The Nature of the Fine Particle and Regional Haze Air 

Quality Problems in the MANE-VU Region: 

A Conceptual Description 

Prepared for the Ozone Transport Commission 

Prepared by NESCAUM 

Boston, MA 

Final 

November 2, 2006 

Contributing Authors 

Tom Downs, Maine DEP 

Iyad Kheirbek, NESCAUM 

Gary Kleiman, NESCAUM 

Paul Miller, NESCAUM 

Leah Weiss, NESCAUM 
ii 

Acknowledgements 

NESCAUM thanks the U.S. EPA’s support of the Mid-Atlantic/Northeast Visibility 

Union Regional Organization whose work has provided the foundational basis of this 

report. 

NESCAUM also thanks the following people for their comments and input during the 

development of this report: 

John Graham, NESCAUM 

Kurt Kebschull, Connecticut Department of Environmental Protection 

Tonalee Key, New Jersey Department of Environmental Protection 

Mohammed A. Majeed, Delaware Department of Natural Resources and Environmental 

Conservation 

David Wackter, Connecticut Department of Environmental Protection 

Susan Wierman, MARAMA 

Mike Woodman, Maryland Department of the Environment 

Martha Webster, Maine Department of Environmental Protection 

Jung-Hun Woo, NESCAUM 
iii 

TABLE OF CONTENTS 

Acknowledgements............................................................................................................. ii 

Executive Summary.......................................................................................................... vii 

1. Introduction................................................................................................................ 1-1 

1.1. Background...................................................................................................... 1-1 

1.2. PM Formation .................................................................................................. 1-2 

1.3. PM Impacts on Visibility................................................................................. 1-3 

1.4. PM2.5 Design Values in the MANE-VU Region.............................................. 1-5 

1.5. Regional haze baseline conditions................................................................... 1-6 

2. A Detailed Look at Fine Particle Pollution and Regional Haze in The MANE-VU 

Region.............................................................................................................................. 2-1 

2.1. Chemical composition of particulate matter in the rural MANE-VU region .. 2-1 

2.2. Rural versus urban chemistry........................................................................... 2-3 

2.3. Geographic considerations and attribution of PM2.5/haze contributors ........... 2-6 

2.4. CAIR Modeling ............................................................................................. 2-10 

2.5. Seasonal differences....................................................................................... 2-12 

2.6. Summary........................................................................................................ 2-17 

3. MANE-VU Emission Inventory Characteristics for Fine Particles........................... 3-1 

3.1. Emissions inventory characteristics................................................................. 3-1 

3.1.1. Sulfur dioxide (SO2) ................................................................................ 3-1 

3.1.2. Volatile organic compounds (VOCs)....................................................... 3-3 

3.1.3. Oxides of nitrogen (NOX) ........................................................................ 3-4 

3.1.4. Primary particulate matter (PM10 and PM2.5)........................................... 3-6 

3.1.5. Ammonia emissions (NH3).................................................................... 3-10 

3.2. Emissions inventory characteristics outside MANE-VU .............................. 3-12 

4. What will it take to clean the air? .............................................................................. 4-2 

4.1. Meteorological and Pollution Overview of August 8-16, 2002....................... 4-2 

4.2. Temporally and spatially resolved PM2.5 measurements................................. 4-7 

4.3. Implications for control strategies ................................................................. 4-10 

4.4. Conclusion: Simplifying a complex problem ................................................ 4-12 

Appendix A: Excerpts from EPA Guidance Document, Guidance on the Use of Models 

and Other Analyses for Demonstrating Attainment of Air Quality Goals for 

Ozone, PM2.5, and Regional Haze 

Appendix B: Monitoring Data from Class I sites in MANE-VU 

Appendix C: Additional Considerations for PM2.5 Air Quality Management 
iv 

FIGURES 

Figure 1-1. View of a good visibility day (left) and a poor visibility day (right) at Acadia 

National Park, Maine in June 2003....................................................................... 1-3 

Figure 1-2. Schematic of visibility impairment due to light scattering and absorption 

(adapted from Malm, 2000). ................................................................................. 1-4 

Figure 2-1. Comparison of contributions during different seasons at Lye Brook 

Wilderness Area on 20% worst visibility (high PM2.5) days (2000-2003). .......... 2-2 

Figure 2-2. Comparison of species contributions on best and worst days at Lye Brook 

Wilderness Area.................................................................................................... 2-3 

Figure 2-3. New York nonattainment area (Elizabeth, NJ) compared to an upwind 

background site (Chester, NJ)............................................................................... 2-5 

Figure 2-4. Boston urban area (Boston, MA) compared to an upwind background site 

(Quabbin Reservoir, MA) ..................................................................................... 2-5 

Figure 2-5. 2002 Seasonal average SO4 based on IMPROVE and STN data................. 2-7 

Figure 2-6. 2002 Annual average PM2.5, sulfate, nitrate and total carbon for MANE-VU 

based on IMPROVE (I) and STN (S) data. PM2.5 mass data are supplemented by 

measurements from the FRM network (•)............................................................. 2-7 

Figure 2-7. 2002 Annual average contribution to PM2.5 sulfate as determined by multiple 

analysis methods for four Class I areas spanning MANE-VU and Virginia ........ 2-9 

Figure 2-8. 2002 Annual average mass contribution to PM2.5 at Brigantine Wilderness in 

New Jersey (IMPROVE) and sulfate contributions as determined by tagged 

REMSAD model simulations (NESCAUM, 2006) ............................................ 2-10 

Figure 2-9. Moving 60-day average of fine aerosol mass concentrations based on longterm data from two northeastern cities................................................................ 2-13 

Figure 2-10. The 30-day average PM2.5 concentrations from 8 northeastern cities during 

2002..................................................................................................................... 2-14 

Figure 2-11. Mean hourly fine aerosol concentrations during 2002 summer months... 2-15 

Figure 2-12. Mean hourly fine aerosol concentrations during 2002 winter months...... 2-15 

Figure 2-13. Summertime at Mt. Washington ............................................................... 2-17 

Figure 2-14. Wintertime in Boston ................................................................................ 2-17 

Figure 3-1. State level sulfur dioxide emissions............................................................. 3-2 

Figure 3-2. 2002 MANE-VU state SO2 inventories ....................................................... 3-2 

Figure 3-3. 2002 MANE-VU state VOC inventories ...................................................... 3-4 

Figure 3-4. State level nitrogen oxides emissions .......................................................... 3-5 

Figure 3-5. Plot of monitored NOX trends in MANE-VU during 1997-2005 ................ 3-5 

Figure 3-6. 2002 MANE-VU state NOX inventories ....................................................... 3-6 

Figure 3-7. State level primary PM10 emissions .............................................................. 3-8 

Figure 3-8. State level primary PM2.5 emissions ............................................................. 3-8 

Figure 3-9. 2002 MANE-VU state primary PM10 inventories......................................... 3-9 

Figure 3-10. 2002 MANE-VU state primary PM2.5 inventories...................................... 3-9 

Figure 3-11. State level ammonia emissions ................................................................. 3-11 

Figure 3-12. 2002 MANE-VU state NH3 inventories.................................................... 3-11 

Figure 4-1. Spatially interpolated maps of fine particle concentrations August 9 – 16, 

2002....................................................................................................................... 4-4 
v 

Figure 4-2. Surface weather maps for August 9-16, 2002............................................... 4-5 

Figure 4-3. HYSPLIT 72-hour back trajectories for August 9-16, 2002......................... 4-6 

Figure 4-4. Hourly average fine aerosol at 8 sites during the August 2002 episode ....... 4-7 

Figure 4-5. 24-hour rolling average fine aerosol at 8 MANE-VU sites during the August 

2002 episode ......................................................................................................... 4-8 

Figure 4-6. Composite images from NASA’s TERRA Satellite on August 13, 2002 

showing fine particle pollution/haze. .................................................................... 4-9 

Figure 4-7. NASA MODIS Terra Satellite Image, Back Trajectories and NOX Inventory

............................................................................................................................... 4-9 

Figure B-1. Monitoring Data from Acadia NP, ME ...................................................... B-2 

Figure B-2. Monitoring Data from Brigantine, ME....................................................... B-3 

Figure B-3. Monitoring Data from Great Gulf, NH....................................................... B-4 

Figure B-4. Monitoring Data from Lye Brook, VT....................................................... B-5 

Figure B-5. Monitoring Data from Moosehorn, ME ..................................................... B-6 

Figure B-6. Monitoring Data from Washington, DC..................................................... B-7 

Figure B-7. 20% Worst and Best 2000-2003 Visibility Days at Acadia NP, ME ......... B-8 

Figure B-8. 20% Worst and Best 2000-2003 Visibility Days at Brigantine, NJ ........... B-9 

Figure B-9. 20% Worst and Best 2000-2003 Visibility Days at Great Gulf, NH........ B-10 

Figure B-10. 20% Worst and Best 2000-2003 Visibility Days at Lye Brook, VT ...... B-11 

Figure B-11. 20% Worst and Best 2000-2003 Visibility Days at Moosehorn, ME .... B-12 

Figure B-12. 20% Worst and Best 2000-2003 Visibility Days at Washington, D.C... B-13 

Figure B-13. 20% Best 2000-2003 Visibility Days Speciated Contributions to Extinction

............................................................................................................................ B-14 

Figure B-14. 20% Best 2000-2003 Visibility Days Speciated Contributions to Extinction

............................................................................................................................ B-15 

Figure C-1. Effects of averaging times (or temporal resolution) on time series 

information........................................................................................................... C-2 

Figure C-2. Difference in FRM data between 10 urban-rural site pairs for 2002 ......... C-4 

Figure C-3. Regional PM2.5 and NOX in 2002 ............................................................... C-6 

Figure C-4. PM2.5 vs. NOX correlation by season.......................................................... C-6 
vi 

TABLES 

Table 1-1. 2004 PM2.5 Design Value for Nonattainment Areas in MANE-VU ............. 1-6 

Table 1-2. Fine mass and percent contribution for 20 percent worst days ..................... 1-7 

Table 1-3. Fine mass and percent contribution for 20 percent best days........................ 1-7 

Table 1-4. Particle extinction and percent contribution for 20 percent worst days ........ 1-8 

Table 1-5. Particle extinction and percent contribution for 20 percent best days........... 1-8 

Table 1-6. Natural background and baseline calculations for select Class I areas ......... 1-8 

Table 2-1. Upwind states that make a significant contribution to PM2.5 in each downwind 

nonattainment county (2001 modeling). ............................................................. 2-11

Table 2-2. Maximum downwind PM2.5 contribution (μg/m3

) for each of the 37 upwind 

states (2001 data). ............................................................................................... 2-11 

Table 3-1. Eastern U.S. RPOs and their state members................................................ 3-12 

Table 3-2. SO2 emissions in eastern RPOs (tons/yr) .................................................... 3-13 

Table 3-3. NOX emissions in eastern RPOs (tons/yr) ................................................... 3-13 

Table 3-4. VOC emissions in eastern RPOs (tons/yr) .................................................. 3-13 

Table C-1. MANE-VU urban-rural site pair information.............................................. C-3
vii 

Executive Summary 

Scientific evidence has established a solid link between cardiac and respiratory 

health risks and transient exposure to ambient fine particle pollution. The same fine 

particles that are capable of penetrating deep into the lungs are also in the size range that 

is most efficient at absorbing and scattering visible light, thus impairing visibility. The 

emission sources, atmospheric chemistry, and meteorological phenomena that influence 

ambient concentrations of fine particle pollution can act on scales that range from 

hundreds to thousands of kilometers. Fine particles are not exclusively a secondary 

pollutant; primary fine particle pollution from local sources can have a significant effect 

on ambient concentrations in some locations. Fine particles are also not exclusively a 

summertime pollutant. There are important differences between the meteorological and 

chemical dynamics that are responsible for high fine particle levels during summer and 

winter. 

In 1997, the U.S. Environmental Protection Agency (USEPA) issued a national 

ambient air quality standard (NAAQS) for fine particles with an aerodynamic diameter of 

2.5 micrometers or less. In 1999, the USEPA followed up with the Regional Haze Rule 

that enforces a national visibility goal laid out in the Clean Air Act. This will ultimately 

restore natural visibility to 156 national parks and wilderness areas across the country 

(called “Class I” areas). To address these Clean Air Act requirements, states will have to 

develop State Implementation Plans (SIPs) detailing their approaches for reducing fine 

particle pollution to meet the health-based fine particle NAAQS. They also must develop 

plans that address the degradation of visibility that exists in various parts of the Northeast 

(referred to as the Mid-Atlantic/Northeast Visibility Union (MANE-VU) region). As part 

of this process, the USEPA urges states to include in their SIPs a conceptual description 

of the pollution problem in their nonattainment and Class I areas. This document 

provides the conceptual description of the fine particulate and regional haze problems in 

the MANE-VU states consistent with the USEPA’s guidance. 

Scientific studies of the regional fine particle problem have uncovered a rich 

complexity in the interaction of meteorology and topography with fine particle formation 

and transport. Large scale high pressure systems covering hundreds of thousands of 

square miles are the source of classic severe fine particle episodes in the eastern United 

States, particularly in summer. These large, synoptic scale systems create particularly 

favorable conditions for the oxidation of sulfur dioxide (SO2) emissions to various forms 

of sulfate which, in turn, serves to form – or is incorporated into – fine particles that are 

subsequently transported over large distances. These synoptic scale systems move from 

west to east across the United States, bringing air pollution emitted by large coal-fired 

power plants and other sources located outside MANE-VU into the region. This then 

adds to the pollution burden within MANE-VU on days when MANE-VU’s own air 

pollution sources are themselves contributing to poor air quality. At times, the high 

pressure systems may stall over the East for days, creating particularly intense fine 

particle episodes. 

In the winter, temperature inversions occur that are effective at concentrating 

local primary particle emissions at the surface overnight and during early morning hours. 

This pollution can then be mixed into regionally transported particle pollution (aloft) later 
viii 

in the morning when convection is restored. Additionally, the lower temperature in the 

winter can shift the chemical equilibrium in the atmosphere slightly toward the 

production of nitrate particle pollution relative to sulfate formation. As a result, nitrate 

can become a significant fraction of measured fine particle mass in parts of the eastern 

U.S. during winter months. 

Primary and secondary emissions of carbon-containing compounds (e.g., diesel 

exhaust, biogenic organic carbon emissions, and anthropogenic volatile organic 

compound emissions) all contribute to a significant presence of carbonaceous aerosol 

across the MANE-VU region, which can vary from urban to rural locations and on a 

seasonal basis. In addition, short range pollution transport exists, with primary and 

precursor particle pollutants pushed by land, sea, mountain, and valley breezes that can 

selectively affect relatively local areas. With the knowledge of the different emission 

sources, transport scales, and seasonal meteorology in various locations adjacent to and 

within MANE-VU, a conceptual picture of fine particle pollution and its impacts 

emerges. 

The conceptual description that explains elevated regional PM2.5 peak 

concentrations in the summer differs significantly from that which explains the largely 

urban peaks observed during winter. On average, summertime concentrations of sulfate 

in the northeastern United States are more than twice that of the next most important fine 

particle constituent, organic carbon (OC), and more than four times the combined 

concentration of nitrate and black carbon (BC) constituents. Episodes of high 

summertime sulfate concentrations are consistent with stagnant meteorological flow 

conditions upwind of the MANE-VU region and the accumulation of airborne sulfate (via 

atmospheric oxidation of SO2) followed by long-range transport of sulfur emissions from 

industrialized areas within and outside the region.

National assessments have indicated that in the winter, sulfate levels in urban 

areas are higher than background sulfate levels across the eastern U.S., indicating that the 

local urban contribution to wintertime sulfate levels is significant relative to the regional 

sulfate contribution from long-range transport. A network analysis for the winter of 2002 

suggests that the local enhancement of sulfate in urban areas of the MANE-VU region 

ranges from 25 to 40% and that the long-range transport component of PM2.5 sulfate is 

still the dominant contributor in most eastern cities. 

In the winter, urban OC and sulfate each account for about a third of the overall 

PM2.5 mass concentration observed in Philadelphia and New York City. Nitrate also 

makes a significant contribution to urban PM2.5 levels observed in the northeastern 

United States during the winter months. Wintertime concentrations of OC and nitrate in 

urban areas can be twice the average regional concentrations of these pollutants, 

indicating the importance of local source contributions. This is likely because winter 

conditions are more conducive to the formation of local inversion layers which prevent 

vertical mixing. Under these conditions, emissions from tailpipe, industrial and other 

local sources become concentrated near the Earth’s surface, adding to background 

pollution levels associated with regionally transported emissions. 

From this conceptual description of fine particle pollution formation and transport 

into and within MANE-VU, air quality planners need to develop an understanding of 
ix 

what it will take to clean the air in the MANE-VU region. Every air pollution episode is 

unique in its specific details. The relative influences of the transport pathways and local 

emissions vary by hour, day, and season. The smaller scale weather patterns that affect 

pollution accumulation and its transport underscore the importance of local (in-state) 

controls for SO2, nitrogen oxides (NOX) and volatile organic compound (VOC) 

emissions. Larger synoptic scale weather patterns, and pollution patterns associated with 

them, support the need for SO2 and NOX controls across the broader eastern United 

States. Studies and characterizations of nocturnal low level jets also support the need for 

local and regional controls on SO2 and NOX sources as locally generated and transported 

pollution can both be entrained in low level jets formed during nighttime hours. The 

presence of land, sea, mountain, and valley breezes indicate that there are unique aspects 

of pollution accumulation and transport that are area-specific and will warrant policy 

responses at the local and regional levels beyond a one-size-fits-all approach. 

The mix of emission controls is also important. Regional fine particle formation 

is primarily due to SO2, but NOX is also important because of its influence on the 

chemical equilibrium between sulfate and nitrate pollution during winter. While the 

effect of reductions in anthropogenic VOCs is less well characterized at this time, 

secondary organic aerosol (SOA) is a major component of fine particles in the region and 

reductions in anthropogenic sources of OC may have a significant effect on fine particle 

levels in urban nonattainment areas. Therefore, a combination of localized NOX and 

VOC reductions in urban centers with additional SO2 and NOX reductions from across a 

larger region will help to reduce fine particles and precursor pollutants in nonattainment 

areas as well improve visibility across the entire MANE-VU region. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-1

1. INTRODUCTION 

1.1. Background 

Fine particle pollution is a persistent public health problem in the MidAtlantic/Northeast Visibility Union (MANE-VU) region. Because of its physical 

structure, fine particulate matter (PM2.5) can bypass conductive airways and deliver 

exogenous materials, such as reactive organic chemicals that adsorb onto the particle 

core, into the deep lung.1

 Studies of particulate matter (PM) in urban areas have found 

associations of short- (daily) and long-term (annual and multiyear) exposure to airborne 

PM as well as PM2.5 with cardiopulmonary health outcomes. These effects include 

increased symptoms, hospital admissions and emergency room visits, and premature 

death (Pope et al. 2004). 

In addition to health implications, visibility impairment in the eastern United 

States is largely due to the presence of light-absorbing and light-scattering fine particles 

in the atmosphere. The United States Environmental Protection Agency (USEPA) has 

identified visibility impairment as the best understood of all environmental effects of air 

pollution (Watson, 2002). A long-established physical and chemical theory relates the 

interaction of particles and gases in the atmosphere with the transmission of visual 

information along a sight path from object to observer. 

The Clean Air Act requires states that have areas designated “nonattainment” of 

the fine particle national ambient air quality standard (NAAQS) to submit State 

Implementation Plans (SIPs) demonstrating how they plan to attain the fine particle 

NAAQS. 2 The Clean Air Act also contains provisions for the restoration and 

maintenance of visibility in 156 federal Class I areas.3 SIPs for dealing with visibility 

impairment (or regional haze) must include a long-term emissions management strategy 

aimed at reducing fine particle pollution in these rural areas. 

As part of the SIP process for both of these air quality issues, the USEPA urges 

states to include a conceptual description of the pollution problem. The USEPA has 

provided guidance on developing a conceptual description, which is contained in 

Chapter 11 of the document “Guidance on the Use of Models and Other Analyses for 

 

1

 PM2.5 or “fine particles” refer to those particles with a diameter ≤ 2.5 micrometers (μm). 

2

 The 1997 PM2.5 NAAQS includes a requirement that the three-year average of yearly annual average 

PM2.5 design values must be below 15 μg/m3

 and a requirement that the three-year average of the 98th

percentile 24-hour average concentration must be below 65 μg/m

3

. In October 2006, the USEPA acted to 

change the daily standard (98th percentile value based on valid 24-hour average concentrations measured at 

a site) from 65 to 35 μg/m3

. 

3

 The Class I designation applies to national parks exceeding 6,000 acres, wilderness areas and national 

memorial parks exceeding 5,000 acres, and all international parks that were in existence prior to 1977. In 

the MANE-VU area, this includes: Acadia National Park, Maine; Brigantine Wilderness (within the Edwin 

B. Forsythe National Wildlife Refuge), New Jersey; Great Gulf Wilderness, New Hampshire; Lye Brook 

Wilderness, Vermont; Moosehorn Wilderness (within the Moosehorn National Wildlife Refuge), Maine; 

Presidential Range – Dry River Wilderness, New Hampshire; and Roosevelt Campobello International 

Park, New Brunswick. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-2

Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze” 

(EPA-Draft 3.2, September 2006) (Appendix A of this report reproduces Chapter 11 of 

the USEPA guidance document). This report provides the MANE-VU states with the 

basis for their conceptual descriptions, consistent with the USEPA’s guidance. In the 

guidance, the USEPA recommends addressing 13 questions related to PM2.5 and eight 

questions related to visibility to help define the problem in a nonattainment or Class I 

area. This report addresses these questions, as well as provides some in-depth data and 

analyses that can assist states in developing conceptual descriptions tailored to their 

specific areas. 

1.2. PM Formation 

Fine particles directly emitted into the atmosphere are called “primary” fine 

particles, and they come from both natural and human sources. These fine particles 

commonly include unburned carbon particles directly emitted from high-energy 

processes such as combustion, and particles emitted as combustion-related vapors that 

condense within seconds of being exhausted to ambient air. Combustion sources include 

motor vehicles, power generation facilities, industrial facilities, residential wood burning, 

agricultural burning, and forest fires. 

Fine particles are also comprised of “secondary” fine particles, which are formed 

from precursor gases reacting in the atmosphere or through the addition of PM to preexisting particles. Although direct nucleation from the gas phase is a contributing factor, 

most secondary material accumulates on pre-existing particles in the 0.1 to 

1.0 micrometer (μm) range and typically account for a significant fraction of the fine PM 

mass. Examples of secondary particle formation include the conversion of sulfur dioxide 

(SO2) to sulfuric acid (H2SO4) droplets that further react with ammonia (NH3) to form 

various sulfate particles (e.g., ammonium sulfate (NH4)2SO4, ammonium bisulfate 

(NH4HSO4), and letovicite ((NH4)3H(SO4)2). The dominant source of SO2 emissions in 

the eastern U.S. is fossil fuel combustion, primarily at coal-fired power plants and 

industrial boilers. Similarly, secondary PM2.5 is created by the conversion of nitrogen 

dioxide (NO2) to nitric acid (HNO3) which reacts further with ammonia to form 

ammonium nitrate (NH4NO3) particles. Nitrate particles are formed from the NOX

emitted by power plants, automobiles, industrial boilers, and other combustion sources. 

Nitrate production in the northeastern U.S. is ammonia-limited and controlled by the 

availability of sulfate and temperature, especially along the East Coast.4

 While human 

sources account for most nitrate precursors in the atmosphere, there are some natural 

sources, including lightning, biological and abiological processes in soils, and 

stratospheric intrusion. Large sources of ammonia arise from major livestock production 

and fertilizer application throughout the Midwest, Gulf Coast, mid-Atlantic, and 

southeastern United States, in addition to the sources of ammonia associated with human 

activities. 

The carbon fraction of fine PM may refer to black carbon (BC) and primary 

organic and/or secondary organic carbon (OC). Most black carbon is primary, which is 

 

4

 Ammonia reacts preferentially with sulfuric acid, and if sufficient excess ammonia is available, it can then 

combine with nitric acid to form particulate nitrate. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-3

also sometimes referred to as elemental carbon (EC) or soot. Black carbon is the lightabsorbing carbonaceous material in atmospheric particles caused by the combustion of 

diesel, wood, and other fuels. Organic carbon includes both primary emissions and 

secondary organic PM in the atmosphere. Secondary organic particles are formed by 

reactions involving volatile organic compounds (VOCs), which yield compounds with 

low saturation vapor pressures that nucleate or condense on existing particles at ambient 

temperature. Organic carbon in both the gas and solid phase is emitted by automobiles, 

trucks, and industrial processes, as well as by many types of vegetation. The relative 

amounts of organic carbon from different sources remain highly uncertain, and data are 

needed to be able to assess the relative contribution of primary versus secondary and 

anthropogenic versus biogenic production. 

1.3. PM Impacts on Visibility 

Under natural atmospheric conditions, the view in the eastern United States would 

extend about 60 to 80 miles (100 to 130 kilometers) (Malm, 2000). Unfortunately, views 

of such clarity have become a rare occurrence in the East. As a result of man-made 

pollution, the average visual range in the eastern half of the country has diminished to 

about 15-30 miles, approximately one-third the visual range that would be observed 

under unpolluted natural conditions. 

In general, the ability to see distant features in a scenic vista is determined less by 

the amount of light reaching the observer than by the contrast between those features and 

their surroundings. For example, the illumination of a light bulb in a greenhouse is 

barely discernible on a sunny day but would be highly visible at night. Similarly, a 

mountain peak is easily seen if it appears relatively dark against the sunlit sky. If, on the 

other hand, a milky haze “fills” the space between the observer and the mountain peak, 

the contrast between the mountain and its background is diminished as both take on a 

similar hue (Figure 1-1). 

Figure 1-1. View of a good visibility day (left) and a poor visibility day (right) at 

Acadia National Park, Maine in June 2003. 

Source: CAMNET, http://www.hazecam.net

In simple terms, this hazy effect occurs when small particles and certain gaseous 

molecules in the atmosphere absorb or scatter visible light, thereby reducing the amount 

of visual “information” that reaches the observer. This occurs to some extent even under 

natural conditions, primarily as a result of the light scattering effect of individual air 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-4

molecules (known as Rayleigh scattering5) and of naturally occurring aerosols.6 The 

substantial visibility impairment caused by manmade pollution, however, is almost 

entirely attributable to the increased presence of fine particles in the atmosphere.7

 

Figure 1-2 presents a simplified schematic of the way such small particles interact 

with packets of light or “photons” as they travel from a distant object to an observer. 

Along the way, particles suspended in the air can deflect or scatter some of the photons 

out of the sight path. Intervening particles can also absorb photons, similarly removing 

them from the total amount of light reaching the observer. 

 

5

 Because air molecules more effectively scatter light of short wavelengths (i.e., blue light), Rayleigh 

scattering explains the blue color of the sky. 

6

 Atmospheric aerosol is a more general term for fine particles suspended in the atmosphere and refers to 

any particle (solid or liquid) that is suspended in the atmosphere. 

7

The only light-absorbing gaseous pollutant present in the atmosphere at significant concentrations is 

nitrogen dioxide (NO2). However, the contribution of NO2 to overall visibility impacts in the Northeast is 

negligible and hence its effects are not generally included in this discussion or in standard calculations of 

visibility impairment. 

Figure 1-2. Schematic of visibility impairment due to light scattering 

and absorption (adapted from Malm, 2000). 

Light from clouds

scattered into

sight path

Sunlight

scattered

Light reflected

from ground

scattered into

sight path

Light absorbed

Image-forming

light scattered

out of sight path
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-5

At the same time, particles in the air can scatter light into the sight path, further 

diminishing the quality of the view. The extraneous light can include direct sunlight and 

light reflected off the ground or from clouds. Because it is not coming directly from the 

scenic element, this light contains no visual information about that element. When the 

combination of light absorption and light scattering (both into and out of the sight path) 

occurs in many directions due to the ubiquitous presence of small particles in the 

atmosphere, the result is commonly described as “haze.” 

1.4. PM2.5 Design Values in the MANE-VU Region 

SIP developers use monitoring data in several important ways to support SIP 

activities. This section as well as Section 1.5 present measurements from the FRM and 

IMPROVE network needed in establishing SIP requirements. Following USEPA 

guidance (40CFR Part 50, Appendix N; USEPA, 2003a; USEPA, 2003b), we use these 

data to preview the Design Values and Baseline Conditions that SIP developers must 

consider for each nonattainment area and Class I area. 

The current annual fine particle National Ambient Air Quality Standard was 

established in 1997 at 15 μg/m3. To meet this standard, the 3-year average of a site’s 

annual mean concentration must not be greater than this level. The current daily standard 

was set at 65 μg/m3 at the 98th percentile level. To meet this standard, the 98th percentile 

value (of valid measurements recorded at a site) must not be greater than this level. No 

counties in MANE-VU have been designated nonattainment for the daily standard, 

however, the USEPA has revised the NAAQS with respect to the 24-hr average 

concentrations and states will have to comply with the new standard (35 μg/m3 at the 98th

percentile level) within five years of designations (expected in 2010). Fine particle data 

from the USEPA’s Air Quality System (AQS) database for years 2002 through 2004 

were used to determine the attainment status of monitoring sites in MANE-VU. 

Table 1-1 shows a summary of areas found to exceed the annual standard (no 

areas exceed the daily standard). As tabulated, 12 areas fail to achieve the annual 

standard, with design values ranging from 15.1 to 20.4 μg/m3. The nonattainment areas 

are concentrated in Pennsylvania and the coastal urban corridor. Sulfates and organic 

carbon represent the largest contributors to these high fine particle levels. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-6

Table 1-1. 2004 PM2.5 Design Value for Nonattainment Areas in MANE-VU 

State(s) Nonattainment Area 

2004 Annual 

Design Value 

2004 24-hr 

Design Value 

MD Baltimore 16.3 41 

PA Harrisburg-Lebanon-Carlisle 15.4 41 

PA Johnstown 15.3 40 

PA Lancaster 16.8 42 

PA Liberty-Clairton 20.4 65 

MD Martinsburg, WV-Hagerstown 16.1 39 

NY-NJ-CT New York-N. New Jersey-Long Island 16.8 50

PA-NJ-DE Philadelphia-Wilmington 15.4 39 

PA Pittsburgh-Beaver Valley 16.5 45 

PA Reading 16.1 42 

DC-MD-VA Washington, DC 15.1 42 

PA York 16.9 43 

1.5. Regional haze baseline conditions 

The Regional Haze Rule requires states and tribes to submit plans that include 

calculations of current and estimated baseline and natural visibility conditions. They will 

use monitoring data from the IMPROVE program as the basis for these calculations. 

Table 1-2 and Table 1-3 present the five-year average8 of the 20 percent worst day mass 

concentrations and 20 percent best day mass concentrations respectively in six Class I 

areas. Five of these areas are in MANE-VU and one (Shenandoah) is nearby but located 

in a neighboring regional planning organization (RPO) region.9 Table 1-4 and Table 1-5 

give the corresponding worst day and best day contributions to particle extinction for the 

six Class I areas. Each of these tables show the relative percent contribution for all six 

Class I sites. Sulfate and organic carbon dominate the fine mass, with sulfate even more 

important to particle extinction. 

To guide the states in calculating baseline values of reconstructed extinction and 

for estimating natural visibility conditions, the USEPA released two documents in the fall 

of 2003 outlining recommended procedures (USEPA 2003a; USEPA 2003b). Recently, 

the IMPROVE Steering Committee endorsed an alternative method for the calculation of 

these values. The IMPROVE alternative methods were used, to create Table 1-6, which 

provides detail on the uniform visibility goals for the 20 percent worst conditions at the 

six Class 1 areas. 

 

8

 Great Gulf calculations are based on four years of data (2001-2004). 

9

 Note that values presented for Shenandoah, a Class I area in the Visibility Improvement State and Tribal 

Association of the Southeast (VISTAS) region, are for comparative purposes only. VISTAS will determine 

uniform rates of progress for areas within its region. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-7

The first column of data in Table 1-6 gives the alternative proposed natural 

background levels for the worst visibility days at these six sites. MANE-VU has decided 

to use this approach, at least initially, for 2008 SIP planning purposes (NESCAUM, 

2006). The second column shows the baseline visibility conditions on the 20 percent 

worst visibility days. These values are based on IMPROVE data from the official fiveyear baseline period (2000-2004) and again were calculated using the IMPROVE 

alternative approach. Using these baseline and natural background estimates, we derive 

the uniform rate of progress shown in the third column.10 The final column displays the 

interim 2018 progress goal based on 14 years of improvement at the uniform rate. 

Table 1-2. Fine mass and percent contribution for 20 percent worst days 

20% Worst-day Fine Mass (μg/m3

)/% contribution to fine mass 

Site SO4 NO3 OC EC Soil 

Acadia 6.3/ 56% 0.8/ 7% 3.2/ 28% 0.4/ 4% 0.5/ 5%

Brigantine 11.6/ 56% 1.7/ 8% 5.8/ 28% 0.7/ 3% 1/ 5%

Great Gulf 7.3/ 59% 0.4/ 3% 3.8/ 31% 0.4/ 3% 0.6/ 5%

Lye Brook 8.5/ 58% 1.1/ 7% 3.9/ 27% 0.5/ 3% 0.6/ 4%

Moosehorn 5.7/ 54% 0.7/ 7% 3.4/ 32% 0.4/ 4% 0.4/ 4%

Shenandoah 13.2/ 68% 0.7/ 3% 4.2/ 22% 0.6/ 3% 0.7/ 4%

Table 1-3. Fine mass and percent contribution for 20 percent best days 

20% Best-day Fine Mass (μg/m3)/% contribution to fine mass 

Site SO4 NO3 OC EC Soil 

Acadia 0.8/ 42% 0.1/ 6% 0.8/ 41% 0.1/ 5% 0.1/ 6%

Brigantine 1.8/ 43% 0.5/ 11% 1.5/ 35% 0.2/ 6% 0.2/ 5%

Great Gulf 0.7/ 43% 0.1/ 7% 0.7/ 40% 0.1/ 5% 0.1/ 6%

Lye Brook 0.6/ 44% 0.1/ 11% 0.4/ 33% 0.1/ 5% 0.1/ 7%

Moosehorn 0.8/ 37% 0.1/ 6% 1/ 47% 0.1/ 5% 0.1/ 5%

Shenandoah 1.4/ 45% 0.5/ 16% 1/ 29% 0.2/ 5% 0.2/ 5%

 

10 We calculate the rate of progress as (baseline – natural background)/60 to yield the annual deciview (dv) 

improvement needed to reach natural background conditions in 2064, starting from the 2004 baseline. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-8

Table 1-4. Particle extinction and percent contribution for 20 percent worst days 

20% Worst-day particle extinction (Mm-1) /% Contribution to particle extinction 

Site SO4 NO3 OC EC Soil CM 

Acadia 69.2/ 64% 8/ 7% 11.2/ 10% 4.3/ 4% 0.5/ 0% 1.9/ 2%

Brigantine 127.1/ 66% 15.7/ 8% 24.2/ 13% 7/ 4% 1/ 1% 5.4/ 3%

Great Gulf 76.6/ 68% 3/ 3% 14.4/ 13% 3.9/ 3% 0.6/ 1% 3/ 3%

Lye Brook 87.3/ 67% 9.1/ 7% 15.3/ 12% 4.8/ 4% 0.6/ 0% 1.8/ 2%

Moosehorn 58.5/ 60% 6.4/ 7% 11.9/ 12% 4.4/ 5% 0.4/ 0% 2.1/ 3%

Shenandoah 155.5/ 79% 5.8/ 3% 16.1/ 8% 5.7/ 3% 0.7/ 0% 2.5/ 1%

Table 1-5. Particle extinction and percent contribution for 20 percent best days 

20% Best-day particle extinction (Mm-1) /% Contribution to particle extinction 

Site SO4 NO3 OC EC Soil CM 

Acadia 6.8/ 28% 1.1/ 4% 2.2/ 9% 0.9/ 4% 0.1/ 0% 0.7/ 6%

Brigantine 14.8/ 35% 3.9/ 9% 4.5/ 11% 2.4/ 6% 0.2/ 1% 3.2/ 11%

Great Gulf 5.8/ 27% 1/ 4% 2/ 9% 0.8/ 4% 0.1/ 0% 0.9/ 8%

Lye Brook 4.4/ 23% 1.2/ 6% 1.3/ 7% 0.6/ 3% 0.1/ 0% 0.5/ 6%

Moosehorn 6.7/ 26% 1.1/ 4% 3.1/ 12% 1/ 4% 0.1/ 0% 1.1/ 8%

Shenandoah 11.2/ 36% 4.2/ 13% 2.9/ 9% 1.6/ 5% 0.2/ 1% 1.1/ 5%

Table 1-6. Natural background and baseline calculations for select Class I areas 

Site 

20 % Worst 

Days Natural 

Background 

(dv) 

20% Worst 

Days 

Baseline 

2000-

04(dv) 

Uniform 

Rate 

(dv/yr) 

Interim 

Progress 

Goal 2018 

(dv) 

20% Best 

Days 

Baseline 

2000-04(dv)

Acadia 12.54 22.89 0.17 20.47 8.77 

Brigantine 12.34 29.01 0.28 25.12 14.33 

Great Gulf 12.12 22.82 0.18 20.32 7.66 

Lye Brook 11.85 24.44 0.21 21.50 6.37 

Moosehorn 12.10 21.72 0.16 19.48 9.15 

Dolly Sods 10.45 29.05 0.31 24.71 12.28 

James River Face 11.20 29.12 0.30 24.94 14.21 

Shenandoah 11.44 29.31 0.30 25.14 10.92 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-9

As demonstrated in Table 1-2, the inorganic constituents of fine particles, sulfates 

and nitrates are the dominant contributors to visibility impairment, accounting for about 

80 percent of total particle extinction. Within the MANE-VU sites, the relative split 

between these two components is ~8 to 1 sulfate to nitrate (at Shenandoah, the average 

20 percent worst day contribution of sulfates is even more dominant). Carbonaceous 

components account for the bulk of the remaining particle extinction, ranging from 12 to 

nearly 20 percent, mostly in the form of organic carbon. The remaining components add 

little to the extinction budget on the worst days, with a few percent attributable to coarse 

mass and around a half percent from fine soil. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 1-10

References 

NESCAUM, Baseline and Natural Background Visibility Conditions: Considerations 

and Proposed Approach to the calculation of Baseline and Natural Background Visibility 

Conditions at MANE-VU Class I areas, Northeast States for Coordinated Air Use 

Management, Boston, MA, June 2006. 

Pope C.A., R.T. Burnett, G.D. Thurston, et al. “Cardiovascular mortality and long-term 

exposure to particulate air pollution: epidemiological evidence of general 

pathophysiological pathways of disease.” Circulation 109:71-7, 2004. 

Malm, W.C., Introduction to Visibility, Cooperative Institute for Research in the 

Atmosphere (CIRA), Colorado State University, Fort Collins, CO, 80523, 2000. 

Watson, J., “Visibility: Science and Regulation”, JAWMA 52:628-713, 2002. 

USEPA, “Guidance for Tracking Progress under the Regional Haze Rule” EPA-454/B03-004 September 2003a. 

USEPA, “Guidance for Estimating Natural Visibility Conditions under the Regional 

Haze Program” EPA-454/B-03-005 September 2003b. 

USEPA. “Guidance on the Use of Models and Other Analyses for Demonstrating 

Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze.” U.S. 

Environmental Protection Agency Office of Air Quality Planning and Standards 

Emissions, Monitoring, and Analysis Division. Draft 3.2- September 2006 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-1

2. A DETAILED LOOK AT FINE PARTICLE POLLUTION 

AND REGIONAL HAZE IN THE MANE-VU REGION 

Developing a conceptual description of fine particle pollution or regional haze 

requires combining experience and atmospheric-science expertise with multiple data 

sources and analysis techniques. This includes measured data on ambient pollutant 

concentrations as well as emission inventory and meteorological data, chemical transport 

modeling, and observationally based models (NARSTO, 2003). Here, we begin with a 

conceptual description based on the existing scientific literature and regional data 

analyses concerning PM2.5 and its effect on visibility. This includes numerous review 

articles and reports on the subject. Subsequent chapters review monitoring data, 

emissions inventory information, and modeling results to support the conceptual 

understanding of regional fine particle pollution presented here. 

Most past assessments of fine particle pollution and visibility impairment have 

tended to be national in scope. For purposes of this discussion, we have selectively 

reviewed the literature in order to present a distinctly eastern U.S. focus. While we 

already know much about fine particle pollution and visibility impairment and their 

causes in the MANE-VU region (see NESCAUM, 2001, 2006; NARSTO, 2003; Watson, 

2002), significant gaps in understanding remain with respect to the nitrate and organic 

component of PM2.5. While research continues, we have assembled the relevant 

information that is available to provide an overview of our current understanding of the 

regional context for PM2.5 nonattainment and visibility impairment in the MANE-VU 

region. 

2.1. Chemical composition of particulate matter in the rural MANEVU region 

Sulfate alone accounts for anywhere from one-half to two-thirds of total fine 

particle mass on high PM2.5 days in rural areas of MANE-VU. Even on low PM2.5 days, 

sulfate generally accounts for the largest fraction (40 percent or more) of total fine 

particle mass in the region (NESCAUM, 2001, 2004b). Sulfate accounts for a major 

fraction of PM2.5, not only in the Northeast but across the eastern United States 

(NARSTO, 2003). 

After sulfate, organic carbon (OC) consistently accounts for the next largest 

fraction of total fine particle mass. Its contribution typically ranges from 20 to 30 percent 

of total fine particle mass on the days with the highest levels of PM2.5. The fact that the 

contribution from organic carbon can be as high as 40 percent at the more rural sites on 

low PM2.5 days is likely indicative of the role played by organic emissions from 

vegetation (so-called “biogenic hydrocarbons”). 

Relative contributions to overall fine particle mass from nitrate (NO3), elemental 

carbon, and fine soil are all smaller (typically under 10 percent), but the relative ordering 

among the three species varies with location and season. Figure 2-1 below, reflects the 

difference between nitrate and organic contributions to rural fine particle concentrations 

during different seasons (monitoring data for additional sites in the MANE-VU region are 

in Appendix B). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-2

Figure 2-1. Comparison of contributions during different seasons at Lye Brook 

Wilderness Area on 20% worst visibility (high PM2.5) days (2000-2003). 

Almost all particle sulfate originates from sulfur dioxide (SO2) oxidation and 

typically associates with ammonium (NH4) in the form of ammonium sulfate 

((NH4)2SO4). Ninety-five percent of SO2 emissions are from anthropogenic sources 

(primarily from fossil fuel combustion), while the majority of ammonium comes from 

agricultural activities and, to a lesser extent, from transportation sources in some areas 

(NARSTO, 2003). 

Two major chemical pathways produce sulfate from SO2 in the atmosphere. In 

the gas phase, production of sulfate involves the oxidation of SO2 to sulfuric acid 

(H2SO4), ammonium bisulfate (NH4HSO4), or ammonium sulfate, depending on the 

availability of ammonia (NH3). In the presence of small wet particles (typically much, 

much smaller than rain drops or even fog), a highly efficient aqueous phase process can 

oxidize SO2 to sulfate extremely quickly (~10 percent per hour). 

Not only is sulfate the dominant contributor to fine particle mass in the region, it 

accounts for anywhere from 60 percent to almost 80 percent of the difference between 

fine particle concentrations and extinction on the lowest and highest mass days at rural 

locations in the northeast and mid-Atlantic states (See Figure 2-2). Notably, at urban 

locations such as Washington DC, sulfate accounts for only about 40 percent of the 

difference in average fine particle concentrations for the 20 percent most versus least 

visibility impaired days (NESCAUM, 2001). 

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 12 days

Summer - 37 days

Spring - 17 days

Fall - 23 days
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-3

Figure 2-2. Comparison of species contributions on best and worst days 

at Lye Brook Wilderness Area. 

2.2. Rural versus urban chemistry 

Contributions to fine particle mass concentrations at rural locations include longrange pollutant transport as well as non-anthropogenic background contributions. Urban 

areas generally show mean PM2.5 levels exceeding those at nearby rural sites. In the 

Northeast, this difference implies that local urban contributions are roughly 25 percent of 

the annual mean urban concentrations, with regional aerosol contributing the remaining, 

and larger, portion (NARSTO, 2003). 

This rural versus urban difference in typical concentrations also emerges in a 

source apportionment analysis of fine particle pollution in Philadelphia (see Chapter 10 

of NARSTO, 2003) using two different mathematical models, UNMIX and Positive 

Matrix Factorization (PMF). This analysis provides additional insight concerning 

sources of fine particle pollution in urban areas of the densely populated coastal corridor 

between Washington DC and New England. Specifically, this analysis found the 

following apportionment of PM2.5 mass in the study area: 

• Local SO2 and sulfate: ~ 10 percent 

• Regional sulfate: ~ 50 percent 

• Residual oil: 4-8 percent 

• Soil: 6-7 percent 

• Motor vehicles: 25-30 percent 

The analysis does not account for biogenic sources, which most likely are 

embedded in the motor vehicle fraction (NARSTO, 2003). The Philadelphia study 

suggests that both local pollution from nearby sources and transported “regional” 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-4

pollution from distant sources contribute to the high sulfate concentrations observed in 

urban locations along the East Coast on an annual average basis. Summertime sulfate 

and organic carbon are strongly regional in eastern North America. Typically 75–95 

percent of the urban sulfate concentrations and 60–75 percent of the urban OC 

concentrations arise from cumulative region-wide contributions (NARSTO, 2003). Urban 

air pollutants are essentially added on top of this regional background. Nitrate plays a 

noticeably more important role at urban sites compared to northeastern and mid-Atlantic 

rural monitoring sites, perhaps reflecting a greater contribution from vehicles and other 

urban pollution sources (NESCAUM, 2001). 

It is difficult to discern any significant meaning about the cause of “excess” mass 

from a single pair of sites. There are many factors that influence the concentrations at a 

particular site and it is likely that for every pair of sites that shows an urban excess, one 

could find some pair of locations that might show something similar to an urban 

“deficit.” While paired sites from an urban and a rural location will typically show 

greater concentrations in the urban location and lower levels of pollution in rural areas, 

great care must be exercised in the interpretation of any two-site analysis such as the 

comparisons of speciated components of PM2.5 presented here. Nonetheless, such 

comparisons do provide a general feel for the typical chemical composition of PM2.5 in 

the eastern U.S. and the relative differences in chemical composition between rural and 

more urban locations. More detailed, “network”-wide analyses (e.g., see NESCAUM 

2004b; relevant sections are attached in Appendix C to this report) indicate that the 

results provided are not anomalous of typical urban environments in the MANE-VU 

region. 

Figure 2-3 and Figure 2-4 compare two urban-rural pairs of speciation monitors: 

the New York nonattainment area (Elizabeth and Chester, New Jersey) and the Boston 

metropolitan area (Boston and Quabbin Reservoir, Massachusetts). The first three sites 

are Speciation Trends locations, while the Reservoir site is part of the IMPROVE 

protocol network.11

 

11 To provide a more direct comparison of the differences between the urban and rural sites, only those days 

for which both monitors in a pair had data were used. Four seasonal averages were computed for 2002, 

with seasons defined as winter (January, February, December), spring (March, April, May), Summer (June, 

July, August) and Fall (September, October, November). July 7 was excluded from the analysis because the 

Quebec forest fires affecting the region on that day would have dominated the summertime averages. The 

major fine particle species categories considered included ammonium sulfate, ammonium nitrate, organic 

carbon, elemental carbon, and soil mass. The traditional assumptions about these constituents were made; 

all sulfate was fully neutralized and a multiplier of 1.4 was used to account for mass of organic carbon. An 

“other PM2.5 mass” category was created to delineate the difference between gravimetric mass determined 

from the Teflon filter and the reconstructed mass sum of the individual mass constituents. Where no 

“other” mass is graphed, the sum of the species either equaled or exceeded the directly measured mass. No 

adjustments were made to account for the different operational definitions of carbon between the 

IMPROVE and STN networks. Average blank corrections were applied to all samples. In the case of New 

York City, both rural and urban monitors were STN. The Boston pair reflects not only inter-site 

differences, but also differences in definition of organic and elemental carbon. However, the general 

interpretation of the data differences remains consistent. Based on current understanding, the rural 

elemental carbon would be even lower than what is shown on the graph if it were made consistent with the 

STN definition of EC. Likewise, the organic carbon value would increase slightly for the rural value, as the 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-5

 

EC would be allocated to OC. The urban OC levels are so much greater than those in the rural area that a 

slight increase in rural OC makes little difference. 

Figure 2-3. New York nonattainment area (Elizabeth, NJ) compared 

to an upwind background site (Chester, NJ) 

2002 Urban-Rural PM2.5

0

5

10

15

20

25

NJ

BG

NJ

BG

NJ

BG

NJ

BG

NJ

BG

Mass (ug/m 

3) 

Other PM2.5

Soil

EC_STN

OCM_STN

AmmNO3

AmmSO4

annual winter spring summer fall

Figure 2-4. Boston urban area (Boston, MA) compared 

to an upwind background site (Quabbin Reservoir, MA) 

2002 Urban-Rural PM2.5

0

2

4

6

8

10

12

14

16

Boston

BG

Boston

BG

Boston

BG

Boston

BG

Boston

BG

Mass (ug/m 

3) 

Other PM2.5

Soil

EC_STN

OCM_STN

AmmNO3

AmmSO4

annual winter spring summer fall
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-6

The urban-rural differences show consistency for both the New York City 

nonattainment area and Boston. On an annual scale, the sulfate levels are comparable, 

with increased mass loading at these urban sites driven primarily by differences in 

nitrates and carbon with smaller differences in “soil” levels. One interesting aspect of this 

comparison is the seasonal differences in the urban-rural sulfate split. On an annual basis, 

sulfate appears to be similar at urban and rural locations (based on these two pair of 

sites); however, during the colder months, the urban sulfate levels are elevated relative to 

the rural levels. This behavior is opposite during the summer. During the wintertime, the 

Northeast urban corridor itself is a substantial source of sulfur emissions. These local 

emissions can be trapped near the surface during the winter and have a corresponding 

higher impact on the urban area relative to the rural area. 

For both urban and rural areas, the summertime OC levels are significantly 

greater than wintertime concentrations. Although the oxidation chemistry slows in 

winter, the cooler temperatures change the phase dynamics, driving more mass into the 

condensed over the gas phase. This along with more frequent temperature inversions 

(which limit atmospheric ventilation of the urban boundary layer) can lead to the 

observed increases in the relative influence of both organic and nitrate levels during 

winter months. EC, OC, and nitrate all are observed to have higher measured levels in the 

urban area (but still lower than the comparable summer values measured at the same 

sites), driven by local sources of these constituents. 

2.3. Geographic considerations and attribution of PM2.5/haze 

contributors 

In the East, both annual average and maximum daily fine particle concentrations 

are highest near heavily industrialized areas and population centers. Not surprisingly, 

given the direct connection between fine particle pollution and haze, the same pattern 

emerges when one compares measures of light extinction on the most and least visibility 

impaired days at parks and wilderness areas subject to federal haze regulations in the 

MANE-VU region (NESCAUM, 2001). An accumulation of particle pollution often 

results in hazy conditions extending over thousands of square kilometers (km2) 

(NARSTO, 2003). Substantial visibility impairment is a frequent occurrence in even the 

most remote and pristine areas of the MANE-VU region (NESCAUM, 2001). 

 PM2.5 mass declines fairly steadily along a southwest to northeast transect of the 

MANE-VU region. This decline is consistent with the existence of large fine particle 

emissions sources (both primary and secondary) to the south and west of MANE-VU. 

This trend is driven, in large part, by the marked southwest-to-northeast gradient in 

ambient sulfate concentrations during three seasons of the year as illustrated in Figure 

2-5. Wintertime concentrations, by contrast, are far more uniform across the entire 

region. Figure 2-6 shows that on an annual basis, both total PM2.5 and sulfate mass are 

highest in the southwestern portions of the MANE-VU region (note the different scales 

for each pollutant). High concentrations of nitrate and organic particle constituents, 

which play a role in localized wintertime PM2.5 episodes, tend to be clustered along the 

northeastern urban corridor and in other large urban centers. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-7

Figure 2-5. 2002 Seasonal average SO4 based on IMPROVE and STN data 

Figure 2-6. 2002 Annual average PM2.5, sulfate, nitrate and total carbon for 

MANE-VU based on IMPROVE (I) and STN (S) data. PM2.5 mass data 

are supplemented by measurements from the FRM network (•). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-8

While these figures provide some preliminary context for identifying sources 

contributing to the region’s particulate matter and visibility problems, they say nothing 

about the relative efficiency of a state’s or region’s emissions in contributing to the 

problem. It is clear that distance from the emissions source matters. Local, nearby 

sources are exceedingly important and sources within about 200 km are much more 

efficient (on a per ton emitted basis) at producing pollution impacts at eastern Class I 

sites such as Shenandoah National Park than emissions sources farther away (USNPS, 

2003). In general, the “reach” of sulfate air pollution resulting from SO2 emissions is 

longest (650–950 km). The reach of ammonia emissions or reduced nitrogen relative to 

nutrient deposition is the shortest (around 400 km), while oxides of nitrogen and sulfur 

— in terms of their impacts with respect to acidic deposition — have a reach between 

550–650 km and 600–700 km, respectively (USNPS, 2003).

Monitoring evidence indicates that non-urban visibility impairment in eastern 

North America is predominantly due to sulfate particles, with organic particles generally 

second in importance (NARSTO, 2003). This makes sense, given the “long reach” of 

SO2 emissions once they are chemically transformed into sulfate and given the ubiquitous 

nature of OC sources in the East. The poorest visibility conditions occur in highly 

industrialized areas encompassing and adjacent to the Ohio River and Tennessee Valleys. 

These areas feature large coal-burning power stations, steel mills, and other large 

emissions sources. Average fine particle concentrations and visibility conditions are also 

poor in the highly populated and industrialized mid-Atlantic seaboard but improve 

gradually northeast of New York City (Watson, 2002). 

A review of source apportionment and ensemble trajectory analyses conducted by 

USEPA (2003) found that all back trajectory analyses for eastern sites associated sulfate 

with the Ohio River Valley area. These studies also are frequently able to associate other 

types of industrial pollutants (e.g., copper or zinc smelting, steel production, etc.) with 

known source areas, lending credibility to their performance. Several studies in the 

USEPA review noted transport across the Canadian border, specifically sulfates from the 

midwestern United States into Canada, and smelter emissions from Canada into the 

northeastern United States. 

A recent, comprehensive analysis of air quality problems at Shenandoah National 

Park conducted by the U.S. National Park Service (USNPS, 2003) focused on 

contributions to particulate pollution and visibility impairment south of the MANE-VU 

region. In descending order of importance, the Park Service analysis determined that 

Ohio, Virginia, West Virginia, Pennsylvania, and Kentucky comprise the top five of 13 

key states contributing to ambient sulfate concentrations and haze impacts at the park. 

West Virginia, Ohio, Virginia, Pennsylvania, and Kentucky comprise the top five 

contributing states with respect to sulfur deposition impacts at the park. Finally, Virginia, 

West Virginia, Ohio, Pennsylvania, and North Carolina were found to be the top five 

states contributing to deposition impacts from oxidized nitrogen at the park (USNPS, 

2003). 

In sum, the Park Service found that emission sources located within a 200 km 

(125 mile) radius of Shenandoah cause greater visibility and acidic deposition impacts at 

the park, on a per ton basis, than do more distant emissions sources (USNPS, 2003). 

When mapping deposition and concentration patterns for all three pollutants using 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-9

contour lines, the resulting geographic pattern shows a definite eastward tilt in the area of 

highest impact. This is the result of prevailing wind patterns, which tend to transport 

most airborne pollutants in an arc12 from the north-northeast to the east. The Park Service 

found, for example, that emissions originating in the Ohio River Valley end up three 

times farther to the east than to the west (USNPS, 2003). 

The recent sulfate attribution work completed by MANE-VU (NESCAUM, 2006) 

finds that a variety of different states contribute to observed sulfate in rural locations 

across the MANE-VU region, but that in the southwest portions of the region, 

neighboring RPOs contribute to a more significant degree relative to rural areas in the 

Northeast. Figure 2-7 shows relative contributions of RPOs to sulfate at three MANEVU Class I areas and one VISTAS Class I area based on a variety of analysis methods. 

Figure 2-8 shows the individual state contributions to sulfate at Brigantine Wilderness 

Area on the New Jersey coast according to tagged REMSAD modeling. 

 

12 The prevailing winds are eastward to northeast. This leads to greater pollution transport to the eastnortheast relative to other directions. 

Figure 2-7. 2002 Annual average contribution to PM2.5 sulfate as determined by 

multiple analysis methods for four Class I areas spanning MANE-VU and Virginia 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-10

2.4. CAIR Modeling 

The CAIR modeling by the USEPA provides information on the upwind areas (by 

state) contributing to downwind nonattainment for PM2.5 in MANE-VU counties. Table 

2-1 presents the upwind states significantly contributing to PM2.5 nonattainment in 

counties within MANE-VU during 2001, according to significance criteria used by the 

USEPA (USEPA, 2005, from Table VII-3). The states listed in the table as significantly 

contributing to downwind nonattainment in MANE-VU counties include states outside of 

MANE-VU, indicating the broad regional scale of the PM2.5 transport problem. 

Table 2-2 provides the maximum contribution from each state to annual average 

PM2.5 nonattainment in a downwind state (not necessarily restricted to MANE-VU 

nonattainment counties) based on CAIR modeling. 

Figure 2-8. 2002 Annual average mass contribution to PM2.5 at 

Brigantine Wilderness in New Jersey (IMPROVE) and sulfate contributions as determined by 

tagged REMSAD model simulations (NESCAUM, 2006) 

0

2

4

6

8

10

12

Brigantine

Sulfate Nitrate EC OC Sea Salt Soil

2000-2004 average

IMPROVE mass

REMSAD 2002 average 

contributions to sulfate

μg/m3

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100% Outside Boundary

Canada

CENRAP

DC

MS

VT

RI

ME

CT

NH

AL

WI

TN

SC

IL

KY

GA

MI

MA

IN

DE

NJ

NC

VA

WV

MD

NY

OH

PA

0

2

4

6

8

10

12

Brigantine

Sulfate Nitrate EC OC Sea Salt Soil

2000-2004 average

IMPROVE mass

REMSAD 2002 average 

contributions to sulfate

μg/m3

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100% Outside Boundary

Canada

CENRAP

DC

MS

VT

RI

ME

CT

NH

AL

WI

TN

SC

IL

KY

GA

MI

MA

IN

DE

NJ

NC

VA

WV

MD

NY

OH

PA
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-11

Table 2-1. Upwind states that make a significant contribution to PM2.5 in each 

downwind nonattainment county (2001 modeling). 

Downwind 

State/County Upwind States 

DE New Castle MD/DC MI NY OH PA VA WV 

DC 

District of 

Columbia NC OH PA VA WV 

MD Anne Arundel NC OH PA VA WV

MD Baltimore City NC OH PA VA WV

NJ Union MD/DC MI NY OH PA WV 

NY New York MD/DC OH PA WV 

PA Allegheny IL IN KY MI OH WV 

PA Beaver IN MI OH WV 

PA Berks MD/DC MI NY OH VA WV 

PA Cambria IN MD/DC MI OH WV 

PA Dauphin MD/DC MI OH VA WV

PA Delaware MD/DC MI OH VA WV

PA Lancaster IN MD/DC MI NY OH VA WV 

PA Philadelphia MD/DC MI OH VA WV 

PA Washington IN KY MI OH WV

PA Westmoreland IN KY MD/DC MI OH WV 

PA York MD/DC MI OH VA WV 

Table 2-2. Maximum downwind PM2.5 contribution (μg/m3) 

for each of the 37 upwind states (2001 data). 

Upwind 

State 

Maximum 

Downwind 

Contribution Upwind State 

Maximum 

Downwind 

Contribution 

Alabama 0.98 Nebraska 0.07 

Arkansas 0.19 New Hampshire <0.05 

Connecticut <0.05 New Jersey 0.13 

Delaware 0.14 New York 0.34 

Florida 0.45 North Carolina 0.31 

Georgia 1.27 North Dakota 0.11 

Illinois 1.02 Ohio 1.67 

Indiana 0.91 Oklahoma 0.12 

Iowa 0.28 Pennsylvania 0.89 

Kansas 0.11 Rhode Island <0.05 

Kentucky 0.9 South Carolina 0.4 

Louisiana 0.25 South Dakota <0.05 

Maine <0.05 Tennessee 0.65 

Maryland/DC 0.69 Texas 0.29 

Massachusetts 0.07 Vermont <0.05 

Michigan 0.62 Virginia 0.44 

Minnesota 0.21 West Virginia 0.84 

Mississippi 0.23 Wisconsin 0.56 

Missouri 1.07 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-12

2.5. Seasonal differences 

Eastern and western coastal regions of the United States and Canada show marked 

seasonality in the concentration and composition of fine particle pollution, while central 

interior regions do not (NARSTO, 2003). While MANE-VU extends inland as far as the 

Pennsylvania and Ohio border, the majority of PM2.5 NAAQS nonattainment areas and 

Class I areas affected by the Regional Haze Rule cluster along the East Coast and thus 

typically show strong seasonal influences. Maximum PM2.5 concentrations typically 

occur during the summer over most of the rural Northeast, with observed summer values 

for rural areas in the region, on average, twice those of winter. In urban locations, 

summertime and wintertime PM2.5 levels are more comparable and whether one season 

dominates over the other is more of a function of inter-annual variability of meteorology 

and fire activity (i.e., summertime fire activity can push average PM2.5 values higher in 

some years). As described below, the reason for the wintertime strength of PM2.5 levels 

in urban areas is related to the greater concentration of local pollution that accumulates 

when temperature inversions are present, significantly boosting the wintertime PM2.5

levels. Winter nitrate concentrations are generally higher than those observed in summer 

and, as mentioned above, urban concentrations typically exceed rural concentrations 

year-round. In addition, local mobile source carbon grows in importance during 

wintertime. Hence, in some large urban areas such as Philadelphia and New York City, 

peak concentrations of PM2.5 can occur in winter. 

The conceptual descriptions that explain elevated regional PM2.5 peak 

concentrations in the summer differs significantly from those that explain the largely 

urban peaks observed during winter. On average, summertime concentrations of sulfate 

in the northeastern United States are more than twice that of the next most important fine 

particle constituent, OC, and more than four times the combined concentration of nitrate 

and black carbon (BC) constituents (NARSTO, 2003). Episodes of high summertime 

sulfate concentrations are consistent with stagnant meteorological flow conditions 

upwind of MANE-VU and the accumulation of airborne sulfate (via atmospheric 

oxidation of SO2) followed by long-range transport of sulfur emissions from 

industrialized areas within and outside the region.

National assessments (NARSTO, 2003) have indicated that in the winter, sulfate 

levels in urban areas are almost twice as high as background sulfate levels across the 

eastern U.S., indicating that the local urban contribution to wintertime sulfate levels is 

comparable in magnitude to the regional sulfate contribution from long-range transport. 

MANE-VU’s network analysis for the winter of 2002 suggests that the local 

enhancement of sulfate in urban areas of MANE-VU is somewhat less with ranges from 

25 to 40% and that the long-range transport component of PM2.5 sulfate is still the 

dominant contributor in most eastern cities. 

In the winter, urban OC and sulfate each account for about a third of the overall 

PM2.5 mass concentration observed in Philadelphia and New York City. Nitrate also 

makes a significant contribution to urban PM2.5 levels observed in the northeastern 

United States during the winter months. Wintertime concentrations of OC and NO3 in 

urban areas can be twice the average regional concentrations of these pollutants, 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-13

indicating the importance of local source contributions (NARSTO, 2003). This is likely 

because winter conditions are more conducive to the formation of local inversion layers 

that prevent vertical mixing. Under these conditions, emissions from tailpipe, industrial, 

and other local sources become concentrated near the Earth’s surface, adding to 

background pollution levels associated with regionally transported emissions. 

It is worth noting that while sulfate plays a significant role in episodes of elevated 

particle pollution during summer and winter months, the processes by which sulfate 

forms may vary seasonally. Nearly every source apportionment study reviewed by 

USEPA (2003) identified secondary sulfate originating from coal combustion sources as 

the largest or one of the largest contributors to overall fine particle mass in the region. It 

often accounted for more than 50 percent of PM2.5 mass at some locations during some 

seasons. In a few cases, source apportionment studies identified a known local source of 

sulfate, but most assessments (in conjunction with back trajectory analysis) have pointed 

to coal-fired power plants in the Midwest as an important source for regional sulfate. 

Studies with multiple years of data have also tended to identify a distinguishable 

chemical “signature” for winter versus summer sources of sulfate, with the summer 

version typically accounting for a greater share of overall fine particle mass. Researchers 

have speculated that the two profiles represent two extremes in the chemical 

transformation processes that occur in the atmosphere between the source regions where 

emissions are released and downwind receptor sites. We note that while coal combustion 

is often referred to as the “sulfate source” because of the dominance of its sulfate 

contribution, coal combustion is often a source of significant amounts of organic carbon 

and is usually the single largest source of selenium (Se) and other heavy metal trace 

elements (USEPA, 2003). 

Figure 2-9. Moving 60-day average of fine aerosol mass concentrations 

based on long-term data from two northeastern cities 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-14

In general, fine particle concentrations in MANE-VU are highest during the 

warmest (summer) months but also exhibit a secondary peak during the coldest (winter) 

months that can dominate during some years, particularly in urban locations. This 

bimodal seasonal distribution of peak values is readily apparent in Figure 2-9. The figure 

shows the smoothed 60-day running average of fine particle mass concentrations using 

continuous monitoring data from two northeastern cities over a period of several years. 

Figure 2-10 also demonstrates this bimodal pattern. Though slightly more 

difficult to discern in just a single year’s worth of data, a “W” pattern does emerge at 

almost all sites across the region during 2002 with the winter peak somewhat lower than 

the summer peak at most sites. Urban monitors in Wilmington, Delaware and New 

Haven, Connecticut have wintertime peak values approaching those of summer. 

In the summertime, MANE-VU sites repeatedly experience sulfate events due to 

transport from regions to the south and west. During such events, both rural and urban 

sites throughout MANE-VU record high (i.e., >15 μg/m

3

) daily average PM2.5

concentrations. Meteorological conditions during the summer frequently allow for 

summer “stagnation” events when very low wind speeds and warm temperatures (upwind 

and over MANE-VU) allow pollution levels to build in an air mass as it slowly moves 

across the continent. During these events, atmospheric ventilation is poor and local 

emission sources add to the burden of transported pollution with the result that 

concentrations throughout the region (both rural and urban) are relatively uniform. 

Generally, there are enough of these events to drive the difference between urban and 

rural sites down to less than 1 μg/m3 during the warm or hot months of the year. As a 

result, concentrations of fine particles aloft will often be higher than at ground-level 

during the summertime, especially at rural monitoring sites. Thus, when atmospheric 

“mixing” occurs during summer13 mornings (primarily 7 to 11 a.m.), fine particle 

concentrations at ground-level can actually increase (see Hartford, CT or Camden, NJ in 

Figure 2-11). 

 

13 Here we define summer as May, June, July and August. 

Figure 2-10. The 30-day average PM2.5 concentrations from 8 northeastern cities during 2002 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-15

Figure 2-11. Mean hourly fine aerosol concentrations during 2002 summer months 

Fine Aerosol Diurnal Pattern at 18 MANE-VU Sites

0

5

10

15

20

25

30

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

ug/m3

Hartford, CT New Haven, CT Waterbury, CT Wilmington, DE

Lewiston, ME Portland, ME Bangor, ME Camden, NJ

Newark, NJ Trenton, NJ Elizabeth, NJ NY City, NY

Buffalo, NY Rochester, NY Pittsburgh, PA Burlington, VT

Rutland, VT Boston, MA

Figure 2-12. Mean hourly fine aerosol concentrations during 2002 winter months 

Fine Aerosol Diurnal Pattern at 18 MANE-VU Sites

0

5

10

15

20

25

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

ug/m3

Hartford, CT New Haven, CT Waterbury, CT Wilmington, DE

Lewiston, ME Portland, ME Bangor, ME Camden, NJ

Newark, NJ Trenton, NJ Elizabeth, NJ NY City, NY

Buffalo, NY Rochester, NY Pittsburgh, PA Burlington, VT

Rutland, VT Boston, MA
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-16

During the wintertime, strong inversions frequently trap local emissions overnight 

and during the early morning, resulting in elevated urban concentrations. These 

inversions occur when the Earth’s surface loses thermal energy by radiating it into the 

atmosphere (especially on clear nights). The result is a cold, stable layer of air near the 

ground. At sunrise, local emissions (both mobile and stationary) begin increasing in 

strength and build-up in the stable ground layer (which may extend only 100 meters or 

less above the ground). Increasing solar radiation during the period between 10 a.m. and 

noon typically breaks this cycle by warming the ground layer so that it can rise and mix 

with air aloft. Because the air aloft during wintertime is typically less polluted than the 

surface layer, this mixing tends to reduce ground-level particle concentrations (see Figure 

2-12). This diurnal cycle generally drives wintertime particle concentrations, although 

the occasional persistent temperature inversion can have the effect of trapping and 

concentrating local emissions over a period of several days, thereby producing a 

significant wintertime pollution episode. 

Rural areas experience the same temperature inversions but have relatively fewer 

local emissions sources so that wintertime concentrations in rural locations tend to be 

lower than those in nearby urban areas. Medium and long-range fine particle transport 

events do occur during the winter but to a far lesser extent than in the summertime. In 

sum, it is the interplay between local and distant sources together with seasonal 

meteorological conditions that drives the observed 3–4 μg/m3

 wintertime urban-rural 

difference in PM2.5 concentrations. 

Visually hazy summer days in the Northeast can appear quite different from hazy 

winter days. The milky, uniform visibility impairment shown in Figure 2-13 is typical of 

summertime regional haze events in the Northeast. During the winter, by comparison, 

reduced convection and the frequent occurrence of shallow inversion layers often creates 

a layered haze with a brownish tinge, as shown in Figure 2-14. This visual difference 

suggests seasonal variation in the relative contribution of different gaseous and particle 

constituents during the summer versus winter months (NESCAUM, 2001). Rural and 

inland areas tend not to experience these layered haze episodes as frequently due to the 

lack of local emission sources in most rural areas (valleys with high wood smoke 

contributions are an exception). 

Overall (regional) differences in summer versus winter particle mass 

concentrations and corresponding visibility impairment (as measured by light extinction) 

are largely driven by seasonal variation in sulfate mass concentrations. This is because 

winter meteorological conditions are less conducive to the oxidation of sulfate from SO2

(as borne out by the previously cited source apportionment studies). In addition, seasonal 

differences in long-range transport patterns from upwind SO2 source regions may be a 

factor. 

The greater presence of nitrate during the cold season is a consequence of the 

chemical properties of ammonium nitrate. Ammonia bonds more weakly to nitrate than it 

does to sulfate, and ammonium nitrate tends to dissociate at higher temperatures. 

Consequently, ammonium nitrate becomes more stable at lower temperatures and hence 

contributes more to PM2.5 mass and light extinction during the winter months relative to 

the summer (NESCAUM, 2001). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-17

2.6. Summary 

The presence of fine particulate matter in ambient air significantly degrades 

public health and obscures visibility during most parts of the year at sites across the 

MANE-VU region. Particle pollution generally, and its sulfate component specifically, 

constitute the principle driver for regional visibility impacts. While the broad region 

experiences visibility impairment, it is most severe in the southern and western portions 

of MANE-VU that are closest to large power plant SO2 sources in the Ohio River and 

Tennessee Valleys. 

Summer visibility impairment is driven by the presence of regional sulfate, 

whereas winter visibility depends on a combination of regional and local influences 

coupled with local meteorological conditions (inversions) that lead to the concentrated 

build-up of pollution. 

Sulfate is the key particle constituent from the standpoint of designing control 

strategies to improve visibility conditions in the northeastern United States. Significant 

further reductions in ambient sulfate levels are achievable, though they will require more 

than proportional reductions in SO2 emissions. 

Long-range pollutant transport and local pollutant emissions are important, 

especially along the eastern seaboard, so one must also look beyond the achievement of 

further sulfate reductions. During the winter months, in particular, consideration also 

needs to be given to reducing urban sources of SO2, NOX and OC (NARSTO, 2003) .

Figure 2-13. Summertime at Mt. Washington 

 Clean Day Typical Haze Event 

 

Figure 2-14. Wintertime in Boston 

 Clean Day Typical Haze Event 

 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 2-18

References 

Husar, R.B. and W.E. Wilson, “Haze and Sulfur Emission Trends in the Eastern United 

States”, Environ. Sci. Technol. 1993, 27 (1), 12-16. 

Malm, W.C., B.A. Schichtel, R. B. Ames, and K. A. Gebhart (2002), “A 10-year spatial 

and temporal trend of sulfate across the United States,” J. Geophys. Res. 107(D22):4627, 

doi:10.1029/2002JD002107. 

NARSTO, Particulate Matter Science for Policy Makers: A NARSTO Assessment, EPRI 

1007735, February, 2003. 

NESCAUM, Regional Haze and Visibility Impairment in the Northeast and Mid-Atlantic 

United States, Northeast States for Coordinated Air Use Management, Boston, MA, 

January, 2001. 

NESCAUM, 2002: A Year in Review, Northeast States for Coordinated Air Use 

Management, Boston, MA, December, 2004b. 

NESCAUM, Contributions to Regional Haze and Visibility Impairment in the Northeast 

and Mid-Atlantic United States, Northeast States for Coordinated Air Use Management, 

Boston, MA, June, 2006. 

USEPA, COMPILATION OF EXISTING STUDIES ON SOURCE APPORTIONMENT 

FOR PM2.5, Second Draft, Emissions, Monitoring, and Analysis Division, Office of Air 

Quality Planning and Standards, Research Triangle Park, NC, August, 2003. 

USNPS, Assessment of Air Quality and Related Values in Shenandoah National Park, 

Technical Report NPS/NERCHAL/NRTR-03/090, U.S. Department of the Interior, 

National Park Service, Northeast Region, Philadelphia, Pennsylvania, May, 2003. 

Watson, J., “Visibility: Science and Regulation”, JAWMA 52:628-713, 2002. 

West, J.J., Ansari, A.S., and S. N. Pandis, “Marginal PM2.5: Nonlinear Aerosol Mass 

Response to Sulfate Reductions in the Eastern United States.” JAWMA 49:1415-1424, 1999. 

USEPA, “Technical Support Document for the Final Clean Air Interstate Rule, Air 

Quality Modeling.” U.S. Environmental Protection Agency Office of Air Quality 

Planning and Standards. March 2005 

.
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-1

3. MANE-VU EMISSION INVENTORY 

CHARACTERISTICS FOR FINE PARTICLES 

The pollutants that affect fine particle formation and visibility are sulfur oxides 

(SOX), NOX, VOCs, ammonia (NH3), and particles with an aerodynamic diameter less 

than or equal to 10 and 2.5 μm (i.e., primary PM10 and PM2.5). The emissions dataset 

illustrated in this section is the 2002 MANE-VU Version 2 regional haze emissions 

inventory. The MANE-VU regional haze emissions inventory version 3.0, released in 

April 2006, has superseded version 2 for modeling purposes. 

3.1. Emissions inventory characteristics 

3.1.1. Sulfur dioxide (SO2) 

SO2 is the primary precursor pollutant for sulfate particles. Ammonium sulfate 

particles are the largest contributor to PM2.5 mass on an annual average basis at MANEVU nonattainment sites. It also accounts for more than 50 percent of particle-related 

light extinction at northeastern Class I areas on the clearest days and for as much as or 

more than 80 percent on the haziest days. Hence, SO2 emissions are an obvious target of 

opportunity for both addressing PM2.5 nonattainment and for reducing regional haze in 

the eastern United States. Combustion of coal and, to a substantially lesser extent, of 

certain petroleum products accounts for most anthropogenic SO2 emissions. In fact, in 

1998 a single source category — coal-burning power plants — was responsible for twothirds of total SO2 emissions nationwide (NESCAUM, 2001). 

Figure 3-1 shows SO2 emissions trends in MANE-VU states14 extracted from the 

National Emissions Inventories (NEI) for the years 1996, 1999 (MARAMA, 2004), and 

the 2002 MANE-VU inventory. Most of the states (with the exception of Maryland) 

show declines in year 2002 annual SO2 emissions as compared to 1996 emissions. Some 

of the states show an increase in 1999 followed by a decline in 2002 and others show 

consistent declines throughout the entire period. The upward trend in emissions after 

1996 probably reflects electricity demand growth during the late 1990s combined with 

the availability of banked SO2 emissions allowances from initial over-compliance with 

control requirements in Phase 1 of the USEPA Acid Rain Program. This led to relatively 

low market prices for allowances later in the decade, which encouraged utilities to 

purchase allowances rather than implement new controls as electricity output expanded. 

The observed decline in the 2002 SO2 emissions inventory reflects implementation of the

second phase of the USEPA Acid Rain Program, which in 2000 further reduced 

allowable emissions and extended emissions limits to more power plants. 

Figure 3-2 shows the percent contribution from different source categories to 

overall annual 2002 SO2 emissions in MANE-VU states. The chart shows that point 

sources dominate SO2 emissions, which primarily consist of stationary combustion 

sources for generating electricity, industrial energy, and heat. Smaller stationary 

combustion sources called “area sources” (primarily commercial and residential heating) 

 

14 The description of MANE-VU state inventories discussed throughout this section does not include the 

portion of Virginia in the Washington, DC metropolitan area. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-2

are another important source category in MANE-VU states. By contrast, on-road and 

non-road mobile sources make only a relatively small contribution to overall SO2

emissions in the region (NESCAUM, 2001). 

Figure 3-1. State level sulfur dioxide emissions 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

NEI 1996

NEI 1999

MV 2002 v.2

Figure 3-2. 2002 MANE-VU state SO2 inventories 

0%

25%

50%

75%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

0.0

0.2

0.4

0.6

0.8

1.0

1.2

million t/y

AREA NONROAD ONROAD POINT Emission

Figure Key: Bars = Percentage fractions of four source categories; Circles = Annual emissions amount 

in 106 tons per year. Note that Version 2 of the MANE-VU inventory was used and the Virginia portion 

of the Washington, DC metropolitan area is not shown in the figure. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-3

3.1.2. Volatile organic compounds (VOCs) 

Existing emission inventories generally refer to VOCs based on their historical 

contribution to ozone formation. From a fine particle perspective, VOCs (also referred to 

as hydrocarbons) are of concern because they can react in the atmosphere to form 

secondary organic aerosol (SOA) as a result of condensation and oxidation processes. 

The SOA component of fine particles also obscures visibility, but this component has a 

smaller impact on visibility (on a per unit mass basis) relative to sulfate or nitrate, which 

have an affinity for water that allows them to significantly “grow” as particles under 

humid conditions. Nonetheless, organic carbon typically has the second largest visibility 

impact at most Class I sites next to sulfate, given its large mass contribution. 

As shown in Figure 3-3, the VOC inventory is dominated by mobile and area 

sources. Most VOC emissions in MANE-VU, however, come from natural sources, 

which are not shown in the figure. Among the human-caused VOC emissions, on-road 

mobile sources of VOCs include exhaust emissions from gasoline passenger vehicles and 

diesel-powered heavy-duty vehicles as well as evaporative emissions from transportation 

fuels. VOC emissions may also originate from a variety of area sources (including 

solvents, architectural coatings, and dry cleaners) as well as from some point sources 

(e.g., industrial facilities and petroleum refineries). 

Naturally occurring (biogenic) VOC emissions are caused by the release of 

natural organic compounds from plants in warm weather. Natural, or biogenic, VOCs 

contribute significantly to fine particle formation. Biogenic VOCs are not included in 

Figure 3-3, but nationally, they represent roughly two-thirds of all annual VOC emissions 

(USEPA, 2006). Biogenic emissions are extremely difficult to estimate, as it requires 

modeling the behavior of many plants as well as their responses to the environment. 

With regard to fine particle formation, understanding the transport dynamics and 

source regions for organic carbon is likely to be more complex than for sulfate. This is 

partly because of the large number and variety of VOC species, the fact that their 

transport characteristics vary widely, and the fact that a given species may undergo 

numerous complex chemical reactions in the atmosphere. Thus, the organic carbon 

contribution to fine particles in the East is likely to include manmade pollution 

transported from a distance, manmade pollution from nearby sources, and biogenic 

emissions, especially terpenes from coniferous forests. 

For fine particles derived from organic carbon, the oxidation of hydrocarbon 

molecules containing seven or more carbon atoms is generally the most significant 

pathway for their formation (Odum et al., 1997). Recent research, however, suggests that 

smaller reactive hydrocarbons like isoprene not only contribute significantly to groundlevel ozone, which may indirectly impact organic aerosol formation, but also contribute 

directly to ambient organic aerosol through heterogeneous processes (Claeys et al., 2004; 

Kroll et al., 2005). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-4

Figure 3-3. 2002 MANE-VU state VOC inventories 

0%

25%

50%

75%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

AREA NONROAD ONROAD POINT Emission

Figure key: Bars = Percentage fractions of four source categories; Circles = Annual 

emissions amount in 106

 tons per year. Note that Version 2 of the MANE-VU inventory 

was used and the Virginia portion of the Washington, DC metropolitan area is not shown 

in the figure. Biogenic VOCs are not included in this figure. 

3.1.3. Oxides of nitrogen (NOX) 

NOX emissions contribute directly to PM2.5 nonattainment and visibility 

impairment in the eastern U.S. by forming nitrate particles. Nitrate generally accounts 

for a substantially smaller fraction of fine particle mass and related light extinction than 

sulfate and organic carbon regionally in MANE-VU. Notably, nitrate may play a more 

important role at urban sites and in the wintertime. In addition, NOX may have an 

indirect effect on summertime visibility by virtue of its role in the formation of ozone, 

which in turn promotes the formation of secondary organic aerosols (NESCAUM, 2001). 

Figure 3-4 shows NOX emissions in MANE-VU at the state level. Since 1980, 

nationwide emissions of NOX from all sources have shown little change. In fact, 

emissions increased by 2 percent between 1989 and 1998 (USEPA, 2000a). This 

increase is most likely due to industrial sources and the transportation sector, as power 

plant combustion sources have implemented modest emissions reductions during the 

same time period. Most states in MANE-VU experienced declining NOX emissions from 

1996 through 2002, except Massachusetts, Maryland, New York, and Rhode Island, 

which show an increase in NOX emissions in 1999 before declining to levels below 1996 

emissions in 2002. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-5

Monitored ambient NOX trends during the summer from 1997 to 2005 corroborate 

the downward trend in NOX emissions seen in the emissions inventories for MANE-VU. 

As seen in Figure 3-5, the 24-hour (lower trend lines) and 6 a.m.-8 a.m. (upper trend 

lines) NOX concentrations indicate decreases in NOX over this time period in MANE-VU. 

The NOX reductions likely come from decreasing vehicle NOX emissions due to more 

stringent motor vehicle standards as well as NOX reductions from MANE-VU NOX

Budget Program and the NOX SIP Call (mainly power plants). 

Figure 3-4. State level nitrogen oxides emissions 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

NEI 1996

NEI 1999

MV 2002 v.2

Figure 3-5. Plot of monitored NOX trends in MANE-VU during 1997-2005 

JUNE, JULY & AUGUST 1997-2005 OTC AVERAGE NOx CONCENTRATIONS

10

15

20

25

30

35

40

45

50

199719981999200020012002200320042005199719981999200020012002200320042005199719981999200020012002200320042005

Average Concentration (ppb) .

JUN (all hrs)

JUL (all hrs)

AUG (all hrs)

JUN (06-08 EST)

JUL (06-08 EST)

AUG (06-08 EST)

Note: Upper trend lines correspond to NOX measured from 0600-0800 EST in the morning. Lower trend 

lines correspond to NOX measured over entire day (created by Tom Downs, Maine Department of 

Environmental Protection). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-6

Power plants and mobile sources generally dominate state and national NOX

emissions inventories. Nationally, power plants account for more than one-quarter of all 

NOX emissions, amounting to over six million tons. The electric sector plays an even 

larger role, however, in parts of the industrial Midwest where high NOX emissions have a 

particularly significant power plant contribution. By contrast, mobile sources dominate 

the NOX inventories for more urbanized mid-Atlantic and New England states to a far 

greater extent, as shown in Figure 3-6. In these states, on-road mobile sources — a 

category that mainly includes highway vehicles — represent the most significant NOX

source category. Emissions from non-road (i.e., off-highway) mobile sources, primarily 

diesel-fired engines, also represent a substantial fraction of the inventory. 

Figure 3-6. 2002 MANE-VU state NOX inventories 

0%

25%

50%

75%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

0.0

0.3

0.6

0.9

AREA NONROAD ONROAD POINT Emission

Figure key: Bars = Percentage fractions of four source categories; Circles = Annual 

emissions amount in 106

 tons per year. Note that Version 2 of the MANE-VU inventory 

was used and the Virginia portion of the Washington, DC metropolitan area is not shown 

in the figure. 

3.1.4. Primary particulate matter (PM10 and PM2.5) 

Directly-emitted or “primary” particles (as distinct from secondary particles that 

form in the atmosphere through chemical reactions involving precursor pollutants like 

SO2 and NOX) also contribute to fine particle levels in the atmosphere. For regulatory 

purposes, we make a distinction between particles with an aerodynamic diameter less 

than or equal to 10 micrometers and smaller particles with an aerodynamic diameter less 

than or equal to 2.5 micrometers (i.e., primary PM10 and PM2.5, respectively). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-7

Figure 3-7 and Figure 3-8 show PM10 and PM2.5 emissions for MANE-VU states 

for the years 1996, 1999, and 2002. Note that, as opposed to the other constituents of 

PM, the 2002 inventory values for PM10 are drawn from the 2002 NEI. Most states show 

a steady decline in annual PM10 emissions over this time period. By contrast, emission 

trends for primary PM2.5 are more variable. 

Crustal sources are significant contributors of primary PM emissions. This 

category includes fugitive dust emissions from construction activities, paved and unpaved 

roads, and agricultural tilling. Typically, monitors estimate PM10 emissions from these 

types of sources by measuring the horizontal flux of particulate mass at a fixed downwind 

sampling location within perhaps 10 meters of a road or field. Comparisons between 

estimated emission rates for fine particles using these types of measurement techniques 

and observed concentrations of crustal matter in the ambient air at downwind receptor 

sites suggest that physical or chemical processes remove a significant fraction of crustal 

material relatively quickly. As a result, it rarely entrains into layers of the atmosphere 

where it can transport to downwind receptor locations. Because of this discrepancy 

between estimated emissions and observed ambient concentrations, modelers typically 

reduce estimates of total PM2.5 emissions from all crustal sources by applying a factor of 

0.15 to 0.25 before including in modeling analyses.

From a regional haze perspective, crustal material generally does not play a major 

role. On the 20 percent best-visibility days during the baseline period (2000-2004), it 

accounted for 6 to 11 percent of particle-related light extinction at MANE-VU Class 1 

sites. On the 20 percent worst-visibility days, however, crustal material generally plays a 

much smaller role relative to other haze-forming pollutants, ranging from 2 to 3 percent. 

Moreover, the crustal fraction includes material of natural origin (such as soil or sea salt) 

that is not targeted under USEPA’s Regional Haze Rule. Of course, the crustal fraction 

can be influenced by certain human activities, such as construction, agricultural practices, 

and road maintenance (including wintertime salting) — thus, to the extent that these types 

of activities are found to affect visibility at northeastern Class I sites, control measures 

targeted at crustal material may prove beneficial. 

Experience from the western United States, where the crustal component has 

generally played a more significant role in driving overall particulate levels, may be 

helpful where it is relevant in the eastern context. In addition, a few areas in the 

Northeast, such as New Haven, Connecticut and Presque Isle, Maine, have some 

experience with the control of dust and road-salt as a result of regulatory obligations 

stemming from their past nonattainment status with respect to the NAAQS for PM10. 

Current emissions inventories for the entire MANE-VU area indicate residential 

wood combustion represents 25 percent of primary fine particulate emissions in the 

region. This implies that rural sources can play an important role in addition to the 

contribution from the region’s many highly populated urban areas. An important 

consideration in this regard is that residential wood combustion occurs primarily in the 

winter months, while managed or prescribed burning activities occur largely in other 

seasons. The latter category includes agricultural field-burning activities, prescribed 

burning of forested areas, and other burning activities such as construction waste burning. 

Limiting burning to times when favorable meteorological conditions can efficiently 

disperse resulting emissions can manage many of these types of sources. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-8

Figure 3-7. State level primary PM10 emissions 

0.0

0.2

0.4

0.6

0.8

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

NEI 1996

NEI 1999

NEI 2002

Figure 3-8. State level primary PM2.5 emissions 

0.0

0.1

0.2

0.3

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

NEI 1996

NEI 1999

MV 2002 v.2

Figure 3-9 and Figure 3-10 show that area and mobile sources dominate primary 

PM emissions. (The NEI inventory categorizes residential wood combustion and some 

other combustion sources as area sources.) The relative contribution of point sources is 

larger in the primary PM2.5 inventory than in the primary PM10 inventory since the crustal 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-9

component (which consists mainly of larger or “coarse-mode” particles) contributes 

mostly to overall PM10 levels. At the same time, pollution control equipment commonly 

installed at large point sources is usually more efficient at capturing coarse-mode 

particles. 

Figure 3-9. 2002 MANE-VU state primary PM10 inventories 

0%

20%

40%

60%

80%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

0.0

0.1

0.2

0.3

0.4

0.5

AREA NONROAD ONROAD POINT Emission

Figure 3-10. 2002 MANE-VU state primary PM2.5 inventories 

0%

25%

50%

75%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

0.00

0.05

0.10

0.15

0.20

AREA NONROAD ONROAD POINT Emission

Figure key: Bars = Percentage fractions of four source categories; Circles = Annual emissions amount in 106 tons 

per year. Note that Version 2 of the MANE-VU inventory was used and the Virginia portion of the Washington, 

DC metropolitan area is not shown in the figure. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-10

3.1.5. Ammonia emissions (NH3) 

Knowledge of ammonia emission sources will be necessary in developing 

effective regional haze reduction strategies because of the importance of ammonium 

sulfate and ammonium nitrate in determining overall fine particle mass and light 

scattering. According to 1998 estimates, livestock and agriculture fertilizer use 

accounted for approximately 85 percent of all ammonia emissions to the atmosphere 

(USEPA, 2000b). We need, however, better ammonia inventory data for the 

photochemical models used to simulate fine particle formation and transport in the 

eastern United States. Because the USEPA does not regulate ammonia as a criteria 

pollutant or as a criteria pollutant precursor, these data do not presently exist at the same 

level of detail or certainty as for NOX and SO2. 

Ammonium ion (formed from ammonia emissions to the atmosphere) is an 

important constituent of airborne particulate matter, typically accounting for 10–20 

percent of total fine particle mass. Reductions in ammonium ion concentrations can be 

extremely beneficial because a more-than-proportional reduction in fine particle mass can 

result. Ansari and Pandis (1998) showed that a one μg/m3

 reduction in ammonium ion 

could result in up to a four μg/m3 reduction in fine particulate matter. Decision makers, 

however, must weigh the benefits of ammonia reduction against the significant role it 

plays in neutralizing acidic aerosol. SO2 reacts in the atmosphere to form sulfuric acid 

(H2SO4). Ammonia can partially or fully neutralize this strong acid to form ammonium 

bisulfate or ammonium sulfate. If planners focus future control strategies on ammonia 

and do not achieve corresponding SO2 reductions, fine particles formed in the atmosphere 

will be substantially more acidic than those presently observed. 

To address the need for improved ammonia inventories, MARAMA, NESCAUM 

and USEPA funded researchers at Carnegie Mellon University (CMU) in Pittsburgh to 

develop a regional ammonia inventory system (Davidson et al., 1999). This study 

focused on three issues with respect to current emissions estimates: (1) a wide range of 

ammonia emission factor values, (2) inadequate temporal and spatial resolution of 

ammonia emissions estimates, and (3) a lack of standardized ammonia source categories. 

Figure 3-11 shows that estimated ammonia emissions were fairly stable in the 

1996, 1999, and 2002 NEI for MANE-VU states, with some increases observed for 

Massachusetts, New Jersey and New York. Area and on-road mobile sources dominate 

the ammonia inventory, according to Figure 3-12. Specifically, emissions from 

agricultural sources and livestock production account for the largest share of estimated 

ammonia emissions in MANE-VU, except in the District of Columbia. The two 

remaining sources with a significant emissions contribution are wastewater treatment 

systems and gasoline exhaust from highway vehicles. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-11

Figure 3-11. State level ammonia emissions 

0.000

0.025

0.050

0.075

0.100

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

NEI 1996

NEI 1999

MV 2002 v.2

Figure 3-12. 2002 MANE-VU state NH3 inventories 

0%

25%

50%

75%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

0.00

0.06

0.12

AREA NONROAD ONROAD POINT Emission

Figure key: Bars = Percentage fractions of four source categories; Circles = Annual 

emissions amount in 106 tons per year. Note that Version 2 of the MANE-VU inventory 

was used and the Virginia portion of the Washington, DC metropolitan area is not shown 

in the figure. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-12

3.2. Emissions inventory characteristics outside MANE-VU

SO2, NOX and VOC emissions from within MANE-VU are only one component 

of the emissions contributing to fine particles affecting the MANE-VU region. As 

regional modeling for the CAIR has shown, emission sources, primarily of SO2 and NOX, 

located outside MANE-VU can significantly contribute to particle sulfate and nitrate 

transported into the MANE-VU region. Here we present regional emissions information 

grouped by the three eastern RPOs – MANE-VU, VISTAS (Visibility Improvement State 

and Tribal Association of the Southeast), and the MWRPO (Midwest RPO). Table 3-1 

lists the states in each RPO. 

The inventory information is extracted from the USEPA final 2002 National 

Emissions Inventory (NEI). For consistency, the MANE-VU information here also 

comes from the 2002 NEI rather than from the MANE-VU Version 2 regional haze 

emissions inventory described in Section 3.1. The differences between the inventories 

are not great, as the NEI and the MANE-VU Version 2 inventory are both based on the 

same inventory information provided by the states. 

Table 3-1. Eastern U.S. RPOs and their state members 

RPO State 

MWRPO Illinois 

MWRPO Indiana 

MWRPO Michigan 

MWRPO Ohio 

MWRPO Wisconsin 

MANE-VU Connecticut 

MANE-VU Delaware 

MANE-VU District of Columbia 

MANE-VU Maine 

MANE-VU Maryland 

MANE-VU Massachusetts 

MANE-VU New Hampshire 

MANE-VU New Jersey 

MANE-VU New York 

MANE-VU Pennsylvania 

MANE-VU Rhode Island 

MANE-VU Vermont 

VISTAS Alabama 

VISTAS Florida 

VISTAS Georgia 

VISTAS Kentucky 

VISTAS Mississippi 

VISTAS North Carolina 

VISTAS South Carolina 

VISTAS Tennessee 

VISTAS Virginia 

VISTAS West Virginia 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-13

Table 3-2 presents SO2 emissions by source sector and RPO for the eastern 

United States. The NOX emissions by source sector and RPO are presented in Table 3-3 

and VOC emissions in Table 3-4. Regionally, SO2 emissions are more important with 

respect to regional particle formation and transport. NOX emissions play an important 

role in determining the equilibrium between ammonium sulfate and ammonium nitrate 

formation, especially during winter. VOC emissions contribute to secondary organic 

aerosol formation. 

Table 3-2. SO2 emissions in eastern RPOs (tons/yr) 

RPO Point Area On-road Non-road Total 

MWRPO 3,336,967 133,415 49,191 82,307 3,601,880

MANE-VU 1,924,573 353,176 39,368 74,566 2,391,683

VISTAS 4,349,437 448,023 83,001 91,307 4,971,769

Table 3-3. NOX emissions in eastern RPOs (tons/yr) 

RPO Point Area On-road Non-road Total 

MWRPO 1,437,284 184,790 1,290,178 723,844 3,636,096

MANE-VU 680,975 268,997 1,297,357 534,454 2,781,783

VISTAS 2,094,228 266,848 2,160,601 812,615 5,334,293

Table 3-4. VOC emissions in eastern RPOs (tons/yr)

RPO Point Area On-road Non-road Total 

MWRPO 234,938 1,182,186 660,010 492,027 2,569,160

MANE-VU 93,691 1,798,158 793,541 494,115 3,179,504

VISTAS 458,740 2,047,359 1,314,979 609,539 4,430,617
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 3-14

References 

Ansari, A.S., and S.N. Pandis. “Response of inorganic PM to precursor concentrations.” 

Environ. Sci. Technol. 32, 2706-2714, 1998. 

Claeys, M., W. Wang, A.C. Ion, I. Kourtchev, A. Gelencser, and W. Maenhaut, 

“Formation of secondary organic aerosols from isoprene and gas-phase oxidation 

products through reaction with hydrogen peroxide.” Atmos. Environ., 38, 4093-4098, 

2004. 

Davidson, C., R. Strader, S. Pandis, and A. Robinson. Preliminary Proposal to 

MARAMA and NESCAUM: Development of an Ammonia Emissions Inventory for the 

Mid-Atlantic States and New England. Carnegie Mellon University, Pittsburgh, PA, 

January 7, 1999. 

Kroll, J.H., N.L. Ng, S.M. Murphy, R.C. Flagan, and J.H. Seinfeld. “Secondary Organic 

Aerosol Formation from Isoprene Photooxidation.” Environ. Sci. Technol. 40, 1869-

1877, 2006.

MARAMA 2004, http://www.marama.org/visibility/2002%20NEI/index.html 

MARAMA. “A Guide to Mid-Atlantic Regional Air Quality,” October 2005. 

NESCAUM. Regional Haze and Visibility in the Northeast and Mid-Atlantic States.

NESCAUM, Boston, MA, January 2001. 

Odum, J.R., T.P.W. Jungkamp, R.J. Griffin, R.C. Flagan, and J.J. Seinfeld. “The 

atmospheric aerosol-forming potential of whole gasoline vapor.” Science 276, 96-99, 

1997. 

USEPA. National Air Quality and Emission Trends Report, 1998, EPA 454/R-00-003, 

available online: http://www.epa.gov/oar/aqtrnd98/, 2000a. 

USEPA. National Air Pollutant Trends, 1900 – 1998, EPA 454/R-00-002, available 

online: http://www.epa.gov/ttn/chief/trends/trends98/trends98.pdf, 2000b. 

USEPA. 2002 Final National Emissions Inventory (NEI), available online: 

ftp://ftp.epa.gov/EmisInventory/2002finalnei/, 2006 (accessed October 10, 2006) [The 

2002 NEI reports national annual emissions for total anthropogenic VOC emissions as 

16.8 million tons, and total biogenic VOC emissions as 41.8 million tons]. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-2

4. WHAT WILL IT TAKE TO CLEAN THE AIR? 

In this chapter we build on the conceptual description of fine particle formation 

and impacts in the MANE-VU region by looking at a typical fine particle pollution event 

and the meteorological and chemical conditions which contributed to its formation. As 

an illustration of how the conceptual elements laid out in Chapter 2 and 3 contribute to a 

pollution event under real-world circumstances, we examine a pollution event from 2002. 

We examine this event from two perspectives: (1) the broad spatial patterns of the 

formation and transport of particle air pollution and (2) the chronological sequence of 

events at a few discrete points where high temporal resolution monitoring was in place. 

We then proceed to examine likely emission reduction strategies that should be 

considered in light of the conceptual understanding of fine particle formation and 

transport developed in this report. 

4.1. Meteorological and Pollution Overview of August 8-16, 2002 

Annual and seasonal statistics are useful for understanding the general patterns of 

air pollution in our region, but it is also instructive to review specific high PM2.5 episodes 

in order to shed more light on the meteorological circumstances under which high 

ambient concentrations of PM2.5 are able to form from emitted precursor pollutants. Here 

we present an analysis of the high PM2.5 and regional haze episode of August 2002 by 

reviewing surface maps from the period to provide a synoptic overview of major weather 

systems that were influencing air quality across the Northeast U.S. during that time. 

Figure 4-1 through Figure 4-3, respectively, show eight-panel displays of 

afternoon fine particle concentrations as well as surface weather maps and back 

trajectories from 12Z (8 a.m. EDT) each day. The following chronology of events 

combines the meteorological insights with PM2.5 concentration information to provide a 

basic storyline for analysis. 

A slow-moving high pressure system centered over the Great Lakes set up 

northerly flow over MANE-VU on August 8. The high drifted southeast-ward and 

became extended over several days bringing high temperatures to the region. Calm 

conditions west of MANE-VU on August 10 were pivotal in the formation of fine aerosol 

concentrations, which began building in the Ohio River Valley. Over the next four days, 

concentrations in MANE-VU climbed into the 60-90 μg/m3 range over a wide area before 

being swept out to sea by a series of frontal passages beginning on August 15. 

8/8 – A high pressure system over the Great Lakes produces NW-N prevailing 

surface winds (~4-8 mph) throughout the region. Maximum daily temperatures approach 

or exceed 80o F. 

8/9 – Wind speeds fall off but direction remains NW-N as the high moves into the 

central portion of MANE-VU. Temperatures rise as cloud cover declines. 

8/10 – The high reaches the East Coast and stalls. Temperatures (except in 

northern-most areas) reach 90o F while surface-level winds turn to more southerly 

directions. Calm conditions through the morning hours in the lower Ohio River Valley 

promote creation of haze noted in surface observations. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-3

8/11 – Circulation around the high (now near Cape Hatteras) becomes well 

established. Peak temperatures are in the low to mid-90’s. Morning winds are light-tocalm in the area east of the Mississippi – the area of haze now reaches from Michigan to 

northern Texas and eastward to West Virginia and eastern Tennessee. A surface-level 

trough descends from north of the Great Lakes during the day, passes eastward through 

the Ohio River Valley and stalls over the Allegheny Mountains and southward. 

8/12 – Temperatures exceed 90o F throughout MANE-VU except in coastal ME. 

The area of concentrated haze has pushed eastward and now extends from central ME to 

central PA. Haze builds throughout the day as circulation forces it to channel NE 

between the stalled trough and a cold front approaching from the Midwest. 

8/13 – Calm conditions prevail as the trough reaches coastal NJ by 8 a.m. 

Generally clear skies allow temperatures to reach the mid-90’s everywhere except in 

coastal ME. Dew points, which had been rising since 8/8, reach the upper 60’s. Peak 

hourly fine aerosol concentrations are greater than 40 μg/m3 everywhere in MANE-VU 

and exceed 90 μg/m3 in some locations. By 8 p.m., showers associated with the 

approaching cold front have reached into Ohio. 

8/14 – By 8 a.m. the trough has dissipated and the high is moving offshore. Dew 

points remain in the upper 60’s and peak temperatures reach into the 90’s everywhere and 

top 100 in several locations. Increased ventilation causes aerosol concentrations to drop 

throughout the day everywhere except ME where some locations peak above 60 μg/m3

after midnight. 

8/15 – The approaching cold front and associated showers fall apart during the 

morning hours. By 8 p.m., a new batch of moderate rain has intruded deeply into the 

region from the SW and has virtually pushed the haze out of the MANE-VU region. 

8/16 – A new high building in over the upper Midwest pushes the remains of the 

showers out of the Northeast. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-4

Figure 4-1. Spatially interpolated maps of fine particle concentrations 

August 9 – 16, 2002 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-5

Figure 4-2. Surface weather maps for August 9-16, 2002 

August 9, 8:00AM EDT August 10, 8:00 AM EDT 

August 11, 8:00 AM EDT August 12, 8:00 AM EDT 

August 13, 8:00 AM EDT August 14, 8:00 AM EDT 

August 15, 8:00 AM EDT August 16, 8:00 AM EDT 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-6

Figure 4-3. HYSPLIT 72-hour back trajectories for August 9-16, 2002 

Aug 9, 2002 8 am EDT Aug 10, 2002 8 am EDT

Aug 11, 2002 8 am EDT Aug 12, 2002 8 am EDT

Aug 13, 2002 8 am EDT Aug 14, 2002 8 am EDT

Aug 15, 2002 8 am EDT Aug 16, 2002 8 am EDT
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-7

4.2. Temporally and spatially resolved PM2.5 measurements 

Higher temporal resolution data provide insight into how the events played out in 

much more detail than can be captured by eight frames on a page; however the most 

complete picture is obtained when these high temporal resolution data can be presented 

in the context of the relatively greater spatial detail provided by maps such as we have 

seen in Figure 4-1 through Figure 4-3. In Figure 4-4 and Figure 4-5, we present 

continuous PM2.5 data (hourly average and 24-hour rolling average filtered, respectively) 

for the August 8-16, 2002 time period. 

Looking at Figure 4-4 in the context of the maps presented in the earlier figures, it 

is interesting to note the rapid increase, first, in Arendtsville, PA at noon on the 11th, 

followed by a rise in concentrations along the East Coast around noon on the 12th. This 

is consistent with Figure 4-1, which shows high PM2.5 levels covering western 

Pennsylvania by 3 p.m. on the 11th and that high PM2.5 area has moved over to cover the 

East Coast by 3 p.m. the next day. This also makes sense with respect to Figure 4-2 and 

Figure 4-3, which show the high pressure system established on the East Coast by the 

11th with surface level back trajectories having shifted from northerly flow to slow 

southwesterly flow in the western portion of the domain by the morning of the 11th and 

the coastal sites having switched by the morning of the 12th. 

Figure 4-4. Hourly average fine aerosol at 8 sites during the August 2002 episode 

-10

0

10

20

30

40

50

60

70

80

90

100

7-Aug8-Aug9-Aug

10-Aug11-Aug12-Aug13-Aug14-Aug15-Aug

ug/m3

Arendtsville, PA

Wilmington, DE

Camden, NJ

New Brunswick, NJ

NYC (Bronx), NY

Hartford, CT

Boston, MA

Portland, ME
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-8

Also note the very high levels observed close to mid-day on the 13th at sites 

between New York City and Portland, Maine. This is consistent with the strong gradients 

shown for 3 p.m. on the 13th in Figure 4-1. These rapid increases in concentration are 

easily explained by the back trajectories of Figure 4-3 that show the advancing front (at 

this point over Lake Michigan) beginning to push, at upper levels of the atmosphere, an 

air mass from the upper Midwest due east across the northern half of MANE-VU. At 

lower levels (see 200 meter trajectories), it can be seen that closer to the surface, this air 

mass had spent the previous three to four days winding around the Tennessee and Ohio 

River Valleys before it was driven into the northern reaches of MANE-VU at the peak of 

the pollution event. 

The following figures bring much of this information together in a single image. 

Figure 4-6 contains satellite photos from MODIS, a mosaic of two consecutive satellite 

passages on August 13, 2002 from NASA’s TERRA satellite. Figure 4-7 shows the same 

image with geo-referenced activity data and inventory information layered on top to 

allow for simultaneous depiction of cities, roads, point source emissions, and back 

trajectories that play a role in the air pollution/haze that affected a large part of the 

Northeast during this episode. 

Figure 4-5. 24-hour rolling average fine aerosol at 

8 MANE-VU sites during the August 2002 episode 

-10

0

10

20

30

40

50

60

70

80

90

100

6-Aug7-Aug8-Aug9-Aug

10-Aug11-Aug12-Aug13-Aug14-Aug15-Aug16-Aug

ug/m3

Arendtsville, PA

Wilmington, DE

Camden, NJ

New Brunswick, NJ

NYC (Bronx), NY

Hartford, CT

Boston, MA

Portland, ME
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-9

Figure 4-6. Composite images from NASA’s TERRA Satellite on 

August 13, 2002 showing fine particle pollution/haze. 

Note the milky/gray haze due to particle pollution as distinct from the puffy white clouds over broad 

regions of southern New England and the eastern Mid-Atlantic region. 

Figure 4-7. NASA MODIS Terra Satellite Image, Back Trajectories and NOX Inventory 

Geo-referenced activity and inventory data (on top of the satellite images presented above) demonstrating 

the relationship between observed pollution and upper level winds (driving weather patterns from West to 

East), mid-level winds (tracking back to major point sources), and lower level winds (tracking back to major 

population centers along the East Coast). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-10

4.3. Implications for control strategies 

A 2003 assessment of fine particulate matter by NARSTO15 states, “[c]urrent airquality management approaches focusing on reductions of emissions of SO2, NOX, and 

VOCs are anticipated to be effective first steps towards reducing PM2.5 across North 

America, noting that in parts of California and some eastern urban areas VOC (volatile 

organic compounds) emissions could be important to nitrate formation.” 

This conclusion seems to be well supported by the historical record which 

documents a pronounced decline in particulate sulfate concentrations across the eastern 

United States during the 1990s. The timing of this observed decline suggests that this is 

linked to reductions in SO2 emissions resulting from controls implemented under the 

federal Acid Rain program beginning in the early to mid-1990s. From 1989 to 1998, SO2

emissions in the eastern half of the country — that is, including all states within a region 

defined by the western borders of Minnesota and Louisiana — declined by about 25 

percent. This decline in SO2 emissions correlated with a decline of about 40 percent in 

average SO2 and sulfate concentrations, as measured at Clean Air States and Trend 

Networks (CASTNet) monitoring sites in the same region over the same time period. In 

fact, at prevailing levels of atmospheric SO2 loading, the magnitudes of the emissions and 

concentration changes were not statistically different. This finding suggests that regional 

reductions in SO2 emissions have produced near-proportional reductions of particulate 

sulfate in the eastern United States (NARSTO, 2003). Reductions since 1990 in 

precursor SO2 emissions are likely also responsible for a continued decline in median 

sulfate concentrations in the northeastern United States. Nevertheless, episodes of high 

ambient sulfate concentrations (with peak levels well above the regional median or 

average) continue to occur, especially during the summertime when regional transport 

from the Ohio River Valley is also at its peak. This suggests that further reductions in 

regional and local SO2 emissions would provide significant further air quality and 

visibility benefits (NARSTO, 2003). 

For urban areas of the eastern United States, an effective emissions management 

approach may be to combine regional SO2 control efforts aimed at reducing summertime 

PM2.5 concentrations with local SO2 and OC control efforts. Local SO2 reductions would 

help reduce wintertime PM2.5 concentrations, while OC reductions can help reduce 

overall PM2.5 concentrations year-round. For areas with high wintertime PM2.5 levels, 

strategies that involve NOX reductions may also be effective (NARSTO, 2003). 

Further support for this general approach may be found in a review of several 

studies by Watson (2002) which concluded that SO2 emission reductions have in most 

cases been accompanied by statistically significant reductions in ambient sulfate 

concentrations. One study (Husar and Wilson, 1993) shows that regionally averaged light 

extinction closely tracks regionally averaged SO2 emissions for the eastern United States 

from 1940 through the mid-1980s. Another study by Malm et al. (2002) shows that 

 

15 NARSTO was formerly an acronym for the "North American Research Strategy for Tropospheric 

Ozone." More recently, the term NARSTO became simply a wordmark signifying a tri-national, publicprivate partnership for dealing with multiple features of tropospheric pollution, including ozone and 

suspended particulate matter. For more information on NARSTO see http://www.cgenv.com/Narsto/. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-11

regionally averaged emissions and ambient concentrations decreased together from 1988 

through 1999 over a broad region encompassing the states of Connecticut, Delaware, 

Illinois, Indiana, Kentucky, Maine, Massachusetts, Maryland, Michigan, New 

Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, 

Virginia, Wisconsin, and West Virginia (Watson, 2002). 

These studies and available data from the IMPROVE (Interagency Monitoring of 

Protected Visual Environment) monitoring network provide strong evidence that regional 

SO2 reductions have yielded, and will continue to yield, reductions in ambient secondary 

sulfate levels with subsequent reductions in regional haze and associated light extinction. 

They indicate that reductions in anthropogenic primary particle emissions will also result 

in visibility improvements, but that these will not have a zone of influence as large as 

those of the secondary aerosols (Watson, 2002). 

Watson (2002) notes that during the 65 years in which the regional haze program 

aims to reach its final visibility goals, several opportunities to revise this basic control 

approach will arise through the decadal SIP cycle. This enables new scientific results to 

continue to exert a positive influence as states implement new regulatory control 

programs for SO2, NOX and VOCs, and as ambient concentrations of these pollutants 

change relative to each other and relative to ambient ammonia levels. As these 

relationships between species change, atmospheric chemistry may dictate a revised 

control approach to those previously described. Further research on these issues should 

be a priority for supporting 2018 SIP submissions. They include the possibility that: 

• Reduction of sulfate in a fully neutralized atmosphere (excess ammonia) 

could encourage ammonium nitrate formation. 

• Ever-greater emissions reductions could be required to produce a given 

level of improvement in ambient pollutant concentrations because of nonlinearities in the atmospheric formation of sulfate. 

• Changes in ambient conditions favoring the aqueous oxidation of sulfate 

(this pathway largely accounts for the non-linearity noted above) may 

have implications for future emissions control programs. Causes of 

changing ambient conditions could include, for example, climate change. 

West et al. (1999) examine a scenario for the eastern United States where PM2.5

mass decreases linearly with ammonium sulfate until the latter is fully neutralized by 

ammonia. Further reductions would free ammonia for combination with gaseous nitric 

acid that, in turn, would slightly increase PM2.5 until all of the nitric acid is neutralized 

and further sulfate reductions are reflected in lower PM2.5 mass. This is an extreme case 

that is more relevant to source areas (e.g., Ohio) where nitric acid (HNO3) is more 

abundant than in areas with lower emissions (e.g., Vermont) (Watson, 2002). 

In most situations with non-neutralized sulfate (typical of the eastern United 

States), ammonia is a limiting agent for the formation of nitrate but will not make any 

difference until sulfate is reduced to the point where it is completely neutralized. At that 

point, identifying large sources of ammonia emissions will be important. This point is 

likely to be many years in the future, however (Watson, 2002). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-12

Based on analyses using the Community Multi-Scale Air Quality (CMAQ) model, 

the aqueous phase production of sulfate in the Northeast appears to be very oxidant 

limited and hence non-linear. Thus, conditions that are conducive to a dominance of the 

gas-phase production pathway drive the summer peaks in ambient sulfate levels. 

Nonetheless, the expected reduction in ambient sulfate levels resulting from a given 

reduction in SO2 emissions is less than proportional overall due to the non-linearity 

introduced by the aqueous pathway for sulfate formation (NARSTO, 2003). These nonlinearity effects are more pronounced for haze than for sulfate deposition, especially at 

higher sulfate air concentrations (USNPS, 2003). 

Finally, we note that because visibility in the clearest areas is sensitive to even 

minute increases in particle concentrations, strategies to preserve visibility on the clearest 

days may require stringent limits on emissions growth. In this context, even the dilute 

emissions from distant sources can be important (NARSTO, 2003) 

4.4. Conclusion: Simplifying a complex problem 

A conceptual understanding of fine particles from a regional perspective across 

MANE-VU and throughout the eastern U.S. is well understood, yet remains complex due 

to the multiplicity of source regions (both regional and local), pollutants (SO2, NOX, 

organic carbon, and primary PM2.5), and seasons (summer and winter) that are involved 

in fine particle formation. 

Regional approaches to the control of precursor SO2 and NOX emissions have 

been started through Title IV of the Clean Air Act, the NOX SIP Call, the CAIR, and the 

establishment and support of Regional Planning Organizations to assist with Regional 

Haze Rule compliance. With the modeling foundation developed for the CAIR program, 

the USEPA has presented a compelling technical case on the need for additional regional 

SO2 and NOX reductions in the eastern U.S. to reduce particulate levels and protect public 

health. While states in the Northeast disagree with the extent of SO2 and NOX reductions 

and the timeline for those reductions to occur, the program is an excellent next step 

toward reducing fine particles in MANE-VU. It is tempting to suggest that the regional 

control of SO2 and NOX are the extent of the problem facing MANE-VU, but as the 

conceptual description contained in this report demonstrates, the reduction of fine 

particles in the eastern U.S. requires a careful balance of regional and local controls for 

SO2, NOX, sources of organic carbon and primary PM2.5 during both summer and winter. 

The (relatively) higher emissions of SO2 and NOX from regions upwind of 

MANE-VU as well as the long “reach” of sulfate pollution requires continued regional 

control of these fine particle precursors. However, local accumulation of SO2-derived 

sulfate, NOX-derived nitrate, and primary PM (mostly in the form of black carbon/diesel 

exhaust) can significantly boost urban PM2.5 levels. Residential wood combustion in 

rural river valleys can significantly raise PM levels as well and affect rural visibility in 

areas near to Class I areas. 

The balance between regional and local controls parallels the balance that needs 

to be achieved between pollutants. The regional contribution to fine particle pollution is 

driven by sulfates and organic carbon, whereas the local contribution to PM2.5 is derived 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page 4-13

from SO2, NOX, organic carbon, and primary PM2.5 (including black carbon/diesel 

exhaust). 

Finally, control strategies which focus on regional SO2 emissions reductions are 

needed throughout the summer and winter months, suggesting that a year-round approach 

to control is needed. Urban nonattainment counties with local emissions of NOX and 

VOC will be driven to reduce these emissions during the summer for ozone benefits, but 

these same pollutants – as well as primary particulate emissions – contribute to high 

PM2.5 levels in winter, suggesting that annual controls for all of these pollutants make 

sense in a multi-pollutant context. Finally, residential wood smoke near Class I areas is 

clearly a winter-only issue, and further controls may be desirable near specific Class I 

sites where organic carbon is a contributor on the 20 percent worst visibility days that 

occur in winter months. 

To bring attainment to the current fine particle nonattainment counties and meet 

reasonable progress goals toward national visibility goals, there continues to be a need for 

more regional SO2 and NOX reductions coupled with appropriate local SO2, NOX, VOC, 

and primary PM2.5 (including diesel exhaust) controls where local accumulation is shown 

to add to the regional burden of sulfate and nitrate PM2.5 (primarily in winter). These 

local controls will vary by location and by season, but the regional control of SO2 and 

NOX should be maintained on an annual basis given the contribution of regional sulfate 

and nitrate to fine particle peaks during both summer and winter months. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page A-1

Appendix A: Excerpts from EPA Guidance 

Document, Guidance on the 

Use of Models and Other Analyses for 

Demonstrating Attainment of Air Quality Goals 

for Ozone, PM2.5, and Regional Haze 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page A-2

APPENDIX A: EPA GUIDANCE DOCUMENT EXERPT 

11.0 How Do I Get Started? - A “Conceptual Description” 

A State/Tribe should start developing information to support a modeled attainment 

demonstration by assembling and reviewing available air quality, emissions and 

meteorological data. Baseline design values should be calculated at each monitoring site, 

as described in Section 3. For PM applications, speciated data should be reviewed to get a 

sense of what component(s) might be contributing most significantly to nonattainment or 

light extinction. If past modeling has been performed, the emission scenarios examined 

and air quality predictions may also be useful. Readily available information should be 

used by a State/Tribe to develop an initial conceptual description of the nonattainment or 

reasonable haze problem in the area which is the focus of a modeled demonstration. A 

conceptual description is instrumental for identifying potential stakeholders and for 

developing a modeling/analysis protocol. It may also influence a State’s choice of air 

quality model, modeling domain, grid cell size, priorities for quality assuring and refining 

emissions estimates, and the choice of initial diagnostic tests to identify potentially 

effective control strategies. In general, a conceptual description is useful for helping a 

State/Tribe identify priorities and allocate resources in performing a modeled 

demonstration. 

In this Section, we identify key parts of a conceptual description. We then present 

examples of analyses which could be used to describe each of these parts. We note that 

initial analyses may be complemented later by additional efforts performed by those 

implementing the protocol. 

11.1 What Is A “Conceptual Description”? 

A “conceptual description” is a qualitative way of characterizing the nature of an area’s 

nonattainment or regional haze problem. It is best described by identifying key 

components of a description. Examples are listed below. There are 3 different examples. 

One each for ozone, annual PM2.5, and regional haze. The examples are not necessarily 

comprehensive. There could be other features of an area’s problem which are important 

in particular cases. For purposes of illustration later in the discussion, we have answered 

each of the questions posed below. Our responses appear in parentheses. 

11.1.1 8-Hour Ozone NAAQS 

1. Is the nonattainment problem primarily a local one, or are regional factors important? 

(Surface measurements suggest transport of ozone close to 84 ppb is likely. There are 

some other nonattainment areas not too far distant.) 

2. Are ozone and/or precursor concentrations aloft also high? 

(There are no such measurements.) 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page A-3

3. Do violations of the NAAQS occur at several monitoring sites throughout the 

nonattainment area, or are they confined to one or a small number of sites in proximity to 

one another? 

(Violations occur at a limited number of sites, located throughout the area.) 

4. Do observed 8-hour daily maximum ozone concentrations exceed 84 ppb frequently or 

just on a few occasions? 

(This varies among the monitors from 4 times up to 12 times per year.) 

5. When 8-hour daily maxima in excess of 84 ppb occur, is there an accompanying 

characteristic spatial pattern, or is there a variety of spatial patterns? 

(A variety of patterns is seen.) 

6. Do monitored violations occur at locations subject to mesoscale wind patterns (e.g., at 

a coastline) which may differ from the general wind flow? 

(No.) 

7. Have there been any recent major changes in emissions of VOC or NOX in or near the 

nonattainment area? If so, what changes have occurred? 

(Yes, several local measures [include a list] believed to result in major reductions in VOC 

[quantify in tons per summer day] have been implemented in the last five years. 

Additionally, the area has seen large regional NOX reductions from the NOX SIP call.) 

8. Are there discernible trends in design values or other air quality indicators which have 

accompanied a change in emissions? 

(Yes, design values have decreased by about 10% at four sites over the past [x] years. 

Smaller or no reductions are seen at three other sites.) 

9. Is there any apparent spatial pattern to the trends in design values? 

(No.) 

10. Have ambient precursor concentrations or measured VOC species profiles changed? 

(There are no measurements.) 

11. What past modeling has been performed and what do the results suggest? 

(A regional modeling analysis has been performed. Two emission scenarios were 

modeled: current emissions and a substantial reduction in NOX emissions throughout the 

regional domain. Reduced NOX emissions led to substantial predicted reductions in 8-

hour daily maximum ozone in most locations, but changes near the most populated area 

in the nonattainment area in question were small or nonexistent.) 

12. Are there any distinctive meteorological measurements at the surface or aloft which 

appear to coincide with occasions with 8-hour daily maxima greater than 84 ppb? 

(Other than routine soundings taken twice per day, there are no measurements aloft. 

There is no obvious correspondence with meteorological measurements other than daily 

maximum temperatures are always > 85 F on these days.) 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page A-4

Using responses to the preceding questions in this example, it is possible to construct an 

initial conceptual description of the nonattainment area’s ozone problem. First, responses 

to questions 1 and 11 suggest there is a significant regional component to the area’s 

nonattainment problem. Second, responses to questions 3, 4, 7, 8, and 11 indicate there is 

an important local component to the area’s nonattainment problem. The responses to 

questions 4, 5 and 12 indicate that high ozone concentrations may be observed under 

several sets of meteorological conditions. The responses to questions 7, 8, and 11 

suggest that ozone in and near the nonattainment area may be responsive to both VOC 

and NOX controls and that the extent of this response may vary spatially. The response to 

question 6 suggests that it may be appropriate to develop a strategy using a model with 12 

km grid cells. 

The preceding conceptual description implies that the State/Tribe containing the 

nonattainment area in this example will need to involve stakeholders from other, nearby 

States/Tribes to develop and implement a modeling/analysis protocol. It also suggests 

that a nested regional modeling analysis will be needed to address the problem. Further, it 

may be necessary to model at least several distinctive types of episodes and additional 

analyses will be needed to select episodes. Finally, sensitivity (i.e., diagnostic) tests, or 

other modeling probing tools, will be needed to assess the effects of reducing VOC and 

NOX emissions separately and at the same time. 

11.1.2 Annual PM2.5 NAAQS 

1. Is the nonattainment problem primarily a local one, or are regional factors important? 

(Surface measurements suggest that only design values in or immediately downwind of 

the city violate the NAAQS. However, other nearby design values come close to the 

concentration specified in the NAAQS) 

2. What is the relative importance of measured primary and secondary components of 

PM2.5 measured at sites violating the NAAQS? 

(Secondary components (i.e., SO4, NO3, OC) constitute about 80% of the measured mass 

of PM2.5 . There are higher concentrations of primary PM2.5 in the core urban area 

compared to the suburbs and more rural areas.) 

3. What are the most prevalent components of measured PM2.5? 

(The most important components in ranked order are mass associated with SO4, OC and 

inorganic primary particulate matter (IP)). 

4. Does the measured mix of PM components appear to roughly agree with mix of 

emission categories surrounding the monitoring sites? 

(No. Relative importance of measured crustal material (IP) appears less than what 

might be inferred from the inventory). 

5. Do there appear to be any areas with large gradients of primary PM2.5 in monitored or 

unmonitored areas? 

(Cannot really tell for sources of crustal material until we resolve the preceding 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page A-5

inventory/monitoring discrepancy. There are no other obvious major sources of primary 

particulate matter). 

6. Is there any indication of what precursor might be limiting formation of secondary 

particulate matter? 

(No indicator species analyses have been performed. Past analyses performed for 

ozone-related SIP revisions suggest that ozone in this area may be limited by availability 

of VOC). 

7. Do monitored violations occur at locations subject to mesoscale wind patterns (e.g., at 

a coastline) which may differ from the general wind flow? 

(No.) 

8. Have there been any recent major changes in emissions of PM or its precursors in or 

near the nonattainment area? What? 

(Yes, measures believed to result in major reductions in VOC and NOX have been 

implemented in the last 5 years. Reductions in power plant NOX have resulted from the 

NOX SIP call and SO2 emissions reductions have resulted from the national program to 

reduce acid deposition.) 

9. Are there discernible trends in design values or other air quality indicators which have 

accompanied a change in emissions? 

(The trend appears to be downward, but the most recent air quality data has been higher. 

Overall, the period of record is insufficiently long to tell). 

10. Is there any apparent spatial pattern to the trends in design values? 

(No.) 

11. What past modeling has been performed and what do the results suggest? 

(A regional modeling analysis has been performed for ozone and PM2.5. Two emission 

scenarios were modeled: current emissions and a substantial reduction in NOX and SO2

emissions throughout a regional domain. Reduced NOX emissions led to substantial 

predicted reductions in 8-hour daily maximum ozone in most locations. Modeled SO2

reductions from the CAIR rule had a strong impact on sulfate concentrations) 

12. Are there any distinctive meteorological measurements at the surface or aloft which 

appear to coincide with occasions with PM2.5 concentrations in excess of 15.0 :g/m3? 

(Other than routine soundings taken twice per day, there are no measurements aloft. 

There is no obvious correspondence with meteorological measurements other than daily 

maximum temperatures are often > 85F on days with the highest PM2.5 observations.) 

13. Do periods with high measured particulate matter or components of particulate matter 

appear to track each other or any other measured pollutant? 

(There appears to be some correspondence between measured high concentrations of 

SO4 and ozone). 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page A-6

Using responses to the preceding questions in this example, it is possible to construct an 

initial conceptual description of the nonattainment area’s ozone problem. First, responses 

to questions 1, 2 and 3 suggest there is a significant regional component to the area’s 

nonattainment problem. Second, responses to questions 1 and 3 indicate there is a local 

component to the problem. The responses to questions 11,12 and 13 suggest that there 

may be a link between reducing ozone and reducing particulate matter. Thus, it may be 

appropriate to assess effects of previously committed to strategies to reduce ozone and 

national PM control measures before simulating additional control measures. The 

responses to questions 4 and 5 suggest that it is premature to determine whether a “local 

area analysis” will be needed. The response to question 7 suggests that it may not be 

necessary to model with very small grid cells, at least for the secondary components of 

PM2.5. 

The preceding conceptual description implies that the State containing the nonattainment 

area in this example will need to involve stakeholders from other, nearby States to 

develop and implement a modeling/analysis protocol. It also suggests that a nested 

regional modeling analysis will be needed to address the problem. 

11.1.3 Example reasonable progress application 

1. What components of particulate matter appear to have high concentrations on days 

with poor visibility? 

(Mass associated with SO4 and coarse particulate matter (CM) seem to have the highest 

concentrations on most such days). 

2. What are typical values for the humidity adjustment factor during the times of year 

when most of the days with poor visibility occur? 

(Typical values appear to be about “4.0"). 

3. Does visibility appear to track well among nearby Class I areas? 

(Yes, but not always). 

4. Does poor visibility seem to occur under any specific meteorological conditions? 

(This information is not readily available). 

5. Does poor visibility seem to coincide with high observed concentrations of any 

particular other pollutant? 

(There seems to be some correspondence with high regional ozone concentrations) 

6. What components of particulate matter appear to have relatively high concentrations 

on days with good visibility? 

(Coarse particulate matter and OC) 

7. What are typical values for the humidity adjustment factor during times of year when 

most of the days with good visibility occur? 

(About “2.3") 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page A-7

8. Does good visibility appear to occur under any specific meteorological conditions? 

(Don’t know.) 

Answers to the preceding questions suggest that strategies to reduce sulfate 

concentrations and, perhaps, regional ozone concentrations might be effective in reducing 

light extinction on days when visibility is currently poor. The responses suggest that a 

strategy which focuses on this alone should first be tried for the days with good visibility 

as well. Even though sulfate concentrations appear low on such days, the fact that sulfates 

scatter light efficiently (see Equation (6.1)) and relative humidity is still high enough to 

enhance this effect is worth considering. Responses suggest that further meteorological 

analyses would be worthwhile prior to selecting strategies to simulate with a resource 

intensive regional model. 

It should be clear from the preceding examples that the initial conceptual description of 

an area’s nonattainment problem draws on readily available information and need not be 

detailed. It is intended to help launch development and implementation of a 

modeling/analysis protocol in a productive direction. It will likely be supplemented by 

subsequent, more extensive modeling and ambient analyses performed by or for those 

implementing the modeling/analysis protocol discussed in Section 12.0. 

Questions like those posed in Section 11.1 can be addressed using a variety of analyses 

ranging in complexity from an inspection of air quality data to sophisticated 

mathematical analyses. We anticipate the simpler analyses will often be used to develop 

the initial conceptual description. These will be followed by more complex approaches or 

by approaches requiring more extensive data bases as the need later becomes apparent. 

These analyses are intended to channel resources available to support modeled attainment 

demonstrations onto the most productive paths possible. They will also provide other 

pieces of information which can be used to reinforce conclusions reached with an air 

quality model, or cause a reassessment of assumptions made previously in applying the 

model. As noted in Section 7, corroboratory analyses should be used to help assess 

whether a simulated control strategy is sufficient to meet the NAAQS. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-1

Appendix B: Monitoring Data from 

Class I sites in MANE-VU 

Below are figures that were developed by Tom Downs of the Maine Department 

of Environmental Protection. These figures represent baseline monitoring data for the 

Class I sites (and Washington DC) based on IMPROVE monitoring network data using 

the EPA approved “default” algorithm for calculating reconstructed extinction and 

estimating natural background conditions. These statistics may need to be recreated 

using the alternative methodology approved by the IMPROVE steering committee and 

adopted by the MANE-VU states. Glide path graphs were created on the VIEWS website 

(http://vista.cira.colostate.edu/views/) using the Annual Summary Trends tool. Seasonal 

graphs were created from data downloaded from the VIEWS website using the Annual 

Summary Composition tool and should be updated to include 2004 data for a complete 

description of regional haze baseline data. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-2

APPENDIX B: MONITORING DATA FROM CLASS I 

SITES IN MANE-VU 

Figure B-1. Monitoring Data from Acadia NP, ME 

April 26, 1995 - Teflon filter was 

increased from 2.2 sq. cm to 3.5 sq. cm 

Extinction Trends

dv

Deciview (dv) Trends
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-3

Figure B-2. Monitoring Data from Brigantine, ME 

Extinction Trends

dv

Deciview (dv) Trends
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-4

Figure B-3. Monitoring Data from Great Gulf, NH 

Extinction Trends

dv

Deciview (dv) Trends
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-5

Figure B-4. Monitoring Data from Lye Brook, VT 

Extinction Trends

dv

Deciview (dv) Trends
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-6

Figure B-5. Monitoring Data from Moosehorn, ME 

Extinction Trends

dv

Deciview (dv) Trends
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-7

Figure B-6. Monitoring Data from Washington, DC 

Extinction Trends

dv

Deciview (dv) Trends
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-8

Figure B-7. 20% Worst and Best 2000-2003 Visibility Days at Acadia NP, ME 

Seasonal Analysis of the 20% Best

 2000-2003 Visibility Days at Acadia National Park

0

1

2

3

4

5

6

7

8

9

10

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 19 days

Summer - 15 days

Spring - 24 days

Fall - 35 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006

Seasonal Analysis of the 20% Worst

 2000-2003 Visibility Days at Acadia National Park

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 16 days

Summer - 39 days

Spring - 17 days

Fall - 23 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-9

Figure B-8. 20% Worst and Best 2000-2003 Visibility Days at Brigantine, NJ 

Seasonal Analysis of the 20% Best

 2000-2003 Visibility Days at Brigantine, NJ

0

2

4

6

8

10

12

14

16

18

20

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 20 days

Summer - 13 days

Spring - 21 days

Fall - 33 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006

Seasonal Analysis of the 20% Worst

 2000-2003 Visibility Days at Brigantine, NJ

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 15 days

Summer - 39 days

Spring - 15 days

Fall - 21 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-10

Figure B-9. 20% Worst and Best 2000-2003 Visibility Days at Great Gulf, NH 

Seasonal Analysis of the 20% Best

 2000-2003 Visibility Days at Great Gulf, NH

0

1

2

3

4

5

6

7

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 28 days

Summer - 7 days

Spring - 17 days

Fall - 29 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006

Seasonal Analysis of the 20% Worst

 2000-2003 Visibility Days at Great Gulf, NH

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 9 days

Summer - 39 days

Spring - 13 days

Fall - 23 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-11

Figure B-10. 20% Worst and Best 2000-2003 Visibility Days at Lye Brook, VT 

Seasonal Analysis of the 20% Best

 2000-2003 Visibility Days at Lye Brook, VT

0

1

2

3

4

5

6

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 29 days

Summer - 11 days

Spring - 22 days

Fall - 24 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006

Seasonal Analysis of the 20% Worst

 2000-2003 Visibility Days at Lye Brook, VT

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 12 days

Summer - 37 days

Spring - 17 days

Fall - 23 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-12

Figure B-11. 20% Worst and Best 2000-2003 Visibility Days at Moosehorn, ME 

Seasonal Analysis of the 20% Best

 2000-2003 Visibility Days at Moosehorn, ME

0

1

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Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 15 days

Summer - 18 days

Spring - 21 days

Fall - 36 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006

Seasonal Analysis of the 20% Worst

 2000-2003 Visibility Days at Moosehorn, ME

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Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 20 days

Summer - 41 days

Spring - 14 days

Fall - 18 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page B-13

Figure B-12. 20% Worst and Best 2000-2003 Visibility Days at Washington, D.C. 

Seasonal Analysis of the 20% Best

 2000-2003 Visibility Days at Washington, D.C.

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Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 22 days

Summer - 9 days

Spring - 26 days

Fall - 31 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006

Seasonal Analysis of the 20% Worst

 2000-2003 Visibility Days at Washington, D.C.

0

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Sulfate Nitrate Org Carbon Elem Carbon Soil Coarse Mass

Extinction (Mm-1)

Winter - 16 days

Summer - 42 days

Spring - 14 days

Fall - 20 days

Created by Tom Downs, Maine DEP-BAQ - 11/02/2006

/2006
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description 

Figure B-13. 20% Best 2000-2003 Visibility Days Speciated Contributions to Extinctio

Washington D.C.

176 Mm-1

(22 km/29.0 dv)

Brigantine

159 Mm-1

(25 km/27.9 dv)

Lye Brook

108 Mm-1

(38 km/23.9 dv)

Great Gulf

(Presidential Range)

94 Mm-1

(45 km/22.5 dv)

Acadia

91 Mm-1

(44 km/22.4 dv)

Mooseh

(Roosevelt Ca

82 Mm

(48 km/21

Mooseh

(Roosevelt Ca

82 Mm

(48 km/21

20% Worst Visi

Speciated Contributi

Extinction (2000-2003 e

Great Gulf 2001-20

Site Sulfate Nitrate Org C Elem C Soil Coarse Mass

Acadia 72 9 11 5 0.6 2Moosehorn 70 8 14 5 0.5 3Lye Brook 72 9 12 5 0.6 2Brigantine 68 11 13 5 0.6 4Washington DC 61 14 15 7 0.7 2Great Gulf 76 3 13 4 0.6 3

percent contributon to particle extinction

Extinction = 3*f(RH)*sulfate(f) + 

1.29*Nitrate(f) + 4*1.4*OC(f) + 10* elementa

carbon (f) + 1* soil(f) +0.6 * coarse mass

Created by TMaine DEP-B
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description 

Figure B-14. 20% Best 2000-2003 Visibility Days Speciated Contributions to Extinctio

Washington D.C.

47.3 Mm-1

(70 km/17.3 dv)

Brigantine

30.3 Mm-1

(101 km/13.8 dv)

Lye Brook

8.8 Mm-1

(215 km/6.1 dv)

Great Gulf

(PresidentialRange)

11.3 Mm-1

(189 km/7.4 dv) Acadia

12.8 Mm-1

(175 km/8.1 dv)

20% Best Visib

Speciated Contribut

Extinction (2000-2003 

for Great Gulf 2001

Site Sulfate Nitrate Org C Elem C Soil Coarse Mass

Acadia 60 9 18 7 1 6Moosehorn 54 9 22 7 1 8Lye Brook 57 14 14 7 1 6Brigantine 53 13 14 7 1 12Washington DC 49 17 16 12 1 5Great Gulf 56 9 18 8 1 8

percent contributon to particle extinction

Created by TMaine DEP-

Mooseho

(Roosevelt Cam

13.9 Mm

(169 km/8.6 

Mooseho

(Roosevelt Cam

13.9 Mm

(169 km/8.6 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page C-1

Appendix C: Additional Considerations for PM2.5

Air Quality Management 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page C-2

APPENDIX C: ADDITIONAL CONSIDERATIONS FOR 

PM2.5 AIR QUALITY MANAGEMENT 

C.1. Averaging times and data interpretation 

In analyzing the chemical data available for interpreting the air quality event of 

August 2002, it is important to point out that the use of different averaging times can 

have a profound effect on our understanding of the progression of any specific episode. 

Many subtleties of synoptic-scale meteorology and atmospheric chemistry are “aliased 

out” of data sets with temporal resolution greater than 3-6 hours. These effects are 

demonstrated in Figure C-1 which show fine aerosol TEOM data from New Haven for 

the “episode” period August 10-16, 2002. In these figures, the hourly TEOM values have 

been aggregated into 3-, 6- and 24-hour mean values. Average concentrations are 

inversely proportional to the length of the averaging period and the ratio of peak hourly 

concentration within a daily average ranges from about 1.5 to 1.75 for this episode. 

Figure C-1. Effects of averaging times (or temporal resolution) on time series information 

Figure 5.6(a) Unfiltered (hourly) TEOM data from New Haven, Conn.

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8/10/02 0:008/11/02 0:008/12/02 0:008/13/02 0:008/14/02 0:008/15/02 0:008/16/02 0:00

Fine Aerosol Mass (ug/m3)

Figure 5.6(b) New Haven, Conn. TEOM data with a 3-hour filter.

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8/10/02 0:008/11/02 0:008/12/02 0:008/13/02 0:008/14/02 0:008/15/02 0:008/16/02 0:00

Fine Aerosol Conc. (ug/m3)

Figure 5.6(c) New Haven, Conn. TEOM data with a 6-hour filter.

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8/10/02 0:008/11/02 0:008/12/02 0:008/13/02 0:008/14/02 0:008/15/02 0:008/16/02 0:00

Fine Aerosol Conc. (ug/m3)

Figure 5.6(d) New Haven, Conn. TEOM data with a 24-hour filter.

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8/10/02 0:008/11/02 0:008/12/02 0:008/13/02 0:008/14/02 0:008/15/02 0:008/16/02 0:00

Fine Aerosol Conc. (ug/m3)
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page C-3

C.2. Rural versus urban PM2.5 mass 

Comparison of PM2.5 concentrations from rural areas with those from 

urban/suburban areas can add significantly to our understanding of the impact on air 

quality of both urban sources and of medium to long-range fine aerosol transport. To 

assist with this approach, data from 10 pairs of rural and urban/suburban FRM sites 

throughout the MANE-VU region were selected and analyzed. 

Table C-1 shows basic site description information including the approximate, 

straight-line distance between the site pairs. 

Due to the difficulty in finding a significant number of urban-rural site pairs that 

operated on the same sampling schedule, sites with a mixture of schedules were used to 

insure samples representative of the entire MANE-VU region. As a result, three of the 20 

sites employed an everyday schedule while two sites sampled every sixth day (the 

remainder sampled every third day). Data from the three everyday sites were edited so as 

to include data from the 1-in-3 schedule only. In all, a total of 1098 data points were 

possible from the 10 site pairs for 2002. Of the 1098 possible point-pairs, 951 (87%) 

were valid and were used in this analysis. 

Table C-1. MANE-VU urban-rural site pair information 

State Site No City Land use Location type Longitude Latitude

Inter-site 

Distance 

(mi)

DE 100051002 Agricultural Rural -75.55560 38.98470

DE 100010002 Seaford Residential Suburban -75.61310 38.64440 24.0

MA 250154002 Ware Forest Rural -72.33472 42.29833

MA 250130016 Springfield Commercial Urban & Center City -72.59140 42.10890 17.6

MD 240030014 Agricultural Rural -76.65310 38.90250

MD 245100049 Baltimore Residential Urban & Center City -76.63750 39.26170 25.2

ME 230052003 Cape Elizabeth Residential Rural -70.20778 43.56083

ME 230010011 Lewiston Commercial Urban & Center City -70.21500 44.08940 37.0

NJ 340218001 Agricultural Rural -74.85470 40.31500

NJ 340210008 Trenton Residential Urban & Center City -74.76360 40.22220 7.7

NY 360010012 Albany Agricultural Rural -73.75690 42.68070

NY 360930003 Schenectady Residential Suburban -73.94020 42.79960 11.7

NY 361030001 Babylon Commercial Rural -73.42030 40.74580

NY 360590013 Bethpage Residential Suburban -73.49060 40.76080 3.3

NY 360130011 Westfield Agricultural Rural -79.60250 42.29080

PA 420490003 Erie Commercial Suburban -80.03860 42.14180 22.2

PA 420030093 Residential Rural -80.02080 40.60720

PA 420030021 Pittsburgh Residential Suburban -79.94140 40.41360 14.0

PA 420290100 Commercial Rural -75.76860 39.83440

DE 100031012 Newark Residential Suburban -75.76170 39.69190 10.0
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page C-4

As expected, urban/suburban areas, with their rich supply of emission sources, 

almost always reported higher concentrations than their nearby sister sites in rural areas. 

Of the 951 valid data pairs, 660 showed higher urban/suburban levels while 291 cases 

showed higher rural levels. 

One interesting aspect of the 2002 urban-rural data concerns the pattern in 

seasonal differences between such site pairs. Figure C-2 shows the difference (urbanrural) between the 10 site pairs as a time series. 

Although some rural-to-urban seasonal differences are to be expected, the 

variation in the magnitude of this difference is surprising. In the warm/hot months, the 

mean rural/urban difference amounts to no more than ~0.7 μg/m3

 (based on a best-fit 2nd

order polynomial curve), which is a relatively small differential. However, during the 

cool/cold months that difference climbs to almost 4 μg/m3, demonstrating a total annual 

seasonal variation of at least 3 μg/m3. Because the mean annual concentration of all sites 

is 12.6 μg/m3, an annual variation of 3 μg/m3 becomes significant. 

One explanation for the observed seasonal variation concerns the temporal 

distribution of local and transported emissions. In the summertime, MANE-VU sites 

repeatedly experience sulfate events due to transport from regions to the south and west. 

During such events, rural and urban sites throughout MANE-VU record high (i.e., 

>15 μg/m3

) daily average PM2.5 concentrations. During summer stagnation events, 

atmospheric ventilation is poor and local emissions are added to the transported burden 

with the result that concentrations throughout the region (rural and urban) are relatively 

Figure C-2. Difference in FRM data between 10 urban-rural site pairs for 2002 

-2.0

-1.0

0.0

1.0

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1/2/20022/1/20023/3/20024/2/20025/2/20026/1/20027/1/20027/31/20028/30/20029/29/200210/29/200211/28/200212/28/2002

Urban-Rural Conc. (ug/m

3

)
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page C-5

uniform. There are enough of these events to drive the urban-rural difference down to 

less than 1 μg/m3

 during warm/hot months. 

During the wintertime, strong local inversions frequently trap local emissions 

during the overnight and early morning periods, resulting in elevated urban 

concentrations. Rural areas experience those same inversions but have relatively fewer 

local sources so that wintertime concentrations in rural locations tend to be lower than 

those in nearby urban areas. Medium and long-range fine aerosol transport events do 

occur during the winter but at a much reduced rate compared to summertime. So, it is the 

interplay between local and distant sources as well as meteorological conditions that 

drive the observed seasonal urban-rural difference in FRM concentrations. 

C.3. Seasonal relationship between PM2.5 and NOX

Because nitrogen oxides (NOX) can be a good indicator of regional as well as 

local emissions, NOX data for the MANE-VU region was downloaded from USEPA’s 

AQS. Ultimately, data from six widely separated MANE-VU NOX sites were selected 

(one site each in CT, DC, MA, NH, PA and VT). Sites were selected both for high data 

capture rates and geographic location. The NOX data were then aggregated into regional 

averages on a daily basis and compared to PM2.5 FRM data from 34 “everyday” sampling 

sites (which were also averaged on a regional basis). 

During 2002, there were virtually no periods when regional mean PM2.5

concentrations rose above 20 μg/m3

 and were not accompanied by rising (or already 

high) NOX concentrations. However, as seen in Figure C-3, NOX concentrations vary 

widely on an annual basis and tend to occur out-of-sync with fine particle concentrations. 

Although the min/max extremes of these two pollutants are offset in time, they are 

highly correlated during some parts of the year. For example, Figure C-4 shows the 

regional PM2.5 and NOX data for the coldest (Jan., Feb., Nov., and Dec.) and hottest 

(May, June, July and Aug.) seasons of 2002. Wintertime NOX and PM2.5 concentrations 

are rather well correlated (r2

=0.67) while summertime concentrations are not at all linked. 

This dichotomy can be explained by several coincident effects including: 1) reduced UV 

radiation during cold months (which prevents photolysis of NO2 to O3); 2) the increase in 

space heating requirements from stationary sources (which preferentially increases 

morning NOX emissions; increased NOX emissions due to “cold-start” mobile source 

engines and 3) decreased mixing height depths due to reduced solar input (which allows 

morning concentrations to build quickly). Note that the Spring/Fall PM2.5 vs. NOX

correlation (not shown) lies about mid-way between the winter/summer values shown in 

Figure C-4. 
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page C-6

Figure C-3. Regional PM2.5 and NOX in 2002 

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1/1/022/1/023/1/024/1/025/1/026/1/027/1/028/1/029/1/0210/1/0211/1/0212/1/02

NOx (ppbv) PM2.5 (ug/m3)

Mean Reg. NOx ( 6 sites)

Mean Reg. PM2.5 (34 FRM sites)

Figure C-4. PM2.5 vs. NOX correlation by season 

MANE-VU Regional PM2.5 vs. Regional NOx - 2002

y = 4.08x - 4.65

R

2

 = 0.67

y = 0.13x + 18.23

R

2

 = 0.05

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NOx Conc. (ppb)

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Summer Months

MANE-VU Regional PM2.5 vs. Regional NOx - 2002

y = 4.08x - 4.65

R

2

 = 0.67

y = 0.13x + 18.23

R

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NOx Conc. (ppb)

Winter Months

Summer Months
PM2.5 and Regional Haze Air Quality Problems in the MANE-VU Region: A Conceptual Description Page C-7