly known as the Bermuda High, forms over the Atlantic Ocean

during the summer and is the key player in the summer climate for most of the East. The clockwise circulation

around the high pressure center brings southerly winds to the East, especially the Southeast.
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A Guide to Mid-Atlantic Regional Air Quality

High and Low Pressure Systems

High pressure systems bring calm, cloudless, hot sunny days in

summer, and may bring bitter cold in winter. They also bring high

humidity (in summer), limited vertical mixing, and stagnation—all the

signatures of a heat wave in the Mid-Atlantic summertime. Air in a high

pressure system circulates clockwise in the Northern Hemisphere,

and sinks. A high pressure system should be thought of as a threedimensional flow which draws air in at high altitude, pushes it downward

to the surface, and spreads out. The sinking motion suppresses vertical

mixing, clouds, and rainfall. The slow spreading motion also means that

winds at the surface will be quite weak.

In contrast, a low pressure system is a fountain of air, drawing strong

surface winds in toward the center, and forcing them out the top. Low pressure systems circulate in the

opposite direction of high pressure systems, or counterclockwise in the Northern Hemisphere. The

upward motion in a low pressure system produces increased mixing, showers, stronger winds, and the

end of a pollution episode.

High pressure systems can produce particularly strong pollution episodes if their circulation drives air

from one polluted area to another. Of particular importance to the Mid-Atlantic Region are episodes

where the Bermuda High produces stagnant conditions over the Mid-Atlantic and winds are either from

the industrialized Midwest or aligned along the East Coast’s urban corridor. Often, this occurs when the

Bermuda High combines with a high pressure system over the North American continent that has been

collecting pollution for days. Most of the longest-lasting Mid-Atlantic pollution episodes have occurred

when the Bermuda High combines with a continental high pressure system. When this happens, the two

form a very large high pressure system. Conditions are made worse because the continental part of the

new, larger high pressure system is already laden with pollution.

The high temperatures and clear skies that accompany summertime high pressure systems also

accelerate smog chemistry, forming ozone, sulfate, and organic carbon aerosols, among others, more

quickly. Cloudless skies let through more of the ultraviolet and visible light that drives smog photochemistry. Because they bring higher temperatures and cloudless skies, slow moving high pressure

systems usually cause air pollution episodes when they remain over the continent.

In winter, high pressure systems often descend out of Canada, ushering in a severe cold snap with very

clean clear air. Wintertime pollution episodes are in some ways different from those in the summer. The

local stagnation and tight cap on mixing that accompany wintertime

high pressure systems will produce a localized pollution episode.

Until recently, the focus of most air pollution studies has been on

summertime ozone, so wintertime particle pollution has been less well

studied. It appears, however, that wintertime episodes are more the

result of local stagnation than their summertime cousins. Summertime episodes typically produce a broad region of high pollution

(ozone or particle), whereas wintertime particle pollution episodes

are localized in cities and near pollution sources.

High pressure systems bring clear

skies and stable conditions,

exactly the situation needed for an

air pollution episode. In contrast,

low pressure systems bring

instability and storms, leading to

considerable mixing and high

winds. Most Mid-Atlantic air

pollution episodes occur when high

pressure is in the area and the air

stagnates.

Air in a high pressure system circulates clockwise in the Northern

Hemisphere, and sinks. A high

pressure system should be thought of

as a three-dimensional flow which

draws air in at high altitude, pushes it

downward to the surface, and spreads

out. The sinking motion suppresses

vertical mixing, clouds, and rainfall.
Mid-Atlantic Regional Air Management Association

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Part III Meteorology

Under unusual circumstances, high and low pressure

systems can team up to produce an air pollution episode.

In July 2002, a departing low pressure system and an

advancing high pressure system over central Quebec

combined to deliver strong northerly winds to the MidAtlantic Region. Ordinarily, northerly winds bring very

clean air to the Region, since there are very few large

sources of emissions in central and northern Quebec.

In early July 2002, this was not the case. Between these

two systems, several forest fires were burning out of

control in central Quebec. Instead of bringing clean air, the colliding high and low pressure systems

funneled smoke from these fires to much of the Eastern United States. The stability of the trailing high

may have helped the smoke to make such a long journey. High concentrations of both particulate matter

and ozone were reported, and woodsmoke could be smelled as far south as Maryland and Virginia.

Fronts

Fronts are the familiar serrated lines shown on weather maps. Warm fronts and cold fronts represent

the boundaries between air masses—large bodies of air with similar properties. Fronts are named after

the character of the advancing air, so a cold front indicates colder or drier air moving into an area of

warmer, moist air, while a warm front indicates warm, moist air moving into colder, drier air.

Cold fronts tend to mark a sharp contrast between air masses, and this contrast often causes the

thunderstorms that bring an air pollution episode to an end. Since cold air tends to stay near the surface,

a cold front is a wedge of cold air that forces warm, moist air upward. This upward forcing produces

the sometimes violent storms associated with the front. Behind the front, the advancing cold air is

typically quite clean, so by bringing cleansing storms and cleaner air, a passing cold front usually

ends an air pollution episode. As the front pushes

from west to east, winds ahead of the front will

blow along it from the southwest to the northeast.

In the Mid-Atlantic Region, this typically means that

winds will be blowing from the southwest before the

front passes through. In the summer, southwest

winds ahead of an approaching cold front can alter

the transport of pollutants on the final day of a pollution episode.

Unlike the violent weather of a cold front, a much

broader area of milder showers generally marks warm

fronts. A warm front is a wedge of warm air that

rides gradually over cold air that is already in place.

Since cold air stays near the surface, a warm front

does not immediately replace the surface air with

warmer air. The transition occurs more gradually as

the cold air retreats. Since they cause broad areas of

showers, the atmosphere in the area of the warm front

is generally quite clean.

Most of the longest-lasting Mid-Atlantic pollution

episodes have occurred when the Bermuda High

combines with a continental high pressure

system. When this happens, the two form a

very large high pressure system. Conditions are

made worse because the continental part of the

new, larger high pressure system is already

laden with pollution.

source: http://earthobservatory.nasa.gov/

Figure 23 Satellite picture of smoke

from 2002 Quebec wildfires

On July 7, 2002 smoke from Quebec, Canada

wildfires blew southward over the United States.
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A Guide to Mid-Atlantic Regional Air Quality

Maryland Aerosol Research

and Characterization

(MARCH Atlantic)

Located between Baltimore and Washington, at Fort Meade,

Maryland, and coordinated with other studies in the region,

MARCH Atlantic began ground- and aircraft-based measurements in 1999 and ended in 2002,

conducting one month of intensive air quality measurements each season. Active data analysis

continues. Peter Mueller [Electric Power Research Institute-EPRI], Bruce Doddridge and Russ

Dickerson [University of Maryland], and Judy Chow [Desert Research Institute - DRI] led the

study, which also included investigators from the University of Southern California [Ron Henry]

and the National Park Service [Bill Malm].

Objectives

• Characterize the seasonal, daily, and spatial changes in the chemical composition of both

gases and particles.

• Identify the most likely sources of airborne particulate matter (PM).

• Contribute to the development of state and federal PM monitoring methods.

Lessons Learned

• In summer and winter, PM exhibits the highest seasonal concentrations and different chemical

composition. In summer, particulate matter reduces visibility more than in winter at similar

concentrations and relative humidity.

• Substantial day-to-day differences in PM occur in several 3- to 5-day weather-driven

episodes in both summer and winter.

• Fine PM (PM2.5) consists primarily of ammonium sulfate and nitrate plus carbonaceous

material (C). Sulfate is higher in summer than winter. Nitrate and C are higher in winter

than in summer.

• Carbonaceous material is about 20% soot and 80% other organics in all seasons

• The most serious haze and PM episodes in the Mid-Atlantic Region occur with a

combination of westerly transport and regional recirculation or with southerly air

flow and localized recirculation of emissions.

• Regional and local emissions influence the composition and concentration of PM

differently. In summer, within-region emissions may contribute about 30% of PM2.5 mass.

In winter, within-region emissions my contribute over 60%.

• Routine public agency monitoring of 24-hour particulate matter should be supplemented

with continuous measurement technology.

For more information and a complete bibliography of related publications, contact Peter

Mueller at pklausm@mac.com.

photo: Bruce Doddridge
Mid-Atlantic Regional Air Management Association

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The low level jet is a river of air a few

hundred feet above the surface. It is

driven by differences in heating

between a mountain range and the air

above a flat plain. Along the East

Coast, it runs from the southwest to the

northeast, following the contours of the

Appalachian Mountains. The low level

jet is typically a few hundred feet thick,

and may run from South Carolina all the

way up to New England.

When a front stalls, it is called a stationary front, marking the boundary between two contrasting air masses. This is often the fate of

summertime cold fronts, which advance as far south as they can

before running out of steam. Stationary fronts sometimes persist for

days, serving as a focal point for storm development. Ripples tend

to form along the frontal boundary, resulting in a series of small

disturbances that roll along the front, usually from west to east. As

these disturbances move along, they mix warm, moist air south of the

front with cool, dry air to the north of it, producing showers and

thunderstorms. A persistent stationary front can generate storm after

storm, often producing copious rain over the same region and causing

flooding.

To the north of a stationary front, conditions are generally quite clean,

since fresh clean air from Canada is transported south to the frontal boundary. In contrast, the stagnant,

hot conditions south of the front often lead to poor air quality. In the Mid-Atlantic Region, a cold front

will often descend south, become stationary, and then return north as a warm front. In this case, the

returning warm air is often quite polluted since it contains several days of emissions that baked under the

warm, cloudless conditions south of the front.

Smaller Scale Motions: Low Level Jet, Appalachian Lee Side Trough, Sea

Breezes, and Mountain Breezes

In addition to the large-scale effects just described, smaller scale weather patterns also influence air

pollution. This section discusses four such weather phenomena: the low level jet, the Appalachian

lee-side trough, sea breezes, and mountain breezes.

Low Level Jet

The low level jet, sometimes called the nocturnal jet, is a low-altitude region of rapid winds that forms at

night under the same calm conditions typically present in a pollution episode. Forming just above the

nighttime temperature inversion mentioned previously, the low level jet depends on the isolation from the

surface provided by the inversion. It is typically found where a range of mountains meets a flat plain. In

the Mid-Atlantic Region, those features are the Appalachians and the Atlantic Coastal Plain. The Great

Plains also have a much stronger low level jet resulting from the

differences in heating between the Rocky Mountains and the Great

Plains. That low level jet fuels some of the enormous thunderstorms

that periodically rumble across the Great Plains.

In some sense, the low level jet is a delicate feature. It only forms

when fronts and storm systems are far away. It is generated by the

temperature difference between the mountainside and the air at a

similar altitude above the coastal plain. As mentioned earlier, land

cools much faster than air, so the mountainside cools relatively

quickly. In contrast, if one traveled a few miles horizontally away from

the mountains so the surface was a few hundred meters below, the air

would be warmer, since it would be far from a rapidly cooling land

surface. This temperature difference drives the low level jet.

Fronts mark boundaries between air

masses, and are labeled by the

character of the advancing air, so a

cold front denotes colder or drier air

pushing into warmer or wetter air. All

fronts are weather makers, though

the conditions caused by each kind

of front are different. Cold fronts

generally usher in cleaner air, while

warm fronts may usher in a pollution

episode.

Part III Meteorology
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A Guide to Mid-Atlantic Regional Air Quality

In the Mid-Atlantic Region, the low level jet was ignored or missed entirely until recently because the

twice-daily weather balloon launches always occurred near dawn and sunset. Since the low level jet is

at its strongest in the middle of the night, these balloon launches missed its peak winds. The advent of

continuous wind profiler systems made this phenomenon considerably easier to study.

The low level jet, as one might expect, blows over the Atlantic Coastal Plain, running parallel to the ridge

of the Appalachians. Physically, it is like a river of air about 500 ft. above the ground that moves from

the southwest to the northeast. Typically, it is a few hundred meters deep, a hundred kilometers wide,

and persists for about six hours. Its peak wind speeds are typically 30 to 40 miles per hour, which

implies that a slug of air could move roughly 200 miles overnight. Once the sun rises the next day, the

thermal differences that created the low level jet disappear as the Earth’s surface warms. Warming

also breaks down the nighttime inversion, eliminating the frictionless surface that the low level jet needs,

and mixing the contents of the low level jet down to the surface.

Appalachian Lee Side Trough

As its name suggests, the Appalachian lee side trough forms on the leeward (downwind) side of the

Appalachian Mountains. In a sense, it is the daytime companion to the low level jet, since it forms under

similar, stagnant conditions, though the mechanism for its formation is entirely different. The lee side

trough forms when winds blow over the mountains and down to the coastal plain. As these winds

descend, the air is compressed, warming it, and making it more buoyant. Its additional buoyancy makes

the air rise, leading to a broad area of low pressure at the surface—in short, a trough.

Since the air is typically rather dry, and the trough itself is rather weak, it does not usually lead

to showers and thunderstorms the way a trough associated with other weather systems would. It does

Figure 24 Time and altitude profile of a low level jet

The low level jet is a river of fast-moving air sometimes present at night about 500 feet above the ground. It

can move air about 200 miles in one night.
Mid-Atlantic Regional Air Management Association

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Upper level winds Upper level winds

from the west... from the west...

...are turned by the are turned by the

lee side trough lee side trough

cause winds to shift their direction, so a wind

that comes over the mountains from the west

will turn and blow from the southwest along

the coastal plain. Therefore, when surface

winds on the coastal plain are from the southwest, if the Appalachian lee side trough is in

place, it may be that the air actually came

from the west, descended, and turned.

The implication for air quality policy is

straightforward. Pollution making its way

over the mountains from the west will turn

once it reaches the coastal plain and come

from the southwest. Since surface winds

are then from the southwest, when the Appalachian lee side trough is in place, the

limits of a city’s airshed will be pushed

farther south and west than they might

otherwise be.

Local winds: Land and Sea Breezes, Mountain and Valley Breezes

In the Mid-Atlantic Region, land and sea breezes, and mountain and valley breezes have important

influences on local air quality. These local winds are all driven by the same mechanism, namely a

difference in temperature that produces a difference in pressure.

A sea breeze forms in the afternoon when the land is considerably hotter than the ocean or bay. The hot

air over land rises, leaving something of a vacuum in its absence. Over the ocean, the opposite happens:

the air over the ocean cools and sinks, creating a localized area of high pressure. Air then flows from

the high pressure over the ocean toward the low pressure over land, creating the refreshing afternoon

breeze loved by beachgoers everywhere. At night, the opposite may happen if the land cools to below

the ocean’s temperature, and a land breeze blows out to sea. Since the nighttime temperature differences are typically much smaller than in the day, the land breeze is likewise

weaker than the sea breeze. Both can form over any sizable body of water,

making the winds of coastal bays notoriously difficult for sailors and meteorologists alike. Sea breezes typically only penetrate a few miles inland, since they

are driven by temperature contrasts which disappear inland.

Air quality is affected by sea and bay breezes in coastal cities because the sea

breeze can act as a bulldozer, pushing a city’s polluted air back over the city.

Picture a city near the water. Emissions have been pouring out of the city all

night and into the early morning, generally moving out towards the sea. Before

the sea breeze circulation sets up, a wall of pollution has moved out over the

water. If this pattern were to continue, the city’s pollution might just be blown

out to sea. When a sea breeze circulation sets up, however, that polluted air is

pushed back toward the city. Furthermore, air that used to leave the city freely

is stuck with nowhere to go. The sea breeze has created a wall and sealed off

Figure 25 Appalachian lee side trough

The Appalachian lee-side trough is an area of low pressure

east of the mountains that channels winds to the northeast.

Part III Meteorology

The Appalachian lee side

trough forms when winds

blow over the Appalachians

and air warms as it flows

down the mountain resulting

in an area of low pressure

on the downwind side of the

mountains. This feature

turns winds that come over

the Appalachians from the

west so they come from the

southwest.
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A Guide to Mid-Atlantic Regional Air Quality

the exit route for pollutants from the city, making the air stagnant and highly polluted. The sea

breeze only pushes a few miles inland, which is where the barrier to mixing lies. Later in the day,

if one is fortunate enough to be on the ocean side of the city, the air may be quite clean, but the air

is usually quite dirty on the inland side. The city suffers from its own recirculated pollution, and by

the wall set up by the sea breeze that does not allow pollution from

the city to flow away from it. The sea breeze is therefore both a

bulldozer and a dam.

For example, bay breezes from the Chesapeake Bay often make

Baltimore’s summertime air quality particularly poor. Air from the

city cannot escape directly across the Bay. On the other hand, a

few miles closer to the Bay, conditions are often considerably cleaner,

since no fresh emissions have gotten into the air there since earlier

that morning.

This is not to say that the sea breeze, or in this case, the Chesapeake

Bay breeze, is an impenetrable wall that prevents all pollution from

crossing it! The bay breeze is a shallow circulation, and may only

extend a couple hundred meters above the surface. Polluted air from

the west side of the Bay can still mix upward, where it meets the stronger winds aloft, pass over the Bay

breeze circulation and come back down on the east side of the Bay. The sea breeze restricts the flow of

air at the surface, where wind speeds tend to be weak anyway, but still allows for transport aloft. This

mechanism is described in more detail later as the “up, over, down” mechanism.

Mountain and valley breezes are also driven by temperature differences, but in this case, the difference

arises because mountain peaks cool more quickly than the valley at night, and heat up more rapidly in the

daytime. At night, cool air sinks and flows down the valley, settling in the lowest points, while in the day,

warm winds blow up toward the peaks from the valley below. Local topography is very important in

generating this phenomenon, making the breeze unique to a particular area.

Mountains and valleys also serve to isolate air in the valleys, while air at the mountaintops may be

coming from very far away. Mountain winds, inversions, and mixing are quite complex. On a quiet

night, the mountaintop may be in the free troposphere, open to long-range transport, while the

valley below is usually capped by a nocturnal inversion, isolating pollution in the valley. Air quality

measurements taken during plane flights in the Shenandoah River Valley have shown that the

air pollutants in the valley may be rather different from the air at the nearby peaks. Cities on the western

side of the mountains will find that the Appalachians are capable of

damming pollution up against them.

Stagnation and Transport in Air Pollution Episodes

To some extent, air stagnation is common to all air pollution episodes. If

pollutants are not diluted by mixing upward or being blown downwind,

they become concentrated near the surface. Pollution episodes that only

feature stagnation are typically short-lived, since a small change in the

weather will usually provide some relief in the form of increased mixing

or increased winds. This is not to say that an extended stagnation

Sea breezes, land breezes, mountain

breezes, and valley breezes are all

local winds driven by differences in

temperature. These small-scale

winds are difficult to predict and

may block flow into or out of a city.

When they block air flow out of a

city, conditions in the city may be

particularly dirty, while conditions a

few miles away may be relatively

clean.

Stagnation is characteristic of

most air pollution episodes,

though most also have some

other transport feature that

increases pollutant levels. Weak

winds and poor mixing ensure that

the pollution emitted by a city

does not go far.
Mid-Atlantic Regional Air Management Association

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Part III Meteorology

Recirculation occurs when a city’s

pollutants are brought back over it by

changing winds. Since the city gets a

second dose of its own pollution, this

weather pattern typically produces

highly polluted conditions.

episode is impossible—only that such episodes typically have additional causes.

Recirculation

Any weather pattern that brings a region’s own pollution back over it

can produce a pollution episode. This recirculation of polluted air is

effectively the same as having a polluted area upwind, since pollution

has time to age in the sun, and air entering the area is already somewhat polluted before it arrives. Recirculation typically results when winds have been blowing from one

direction for a time and then reverse, bringing the pollution of the previous hours and days back over the

region. In the Mid-Atlantic Region this often happens when a weak cold front pushes slowly from north

to south, stalls, and then retreats back north. The air south of that front, as mentioned before, is

recirculated, polluted air.

Along-Corridor Flow

Since most of the East Coast’s population is located along the I-95 corridor on the coastal plain east of

the Appalachian Mountains, a particularly smoggy episode can result when winds blow along the

corridor. Typically, winds blow from the southwest to the northeast, pushing pollution from one city to

the next up the coast. Hypothetically, this pattern could also work for winds from the northeast, but

those are usually associated with storm systems and strong winds, which do not produce pollution

episodes. The low level jet, the Appalachian lee-side trough, a properly oriented high pressure system,

and an advancing cold front can all lead to along-corridor flow. This flow pattern is often associated

with the end of an episode where flow is from the southwest ahead of a cold front and behind a

retreating high pressure system, though that is not the only time it occurs.

Up, Over, Down

In a heat wave, surface winds are ordinarily quite weak, to the great frustration of those who must

suffer through it, so it might appear at first that long-range transport of air pollution is rather unlikely.

Above the surface, however, winds are considerably stronger than at the surface, so if pollution can be

lofted above the well-mixed layer, it may be transported rapidly over long distances. The overall

mechanism is simply summarized as “up, over, down.”

During the day, air pollution mixes upward, carried by the heat of the day. By the middle of the day, the

lowest part of the atmosphere is fairly well mixed. Research aircraft routinely measure constant

concentrations of carbon monoxide, ozone, and other pollutants throughout this layer.

For the sake of illustration, suppose that this well mixed layer is 6000 ft. deep, a typical depth in the

Mid-Atlantic Region. As the day progresses into night, the nighttime inversion forms a few hundred feet

above the surface. Again, for sake of illustration, take the nighttime inversion to be at a height of 1000

feet above the surface, though this is perhaps a bit high. Once the inversion forms, it isolates the surface

from the air above, so the lower atmosphere is divided into two reservoirs: one below 1000 ft. and one

above, between 1000 ft. and 6000 ft. In the lower reservoir, winds are the familiar calm summertime

winds, while in the upper reservoir, winds can be quite strong. So while long-range transport along the

surface is not likely, transport above the inversion continues unabated.
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A Guide to Mid-Atlantic Regional Air Quality

So far, only the air above one city has been considered. Now a second city, downwind of the first, will

be added to the picture. During the first day, pollution mixed up to 6000 ft., and that night the lowest

1000 ft. remains near the ground of both cities. The top 5000 ft. is free to move about, isolated from the

ground the way an air hockey table isolates the surface from a puck on a cushion of air. Overnight,

winds above the inversion blow from the first city to the second, carrying this pollution along. The

following morning, the downwind city is faced with a new problem. On the previous day, the afternoon

heat resulted in mixing of that city’s air up to 6000 ft., into a pristine atmosphere. On this day, however,

between 1000 ft. and 6000 ft. lies the pollution from an upwind city. So when the heat of the day sets in,

dirty air mixes down from above. On this day, pollution levels will certainly be worse in the downwind

city, since the pollution of two cities is involved. In the middle of the afternoon, the pollution over the

downwind city is a mixture of its own pollution and that which came in from the upwind city.

The overall picture involves mixing up to a considerable height over one city, producing a column of

pollution up to 6000 ft. At night, the bottom of that column is sealed near the ground by a temperature

inversion, while the top 5000 ft. slips away uninhibited. The next day, an unfortunate downwind city has

a large plume of air pollution overhead, just waiting to mix down in the heat of the day. In the afternoon,

the local plume from that city mixes upward into a dirty, transported plume from a distant city. The

result is a surge in ozone and other pollutants in the mid- to late- morning as the nighttime inversion

breaks down.

This mechanism has implications for air pollution control strategies and the areas over which they should

be implemented. At times, power plants have appeared to take the bulk of the blame for long-range

transport of air pollution, but power plants are not the only concern in considering long-range transport.

Power plants and other tall-stack industrial facilities do have something of a head start, in that their

emissions are typically lofted to greater heights than those from automobiles or other surface sources.

But surface-based emissions can also be lofted by mixing and then transported over large distances.

The heights here should not be taken to mean that the downwind city is only responsible for 1/6th of its

ozone problem. The concentrations of volatile organic compounds (VOCs) and NOx

 in that surface

layer have not been mentioned here, and it should be remembered that the downwind city does not

cease emissions once the nocturnal inversion is broken! Emissions from both cities are important in

producing the problem, and will have to be taken into account if an effective air pollution control strategy

is to be designed for the downwind city.

The Airshed and the Range of

Transport

The term airshed is a useful concept, similar to its cousin,

the watershed, only the airshed of a city refers to the

area from which that city receives a particular pollutant.

As such, it has no concrete boundaries, and differs from

pollutant to pollutant. For long-lived pollutants such as

methane and chlorofluorocarbons (CFCs), the airshed may

be the entire globe, while highly unstable compounds may

have an airshed of only a few city blocks. The range that

is relevant to transport therefore varies by pollutant.

The up, over, down mechanism is responsible

for carrying pollutants from the surface over

great distances. Pollutants mix upward with

daytime heating, and then are caught up in the

stronger winds aloft. Overnight, those winds

may carry pollutants over great distances,

particularly when a nighttime inversion is

present. The next day, those pollutants mix

back down to the surface when daytime heating

breaks down the nighttime inversion, polluting a

downwind area.
Mid-Atlantic Regional Air Management Association

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Part III Meteorology

The airshed is the entire area

whose emissions affect a

city or region. It is not as

well defined as a watershed,

and varies from pollutant to

pollutant.

The relevant distance of transport is longer in

the north than in the south. Transport is

important throughout the Region, and local

emissions add pollution to long-range transport.

The meteorological patterns alluded to earlier when discussing global

circulation dictate that transport distances are necessarily longer in

the northern Mid-Atlantic Region than in the southern part of the Region.

Subtropical high pressure systems spend more time over the south, limiting

the range of transport. In the north, the Region is closer to the storm track,

meaning that winds are stronger, and the distances over which pollution may

be transported are necessarily longer.

While long-range transport and local stagnation are important throughout

the Region, the relevant range of transport is shorter in the south than in the north. Individual

episodes vary widely, so an individual episode may be almost entirely due to localized stagnation,

while another episode may show a strong influence from long-range transport. On the whole,

transport is important throughout the Region, and high local emissions add pollution to long-range

transport.

The Whole Picture: Everything at Once

Breaking the meteorology of an air pollution episode into parts makes it easier to understand, but we

must recognize that these weather patterns do not exist in isolation. A typical pollution episode reflects

influences of several, if not all of these weather patterns by the time it is over. High pressure typically

dominates, producing limited mixing and weak surface winds. Winds aloft will often bring pollution from

the industrialized Midwest across the mountains via the up,

over, down mechanism. Those winds will then be steered

from the west to the southwest by the Appalachian lee

side trough in the daytime and by the low level jet at

night. Sea breezes and bay breezes typically recirculate

air back over coastal cities and prevent polluted air from

those cities from flowing away from them. Vertical mixing is inhibited by the nocturnal inversion at night, and by the overall subsidence of a high pressure

system. In the mountains, air may also have a difficult time escaping valleys, and cities on the

western side of the mountains will find that the Appalachians are capable of damming pollution up

against them.

Some or all of these mechanisms will be active during any given air pollution episode. Together, their

combined effect is to confine pollution nearer to the surface, to prevent it from escaping horizontally, and

to circulate already polluted air from one region to the next or from one region back onto itself. The

combination of so many different mechanisms gives each episode its own

unique character. In addition, for a large-scale episode, conditions typically

vary across the Region, so long-range transport may be important in one area,

while stagnation rules in another.

Meteorological processes do

not exist in isolation. Any

given day in an air pollution

episode will typically feature

many different transport

phenomena.
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A Guide to Mid-Atlantic Regional Air Quality

The emissions most important to forming ozone and fine particles are nitrogen oxide (NOx), volatile

organic compounds (VOC), sulfur dioxide (SO2

), ammonia (NH3), and direct emissions of fine particles

(PM2.5). Before discussing emissions, a few terms should be defined. Emissions sources are grouped

in broad categories. Natural sources include vegetation, soils, oceans, and volcanos. Anthropogenic

sources involve human activities. The following discussion focuses on anthropogenic sources.

Anthropogenic Sources

On-road mobile sources are automobiles, trucks, and any other road-based sources of pollution.

Non-road mobile sources include motorized equipment used away from roads, such as construction

equipment, pleasure craft, ships, airplanes, trains, and farm machinery. Other non-road sources include

lawn and garden equipment, recreational vehicles, and logging machinery. Point sources are facilities

that are sufficiently large to be considered individually. A single very large facility may emit as much

pollution as all other sources in a city combined. Examples of point sources are power plants, oil

refineries, and steel mills. Finally, area sources represent something of a catchall category. These are

small, non-mobile sources that are so numerous that they can be modeled as coming from an area

instead of a specific source. Home heating, evaporation from animal waste, paint fumes, and consumer

solvent use are all examples of area sources.

The emissions listed in any inventory are necessarily just estimates of emissions. Other than large

point sources, it is impossible to place sophisticated emissions monitoring equipment on every source.

Large point sources are required to report their emissions, so theirs are better known than those from

other sources.

Pollution Sources

Part IV

Figure 26 2002 Annual anthropogenic sources (MARAMA+Northeast)

This chart shows the relative importance of various types of emissions sources for each of the major air pollutants.

Emissions from natural sources of VOCs are not included in this chart.

0%

20%

40%

60%

80%

100%

pollutant by source category

percent

Point (tons/y) 593,381 12,723 1,295,857 165,384 111,167 3,309,186 226,656 

On-Road (tons/y) 16,088,190 70,778 1,806,315 43,709 30,907 57,669 1,083,914 

Non-Road (tons/y) 5,960,416 1,356 630,874 64,214 58,728 82,102 631,763 

Area (tons/y) 2,453,073 463,171 325,248 1,176,114 220,157 339,811 2,431,371 

CO NH3 NOx PM10 PM25 SO2 VOC
Mid-Atlantic Regional Air Management Association

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Emission inventories represent only the starting point of a

pollutant’s lifetime in the atmosphere. They cannot, for

example, show how pollution transport and transformation

affects the Region. To fully answer the question of what

emissions are affecting an area, one must employ a number of different techniques including measurements, data

analysis, and photochemical modeling.

While this section focuses on emissions from the MidAtlantic Region, upwind sources are also important

throughout the Region. Maps of sulfur dioxide and sulfate concentrations illustrate this point. (See Figures

27 and 28.) One shows sulfur dioxide concentrations, while the other shows sulfate concentrations as measured. These maps are made by smoothing and interpolating measurements from a national

network of air quality monitors, so care must be taken when reading them, since there is not a monitor

at every point. That said, the industrialized Midwest clearly has high concentrations of sulfur dioxide.

Sulfur dioxide is relatively short-lived in the lower atmosphere, generally turning into sulfate or

depositing to the ground within a day. Therefore, higher concentrations of sulfur dioxide tend to be

located nearer to its sources, as is the case in the Midwest. The effects of those sulfur dioxide

emissions are more readily seen once it has turned into sulfate, which spreads out over the entire

eastern United States. This is not to say that atmospheric sulfur comes exclusively from the Midwest,

but rather to point out that emissions upwind of the Regions also play a significant role in determining

Mid-Atlantic and Northeast Regional air quality. Airborne measurements taken in the western part of the Region consistently show high

levels of air pollution being transported into the Region, particularly

during pollution episodes.

Sulfur Dioxide

Sulfur dioxide emissions are dominated by point sources, particularly

coal-fired power plants and industrial facilities. (See Figures 26, 29,

and 30.) Many similar but smaller facilities are incorporated into the area source category. All these

facilities emit sulfur dioxide because the fuel they burn contains a small amount of sulfur. The sulfur

burns along with the rest of the coal or oil and is emitted from the stack. The spotty geographic

distribution of this pollutant arises because most of its emissions are from point sources. (See Figures 27

and 31.) Emissions of sulfur dioxide are relatively well quantified in comparison with those of other

pollutants because the largest sources are all monitored by continuous emissions monitors (CEMs).

Nitrogen Oxide

Nitrogen Oxides (NOx) emissions are also dominated by fuel burning sources, mostly by point and

on-road sources. (See Figures 26, 32, and 33.) In the Mid-Atlantic Region NOx emissions are dominated by vehicle use, though many large point sources of NOx

 are in and just upwind of the Region.

Volatile Organic Compounds

Volatile Organic Compounds (VOC) emissions resulting from human activity (anthropogenic VOCs)

are dominated by emissions from mobile and area sources. (See Figures 26, 34, and 35.) Mobile sources

emit VOCs in two ways: evaporation from the fuel tank and other parts of the equipment, and discharge

Emissions sources are lumped into broad

categories: point sources, on-road and non-road

mobile sources, and area sources. Point

sources are large industrial facilities, while

area sources are numerous smaller sources

that are spread out over an area. Onroad

mobile sources are road-based vehicles, while

non-road mobile sources are off-road engines

such as construction equipment and airplanes.

Emissions inventories are usually

composed of estimates of emissions

rather than direct measurements.

Sources outside the Mid-Atlantic

Region are important to air pollution

Part IV Pollution Sources
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A Guide to Mid-Atlantic Regional Air Quality

Figure 28 Sulfate concentrations in the eastern United States

SO2 is gradually converted to sulfate. These maps are based on measurements of sulfates in the air. Reductions

in SO2 emissions since 1990 under the acid rain program have reduced sulfate.

Figure 27 Sulfur dioxide concentrations in the eastern United States

EPA maps show improvement over the decade of the 1990s in SO2 pollution. Higher concentrations are located

near major sources. http://www.epa.gov/airmarkets/cmap/mapgallery/index.html http://www.epa.gov/airmarkets/cmap/mapgallery/index.html
Mid-Atlantic Regional Air Management Association

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Part IV Pollution Sources

of unburned or partially burned hydrocarbons from the exhaust pipe. VOCs from area sources are

dominated by combustion of wood and other fuels in residences, solvent use, and other evaporative

emissions.

Most VOC emissions in the Region come from natural sources, which are not shown in Figures 26, 34,

and 35. Naturally occurring (biogenic) VOC emissions are caused by evaporation of natural organic

compounds from plants in warm weather. Many natural VOCs that contribute to ozone formation are

highly reactive. Because biogenic VOC emissions are large and reactive, they are the most important

part of the VOC inventory for understanding and predicting ozone formation. Biogenic VOCs are not

included in Figures 34 or 35, but nationally, they represent roughly two-thirds of all annual VOC

emissions. Biogenic emissions are extremely difficult to estimate, since doing so requires modeling

the behavior of many plants and animals as well as their responses to the environment. Further

complicating the situation, the processes that govern the release of these compounds are complex and

poorly understood.

Carbon Monoxide

Carbon Monoxide (CO) results from incomplete burning. Since engines never burn their fuel

completely, it is no surprise that CO emissions come predominantly from engines. Indeed, engines will

run quite poorly if forced to burn their fuel completely. Non-road and on-road mobile sources make up

90 percent of the CO inventory. Geographically, carbon monoxide emissions tend to be located in the

urban centers with people and their cars. In contrast, power plants emit very little carbon monoxide

Figure 29 Trends in sulfur dioxide emissions from utilities 1980 - 1997

Sulfur dioxide emissions from electricity generating facilities have declined in much of the eastern U.S. since

1990 due to the federal acid rain control program.

http://www.epa.gov/airmarkets/cmap/mapgallery/index.html
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A Guide to Mid-Atlantic Regional Air Quality

because they burn their fuel almost completely, removing

nearly every bit of energy from the fuel. Emissions inventories only describe the primary sources of carbon monoxide. Carbon monoxide also comes from the breakdown of

carbon compounds in the atmosphere, and as such, carbon

monoxide is both a primary and secondary pollutant. Much

of the global background level of carbon monoxide comes

from the breakdown of methane and organic compounds,

and effectively comes from an incomplete low-temperature burning process.

Ammonia

Ammonia (NH3) comes predominantly from animal waste

and fertilized soils, though some also comes from vehicles.

(See Figure 36.) This leads to an interesting geographic

distribution. Large emissions coming from urban centers

may seem surprising, but water treatment plants and automobiles also emit ammonia. Peak emissions from the

hog farms of eastern North Carolina, the dairies of southeastern Pennsylvania, and the chicken

farms of the Delmarva Peninsula may be seen in the annual map (Figure 37), but would be much more

noticeable in a summertime map. The uncertainty in ammonia emissions is greater than the uncertainties in emissions of other pollutants, because ammonia sources are diverse, and the data on agricultural

activities and the relationship of those activities to emissions are scarce.

Direct Fine Particle Emissions

Emission inventories of fine particles must be considered carefully, since these inventories only include

the primary particles emitted directly from their sources. Secondary particles (those formed in the

atmosphere) are not counted in the inventory of particle emissions. Primary fine particle emissions are

largely composed of crustal materials, soils, sea salt, and soot. PM emissions from point sources have

been reduced tremendously by emission controls, so that most direct PM emissions now come from

area sources. (See Figure 38.)

Each pollutant comes from characteristic

sources. Sulfur dioxide comes predominantly

from point sources such as large coal-fired

boilers. Carbon monoxide is a product of

incomplete combustion, and is emitted largely

by on-road and off-road engines as well as some

open burning. NOx is emitted by fuel burning

sources. VOCs come from biogenic sources as

well as from human activities, primarily mobile

and area sources. Ammonia comes predominantly from animal waste and fertilized soils.

Primary particle emissions come mostly from

soils, sea salt, and soot. Most of the fine

particles in the atmosphere are secondary

pollutants formed in the atmosphere.

Particulate matter (PM) is the general term for the mix of solid particles and liquid droplets suspended

in the air.

• PM2.5 – Particles that are less than 2.5 micrometers in diameter; they are also known as fine particles.

Because of their size, these fine particles can travel deep into the lungs. The health impacts of exposure

to these particles include aggravation of respiratory and cardiovascular disease, decreased lung function,

and premature death. Primary fine particle emissions are largely composed of crustal materials, soils, sea

salt, and soot.

• PM10 – Particulate matter that is less than 10 micrometers in diameter. Major sources of PM10

include road dust, soil, and wood smoke. Due to increased wood smoke and meteorological conditions, PM10 concentrations are greatest in the winter and lowest in the summer.
Mid-Atlantic Regional Air Management Association

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Part IV Pollution Sources

Analysis of the 2002 Emissions Inventory

Charts and maps summarizing the inventory help us understand the relative importance of various sources

of emissions and their locations. We can also evaluate the accuracy of the inventory by judging whether

the distribution and location of emissions makes sense. Air quality managers work hard to improve

emissions inventories to get a clearer picture of what is causing air pollution and the effectiveness of

pollution control strategies.

EPA released a preliminary 2002 National Emissions Inventory early in 2004. State and local agencies

have worked with MARAMA to revise and update these preliminary estimates and produced the MANEVU inventory. Similarly, VISTAS worked with southern states including North Carolina, Virginia, and

West Virginia in improving their regional inventory. The data used for the following charts comes from

1) the MANE-VU regional inventory; 2) the VISTAS regional inventory for point, area, and non-road

mobile sources; and 3) EPA’s 2002 National Mobile Emissions Inventory for mobile sources for North

Carolina, Virginia, and West Virginia.

The characteristics presented in the following summary charts and maps provide a general overview of

pollution sources in the Region, recognizing that developing emission inventories is a continual process

of updates that may result in changes.
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A Guide to Mid-Atlantic Regional Air Quality

0

0.2

0.4

0.6

0.8

1

1.2

Delaware District of

Columbia

Maryland New Jersey Pennsylvania North Carolina** Virginia** West Virginia**

State

Millions tons/y

Point

ONROAD

NONROAD

Area

Figure 30 Annual sulfur dioxide emissions by state -- 2002

Emissions from coal fired electric generating units and large boilers dominate the inventory for sulfur

dioxide emissions. Larger states and states with more coal-fired units have greater emissions.

Figure 31 Annual point source sulfur dioxide emissions density map -- 2002

Point sources are responsible for most of the sulfur dioxide emissions in the Region. This emissions

density map (by county) highlights counties where large sources are located.
Mid-Atlantic Regional Air Management Association

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Part IV Pollution Sources

Figure 32 Annual nitrogen oxide emissions by state -- 2002

All combustion processes discharge nitrogen oxide emissions. Most large point sources are subject to recent

emissions control requirements, so mobile sources (on-and off-road) dominate the remaining inventory.

Figure 33 Annual on-road nitrogen oxide emissions density map --2002

This density map shows higher motor vehicle NOx

 emissions from major highways and urban areas.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Delaware District of

Columbia

Maryland New Jersey Pennsylvania North Carolina** Virginia** West Virginia**

State

Millions tons/y

Point

ONROAD

NONROAD

Area
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A Guide to Mid-Atlantic Regional Air Quality

-

Figure 34 Annual volatile organic compound emissions by state -- 2002

Annual anthropogenic VOC emissions are primarily from area and mobile sources. This graph does not

include natural sources of VOCs, which are very large.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Delaware District of

Columbia

Maryland New Jersey Pennsylvania North Carolina** Virginia** West Virginia**

State

Millions tons/y

Point

ONROAD

NONROAD

Area

Figure 35 Annual area source volatile organic compound emissions density map -- 2002

Area source VOC emissions are higher in populated areas and in areas with commercial or industrial use of

solvents and other VOCs
Mid-Atlantic Regional Air Management Association

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0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Delaware District of

Columbia

Maryland New Jersey Pennsylvania North Carolina** Virginia** West Virginia**

State

Millions tons/y

Point

ONROAD

NONROAD

Area

Part IV Pollution Sources

Figure 36 Annual ammonia emissions by state -- 2002

Ammonia emissions are dominated by area sources. States with large animal feeding operations have higher

total emissions. Motor vehicles with catalytic converters also discharge ammonia.

Figure 37 Annual area source ammonia emissions density map -- 2002

This map shows the link between agricultural areas and area-source ammonia emissions.
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A Guide to Mid-Atlantic Regional Air Quality

Figure 38 Annual fine particle (PM2.5) emissions by state -- 2002

Primary fine particle emissions are dominated by road dust. In some states, major point sources also make

significant contributions. Fire emissions can be substantial on an episodic basis but do not have much

influence on this annual summary.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Delaware District of

Columbia

Maryland New Jersey Pennsylvania North Carolina** Virginia** West Virginia**

State

Millions tons/y

Point

ONROAD

NONROAD

Area
Mid-Atlantic Regional Air Management Association

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A Guide to Mid-Atlantic Regional Air Quality

Scientists have several techniques to determine the nature and causes of the air pollution problems

in a given area. Direct measurement, data analysis, and photochemical modeling are three broad

categories of these techniques. Each has strengths and weaknesses, and they can effectively

complement each other. The details of each technique would consume volumes, so they are not

presented in this report. However, knowing the general characteristics of each technique helps

ensure that their results are used appropriately.

Measurement

Direct measurement of air pollution has the most appeal of the three techniques, since it is difficult

to argue with someone who has gone out in the field and measured the concentration of an air

pollutant such as ozone in the atmosphere at a particular time and place. MARAMA member

agencies operate an extensive network of air quality monitors throughout the Region. Most of these

monitors are located in urban areas and downwind of cities or major emissions sources. These

monitors are intended to measure the highest levels of pollution in the area. Some monitors are also

placed at rural sites and in national parks and wilderness areas. It is important to measure rural

background as well as urban levels.

Measurements are reliable but expensive, and pollution cannot be measured everywhere all the

time. Furthermore, most measurements are confined to the surface, whereas the atmosphere is a

three-dimensional system. Measurements made from balloons and aircraft are more expensive

than their ground-based cousins, and unlike surface measurements, they cannot run unattended.

New techniques are emerging that allow more pollutants to be measured throughout a greater part

of the atmosphere. Satellites and laser instruments offer the possibility of attaining uninterrupted

and largely unattended measurements. These techniques do have their own limitations. Satellites

have difficulty measuring pollutants close to the ground and over complex terrain. Most laser

techniques have trouble with clouds and suffer from interferences from other pollutants.

Obtaining quality measurements requires great attention and care in both experimental design and

instrument maintenance. All instruments suffer from interferences—compounds which either

impede the instrument’s ability to measure a particular pollutant or give a false response, indicating

the presence of a pollutant when none is there. All instruments must be calibrated in some way. For

satellite instruments and other remote sensing measurements such as lidar and radar, this problem is particularly

difficult, since the pollutant must be observed over a large

area and depth to evaluate the measurement. Finally, some

measurements are difficult to obtain, and necessarily

subject to interpretation, because the measurement technique defines the measurement itself. An example of this

phenomenon is dividing carbon compounds between

Measurements, Data Analysis, and

Modeling

Measurements are the most straightforward

tool in the atmospheric scientist’s toolbox,

but they must be interpreted with caution.

Users of measurements should be aware of

the limitations of the techniques used to

gather the data.

Part V
Mid-Atlantic Regional Air Management Association

-60-

organic carbon and soot (elemental carbon).

While it might seem simple to

distinguish organic carbon, which

is oily, from elemental carbon,

which is a sooty solid, separating

the two requires complex physicalchemical analyses. The carbon

sample is collected on a filter for

a specified time and then baked in

a chamber, first under a heliumonly atmosphere, and then under

a helium-oxygen atmosphere. The

gases coming off the sample while

it bakes are analyzed to determine

the amount of carbon released.

Depending on the temperature and

the time for which the sample is

baked, a different organic carbon

/elemental carbon split may be

obtained. Further complicating

things, the total masses of organic

carbon and elemental carbon are

not measured directly—just the

mass of the carbon they contain is

measured. To get the total mass

of organic carbon compounds, the

measured organic carbon mass is

multiplied by an assumed factor to

account for all the non-carbon portion of these oily compounds. This factor actually varies with the mix of

hydrocarbons present in the sample. Organic carbon measurements therefore can change with the

technique used and the assumptions made in analyzing the data. This is one of the most difficult

measurements routinely made in atmospheric chemistry, and it illustrates that measurements are subject to

some interpretation by the users of the data.

In addition to the ongoing air quality monitoring networks maintained by MARAMA state and local

agencies, there have been several special scientific monitoring projects in the Region over the past few

years. Many of these projects are highlighted in this report (Northeast Oxidant and Particle Study, page

6; Pittsburgh Air Quality Study, page 26; MARCH Atlantic, page 39; Southern Appalachian Mountain

Initiative, page 65).

Air Quality data collected by MARAMA members is stored in a national database called AQS, which is

accessible via the EPA website at http://www.epa.gov/air/data. Daily information about air quality is

available on the internet at www.airnow.gov.

Part V Measurements, Analysis & Modeling

Figure 39 Monitors used for nonattainment designations in

the MARAMA Region

MARAMA’s member agencies operate an extensive air quality monitoring

network throughout the Region. Monitors may collect data about ozone,

carbon monoxide, sulfur dioxide, nitrogen oxide, coarse and fine particles,

as well as other contributors to poor air quality.
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A Guide to Mid-Atlantic Regional Air Quality

Data Analysis

Data analysis includes assessing current air quality, determining spatial and temporal trends

and patterns, and identifying

potential air pollution sources.

Most air quality measurements

are of limited worth by themselves, and must be combined

with other data sets to broaden

their value. Sometimes a pollutant may be so ubiquitous that

only a few measurements are

necessary to determine the

uniform concentration of that

pollutant. Outside of a few rare

cases, however, measurements

need to be placed in a broader

context and combined with

other data to allow broader conclusions to be drawn.

Data analysis is the process of

capturing the essence of what

is happening through the

analysis of large data sets. This

process involves many data

analysis techniques, both simple

and complex. Most analysis

techniques are statistical, seeking underlying relationships in

a data set. Many combine measurements of pollutant concentrations with meteorological data to get an

impression of the source regions and transport patterns that bring air pollution to a region. These

techniques typically group measurements by pollutant concentration or by meteorological conditions.

For example, daily measurements of particle composition may be classified first into similar categories

according to their composition, producing several groups. One

group might be dominated by high sulfate while another might

contain a fair amount of sea salt. Subsequent analysis can find

the weather conditions present when sulfate particles dominate

and when sea salt dominates. If more chemical species are

measured, more patterns linked to various types of sources may

emerge. This technique is called source apportionment analysis

or source attribution by receptor-based methods.

Air quality data analysis

• Assesses current air quality

 Does it meet national standards?

• Determines spatial and temporal trends

 Is it getting better or worse?

• Identifies potential air pollution sources

 What’s causing high concentrations?

Figure 40 Air quality monitoring sites measuring additional

pollutants

In addition to the network of monitoring sites shown in Figure 39, various

state, local, and federal agencies operate air quality monitors in the region

that measure concentrations of other pollutants. NADP and CASTNet sites

help study acid deposition; CASTNet, PAMS, and RAIN sites help study

ozone; and IMPROVE, PM speciation, and RAIN sites focus on particulate

matter and haze. (See page 62.)
Mid-Atlantic Regional Air Management Association

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Part V Measurements, Analysis & Modeling

Air Quality Monitoring Sites Measuring

Additional Pollutants

Rural Aerosol Intensive Network – RAIN

The monitoring site at Piney Run in western Maryland is a research site operated by the State in

collaboration with the Appalachian Laboratory and the University of Maryland. It is part of the

RAIN network organized by NESCAUM. The site tracks the impact of interstate pollutant

transport via measurements of ozone, PM2.5, and precursor and constituent species.

Enhanced Ozone Monitoring – PAMS

New Jersey, Philadelphia, Maryland, the District of Columbia, and Virginia have established Photochemical Assessment Monitoring Stations (PAMS), which collect and report data for ozone and its

precursors, including numerous individual volatile organic compounds and NOx

. Data from these

and other PAMS locations in the US help EPA and the states in understanding the causes of ozone

pollution. http://www.epa.gov/oar/oaqps/pams

National Atmospheric Deposition Program – NADP

The NADP is a cooperative monitoring network used to collect weekly data on the chemistry of

precipitation. Precipitation is collected and analyzed for acidity, sulfate, nitrate, ammonium,

chloride, calcium, magnesium, potassium, and sodium. The network has also expanded to monitor

the amount of mercury found in precipitation. Key Mid-Atlantic NADP monitoring stations are

operated by the University of Maryland, Penn State University, the National Oceanic and

Atmospheric Administration, Canaan Valley Institute, and others.

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

Interagency Monitoring of Protected Visual Environments – IMPROVE

Federal Land Managers at Class I national parks and wilderness areas in the Mid-Atlantic Region

operate IMPROVE monitors to measure particles that degrade visibility (as described in Appendix

E). Monitors of the IMPROVE design have also been sited in several other rural locations in

Pennsylvania and Maryland as well as in the District of Columbia. Measurement of PM species

helps identify the sources of fine particles in the air. Monitors that are not at Class I sites are

referred to as “IMPROVE Protocol” monitors because they use the monitoring protocols required

for the Class I sites. http://vista.cira.colostate.edu/improve/

PM Speciation Network

These urban monitors provide data on the concentration of key species of PM2.5. The monitors are

operated by state and local agencies pursuant to EPA guidance. Data on species of PM2.5 helps

identify the sources of PM and supports health effects and exposure research.

Clean Air Status and Trends Network (CASTNet)

EPA and the National Park Service operate CASTNet monitoring stations to provide data on dry

acidic deposition and rural ground-level ozone. CASTNet data is used in conjunction with other

monitoring networks to evaluate the effectiveness of national emission control programs.

http://www.epa.gov/castnet/

(See map page 61.)
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A Guide to Mid-Atlantic Regional Air Quality

Emissions-based models begin with emissions inventories and

act on them in a “forward” direction with atmospheric physical

and chemical processes to predict downwind concentrations at

multiple “receptor locations.” Once validated by comparison to

ambient measurement data, these models can be used for apportioning ambient pollution concentrations to specific sources,

as well as for evaluating potential effects of future changes in emissions or meteorology. Receptor

based models begin with ambient measurement data at one or more receptor locations and work

“backward” to identify sources contributing to historical ambient pollutant concentrations at the receptor

locations. Receptor models cannot be used to predict effects of future emissions changes, but can be

applied to long historical records, providing a long-term “climatological” indication of past sourcereceptor relationships and to evaluate the effects of historical emissions changes, thus providing a

valuable complement to emissions-based models for determining effective future emissions control

technologies.

Data analysis techniques provide general information about the types of sources affecting air quality at

one or more monitoring stations. While general assertions about conditions at a site or throughout a

region are possible, these techniques typically do not pin down a specific power plant, smelter, or city as

the source of a region’s problems. Data analysis can help identify gaps in emissions inventories and vice

versa. Additionally, the statisticians adage “correlation does not imply causality” is particularly relevant

in this type of analysis. Perhaps the simplest example of this kind of limitation is where two unrelated

sources sit near each other. If a smelter, the intersection of two enormous freeways, and a feed lot all

are within a mile of each other, analysts must be very careful in drawing conclusions about the air

coming from such an area. Results must be interpreted in the context of other information about

emissions and sources in the area and with an understanding of how pollutants are transported and

transformed in the atmosphere.

Air Quality Modeling

Measurements and data analysis help assess current and past air quality. To predict future air quality

and evaluate the air quality benefits of potential controls, scientists use computer-based models. Air

quality models are mathematical representations of the relationships between emissions, weather, and

air quality.

Photochemical models are one of the most powerful tools in the scientist’s toolbox, but the results must

be used with great caution. Because they can produce maps showing simulated air quality throughout a

region, it is tempting to view photochemical models as providing an all-encompassing view of air quality.

However, when interpreting these results, the limitations of the model must always be considered.

Models can only represent the physics and chemistry that are understood by their developers. In fact,

models typically only represent a small fraction of the known atmospheric chemistry and physics.

Compromises are always made to get the

model to run in a reasonable time. Over 10,000

reactions are important to atmospheric chemistry, while most air quality models contain only

a hundred or so. To obtain this simplification,

compounds with similar properties are

Photochemical grid models are very powerful tools that allow

one to simulate experiments that would be too costly or

difficult to perform. The results should always be interpreted

with a keen eye for the limitations of the model.

“One-atmosphere” modeling recognizes the

importance of interactions between different

pollutants by modeling all processes

simultaneously.
Mid-Atlantic Regional Air Management Association

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Part V Measurements, Analysis & Modeling

A “weight of evidence” approach allows

scientists to review several studies, seeking

similarities and noting differences. If

several methods yield similar results, there

is greater confidence in the conclusions.

grouped to avoid calculating the reactions of, for example,

each hydrocarbon in the atmosphere.

Models represent some phenomena in a very simple way

because they are not well understood. Interactions between

aerosols and gases fall into this category, as do small-scale

winds like the low level jet. Sometimes these simplifications

can be so severe as to give the wrong answer when attempting

to diagnose a problem. Model results, therefore, should always be interpreted with an eye towards the

potential shortcomings of the model.

Models are only as good as the data that goes into them. Emissions inventories often are uncertain.

Even weather models that use an enormous weather database from the National Weather Service

suffer from incomplete, missing, and sparse data. There is no way, for example, to accurately measure

the extent of the sea breeze or the low level jet using National Weather Service data.

A model should not be expected to simulate every nuance of air quality measurements at a given time

and place. Instead, regional models can best be used in a general, relative sense, to estimate trends, the

relative impacts on different regions, or the relative impacts of different control programs.

Comparing model output with measurements indicates how well the model is simulating reality. Perhaps

it is obvious that model results should be compared with observations, but the key is that the model must

be tested with relevant data. Many processes could be entirely misrepresented in a model if, for

example, its results were only compared with surface measurements. The goal is to examine the

processes in the model, not just the final output of the model. This is difficult, since it involves detailed

measurements of multiple species, but it is the best way to truly evaluate a model’s abilities.

These caveats are not to say that models should not be used—only that they should not be used blindly.

Processes do not need to be represented perfectly in the model for the results to be useful. If a model

is used for its intended purpose, and evaluated carefully, it may be very helpful.

Combining Techniques

Air quality analysts increasingly combine measurement, data analysis, and modeling into a comprehensive “weight of evidence” approach. Rather than rely on one model, or a few data analysis projects,

analysts review numerous studies seeking similarities and noting differences. If several methods yield

similar results there is greater confidence in the conclusions. The SAMI Integrated Assessment

described on the following pages is an example of an assessment using many analytical techniques.
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A Guide to Mid-Atlantic Regional Air Quality

Southern Appalachian Mountain Initiative (SAMI)

Overview

SAMI was a voluntary partnership of state and federal environmental regulatory agencies, federal

land managers, industry, academia, environmental groups, and interested public participants. SAMI

provided a forum for stakeholders with diverse interests and viewpoints to work together

constructively to conduct the technical and policy assessments necessary to recommend regional

solutions to air pollution problems.

SAMI focused on the impacts of ozone, regional haze, and acid deposition on the natural resources

of the Southern Appalachian Mountains. The SAMI Integrated Assessment linked the understanding of air emissions, atmospheric transport, environmental effects, and socioeconomic consequences to assess emissions management alternatives.

SAMI evaluated the costs and benefits in the years 2010 and 2040 of current air regulations,

and of emissions management strategies that SAMI might recommend. The Assessment results

were summarized in a final report issued in August 2002, which is the basis of SAMI’s

recommendations to policy makers.

Among SAMI’s key findings from atmospheric modeling were that each state benefits most from

emissions reductions that occur in that state and each state will also benefit from emissions

reductions in surrounding states.

Conclusions

• To improve visibility, it is most important to reduce sulfur dioxide emissions, and it

could become necessary, under certain future sulfur dioxide control strategies, to reduce

ammonia emissions.

• To reduce acid deposition affecting streams in the central and northern part of the SAMI

region, it is important to reduce sulfur dioxide emissions.

• To reduce acid deposition affecting streams in some geographically limited areas, it is

important to reduce nitrogen oxide and ammonia emissions.

• For high elevation spruce-fir forests, it is important to reduce nitrogen oxide and ammonia

emissions.

• Ozone exposure does not produce a region-wide effect on forest basal areas, so nitrogen

oxide or volatile organic compound reductions are not needed for this purpose. However,

site-specific ozone effects to certain forest species are a concern for Federal Land

Managers and other stakeholders. Nitrogen oxide emission reductions are important to

address that concern.

more...
Mid-Atlantic Regional Air Management Association

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Part V Measurements, Analysis & Modeling

The SAMI Governing body adopted the recommendations listed below on April 18, 2002 by consensus among

the state representatives.

• The SAMI states support and will promote strong

national multi-pollutant legislation for electric utility

plants to assure significant sulfur dioxide and nitrogen oxides reductions both in and outside the SAMI

region. This national multi-pollutant legislation should

result in no less than the reductions for sulfur dioxide and for nitrogen oxides represented by

the Administration’s Clear Skies Initiative. Reductions from other source categories should

also be considered in national legislation, and such national legislation should contain sufficient measures to protect Class I areas. Should the national legislation fail to materialize, the

states that participated in SAMI will work together to consider regulatory alternatives and to

encourage non-SAMI states to participate. Leadership by states ahead of national legislation

is encouraged.

• Each SAMI State should seek ways to reduce ammonia emissions from animal feeding

operations. Also, support should be given in future work such as VISTAS to improve the

understanding of the sources of ammonia, to develop better inventories, and to seek more

effective control approaches.

• Where States have control strategy choices in their eight hour ozone and fine particle State

Implementation Plans, they should choose options that also have co-benefits for the environmentally sensitive Class I areas. Ambient ozone monitoring should be conducted near all

Class I areas in the future.

• Each SAMI state should encourage energy efficiency, conservation, and use of renewable

energy to reduce the emissions from stationary and mobile sources.

The states agreed to work towards the implementation of these recommendations. Each SAMI

state will determine the most appropriate strategy for its own unique circumstances that will lead

to successful implementation of SAMI’s final recommendations.

Recommendations
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A Guide to Mid-Atlantic Regional Air Quality

Closing Thoughts

Part VI

Understanding A Diverse Region

The MARAMA Region reaches from Pennsylvania and New Jersey through North Carolina, and from

the Ohio Valley to the Atlantic shore. In this diverse region, air pollution problems vary greatly, but share

many common characteristics.

To continue to frame appropriate air pollution control strategies, it is important to understand how weather

patterns affect air quality. A typical air pollution episode will last several days and contain several

weather patterns affecting different parts of the Region. One source of variation is the effects of the

Region’s major topographical features on meteorology and air quality.

High pressure systems typically dominate air pollution episodes, producing stagnant air and weak winds

at the surface. Winds aloft often bring pollution from the industrialized Midwest across the mountains.

Those same winds are frequently steered northeast by various meteorological phenomena.

For example, the low-level jet that often forms at night east of the Appalachian Mountains transports air

northeast along the Piedmont. This natural phenomenon can transport polluted air from one part of the

region to another very efficiently.

The location of the Bermuda High pressure system as it moves into the Region, and the tracks of frontal

boundaries, also affect the nature and severity of air pollution within the Region. For example,

subtropical high pressure systems spend more time over the southern part of the Region, limiting the

range of transport there and making local air pollution sources more important. In the northern part of

the Region, which is closer to the usual storm track, winds are often stronger, and the distances over

which pollution may be transported are generally longer than in the southern part of the Region.

The combination of many different natural phenomena gives each air pollution episode its own unique

character. For a large-scale episode, conditions typically vary across the region and change from day to

day, so long-range transport may be important in one part of the region while stagnation dominates in

another part. Understanding which factors typically generate a pollution episode in a given area is

essential to being able to address the sources of pollutants and improve air quality.

Pollutant Interactions are Important

The nature of air pollutants themselves also affects the choice of appropriate control strategies. Air

pollutants exist in complex mixtures, and pollutants react and re-react with each other and with other

compounds and surfaces. Some of the most important interactions are summarized here.

NOx Titration

NOx titration is one example of an interaction between cycles and families of compounds. When NOx

is very abundant, as is the case in the plume from a major city or power plant, it reacts with ozone

directly, destroying the molecule, and reducing ozone concentrations. Later, as the plume disperses and

more VOCs mix into the plume, conditions become more favorable for ozone production, and ozone

increases again.
Mid-Atlantic Regional Air Management Association

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NOx Limited and VOC Limited Ozone Production

The amount of ozone produced in an area depends in part on the balance of NOx and VOC in the area.

The amount of ozone produced may be limited when there is not enough VOC or NOx for rapid ozone

production. NOx

 limited conditions occur when the amount of ozone produced is limited by the amount

of NOx

 available. In this situation, the best way to reduce ozone pollution is by further reducing the

amount of NOx

 emissions. When VOCs are relatively scarce, conditions are VOC limited, and VOC

controls will have a greater effect.

It can be difficult to determine whether an area is NOx limited or VOC limited, because conditions vary

depending on how much NOx

 is being transported into the area, traffic conditions, temperature

variations that affect the production of VOCs, the effects of emissions controls, and many other factors.

The plume from a city, for example, is typically VOC limited in the city, and switches over to NOx

 limited

some distance downwind. The same area may change back and forth from being NOx

 limited to being

VOC limited, meaning that reducing both pollutants will be necessary.

Nitrate Replacement

Sulfur dioxide emissions are converted to sulfates, which then form fine particles in a variety of

reactions. The presence of ammonia speeds the process of particle formation. Reducing emissions of

sulfur dioxide can be expected to reduce airborne particle pollution. However, the effect on fine particle

concentrations may not be as dramatic as might be expected. Some of the sulfate may be replaced by

increased amounts of particulate nitrate. Nitrate formation increases if ammonia in the atmosphere

cannot react with sulfate, but is instead available to help form nitrate particles. This process is called

“nitrate replacement.” Nitrate replacement is not as big an issue in the eastern U.S. as it is in Southern

California, where sulfur dioxide emissions are considerably lower.

Sulfates are the major component of fine particle pollution in the eastern U.S. in the summer, when

concentrations are the highest. Significant reductions of sulfur dioxide will be needed in order to reduce

fine particle pollution and regional haze. In some areas, particularly in the winter, it will also be important

to reduce various nitrogen emissions, such as NOx

 and ammonia (NH3).

Emissions Must be Reduced

Scientists have learned much about the Mid-Atlantic Region’s air quality and are continuing to explore

outstanding questions. Some of the major studies that have helped us understand air pollution in the

region have been highlighted in this report.

We know we need substantial reductions in NOx

 emissions in order to reduce ozone pollution. Exactly

how much will be enough is difficult to predict, but we know enough to move ahead. We know we need

substantial reductions of SO2

 emissions in order to help address particle pollution and haze. Power

plants will have to scrub more of their emissions. Emissions from trucks and automobiles will need to be

cleaner.

We are less certain about what measures are needed to reduce organic carbon particles, but it is clear

that air quality will improve if more diesels use clean fuels and are fitted with particle traps.

Part VI Closing Thoughts
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A Guide to Mid-Atlantic Regional Air Quality

Reducing acid rain and the impacts of air pollution on ecosystems will require cuts in emissions on a

year-round basis. Some current ozone control programs are seasonal, whereas controls to address acid

rain, particle pollution, and haze will have to be implemented year-round. The best available information

indicates emission reductions have and will continue to improve air quality.

Transport and Local Sources are Both Important

The question is not whether there is transport, but how much? And from where?

To improve air quality, we must reduce pollutant emissions from sources affecting polluted areas.

This includes local sources as well as distant sources. In particular, emission reductions from the

industrialized Midwest will greatly aid Mid-Atlantic Regional air quality. Local emissions are significant

as well, and we cannot lay all the blame for our air pollution problems at the doorstep of the Midwest—

we must also reduce our own emissions.

While long-range pollution transport and local pollution stagnation are important throughout the Region,

the relevant range of transport is generally shorter in the south than in the north. It is also important to

note that despite this general tendency, the characteristics of individual episodes vary widely. For

example, despite the importance of transport in the northern states, a specific episode in the northern

Mid-Atlantic Region may be almost entirely due to localized stagnation, while a particular episode in the

southern Mid-Atlantic Region may show a strong influence from long-range transport. Transport is

important throughout the Region, and high local emissions add pollution to long-range transport.

A Commitment to Improving Air Quality

Effective air pollution control requires a partnership of local, state, and federal authorities as well as

private citizens, businesses, and industry. Reducing pollution is important to everyone’s health and

well-being. It requires development of cleaner technology (such as low emission vehicles), the use of

pollution control devices (such as scrubbers to remove SO2

 from smokestacks or filters to trap diesel

smoke), energy efficiency and pollution prevention measures to improve industrial processes, cleaner

fuels (such as low-sulfur gasoline), and decisions that exhibit good stewardship of the environment, such

as carpooling, doing more walking or bicycling, and observing burn bans.

Above all, achieving good air quality requires a commitment to continue to seek ways to reduce

emissions of VOCs, NOx

, SO2, and particles. Each state and local government must develop and

implement plans to improve air quality, recognizing the need for both local and regional improvements.

The problem will not be solved by local controls alone, nor will it be solved by upwind controls alone.

The problem is not just automobiles, nor is it just power plants. A wide variety of sources must reduce

emissions for citizens of the Mid-Atlantic Region to breathe clean air.
Mid-Atlantic Regional Air Management Association

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Mid-Atlantic Regional Air Management Association

Appendix List

Appendix A Health Effects of Air Pollutants

Appendix B Air Pollution Effects on Ecosystems and

the Environment

Appendix C Air Quality Standards and Goals

Appendix D MARAMA Region Data Tables

Appendix E Measuring and Calculating Visibility

Impairment

Appendix F Bibliography and Suggested Readings
Mid-Atlantic Regional Air Management Association
Page A-1

A Guide to Mid-Atlantic Regional Air Quality

Pollutants

Ozone

The reactivity of ozone causes health problems because it damages lung tissue, reduces lung function,

and sensitizes the lungs to other irritants. Ozone has long been known to increase the incidence of

asthma attacks in asthmatics. The general mechanism is fairly simple, though the exact details of how

ozone or any other pollutant causes these problems are considerably more complex.

As air enters the lungs, it passes through the trachea and then into passages called bronchi that divide

into smaller and more numerous passageways. Farther down in the lung, the passages only split, and do

not become smaller. At the ends of the last bronchi are tiny sacs called alveoli, which increase in volume

when a breath is taken. The alveoli exchange incoming oxygen for outgoing carbon dioxide, so they are

home to the most crucial part of the breathing process. If the alveoli cannot get fresh air to replace the

carbon dioxide, you cannot breathe. The bronchi that lead to those sacs are very narrow. Here, ozone

and other lung irritants have their worst effects.

Ozone and fine particles irritate the lining of these small passageways, making them swell and secrete

extra mucus. The swelling narrows the tiny passageway, letting very little air through to the alveoli, and

dramatically reducing the lung’s capacity. The lung’s capacity drops further in asthmatics when the

muscles surrounding the bronchi contract and irritated tissues respond by

producing more mucus. Muscle spasms and excess mucus further

narrow the bronchial passages, making it still more difficult to breathe.

Ozone exposure also makes the lungs more vulnerable to lung diseases

such as pneumonia and bronchitis. Ozone not only affects people with

impaired respiratory systems, such as asthmatics, but healthy adults and

children as well. Exposure to ozone for several hours at relatively low

concentrations significantly reduces lung function and induces respiratory

inflammation in normal, healthy people during exercise. This decrease in

lung function is generally accompanied by symptoms such as chest pain, coughing, sneezing, and

pulmonary congestion. Recent research in Southern California strongly suggests that, in addition to

exacerbating existing asthma, ozone also causes asthma in children. Longer term exposure to ozone

can also lead to scarring of the lung tissue and permanent reductions in lung capacity.

Carbon Monoxide

Carbon monoxide is a colorless, odorless, poisonous gas. Carbon monoxide is absorbed more readily

than oxygen in the bloodstream and takes up oxygen-carrying sites in the blood. When carbon monoxide

enters the bloodstream, it reduces the delivery of oxygen to the body’s organs and tissues. Health

threats from carbon monoxide are most serious for those who suffer from cardiovascular disease,

particularly those with angina or peripheral vascular disease. Exposure to elevated carbon monoxide

levels can impair visual perception, manual dexterity, learning ability, and the performance of complex

tasks.

Ozone burns the tissues of the

lungs, causing swelling, and

making breathing difficult. Ozone

exacerbates asthma and reduces

lung function. Recent studies

suggest that ozone may also

cause asthma.

Appendix A

Health Effects of Air Pollutants
Mid-Atlantic Regional Air Management Association

Page A-2

Sulfur Dioxide

High concentrations of sulfur dioxide affect breathing and may aggravate existing respiratory and

cardiovascular disease. Longer-term exposure to high levels of sulfur dioxide causes respiratory illness

and aggravates existing heart disease. Sulfur dioxide reacts in the air and turns into sulfate, which is

associated with negative health effects as part of particulate matter. Sensitive populations include

asthmatics, individuals with bronchitis or emphysema, children, and the elderly.

Nitrogen Dioxide

High concentrations of nitrogen dioxide can irritate the lungs, cause bronchitis and pneumonia, and

lower resistance to respiratory infections. While concentrations of nitrogen oxides in the Mid-Atlantic

Region are low enough to meet health standards, nitrogen oxides are important precursors to both ozone

and acid rain, and may affect both terrestrial and aquatic ecosystems. When nitrogen oxides react with

volatile organic compounds in the atmosphere, they may form nitrogenated hydrocarbons, most of which

are extremely toxic. Some nitrogenated hydrocarbons are known to cause mutations.

Particulate Matter

Studies of people exposed to high concentrations of particles (sometimes with gaseous pollutants) and

laboratory studies of animals and humans have shown that fine particles can cause serious health

effects. These include increased coughing, difficult or painful breathing, chronic bronchitis, decreased

lung function, aggravation of existing respiratory and cardiovascular disease, alterations in the body’s

defense systems against foreign materials, damage to lung tissue, cancer, and premature death. The

major subgroups of the population that appear to be most sensitive to the effects of particulate

matter include individuals with chronic obstructive pulmonary or cardiovascular disease or influenza, asthmatics, the elderly, and children.

A number of studies are underway to determine which components of

particulate matter cause health problems. The answers are likely to be

quite complex, owing to the complex nature of the pollutant. Composition likely plays a role, since some aerosols are thought to be considerably more harmful than others. Aerosols are also efficient carriers of

toxic compounds, which are dangerous by themselves. Particle size

likely also plays a role, since smaller particles are inhaled more deeply

into the lungs.

Furthermore, composition varies widely with size, so these two are

linked. The finest particles tend to contain more metals, while larger particles tend to be mostly soils and

other crustal material. Finally, individual variability will probably play a role as well—some individuals

may be sensitive to a particular component, while others may be sensitive to the number of particles, and

still others may only be sensitive to the total mass of particles they inhale.

Lead

Exposure to lead can occur in many ways, including inhalation of air and ingestion of lead in food, water,

soil or dust. Excessive lead exposure can cause seizures, mental retardation, and behavioral disorders.

A recent National Health and Nutrition Examination Survey reported a 78 percent decrease in blood

lead levels from 12.8 to 2.8 μg/dL between the periods 1976-1980 and from 1988-1991. This dramatic

decline can be attributed to the reduction of leaded gasoline and to the removal of lead from soldered

The exact details of the mechanism

by which fine particles cause health

effects is not well understood. Size

and composition are likely important,

since smaller particles are inhaled

more deeply into the lungs and

particles in different areas of the

country appear to generate health

effects of differing severity.

Appendix A
Page A-3

A Guide to Mid-Atlantic Regional Air Quality

cans. Although this represents great progress, infants and young children are especially susceptible to

low doses of lead, and this age group still shows the highest levels. Low doses of lead can lead to central

nervous system damage. Recent studies have also shown that lead may be a factor in high blood

pressure and in subsequent heart disease in middle-aged men.

Air Quality Index (AQI)

The AQI is a tool for reporting daily air quality. It tells you how clean or polluted your air is, and what

associated health effects might be of concern. The AQI focuses on health effects an individual may

experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five

major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as

particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants,

EPA has established national air quality standards to protect public health.

How Does the AQI Work?

Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level

of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air

quality with little potential to affect public health, while an AQI value over 300 represents hazardous air

quality.

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is

the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain

sensitive groups of people, then for everyone as AQI values get higher.

Understanding the AQI

The purpose of the AQI is to help people understand what local air quality means to their health. To

make it easier to understand, the AQI is divided into six categories. Each category corresponds to a

different level of health concern.

AQI colors

EPA has assigned a specific color to each AQI category to make it easier for people to understand

quickly whether air pollution is reaching unhealthy levels in their communities. For example, the color

orange means that conditions are “unhealthy for sensitive groups,” while red means that conditions may

be “unhealthy for everyone,” and so on.

Reporting & Forecasting

Each MARAMA member reports the daily AQI level via websites or other public announcements. For

major cities in the Region a daily forecast of the AQI can be found at http://airnow.gov/.
Mid-Atlantic Regional Air Management Association

Page A-4

Air Quality Index 

Levels of Health Concern

Numerical 

Value Meaning

Good 0-50 Air quality is considered satisfactory, and air pollution 

poses little or no risk. 

Moderate 51-100 

Air quality is acceptable; however, for some pollutants 

there may be a moderate health concern for a very small 

number of people who are unusually sensitive to air 

pollution. 

Unhealthy for 

Sensitive Groups 101-150 Members of sensitive groups may experience health effects. The general public is not likely to be affected. 

Unhealthy 151-200 

Everyone may begin to experience health effects; 

members of sensitive groups may experience more 

serious health effects. 

Very Unhealthy 201-300 Health alert: everyone may experience more serious 

health effects. 

Hazardous > 300 Health warnings of emergency conditions. The entire 

population is more likely to be affected.

AQI Index, Color Ranges and Messages

Appendix A

AQI Color Ranges, Index and PM2.5 and 8-Hr Ozone Breakpoints
Page A-5

A Guide to Mid-Atlantic Regional Air Quality

Air Quality 

Air 

Quality 

Index 

Protect Your Health 

Good 0-50 N o health im pacts are expected when air quality is in this 

range.

Moderate 51-100 U nusually sensitive people should consider lim iting prolonged 

outdoor exertion.

Unhealthy for 

Sensitive 

Groups

101-150

Active children and adults, and people with respiratory 

disease, such as asthm a, should lim it prolonged outdoor 

exertion.

Unhealthy 151-200

Active children and adults, and people with respiratory 

disease, such as asthm a, should avoid prolonged outdoor 

exertion; everyone else, especially children, should lim it 

prolonged outdoor exertion.

Very 

Unhealthy 

(Alert) 

201-300

Active children and adults, and people with respiratory 

disease, such as asthm a, should avoid all outdoor exertion; 

everyone else, especially children, should lim it outdoor 

exertion.

Air Quality Air Quality Index Health Advisory

Good 0-50 None. 

Moderate 51-100 Unusually sensitive people should consider 

reducing prolonged or heavy exertion. 

Unhealthy for 

Sensitive Groups 101-150

People with heart or lung disease, older 

adults, and children should reduce 

prolonged or heavy exertion. 

Unhealthy 151-200

People with heart or lung disease, older 

adults, and children should avoid prolonged 

or heavy exertion. Everyone else should 

reduce prolonged or heavy exertion.

Very 

Unhealthy 

(Alert) 

201-300

People with heart or lung disease, older 

adults, and children should avoid all 

physical activity outdoors. Everyone else 

should avoid prolonged or heavy exertion.

AQI Color Ranges, Index and Health Messages for 8-Hr Ozone

AQI Color Ranges, Index and PM2.5
Mid-Atlantic Regional Air Management Association

Page A-6
Page B-1

A Guide to Mid-Atlantic Regional Air Quality

Ozone

Ozone interferes with the ability of plants to produce and store their own food. The additional stress

makes them more susceptible to disease, insects, other pollutants, and harsh weather. Ozone damages

the leaves of trees and other plants. Certain plant species are so susceptible that they may be used as

indicators of long-term exposure to ozone. By interfering with the ability of plants to produce and store

food, damaging their leaves, and increasing the stress on plants ozone also reduces the yield of certain

crops and the growth of certain trees.

Sulfur Dioxide

Sulfur dioxide is a primary contributor to acid rain, or acid deposition, which causes acidification of lakes

and streams and can damage trees, crops, historic buildings, and statues. In part, this damage occurs

when sulfur dioxide deposits directly to surfaces, but sulfur dioxide also reacts in the atmosphere to

become sulfate and sulfuric acid. Sulfates dominate visibility impairment throughout the Mid-Atlantic

Region. Sulfuric acid is one of the dominant components of acid rain.

Nitrogen Dioxide

Nitrogen dioxide forms nitric acid in the atmosphere, contributing to acid rain. Nitrogen oxides also

react with volatile organic compounds to form ozone and may contribute to a whole host of nitrogenated

hydrocarbons, most of which are extremely toxic. Some nitrogenated hydrocarbons serve as reservoir

species which exist for some time in the atmosphere before breaking down to re-release nitrogen

oxides.

Nitrogen dioxide also forms nitrate, which is a fertilizer for plant and algae growth. When nitrate (as

either nitric acid or nitrate itself) deposits directly to a body of water, it enters via the most active part:

the surface. Atmospheric nitrogen is thought to comprise between 10 percent and 45 percent of the

nitrogen reaching bodies of water such as the Chesapeake Bay. As such, atmospheric nitrogen

leads directly to excessive nutrient loading of those water bodies. Nitrogen loading accelerates

eutrophication, which is the aging process of a body of water. Among other effects, excessive nutrient

loading causes algae blooms, low oxygen levels, red tides, fish kills, and general ecological degradation.

The ecosystem can no longer support certain fish species, which may be replaced by less desirable

species, if at all. Oysters are stressed, and greatly reduced in number. Atmospheric nitrogen is not the

sole contributor to these effects, but is certainly one of many that must be controlled to improve the

health of streams, rivers, and estuaries.

Particulate Matter

The impacts of fine particles are largely those of acid rain, increased nutrient loading, and the effects

mentioned under sulfur dioxide and nitrogen dioxide. Fine particles are also very efficient carriers of air

toxics, which each have their own impacts on ecosystems. Since fine particles are the dominant cause

of haze, they also lead to significant visibility reduction, as discussed previously in this document. Fine

particles also form grimy deposits on, stain, and damage buildings, cars, and other surfaces.

Appendix B

Air Pollution Effects on Ecosystems and the

Environment
Page B-2

Mid-Atlantic Regional Air Management Association

Lead

Wild and domestic animals can ingest lead while grazing, and can experience the same kind of effects as

people who are exposed to lead. Low concentrations of lead can slow plant growth near industrial

facilities. Lead can enter water systems through runoff and from sewage and industrial waste streams.

Elevated levels of lead in the water can cause reproductive damage in some aquatic life and cause blood

and neurological changes in fish and other animals.

Acid Rain

Acidity is measured on the pH scale, where 7.0 is neutral, 0.0 is strongly acidic, and 14.0 is strongly

basic. The scale is logarithmic, so a pH of 5.0 represents ten times more acidity than a pH of 6.0. The

scale allows a wide range of acid content to be communicated with a single number.

Nitrogen oxides and sulfur dioxide may both deposit directly to the surface, where they can form acids

in the ecosystem. Much of the time, nitrogen oxides form acids before they reach the surface, and are

deposited directly to the ecosystem as such. The effects of acid rain range from degradation of buildings

and surfaces to acidification of streams and soils. Acids also leach metals and other nutrients from soils.

Certain metals, particularly aluminum, are toxic to trees. By increasing the load of certain metals in the

soil, many trees and plants are stressed or may be killed outright. Increased stress on plants and trees

makes them more susceptible to disease and insect infestations, leading to an overall decline of the

ecosystem.

Once acids make it into a stream, pond, or lake, the impact depends on the nature of the body of water.

If the area is surrounded by limestone, the lime may be sufficient to neutralize the acid. If not, the body

of water will tend to acidify. The nutrients leached from the soil will have additional effects on the

ecosystem. Aluminum, for example, is particularly toxic to fish. Streams and lakes can be rendered

barren of certain acid sensitive species such as bass, clams, snails, and crayfish. The eggs and young

tend to be the most sensitive to acidity. Below a pH of 5, most fish eggs cannot hatch.

The impact of acid rain is felt throughout the ecosystem. For example, frogs can tolerate relatively

acidic conditions, but the mayflies they eat cannot, so frogs may disappear from an acidified pond at a

pH they are supposedly able to tolerate. The pH of a body of water need not always be low to have

disastrous effects on the animals living in it. A sudden acidic rainstorm

or snowmelt can produce a pulse of acidity that pushes the pH below

the limit which a particular fish can tolerate, resulting in a sudden fish

kill.

Much of the Mid-Atlantic Region, particularly the Mid-Appalachian

highlands, is highly sensitive to acidity. Many of the streams in the

Mid-Atlantic Regional coastal plain are acidic, due to acid deposition in

their watersheds. In the New Jersey Pine Barrens, for example, over

90 percent of the streams are acidic.

Though many of the air quality

standards in the United States are

health-based standards, it is

important to remember that air

pollution harms the environment as

well. Many of the same pollutants

that lead to elevated ozone and PM

also affect the environment directly

via acid rain, excess nutrient

loading, and visibility impairment,

not to mention the direct effects of

these pollutants themselves.

Appendix B
Page C-1

A Guide to Mid-Atlantic Regional Air Quality

Appendix C

Air Quality Standards and Goals

EPA uses six “criteria pollutants” as indicators of air quality, and has established a maximum concentration for each. Concentrations above these limits may cause adverse health effects. These threshold

concentrations are called National Ambient Air Quality Standards (NAAQS). There are two classes of

standards, primary and secondary, which are not to be confused with primary and secondary pollutants.

Primary standards set limits to protect public health, including the health of sensitive populations such as

asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including

protection against decreased visibility, damage to animals, crops, vegetation, and buildings. This section

gives a quick overview of the standards.

Ozone

The first ozone threshold value is 0.12 parts per million (ppm), averaged over one hour. An area meets

the ozone standard if the highest hourly value exceeds the threshold on average no more than one day

per year at each monitor. Each monitor in an area is treated individually under this standard, so the ozone

concentration at a given monitor is allowed to exceed the standard only three times in a three year

period. The fourth highest hour-average ozone concentration in a three year period therefore becomes

the figure of merit for determining whether or not an area is in compliance with the standard. The fourth

highest ozone value is termed the “design value” for that monitor. The highest design value for any

monitor is then used as the design value for the entire area.

The threshold value for the 8-hour standard is 0.08 ppm of ozone for an eight-hour average. On a

monitor-by-monitor basis, the design value is the annual fourth highest 8-hour value averaged over a

three-year period. The 8-hour standard has replaced the 1-hour standard, and is stricter .

Carbon Monoxide

The standard for carbon monoxide is a 9 ppm 8-hour average not to be exceeded more than once per

year. An area meets the carbon monoxide standard if no more than one 8-hour value per year exceeds

the threshold, provided the area meets the standard for two consecutive years and carries out air quality

monitoring during the entire time. In addition, there is a 1-hour standard for carbon monoxide at 35 ppm,

that also may not be violated more than once per year. The areas in violation of the carbon monoxide

standard are predominantly in the West. Currently, no areas in the eastern United States are in violation

of the carbon monoxide standard. Reformulated gasoline and improved emissions control technologies

have greatly reduced carbon monoxide levels.

Sulfur Dioxide

There are three standards for sulfur dioxide:

· an annual average of 0.03 ppm (80 micrograms per cubic meter, μg/m3

)

· a 24-hour average level of 0.14 ppm (365 μg/m3

)

· a 3-hour average level of 0.50 ppm (1300 μg/m3

)
Page C-2

Mid-Atlantic Regional Air Management Association

Appendix C

Pollutant Primary Stds. Averaging Times Secondary Stds. 

9 ppm (10 mg/m3) 8-hour1 Carbon Monoxide None 

35 ppm 

(40 mg/m3

) 

1-hour1

 None 

Lead 1.5 μg/m3 Quarterly Average Same as Primary 

Nitrogen Dioxide 0.053 ppm (100 μg/m3) Annual (Arithmetic Mean) Same as Primary 

50 μg/m3 Annual2 Particulate Matter (Arith. Mean) Same as Primary 

(PM10) 150 μg /m3

 24-hour1 

15.0 μg/m3 Annual3 Particulate Matter (Arith. Mean) Same as Primary 

(PM2.5) 65 μg m3

 24-hour4 

Ozone 0.08 ppm 8-hour5 Same as Primary 

0.03 ppm Annual (Arith. Mean) ------- 

0.14 ppm 24-hour1 ------- 

Sulfur Oxides 

------- 3-hour1

 0.5 ppm (1300 μg /m3) 

NAAQS Summary Table

The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient

Air Quality Standards (NAAQS) for wide-spread pollutants from numerous and diverse

sources considered harmful to public health and the environment. The Clean Air Act

established two types of national air quality standards. Primary standards set limits to protect

public health, including the health of “sensitive” populations such as asthmatics, children, and

the elderly. Secondary standards set limits to protect public welfare, including protection

against visibility impairment, damage to animals, crops, vegetation, and buildings. The Clean

Air Act requires periodic review of the science upon which the standards are based and the

standards themselves.

Source — http://www.epa.gov/air/criteria.html

1

 Not to be exceeded more than once per year.

2

 To attain this standard, the 3-year average of the weighted annual mean PM10 concentration at each

monitor within an area must not exceed 50 μg/m3.

3

 To attain this standard, the 3-year average of the weighted annual mean PM2.5 concentrations from

single or multiple community-oriented monitors must not exceed 15.0 μg/m3.

4

 To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each

population-oriented monitor within an area must not exceed 65 μg/m3.

5

 To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone

concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm.
Page C-3

A Guide to Mid-Atlantic Regional Air Quality

The first two standards are primary (health-related) standards, while the 3-hour standard is a secondary

(welfare-related) standard. Annual mean sulfur dioxide concentrations cannot exceed the standard.

The short-term standards cannot be exceeded more than once per year. A few areas in the Mid-Atlantic

currently violate the sulfur dioxide standard.

Nitrogen Dioxide

The nitrogen dioxide standard is an annual average concentration of 0.053 ppm (100 μg/m3). All areas of

the United States are currently in compliance with the nitrogen dioxide standard.

Particulate Matter

Standards for particulate matter (PM) are set for different sizes of particles. There are standards for

PM with a diameter of 10 micrometers (PM10) or less and for smaller particles of 2.5 micrometers

(PM2.5) or less.

The standards in effect for PM10 are an annual mean of 50 μg/m3

 and a daily standard of 150 μg/m3. For

the daily standard, the annual mean PM10 may not exceed 150 μg/m3

 more than three times in three

years. For the annual standard, the average of three sequential annual averages must fall below 50 μg/

m3

. Annual averages are calculated from previously obtained quarterly averages.

Two standards are in effect for PM2.5: an annual standard of 15 μg/m3

, and a daily standard of 65 μg/m3.

All areas in the Mid-Atlantic will comply with the daily standard, but some exceed the annual standard.

The annual standard appears to have been placed very near the average annual concentration of PM2.5

in the Region. The rules for calculating design values for these standards are somewhat complex, so

they are best broken down into step-by-step procedures.

 Annual standard

1. Average 24-hour measurements to obtain quarterly means at each monitor.

2. Average quarterly means to obtain annual means at each monitor.

3. Average across designated monitoring sites to obtain an annual spatial mean for an

 area. (Optional for areas designated for spatial averaging. Such averaging may be used to

 blend data from more than one monitoring site if approved by the state and EPA.)

4. Average three years of annual means to obtain a three-year average of annual means.

 Daily standard

1. Calculate the 98th percentile 24-hour average PM concentration for each year.

2. Average the 98th percentile concentration over three years.

Lead

The lead standard is a quarterly average particulate concentration of 1.5 μg/m3. Only three areas in

Montana and Missouri currently do not comply with the lead standard.
Page C-4

Mid-Atlantic Regional Air Management Association

Haze: A 60-Year Return to Natural Conditions

The haze rule is fundamentally different from those mentioned previously in that it is not a health-based

standard, and goals are to be set individually for each area that represent natural conditions at that site.

EPA’s haze rule requires that Class I areas (large national parks and wilderness areas) return to natural

visibility by 2064. The regulation has two parts: one concerns sources that have a readily discernible

impact on a Class I area, while the other concerns regional haze where specific sources may not be

identifiable.

The haze rule divides days into the 20 percent best and 20 percent worst visibility days. Visibility on the

best days can get no worse, while visibility on the worst days must make steady progress as measured

in deciviews back toward natural conditions. The logarithmic nature of the deciview scale means that

big reductions in particle concentrations are required at first, with smaller ones later. While this may

sound like the big burden is up front, it is likely that the most difficult part will come later. By 2064, if

visibility is to return to natural conditions, emissions from human activities will have to be quite small.

Most Class I areas are in the West, but there are some in the eastern United States. In the Mid-Atlantic,

the Class I areas are: Brigantine Wilderness (NJ), Dolly Sods Wilderness (WV), Otter Creek

Wilderness (WV), Shenandoah National Park, (VA), James River Face Wilderness (VA), Linville Gorge

Wilderness (NC), Swanquarter Wilderness (NC), Shining Rock Wilderness (NC), Great Smoky

Mountains National Park (NC), and Joyce Kilmer-Slickrock Wilderness (NC). All states in the

Mid-Atlantic Region will be affected by this regulation, since pollution transport from neighboring states

is part of the regional haze problem. Mid-Atlantic Region states will also have to reduce emissions to

improve visibility in Class I areas outside the Mid-Atlantic Region.

Appendix C
Page D-1

A Guide to Mid-Atlantic Regional Air Quality

Appendix D

MARAMA Region Data Tables

Table D-1 PM 2.5 Design Values for the Annual Standard (2001-2003)

Table D-2a 8-hr Ozone Design Values by Nonattainment County (2001-2003)

Table D-2b 8-hr Ozone Design Values by Attainment County (2001-2003)

Table D-3 8-hr Ozone Design Values by Nonattainment Area (2001-2003)

Table D-4 Days Above the 8-Hour Ozone Standard 1998-2003 by EPA Planning/

Nonattainment Area

Table D-5 Days Above the 8-Hour Ozone Standard 1998-2003 by State

Table D-6 Days Above the 1-Hour Ozone Standard 1986-2003 by Nonattainment Area

Table D-7 Days Above the 1-Hour Ozone Standard 1986-2003 by State
Page D-2

Mid-Atlantic Regional Air Management Association

Table D-1

PM 2.5 Design Values for the Annual Standard (2001-2003)

State Monitor Site County 

PM 2.5 Design Value 

μg/m3

EPA Site 

Code 

 

DE MLK New Castle 16.2 100032004 

 

DE Newark New Castle 15.1 100031012 

 

DE Bellefonte New Castle 15.0 100031003 

 

DE Seaford Sussex 13.6 100051002 

 

DE Dover Kent 13.1 100010003 

 

DE 

Killens Pond State 

Park Kent 13.0 100010002 

 

DC 

River Terrace 

School Washington DC 15.8 110010041 

 

DC McMillan Reservoir Washington DC 15.2 110010043 

 

MD Old Town Baltimore City 16.6 245100040 

 

MD FMCA Baltimore City 15.9 245100035 

 

MD Westport Baltimore City 15.4 245100049 

 

MD Glen Burnie Anne Arundel 15.3 240031003 

 

MD Essex Baltimore Co. 15.2 240053001 

 

MD NWPS Baltimore City 15.0 245100007 

 

MD Riviera Beach Anne Arundel 14.2 240032002 

 

MD Padonia Baltimore Co. 14.2 240051007 

 

MD Hagerstown Washington 13.9 240430009 

Appendix D
Page D-3

A Guide to Mid-Atlantic Regional Air Quality

Table D-1, continued

PM 2.5 Design Values for the Annual Standard (2001-2003)

State Monitor Site County 

PM 2.5 Design Value 

μg/m3

EPA Site 

Code 

MD Fort Meade Anne Arundel 13.0 240030019 

 

MD Edgewood Harford 12.8 240251001 

 

MD Rockville Montgomery 12.6 240313001 

 

MD Davidsonville Anne Arundel 12.1 240030014 

 

NJ Elizabeth Lab Union 15.7 340390004 

 

NJ 

Jersey City 

Firehouse Hudson 14.8 340171003 

 

NJ Trenton Mercer 14.0 340210008 

 

NJ Phillipsburg Warren 13.5 340410006 

 

NJ Rahway Union 13.1 340392003 

 

NJ New Brunswick Middlesex 12.7 340230006 

 

NC Lexington Davidson 15.8 370570002 

 

NC Hickory 1st Street Catawba 15.5 370350004 

 

NC 

Charlotte #10 Fire 

Station Mecklenberg 14.9 371190010 

 

NC 

Winston-Salem 

Hattie Avenue Forsyth 14.6 370670022 

 

NC Kannapolis Cabarrus 14.5 370250004 

 

NC 

Charlotte 

Montclaire Mecklenberg 14.2 371190042 

 

NC Marion McDowell 14.1 371110004 
Page D-4

Mid-Atlantic Regional Air Management Association

Table D-1, continued

PM 2.5 Design Values for the Annual Standard (2001-2003)

State Monitor Site County 

PM 2.5 Design Value 

μg/m3

EPA Site 

Code 

NC Charlotte Garinger Mecklenberg 14.1 371190041 

 

NC 

Winston-Salem 

North Forsyth 14.0 370670024 

 

NC Gastonia Gaston 14.0 370710016 

 

NC 

Greensboro 

Mendenhall Guilford 14.0 370810013 

 

NC Fayetteville Cumberland 13.9 370510009 

 

NC Durham Durham 13.9 370630001 

 

NC Raleigh Millbrook Wake 13.8 371830014 

 

NC Burlington Alamance 13.7 370010002 

 

NC Goldsboro Wayne 13.6 371910005 

 

NC 

Raleigh St. 

Augustine Wake 13.5 371830015 

 

NC Waynesville Haywood 13.4 370870010 

 

NC Cherry Grove Caswell 13.3 370330001 

 

NC Spruce Pine Mitchell 13.3 371210001 

 

NC Chapel Hill Orange 13.1 371350007 

 

NC Asheville Buncombe 12.9 370210034 

 

NC 

Lumberton 

Linkhaw Robeson 12.8 371550005 

 

NC Cherokee Jackson 12.6 370990006 

Appendix D
Page D-5

A Guide to Mid-Atlantic Regional Air Quality

Table D-1, continued

PM 2.5 Design Values for the Annual Standard (2001-2003)

State Monitor Site County 

PM 2.5 Design Value 

μg/m3

EPA Site 

Code 

NC Bryson City Swain 12.6 371730002 

 

NC Greenville Pitt 12.3 371470005 

 

NC Pittsboro Chatham 12.2 370370004 

 

NC Candor Montgomery 12.1 371230001 

 

NC Kenansville Duplin 11.9 370610002 

 

NC Kinston Lenoir 11.4 371070004 

 

NC Jacksonville Onslow 11.1 371330005 

 

PA Liberty Allegheny 21.2 420030064 

 

PA Clairton Allegheny 17.2 420033007 

 

PA Lancaster Lancaster 17.0 420710007 

 

PA York York 17.0 421330008 

 

PA North Braddock Allegheny 16.9 420031301 

 

PA Reading Berks 16.4 420110009 

 

PA 

500 South Broad 

Street Philadelphia 16.2 421010047 

 

PA Beaver Falls Beaver 16.0 420070014 

 

PA Harrison Allegheny 15.9 420031008 

 

PA Johnstown Cambria 15.8 420210011 

 

PA Lawrenceville Allegheny 15.7 420030008 
Page D-6

Mid-Atlantic Regional Air Management Association

Table D-1, continued

PM 2.5 Design Values for the Annual Standard (2001-2003)

State Monitor Site County 

PM 2.5 Design Value 

μg/m3

EPA Site 

Code 

PA Harrisburg Dauphin 15.7 420430401 

 

PA Charleroi Washington 15.5 421250005 

 

PA Greensburg Westmoreland 15.5 421290008 

 

PA Chester Delaware 15.4 420450002 

 

PA AMS Laboratory Philadephia 15.2 421010004 

 

PA Washington Washington 15.0 421250200 

 

PA Freemansburg Northampton 14.6 420950025 

 

PA Allentown Lehigh 14.4 420770004 

 

PA Bristol Bucks 14.3 420170012 

 

PA Farrell Mercer 14.3 420850100 

 

PA 

Belmont Water 

Treatment Philadelphia 14.3 421010020 

 

PA Norristown Montgomery 14.1 420910013 

 

PA Arendtsville Adams 13.4 420010001 

 

PA Perry County Perry 13.0 420990301 

 

PA WilkesBarre Luzerne 12.9 420791101 

 

PA Scranton Lackawanna 12.5 420692006 

 

VA 

Market Street Fire 

Station Salem 14.7 517750010 

Appendix D
Page D-7

A Guide to Mid-Atlantic Regional Air Quality

Table D-1, continued

PM 2.5 Design Values for the Annual Standard (2001-2003)

State Monitor Site County 

PM 2.5 Design Value 

μg/m3

EPA Site 

Code 

VA 

Aurora Hills 

Visitors Center Arlington 14.6 510130020 

 

VA 

Highlands View 

Elementary School Bristol 14.3 515200006 

 

VA 

Raleigh Court 

Library Roanoke 14.2 517700014 

 

VA Lewinsville Fairfax 14.0 510595001 

 

VA 

DEQ Air 

Monitoring Office Richmond 14.0 517600020 

 

VA 

Mathematics & 

Science Center Henrico 13.7 510870014 

 

VA Bensley Armory Chesterfield 13.6 510410003 

 

VA Lee District Park* Fairfax 13.6 510590030 

 

VA 

Broad Run High 

School Loudoun 13.6 511071005 

 

VA NOAA Facility Norfolk 13.0 517100024 

 

VA 

DEQ Regional 

Office Henrico 12.9 510870015 

 

VA 

Luray Caverns 

Airport Page 12.9 511390004 

 

VA Off Routh #608 Charles City 12.8 510360002 

 

VA 

DEQ Regional 

Office Virginia Beach 12.6 518100008 

 

VA 

Oscar Smith 

Stadium Chesapeake 12.5 515500012 

*The completeness criteria were not met for Lee District Park (510590030)
Page D-8

Mid-Atlantic Regional Air Management Association

Table D-1, continued

PM2.5 Design Values for the Annual Standard (2001-2003)

State Monitor Site County 

PM 2.5 Design Value 

μg/m3

EPA Site 

Code 

VA Virginia School Hampton 12.5 516500004 

 

VA Pump Station #103 Newport News 11.9 517000013 

 

WV Weirton/Oak Street Hancock 17.4 540291004 

 

WV South Charleston Kanawha 17.1 540391005 

 

WV Follansbee Brooke 16.8 540090005 

 

WV Huntington Cabell 16.6 540110006 

 

WV Martinsburg Berkeley 16.3 540030003 

 

WV 

Weirton/Marland 

Heights Hancock 16.2 540290011 

 

WV Vienna Wood 16.0 541071002 

 

WV Moundsville Marshall 15.7 540511002 

 

WV Charleston Kanawha 15.5 540390010 

 

WV Fairmont Marion 15.4 540490006 

 

WV Wheeling Ohio 15.2 540690008 

 

WV Morgantown Monongalia 14.9 540610003 

 

WV Clarksburg Harrison 14.0 540330003 

 

WV Beckley Raleigh 13.1 540810002 

 

WV Bluefield Mercer 12.5 540550002 

 

WV Keeney Knob Summers 10.1 540890001 

Appendix D
Page D-9

A Guide to Mid-Atlantic Regional Air Quality

Table D-2a

8-hour Ozone Design Values

by Nonattainment County (2001-2003)

State County Design Value (ppb) 

DE Kent 89 

DE New Castle 93 

DE Sussex 91 

DE Washington 94 

MD Anne Arundel 98 

MD Baltimore 93 

MD Carroll 89 

MD Cecil 98 

MD Charles 94 

MD Frederick 88 

MD Harford 103 

MD Kent 95 

MD Montgomery 88 

MD Prince George's 93 

MD Washington 86 

NC Alexander 88 

NC Caswell 88 

NC Cumberland 87 

NC Davie 93 

NC Durham 89 

NC Edgecombe 89 

NC Forsyth 93 

NC Franklin 90 

NC Granville 94 

NC Guilford 89 

NC Haywood 85 

NC Johnston 85 

NC Lincoln 92 

NC Mecklenburg 98 

NC Person 91 

NC Randolph 85 

NC Rockingham 91 

NC Rowan 100 

NC Union 88 

NC Wake 92 

NJ Atlantic 91 

NJ Bergen 95 

NJ Camden 102 

NJ Cumberland 98 

NJ Gloucester 100 

NJ Hudson 87 

NJ Hunterdon 97 
Page D-10

Mid-Atlantic Regional Air Management Association

Table D-2a, continued

8-hour Ozone Design Values

by Non-attainment County (2001-2003)

State County Design Value (ppb) 

NJ Mercer 99 

NJ Middlesex 98 

NJ Monmouth 97 

NJ Morris 98 

NJ Ocean 109 

NJ Passaic 88 

PA Allegheny 93 

PA Armstrong 93 

PA Beaver 94 

PA Berks 91 

PA Blair 85 

PA Bucks 100 

PA Cambria 87 

PA Centre 88 

PA Chester 98 

PA Clearfield 90 

PA Dauphin 88 

PA Delaware 93 

PA Erie 92 

PA Franklin 93 

PA Greene 89 

PA Lackawanna 85 

PA Lancaster 92 

PA Lehigh 92 

PA Luzerne 86 

PA Mercer 94 

PA Montgomery 94 

PA Northampton 91 

PA Perry 87 

PA Philadelphia 97 

PA Tioga 86 

PA Washington 89 

PA Westmoreland 91 

PA York 89 

VA Alexandria 92 

VA Arlington 99 

VA Charles City 91 

VA Chesterfield 86 

VA Fairfax 97 

VA Frederick 85 

VA Hampton 90 

VA Hanover 94 

Appendix D
Page D-11

A Guide to Mid-Atlantic Regional Air Quality

Table D-2a, continued

8-hour Ozone Design Values

by Non-attainment County (2001-2003)

State County Design Value (ppb) 

VA Henrico 90 

VA Loudon 92 

VA Madison 87 

VA Prince William 87 

VA Roanoke 85 

VA Stafford 88 

VA Suffolk 88 

WV Berkeley 86 

WV Cabell 88 

WV Hancock 86 

WV Kanawha 86 

WV Ohio 87 

WV Wood 87 
Page D-12

Mid-Atlantic Regional Air Management Association

Table D-2b

8-hour Ozone Design Values by

 Attainment County (2001-2003)

State County Design Value (ppb) 

NC Northampton 84 

NC Pitt 82 

NC Swain 74 

NC Yancey 83 

NC Avery 78 

NC Buncombe 78 

NC Caldwell 84 

NC Chatham 82 

NC Duplin 79 

NC Lenoir 81 

NC Martin 81 

NC New Hanover 78 

PA Lawrence 80 

PA Lycoming 83 

VA Caroline 84 

VA Fauquier 80 

VA Page 82 

VA Rockbridge 78 

VA Wythe 80 

WV Greenbrier 80 

WV Monongalia 79 

Appendix D
Page D-13

A Guide to Mid-Atlantic Regional Air Quality

Table D-3

8-hour Ozone Design Values by

Nonattainment Area (2001-2003)

State Nonattainment Area 

8-hr Ozone Design Value 

(ppb) 

DC Washington DC, MD, VA 99 

MD Baltimore 103 

MD Kent and Queen Anne's Counties 95 

MD Washington County (Hagerstown) 86 

NC Charlotte-Gastonia-Rock Hill 100 

NC Fayetteville 87 

NC Greensboro-Winston Salem-High Point 93 

NC 

Haywood and Swain Counties (Great Smoky 

NP) 85 

NC Hickory-Morganton-Lenoir 88 

NC Raleigh-Durham-Chapel Hill 94 

NC Rocky Mount 89 

NJ New York-N. New Jersey-Long Island 102 

PA Allentown-Bethlehem-Easton 91 

PA Altoona 85 

PA Clearfield and Indiana Counties 90 

PA Erie 92 

PA Franklin County 93 

PA Greene County 89 

PA Harrisburg-Lebanon-Carlisle 88 

PA Johnstown 87 

PA Lancaster 92 

PA Pittsburgh-Beaver Valley 94 

PA Reading 91 

PA Scranton-Wilkes Barre 86 

PA State College 88 

PA Tioga County 86 

PA York 89 

PA Youngstown-Warren-Sharon 95 

PA, NJ, MD, 

DE Philadelphia-Wilmington-Atlantic City 106 

VA Frederick County 85 

VA Fredericksburg 99 

VA Madison and Page Counties (Shenandoah NP) 87 

VA Norfolk-Virginia Beach-Newport News 90 

VA Richmond-Petersburg 94 
Page D-14

Mid-Atlantic Regional Air Management Association

Table D-3, continued

8-hour Ozone Design Values

 by Nonattainment Area (2001-2003)

State Nonattainment Area 

8-hr Ozone Design Value 

(ppb) 

VA Roanoke 85 

WV Berkeley and Jefferson Counties 86 

WV Charleston 86 

WV Huntington-Ashland 91 

WV Parkersburg-Marietta 87 

WV Steubenville-Weirton 86 

WV Wheeling 87 

Appendix D
Page D-15

A Guide to Mid-Atlantic Regional Air Quality

Table D-4

Days Above the 8-Hour Ozone Standard (1998-2003)

by EPA Planning/Nonattainment Area

EPA Planning 

Areas/Nonattainment Areas 1998 1999 2000 2001 2002 2003 

Allentown-Bethlehem-Easton PANJ 19 23 6 15 19 4 

Altoona PA 17 6 2 3 9 3 

Cumberland-Keyser Interstate MD NA NA NA 6 15 3 

Atlantic City NJ 23 13 4 9 11 4 

Baltimore MD 51 41 17 29 37 9 

Charleston WV 12 14 4 1 6 4 

Charlotte-Gastonia NC 51 43 27 26 36 9 

Erie PA 12 13 2 4 17 4 

Greenbrier WV 11 2 1 2 2 0 

Greensboro-Winston-Salem-High 

Point NC 31 30 21 21 29 7 

Hampton Roads VA 15 16 5 6 15 4 

Harrisburg-Lebabnon-Carlisle PA 22 17 5 16 16 3 

Huntington-Ashland WV-KY 16 16 1 5 20 3 

Johnstown PA 13 11 5 5 6 2 

Kent County and Queen Anne's 

County MD 16 23 6 13 17 4 

Lancaster PA 27 18 5 15 18 3 

Lawrence Co PA 2 5 0 1 6 2 

New York-N. New Jersey-Long 

Island NY-NJ-CT 41 40 18 34 41 14 

Norfolk-Virginia Beach-Newport 

News-VA 15 16 5 6 15 4 

Parkersburg WV 19 13 4 2 19 2 

Philadelphia-Wilmington-Trenton 

PA-NJ-DE-MD 41 36 19 31 41 15 

Pittsburgh-Beaver Valley PA 44 29 5 24 33 9 

Raleigh-Durham NC 43 35 11 9 29 7 

Reading PA 18 17 3 8 14 3 

Richmond-Petersburg VA 28 27 6 14 25 5 

Roanoke VA 12 5 2 5 5 1 

Scranton-Wilkes-Barre PA 15 21 1 10 16 3 

Sharon PA 25 8 2 15 20 6 

Shenandoah National Park 22 15 1 8 6 6 

State College NA NA 2 5 13 4 

Steubenville WV 6 6 1 3 16 2 

Sussex Co DE 22 20 7 10 16 5 

Washington DC-MD-VA 47 39 10 24 38 7 

Wheeling WV 5 7 2 6 11 0 

Williamsport PA 1 NA 1 1 7 0 

York PA 19 10 6 8 12 0 
Page D-16

Mid-Atlantic Regional Air Management Association

Table D-5

Days Above the 8-hour Ozone Standard (1998-2003)

 by State

 All Mid-Atlantic States 1998 1999 2000 2001 2002 2003 

Delaware 36 13 10 21 26 7 

District of Columbia 47 39 10 24 38 7 

Maryland 55 20 21 30 39 9 

New Jersey 47 46 19 35 44 20 

North Carolina 71 20 33 33 51 14 

Pennsylvania 55 51 22 39 50 19 

Virginia 49 18 10 22 45 11 

West Virginia 30 28 6 19 31 6 

Appendix D
Page D-17

A Guide to Mid-Atlantic Regional Air Quality

EPA Planning/ 

Nonattainment Areas 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Allentown-BethlehemEaston PA-NJ 0 3 12 0 0 1 0 0 0 0 0 1 1 2 1 2 0 0 Altoona PA 0 2 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 AQCR 113 CumberlandKeyser Interstate MD NA NA NA NA NA NA NA NA NA NA 0 0 0 0 0 0 0 0 Atlantic City NJ 0 5 6 1 5 2 1 0 0 0 0 3 0 0 0 0 1 0 Baltimore MD 13 23 36 4 8 14 3 11 10 13 3 12 6 11 1 9 16 2 Charleston WV 1 0 7 0 0 1 0 0 0 0 0 0 1 2 0 0 0 0 Charlotte-Gastonia NC 7 7 14 2 1 1 0 3 0 1 0 2 6 5 3 0 0 3 Erie PA 0 1 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Greenbrier W V 0 0 4 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Greensboro-WinstonSalem-High Point NC 2 1 10 0 2 0 0 1 0 1 0 0 1 3 0 0 0 0 Harrisburg-LebabnonCarlisle PA 0 2 8 0 1 0 0 0 0 0 0 0 1 2 0 0 2 0 Huntington-Ashland WV-KY 3 8 14 1 4 3 0 1 3 2 0 1 2 1 0 0 0 0 Johnstown PA 0 0 7 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 Kent County and Queen Anne's County MD 0 0 0 1 1 6 0 2 0 1 0 4 1 2 3 0 3 1 Lancaster PA 0 1 3 0 0 0 0 0 0 1 0 3 1 2 0 2 0 1 Lawrence Co PA 0 0 3 0 0 0 0 2 0 0 0 0 0 1 0 0 0 1 New York-N. New JerseyLong Island NY-NJ-CT 20 31 42 21 22 25 7 13 11 16 4 7 4 12 4 8 14 5 Norfolk-Virginia BeachNewport News-VA 1 2 4 0 0 1 2 3 0 0 0 0 0 4 0 1 3 1 Parkersburg WV 1 3 11 1 0 0 0 0 1 0 0 0 0 0 0 0 1 0 Philadelphia-WilmingtonTrenton PA-NJ-DE-MD 16 31 42 18 15 28 7 21 8 11 5 11 6 11 3 12 15 2 Pittsburgh-Beaver Valley PA 2 5 19 4 0 2 0 2 2 9 0 3 7 4 0 0 0 1 Raleigh-Durham NC 1 4 12 3 0 0 0 2 0 0 0 2 4 5 1 0 0 0 Reading PA 0 2 14 0 0 1 0 0 1 0 0 1 0 2 0 2 0 1 

Table D-6

Days Above the 1-hour Ozone Standard (1998-2003)

by Nonattainment Area
Page D-18

Mid-Atlantic Regional Air Management Association 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Richm ond-Petersburg VA 0 5 14 0 1 1 1 5 1 2 0 3 3 8 0 1 5 1 R oanoke VA 0 0 2 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 Scranton-W ilkes-Barre PA 0 1 10 0 0 2 0 0 0 0 0 0 0 1 0 0 1 0 Sharon PA N A N A N A N A N A N A NA NA NA NA 0 0 0 0 0 0 0 0 Shenandoah National Park 0 0 2 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 State C ollege N A N A N A N A N A N A NA NA NA NA 0 0 0 0 0 0 0 0 Steubenville W V NA NA NA NA NA NA NA NA NA NA 0 0 0 1 0 0 0 0 Sussex C o D E 0 0 8 0 1 3 0 0 0 0 0 3 1 0 0 1 0 2 W ashington DC-MD-VA 6 18 31 3 5 6 2 8 4 6 1 6 6 7 2 3 9 3 W heeling W V N A N A N A N A N A N A NA NA NA NA 0 0 0 0 0 0 0 3 W illiam sport PA NA NA NA NA NA NA NA NA NA NA 0 0 0 0 0 0 0 4 W inchester, VA N A N A N A N A N A N A 0 0 0 0 0 0 0 0 0 0 0 0 York PA 0 0 4 0 0 0 0 0 0 0 0 0 0 1 0 0 1 3 Table D-6, continued Days Above the 1-Hour Ozone Standard (1986-2003) by Nonattainment Area

Appendix D
Page D-19

A Guide to Mid-Atlantic Regional Air Quality

Table D-7

Days above the 1-Hour Ozone Standard (1986-2003)

by State

Year Delaware 

District of 

Columbia Maryland 

New 

Jersey 

North 

Carolina Pennsylvania Virginia 

West 

Virginia 

1986 0 0 17 22 8 14 5 4 

1987 11 6 23 32 8 23 16 4 

1988 28 6 36 45 22 39 29 22 

1989 4 1 4 18 5 13 3 2 

1990 6 0 10 23 3 7 6 0 

1991 9 1 16 26 1 14 11 2 

1992 2 0 5 9 1 2 3 0 

1993 5 8 16 18 6 10 11 1 

1994 2 4 11 7 0 5 3 2 

1995 6 4 14 14 3 11 5 2 

1996 0 0 4 6 5 3 1 0 

1997 7 5 14 10 4 7 4 1 

1998 6 0 10 4 9 11 9 5 

1999 4 3 11 10 10 11 10 4 

2000 3 0 4 4 3 2 1 0 

2001 2 4 10 11 2 4 3 0 

2002 3 9 16 16 12 11 9 1 

2003 2 3 2 4 3 3 3 0 
Page D-20

Mid-Atlantic Regional Air Management Association
Page E-1

A Guide to Mid-Atlantic Regional Air Quality

Appendix E

Measuring and Calculating Visibility Impairment

Visibility is impaired by light scattering and absorption due to particles and gases in the air.1 Light

extinction is the sum of light scattering plus light absorption. Light extinction may be thought of as a

measure of the amount of light that is extinguished as the light moves through the atmosphere. The more

light that is lost, the greater the loss of visibility.

Scientists have studied the effect of various air pollutants on light extinction and have developed an

equation to estimate light extinction based on measurements of these pollutants in the air. Measuring the

concentration of sulfates, nitrates, organic carbon, and other particles allows scientists to “reconstruct”

the amount of visibility impairment. Sulfates and nitrates have a stronger effect on visibility impairment

than other particles because they combine with water, thereby growing larger and scattering more light.

Therefore, relative humidity measurements are also needed in order to calculate visibility impairment.

The Interagency Monitoring of Protected Visual Environments (IMPROVE) program is a cooperative measurement effort governed by a steering committee composed of representatives from Federal, regional, and

state organizations. The IMPROVE monitoring program was established in 1985 to plan to improve and

protect the visibility in Class I areas (156 national parks and wilderness areas) as stipulated in the 1977

amendments to the Clean Air Act.

The objectives of the IMPROVE program are:

(1) to establish current visibility and aerosol conditions in mandatory Class I areas;

(2) to identify chemical species and emission sources responsible for existing man-made visibility

impairment;

(3) to document long-term trends for assessing progress towards the national visibility goal; and

(4) as required by EPA’s Regional Haze Rule, to provide regional haze monitoring representing all

visibility-protected federal Class I areas, where practical.

IMPROVE has also been a key participant in visibility-related research, including the advancement of monitoring instrumentation, analysis techniques, visibility modeling, policy formulation, and source attribution field

studies.

Interagency Monitoring of Protected Visual Environments

(IMPROVE)

Source: “Improve Monitoring Program Overview”, http://Vista.cira.colostate.edu/IMPROVE/

1

 Light scattered by gases in the atmosphere is termed Rayleigh or natural scattering, and is taken to be a constant

at 12 inverse megameters (Mm-1) at sea level. The only significant gas that absorbs light is nitrogen dioxide (NO2),

and its absorption is generally small, except in concentrated plumes from emission sources.
Page E-2

Mid-Atlantic Regional Air Management Association

In order to determine compliance with the Clean Air Act and EPA regulations, state, federal, and

regional agencies have organized a collaborative effort to monitor visibility in Class I areas where

visibility is important. This program is called the Interagency Monitoring of Protected Visible

Environments (IMPROVE) program. The IMPROVE program uses various equipment to measure

air quality at Class I areas. These measurements are used to calculate visibility (light extinction), as

explained below.

Scientists can measure the brightness of light at a distance using a transmissometer. This equipment

measures the amount of light seen by looking directly at a light and compares that to the amount of light

from the same source reflected from a distant mirror. Transmissometers are difficult to operate in

remote locations, and measurements can be affected by unknowns such as fogging of lenses,

swarming insects, clouds, and the age of the light source, among other things. The transmissometer

measurement is not considered a direct measurement of extinction, and only selected IMPROVE

monitoring sites have transmissometers, including one at Shenandoah National Park.

Scientists can also measure light scattering (not including absorbtion) using nephelometers. A nephelometer measures scattering in a measured volume of air. This equipment also has operational limitations,

so only some Class I sites have nephelometers. IMPROVE sites at Great Gulf Wilderness, Lye Brook

Wilderness, Mammoth Cave, and Shenandoah National Park have nephelometers.

The standard equipment at an IMPROVE site measures PM2.5 on three types of filters (quartz, nylon,

and Teflon) as well as PM10 on a Teflon filter. In addition to quantifying PM2.5 and PM10 mass, lab

analysis of these filters provides measurements of numerous substances, the most prevalent of which

are sulfates, nitrates, and various forms of carbon. (See the following text box for more details.)

To calculate light extinction from these measurements, scientists calculate the mass of ammonium

sulfate, ammonium nitrate, organic carbon, soil, coarse particles, and light absorbing carbon. Then they

multiply these values by constants that reflect how efficient that type of particle is at scattering or

absorbing light and, finally, they sum the results. This process is represented by the following equation:

bext = 3.0 f(RH)[AS] + 3 f(RH)[AN] +4ROC[OC] + [Soil] + 6[CM] + 10.0[LAC] + bRay

where

bext = extinction

f(RH) = a function of Relative Humidity that accounts for absorption of water

AS = Ammonium Sulfate (NH4

)2SO4

AN = Ammonium Nitrate (NH4)NO3

ROC = the ratio of the mass of the organic aerosol to the total mass of carbon

OC = organic carbon

Soil = calculated from the measurements of aluminum, silicon, titanium, calcium, and iron

= 2.2Al + 2.49Si + 1.94Ti + 1.63Ca + 2.4Fe

CM = coarse mass = PM10 – PM2.5

bRay = Rayleigh (natural) scattering

Appendix E
Page E-3

A Guide to Mid-Atlantic Regional Air Quality

There are a number of uncertainties in the

equation for calculating light extinction. The

uncertainties arise from assumptions that all

sulfate and nitrate are present as ammonium

sulfate and ammonium nitrate, the functions

used to estimate the effect of relative humidity on those particles, the use of average

rather than site- and day-specific humidity

measurements, assumptions about the noncarbon content of organic compounds and

their behavior in varying humidity, and the

accuracy and precision of measurements.

The Northeast States for Coordinated Air Use

Management’s (NESCAUM) February 2002

report on “Updated Visibility Statistics for

the Mid-Atlantic Northeast Visibility Union

(MANE-VU) Region” concluded that there

was reasonable agreement between calculated and measured light scattering (measured

by nephelometers) at some locations, and that

further study of the effects of uncertainties in

the IMPROVE equation was warranted.

(See www.nescaum.org/ select Air Topics,

Regional Haze, and find Technical Report #1

listed under Technical Memoranda.)

A May 2005 report by Jenny L. Hand and

William C. Malm, “Review of the IMPROVE

Equation for Estimating Ambient Light Extinction Coefficients” recommended consideration of several

changes in the IMPROVE equation. Their recommended changes would modify the constants used for

sulfates, nitrates, and organic carbon, and would add a term to account for the effect of sea salt.

(See http://vista.cira.colostate.edu/IMPROVE/Publications/ and select Gray Literature.) These modifications are currently under review. The Regional Planning Organizations developing plans to improve

visibility at Class I areas are seeking to use the best available scientific information, including the most

appropriate equation for calculating visibility impairment.

The IMPROVE monitoring network continues to generate important information on visibility and trends

in the concentrations of particles that affect visibility. While there are uncertainties in the calculation of

visibility impairment, and some changes in the equation may be made, the data provide a reasonable and

consistent basis for measuring the results of efforts to achieve air quality improvement.

The standard IMPROVE sampler has four sampling modules,

listed below.

Module A: PM2.5 particles (0-2.5 μm) on Teflon. These are

analyzed by five methods:

• gravimetric mass for PM2.5

• hybrid integrating plate/sphere method for optical absorption

• Proton Elastic Scattering Analysis (PESA) for hydrogen

• Proton Induced X-ray Emission (PIXE) for Na-Mn

• X-Ray Fluorescence (XRF) for Fe-Pb

Module B: PM2.5 particles (0-2.5 μm) on nylon. A denuder

before the nylon filter removes nitric acid vapors. These are

analyzed by ion chromatography (IC) for nitrate (NO3

-

), chloride (CL-

), sulfate (BSO4), and nitrite (NO2

-

).

Module C: PM2.5 particles (0-2.5 μm) on quartz. These are

analyzed for carbon using the Thermal Optical Reflectance

(TOR) combustion method. A secondary filter at selected sites

is used to determine artifact. These samples are baked and

oxidized at a series of temperatures; the results are reported at

8 temperature steps.

Module D: PM10 particles (0-10 μm) on Teflon. All are measured for PM10 mass. Approximately 4% are analyzed by the

other four methods listed for Module A.

Source: “Improve Particulate Monitoring Network Standard Operating

Procedures,” Air Quality Group, Crocker Nuclear Laboratory, University

of California at Davis, http://vista.cira.colostate.edu/improve/Publications/
Page E-4

Mid-Atlantic Regional Air Management Association
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A Guide to Mid-Atlantic Regional Air Quality

Reference Books / Reports

Finlayson-Pitts, B. J., and J. N. Pritts, Chemistry of the Upper and Lower Atmosphere: Theory,

Experiments, and Applications, Academic Press, San Diego, 2000.

NARSTO, Particulate Matter Science for Policy Makers, February 2003.

NARSTO, Assessment of Tropospheric Ozone Pollution: A North American Perspective, July 2000.

National Research Council, Committee on Tropospheric Ozone Formation and Measurement, Rethinking the Ozone problem in Urban and Regional Air Pollution, National Academy Press, Washington,

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Seinfeld, J. H., and S. N. Pandis, Atmospheric Chemistry and Physics: from Air Pollution to Climate

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Southern Appalachian Mountain Initiative, Final Report, August 2002

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Air Quality

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Day, D. E., W. C. Malm, S. M. Kreidenweis, Seasonal variations in aerosol composition and acidity at

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March 1997.

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G. Lindsey, W. G. N. Slinn, T. J. Kelly, A. C. Delany, J. P. Greenberg, P. R. Zimmerman, J. F. Boatman,

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008 Office of Air Quality Planning and Standards, RTP NC 27711.

Hallock-Waters, K. A., B. G. Doddridge, R. R. Dickerson, S. Spitzer, and J. D. Ray, Carbon monoxide

inthe U.S. Mid-Atlantic troposphere: Evidence for a decreasing trend, Geophys. Res. Lett. 26 (18):

2861-2864, 1999

Appendix F

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Measurements

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Web Sites

General

EPA’s AIRNow Web site: www.airnow.gov

EPA’s General Pollution information Web site: www.epa.gov/air/urbanair/6poll.html

EPA’s monitoring and emissions Web portal: www.epa.gov/air/data/geosel.html

Appendix F Bibliography & Suggested Reading
 Bibliography F-7

A Guide to Mid-Atlantic Regional Air Quality

Visibility

National Park Service IMPROVE site: http://vista.cira.colostate.edu/improve/

Introduction to Visibility, by W. C. Malm for the National Park Service:

www2.nature.nps.gov/ard/vis/intro_to_visibility.pdf

...and a newer version with animated figures:

vista.cira.colostate.edu/improve/Education/IntroToVisinstr.htm

Colorado State IMPROVE site: vista.cira.colostate.edu/improve/

EPA’s visibility site: www.epa.gov/air/visibility

Pictures and summaries for Class I areas: www.epa.gov/air/visibility/monitor.html

PM

NARSTO’s 1998 PM assessment: www.cgenv.com/Narsto/Finepart.html

Ozone

NARSTO’s 2000 Ozone Assessment: www.cgenv.com/Narsto/assess.doc.html

EPA’s Ozone Web site (general information): www.epa.gov/air/urbanair/ozone/index.html

Health

The Health Effects Institute: www.healtheffects.org

EPA’s Health effects site: www.epa.gov/airnow/health

Regional Organizations

Mid-Atlantic Regional Air Management Association (MARAMA): www.marama.org

Northeast States for Coordinated Air Use Management (NESCAUM): www.nescaum.org

Ozone Transport Commission (OTC): www.otcair.org

Mid-Atlantic Northeast Visibility Union (MANE-VU): www.mane-vu.org

Visibility Improvement State & Tribal Association of the Southeast (VISTAS):www.vistas-sesarm.org

Southeast States Air Resource Managers (SESARM): www.metro4-sesarm.org

Regional Experiments in the Mid-Atlantic

Southern Appalachian Mountains Initiative (SAMI): http://www.epa.gov/ttn/gei/samiinfo.html

Southern Oxidants Study (SOS): www2.ncsu.edu/ncsu/CIL/southern_oxidants
Mid-Atlantic Regional Air Management Association

Bibliography F-8

Bibliography & Suggested Reading

Pittsburgh Air Quality Study (PAQS): http://homer.cheme.cmu.edu

Baltimore PM supersite:www.chem.umd.edu/supersite

Maryland Aerosol Research and Characterization (MARCH-Atlantic)

www.atmos.umd.edu/~bruce/MARCH-Atl.html

Northeast - Oxidant and Particle Study (NE-OPS): lidar1.ee.psu.edu/narsto-neops
Executive Board, 2005

Roger C. Westman, Allegheny County, Chair

Ali Mirzakhalili, Delaware, Vice Chair

Keith Overcash, North Carolina, Treasurer

Donald E. Wambsgans III, District of Columbia

Thomas C. Snyder, Maryland

Bill O’Sullivan, New Jersey

Joyce Epps, Pennsylvania

Morris Fine, Philadelphia

John M. Daniel, Jr., Virginia

John Benedict, West Virginia

 MARAMA Staff

Susan S.G. Wierman, Executive Director

Serpil Kayin, Ph.D., Senior Environmental Scientist

Bill Gillespie, Senior Environmental Scientist

Susan Stephenson, Air Quality Planner/

Public Outreach Coordinator

Megan Schuster, Air Quality Specialist

Katie Sheen-Abbott, Air Quality Planner/

Public Outreach Coordinator

Pat Davis, Environmental Analyst/Statistician

Alice R. Lutrey, Office Manager/Training Coordinator

Joan Walstrum, Administrative Assistant

Katie Cooney, Air Quality Specialist

Mid-Atlantic Regional Air Management Association

711 West 40th Street, Suite 312

Baltimore, Maryland 21211-2109

phone 410.467.0170 ~ fax 410.467.1737

www.marama.org

Members

The following State and Local governments are MARAMA members: Delaware, the District of

Columbia, Maryland, New Jersey, North Carolina, Pennsylvania, Virginia, West Virginia, Philadelphia,

and Allegheny County, Pennsylvania. Members of MARAMA’s Board of Directors are listed below.

Mission

MARAMA’s mission is to strengthen the skills and capabilities of member agencies and help them

work together to prevent and reduce air pollution impacts in the Mid-Atlantic Region.

What is MARAMA?

The Mid-Atlantic Regional Air Management Association is a voluntary, non-profit association of ten

state and local air pollution control agencies.

MARAMA provides cost-effective approaches to regional collaboration by pooling resources to develop and analyze data, share ideas, and train staff to implement common requirements.