Technical Support Document (TSD) for 2008 Ozone NAAQS Designations

Connecticut

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

Connecticut portion of the New York-Newark-Bridgeport, NY-NJ-CT Area

The table below identifies the areas and associated counties or parts of counties in Connecticut that EPA 

intends to designate as nonattainment for the 2008 ozone national ambient air quality standards (2008

NAAQS). In accordance with section 107(d) of the Clean Air Act, EPA must designate an area (county 

part of a county) “nonattainment” if it is violating the 2008 ozone NAAQS or if it is contributing to a 

violation of the 2008 ozone NAAQS in a nearby area. The technical analysis supporting the boundaries 

for the individual nonattainment areas are provided below.

Intended Ozone Nonattainment Areas in Connecticut (state-wide nonattainment)

Area

Connecticut Recommended 

Nonattainment Counties

EPA’s Intended 

Nonattainment Counties

Connecticut portion of the New 

York-Newark-Bridgeport, NYNJ-CT area

Fairfield, New Haven and

Middlesex

Fairfield, New Haven and

Middlesex

Greater Connecticut1area Hartford, Litchfield, New 

London, Tolland and Windham

Hartford, Litchfield, New 

London, Tolland and Windham

EPA intends to designate the entire state of Connecticut as nonattainment. The analysis below provides 

the basis for intended nonattainment area boundaries. It relies on our analysis of whether and which 

monitors are violating the 2008 ozone NAAQS, based on certified air quality monitoring data from 

2008-2010 and an evaluation of whether nearby areas are contributing to such violations. EPA has 

evaluated contributions from nearby areas based on a weight of evidence analysis considering the factors 

identified below. The analysis below provides the basis for intended nonattainment area boundaries for 

the Connecticut portion of the New York-Newark-Bridgeport, NY-NJ-CT ozone nonattainment area. A 

separate TSD has been prepared for the rest of Connecticut. The rest of Connecticut will also be 

designated nonattainment for the 2008 ozone NAAQS, and referred to as the 2008 Greater Connecticut 

ozone nonattainment area. EPA issued guidance on December 4, 2008 that identified these factors as 

ones EPA would consider in determining nonattainment area boundaries and recommended that states 

consider these factors in making their designations recommendations to EPA.

2

 

1. Air quality data (including the design value calculated for each FRM or FEM monitor in the 

area);

2. Emissions and emissions-related data (including location of sources and population, amount of 

emissions and emissions controls, and urban growth patterns);

3. Meteorology (weather/transport patterns);

4. Geography and topography (mountain ranges or other basin boundaries);

 

1 Greater Connecticut is a multijurisdictional nonattainment area that includes areas of Indian Country.

2 The December 4, 2008 guidance memorandum “Area Designations for the 2008 Revised Ozone National Ambient Air 

Quality Standards” refers to 9 factors. In this technical support document we have grouped the emissions-related factors 

together under the heading of “Emissions and Emissions-Related Data,” which results in 5 categories of factors.
2

5. Jurisdictional boundaries (e.g., counties, air districts, existing nonattainment areas, Indian 

country, metropolitan planning organizations (MPOs))

Ground-level ozone is not emitted directly into the air, but is created by chemical reactions between 

oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Because 

NOx and VOC emissions from a broad range of sources over a wide area typically contribute to 

violations of the ozone standards, EPA believes it is important to consider whether there are contributing 

emissions from a broad geographic area. Accordingly, EPA chose to examine the 5 factors with respect 

to the larger of the Combined Statistical Area (CSA) or Core Based Statistical Area (CBSA) associated 

with the violating monitor(s).

3 All data and information used by EPA in this evaluation are the latest 

available to EPA and/or provided to EPA by states or tribes.

In EPA’s designations guidance for the 2008 ozone NAAQS, EPA recommended examining 

CSA/CBSAs because certain factors used to establish CSAs and CBSAs are similar to the factors EPA is 

using in this technical analysis to determine if a nearby area is contributing to a violation of the 2008

ozone NAAQS. EPA used the same basic approach in the designation process for the 1997 ozone 

NAAQS. Where a violating monitor is not located in a CSA or CBSA, EPA’s guidance recommended

using the boundary of the county containing the violating monitor as the starting point for considering 

the nonattainment area’s boundary. 

Technical Analysis for Connecticut Portion of the New York-Newark-Bridgeport, NY-NJ-CT 

ozone nonattainment area

Figure 1 is a map of the Connecticut Portion of the New York-Newark-Bridgeport, NY-NJ-CT intended 

nonattainment area. The map provides information, including the locations and design values of air 

quality monitors, county and other jurisdictional boundaries, CSA/CBSA boundaries, existing 

nonattainment boundaries and state borders, and major highways.

For purposes of the 1997 8-hour ozone NAAQS, the area’s boundaries were the same as the State 

initially recommended for the 2008 ozone NAAQS and the same as the area we intend to designate as 

nonattainment for the 2008 ozone NAAQS.

In March 2009, Connecticut recommended that the entire State of Connecticut be designated 

nonattainment for the 2008 ozone NAAQS based on air quality data from 2006-2008. In its March 2009 

letter, Connecticut recommended that the state be split between two ozone nonattainment areas, with the 

same boundaries as for the 1997 ozone NAAQS. On October 28, 2011, Connecticut submitted an 

updated recommendation in which it recommended including all of Connecticut as part of a large multistate nonattainment area that included all or portions of 17 other States. On November 23, 2011,

Connecticut clarified their position that, if EPA does not agree with creating a large 18 state 

nonattainment area, the State of Connecticut should be split between two 2008 ozone nonattainment 

areas, with the same boundaries as for the 1997 ozone NAAQS. All ozone data referenced in the 

recommendations submitted by the State are from Federal Reference Method monitors, sited and 

operated in accordance with 40 CFR Part 58. (See letter to EPA dated November 23, 2011.)

 

3 Lists of CBSAs and CSAs and their geographic components are provided at 

www.census.gov/population/www/metroareas/metrodef.html . The lists are periodically updated by the Office of 

Management and Budget. EPA used the most recent update, based on 2008 population estimates, issued on December 1, 

2009 (OMB Bulletin No. 10-02).
3

After considering these recommendations and based on EPA's technical analysis described below, EPA 

intends to designate Fairfield, New Haven, and Middlesex counties as “nonattainment” for the 2008

ozone NAAQS. EPA intends to include these three counties as part of the larger tri-state New YorkNewark-Bridgeport, NY-NJ-CT ozone nonattainment area. We intend to designate the remaining 

counties in Connecticut (Hartford, Litchfield, New London, Tolland and Windham Counties) as the 

Greater Connecticut area. The main issue at hand is how to “split” the counties in Connecticut between 

two nonattainment areas: The New York-Newark-Bridgeport, NY-NJ-CT ozone nonattainment area, and 

the Greater Connecticut area. Information for the Greater Connecticut area is in a separate TSD.

Because Connecticut, in its clarifying recommendation of November 23, 2011, is recommending that all 

areas in the State be designated nonattainment and included in one of two different nonattainment areas, 

EPA focused its analysis on whether the boundaries for Connecticut’s proposed nonattainment areas for 

the 2008 eight-hour ozone NAAQS are supported by available data. EPA intends to designate the areas 

as requested, in the aforementioned letter from Connecticut, in the absence of information strongly 

supporting that one or more of the counties should be included in an area different than the one 

recommended by the State. In sum, Connecticut recommended two nonattainment areas: The New 

York-Newark-Bridgeport, NY-NJ-CT ozone nonattainment area, and the Greater Connecticut area. 

Information for the Greater Connecticut area is in a separate TSD.

Table 1. State's Recommended and EPA’s Intended Designated Nonattainment Counties for

Connecticut Portion of the New York-Newark-Bridgeport, NY-NJ-CT and Greater Connecticut 

Ozone Nonattainment Areas

Area State-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

Connecticut Portion of 

the New York-NewarkBridgeport, NY-NJ-CT 

area

Fairfield Fairfield

New Haven New Haven

Middlesex Middlesex

Greater CT

Hartford Hartford

Litchfield Litchfield

New London New London

Tolland Tolland

Windham Windham
4

Factor Assessment

Factor 1: Air Quality Data 

For this factor, we considered 8-hour ozone design values (in parts per million (ppm)) for air quality 

monitors in counties in the Connecticut Portion of the New York-Newark-Bridgeport, NY-NJ-CT ozone 

nonattainment area counties based on data for the 2008-2010 period (i.e., the 2010 design value, or DV), 

which are the most recent years with fully-certified air quality data. A monitor’s DV is the metric or 

statistic that indicates whether that monitor attains a specified air quality standard. The 2008 ozone 

NAAQS are met when the annual fourth-highest daily maximum 8-hour average concentration, 

averaged over 3 years is 0.075 ppm or less. A DV is only valid if minimum data completeness criteria 

are met. See 40 CFR part 50 Appendix P. Where several monitors are located in a county (or a 

designated nonattainment area or maintenance area), the DV for the county or area is determined by the 

monitor with the highest level.

The 2010 DVs for the ozone NAAQS for counties in the Connecticut Portion of the New York-NewarkBridgeport, NY-NJ-CT ozone nonattainment area and the Greater Connecticut ozone nonattainment area 

are shown in Tables 2a and 2b. 

Table 2a. Air Quality Data in the Three Counties of the Connecticut Portion of the New YorkNewark-Bridgeport, NY-NJ-CT Ozone Nonattainment Area

County State Recommended 

Nonattainment?

2008-2010 Design Value

(ppm)

Fairfield Yes 0.081

New Haven Yes 0.076

Middlesex Yes 0.077

Table 2b. Air Quality Data for the Greater Connecticut Ozone Nonattainment Area

County State Recommended 

Nonattainment?

2008-2010 Design Value

(ppm)

Hartford Yes 0.074

Litchfield Yes 0.0734

New London Yes 0.076

Tolland Yes 0.079

Windham Yes No monitor in county

Fairfield, New Haven, and Middlesex Counties show violations of the 2008 ozone NAAQS, therefore 

these counties are included in the nonattainment area. EPA believes that since Connecticut has 

recommended the entire state be nonattainment, air quality is not important for purposes of determining 

in which of the two nonattainment areas these counties should be placed.

 

4

2008-2010 ozone data used to compute the Design Value for Litchfield County is incomplete. 40 CFR part 50 Appendix P 

requires a monitoring site to meet a 3-year data completeness of 90 percent. The Litchfield County monitor is meeting a 3-

year data completeness of 89 percent.
5

Factor 2: Emissions and Emissions-Related Data

EPA evaluated emissions of ozone precursors (NOx and VOC) and other emissions-related data that 

provide information on areas contributing to violating monitors.

Emissions Data

EPA evaluated county-level emission data for NOx and VOC derived from the 2008 National Emissions 

Inventory (NEI), version 1.5. This is the most recently available NEI. (See

http://www.epa.gov/ttn/chief/net/2008inventory.html) Significant emissions levels in a nearby area 

would indicate the potential for the area to contribute to observed violations. We will also consider any 

additional information we receive on changes to emissions levels that are not reflected in recent 

inventories. These changes include emissions reductions due to permanent and enforceable emissions 

controls that will be in place before final designations are issued and emissions increases due to new 

sources.

Tables 3a and 3b show emissions of NOx and VOC (given in tons per year (tpy)) for violating and 

potentially contributing counties in the Connecticut Portion of the New York-Newark-Bridgeport, NYNJ-CT, and the Greater CT ozone nonattainment areas.

Table 3a. Total 2008 NOx and VOC Emissions in the Three Counties of the Connecticut Portion 

of the New York-Newark-Bridgeport, NY-NJ-CT Ozone Nonattainment Area

County State Recommended

Nonattainment?

NOx (tpy) VOC (tpy)

Fairfield Yes 24,983 22,700

New Haven Yes 20,789 19,705

Middlesex Yes 4,484 5,130

Three County Total: 50,256 47,535

Table 3b. Total 2008 NOx and VOC Emissions Greater Connecticut Ozone Nonattainment Area

County State Recommended

Nonattainment? NOx (tpy) VOC (tpy)

Hartford Yes 20,253 20,808

Litchfield Yes 3,429 6,115

New London Yes 8,558 9,160

Tolland Yes 3,553 3,764

Windham Yes 3,469 3,626

Areawide: 39,262 43,473

EPA believes that this factor is not important for purposes of determining in which of the two 

nonattainment areas these counties should be placed.
6

Population density and degree of urbanization

EPA evaluated the population and vehicle use characteristics and trends of the area as indicators of the 

probable location and magnitude of non-point source emissions. These include ozone-creating 

emissions from on-road and off-road vehicles and engines, consumer products, residential fuel 

combustion, and consumer services. Areas of dense population or commercial development are an 

indicator of area source and mobile source NOx and VOC emissions that may contribute to ozone 

formation. Rapid population or VMT growth (see below) in a county on the urban perimeter signifies 

increasing integration with the core urban area, and indicates that the associated area source and mobile 

source emissions may be appropriate to include in the nonattainment area. Tables 4a and 4b show the

population, population density, and population growth information for each county in the state.

Table 4a. Population and Growth in the Three Counties of the Connecticut Portion of the New 

York-Newark-Bridgeport, NY-NJ-CT Ozone Nonattainment Area

County

State 

Recommended 

Nonattainment?

2010 Population

2010 Population 

Density

(1000 pop/sq mi)

Absolute change 

in population

(2000-2010)

Population % 

change

(2000-2010)

Fairfield Yes 916,829 1.41 32,348 3.7

New Haven Yes 862,477 1.39 37,492 4.5

Middlesex Yes 165,676 0.43 10,061 6.5

Three County Total: 1,944,982 79,901

Sources: U.S. Census Bureau population estimates for 2010 as of August 4, 2011 

Table 4b. Population and Growth for the Greater Connecticut Ozone Nonattainment Area

County

State 

Recommended 

Nonattainment?

2010 

Population

2010 Population

 Density

(1000 pop/sq mi)

Absolute change

 in population

 (2000-2010)

Population 

% change

(2000-2010)

Hartford Yes 894,014 1.19 35,575 4.1

Litchfield Yes 189,927 0.20 7,313 4.0

New London Yes 274,055 0.39 14,519 5.6

Tolland Yes 152,691 0.37 15,839 11.6

Windham Yes 118,428 0.23 9,236 8.5

Areawide: 1,629,115 82,482

Sources: U.S. Census Bureau population estimates for 2010 as of August 4, 2011 

The population in the Connecticut Portion of the New York-Newark-Bridgeport, NY-NJ-CT Ozone 

Nonattainment Area is growing modestly and the population density is rather high, since the area 

includes the I-95 corridor. EPA believes that this factor is not important for purposes of determining in 

which of the two nonattainment areas these counties should be placed.

Traffic and commuting patterns

EPA evaluated the commuting patterns of residents in the area, as well as the total Vehicle Miles 

Traveled (VMT) for each county. In combination with the population/population density data and the 

location of main transportation arteries (Figure 1), this information helps identify the probable location 

of non-point source emissions. A county with high VMT is generally an integral part of an urban area 

and indicates the presence of motor vehicle emissions that may contribute to ozone formation. Rapid 

population or VMT growth in a county on the urban perimeter signifies increasing integration with the 

core urban area, and indicates that the associated area source and mobile source emissions may be 

appropriate to include in the nonattainment area. Tables 5a and 5b shows total 2008 VMT.
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Table 5a. Traffic for the Three Counties of the Connecticut 

Portion of the New York-Newark-Bridgeport, NY-NJ-CT 

 Ozone Nonattainment Area

County State Recommended 

Nonattainment?

2008 VMT*

(million miles)

Fairfield Yes 7,803

New Haven Yes 7,248

Middlesex Yes 1,394

Three County total: 16,445

* MOBILE model VMTs are those inputs into the NEI version 1.5. 

Table 5b. Traffic for the Greater Connecticut 

 Ozone Nonattainment Area

County State Recommended 

Nonattainment?

2008 VMT*

(million miles)

Hartford Yes 8,330

Litchfield Yes 1,258

New London Yes 2,916

Tolland Yes 1,499

Windham Yes 1,202

Areawide: 15,205

* MOBILE model VMTs are those inputs into the NEI version 1.5. 

EPA believes that this factor is not important for purposes of determining in which of the two 

nonattainment areas these counties should be placed.

Factor 3: Meteorology (weather/transport patterns)

EPA evaluated meteorological data to help determine how meteorological conditions, such as weather, 

transport patterns and stagnation conditions, would affect the fate and transport of precursor emissions 

contributing to ozone formation. During the ozone season the winds are generally southwesterly. The 

only area downwind of Connecticut that is recommended to be nonattainment is the Dukes County area 

of Massachusetts. 

EPA believes that this factor is not important for purposes of determining in which of the two 

nonattainment areas these counties should be placed.

Factor 4: Geography/topography (mountain ranges or other air basin boundaries)

The geography/topography analysis evaluates the physical features of the land that might affect the air

shed and, therefore, the distribution of ozone over the area. The Connecticut Portion of the New YorkNewark-Bridgeport, NY-NJ-CT ozone nonattainment area does not have any geographical or 

topographical barriers significantly limiting air pollution transport within its air shed. 

EPA believes that this factor is not important for purposes of determining in which of the two 

nonattainment areas these counties should be placed.
8

Factor 5: Jurisdictional boundaries

Once the general areas to be included in the nonattainment area were determined, EPA considered

existing jurisdictional boundaries for the purposes of providing a clearly defined legal boundary and 

carrying out the air quality planning and enforcement functions for nonattainment areas. Examples of 

jurisdictional boundaries include existing/prior nonattainment areas for ozone or other urban-scale 

pollutants, counties, air districts, townships, metropolitan planning organizations, state lines, urban 

growth boundary, etc. Where existing jurisdictional boundaries are not adequate to describe the 

nonattainment area, other clearly defined and permanent landmarks or geographic coordinates are

considered.

The Connecticut Portion of the New York-Newark-Bridgeport, NY-NJ-CT ozone nonattainment area

has previously established nonattainment boundaries associated with the 1997 8-hour ozone NAAQS. 

The state has recommended, in its most recent clarifying letter to EPA dated November 23, 2011, that 

the boundary for nonattainment areas for the 2008 ozone NAAQS be the same as those that exist for the 

1997 8-hour NAAQS. Connecticut’s reasoning was to “avoid unnecessary confusion among 

Connecticut’s regulated community and the general public that may otherwise result from having three 

distinct nonattainment area boundaries within Connecticut for the 2008 8-hour ozone NAAQ.” This is 

the most important factor for determining which Connecticut counties are to be in which Connecticut 

nonattainment area. 

There are no tribes in the three county area of Connecticut Portion of the New York-Newark-Bridgeport, 

NY-NJ-CT ozone nonattainment area.

EPA Position on the Connecticut Recommendation of a “Super-Regional” Ozone Nonattainment 

Area for the 2008 Ozone NAAQS

In a letter dated October 28, 2011, Connecticut recommended that EPA designate the entire State as part 

of a large multi-state nonattainment area including all or portions of 17 other states, and the District of 

Columbia. Section 107(d) of the Clean Air Act (CAA) requires EPA to designate as nonattainment all 

areas violating the ozone NAAQS and any nearby areas that are contributing to a violation in another 

area. Under the designation provision, only "nearby" areas that contribute to the violation must be 

included as part of the nonattainment area. There are other provisions of the CAA that address longer 

range transport of ozone pollutions, such as sections 110(a)(2)(D), 126, and 184. The phenomenon of 

ozone transport must be balanced against the need to have smaller areas that can focus on local control 

measures. We note that most of the States that Connecticut seeks to include as part of this large 

nonattainment area did not make a similar request. While a few other states did request that EPA 

designate a broad area in the eastern part of the United States as nonattainment, each of those 

recommendations varied from the others. In the absence of broad agreement among a large group of 

states to create such a large nonattainment area, demonstrating a commitment to work together to 

address both long-range and local transport of emissions, we do not intend to designate a large 

nonattainment area as suggested by Connecticut.

Conclusion

Based on the assessment of factors described above, especially Factor 5, EPA preliminarily proposes to 

keep the nonattainment boundaries in Connecticut the same for the 2008 ozone NAAQS as for the 1997 

ozone NAAQS, both to avoid confusion and for ease in planning, permitting, transition and enforcement

for the 2008 ozone NAAQS. EPA concludes that Connecticut’s Fairfield, New Haven, and Middlesex 
9

Counties meet the CAA criterion for inclusion as part of the tri-state New York-Newark-Bridgeport,

NY-NJ-CT ozone nonattainment area. The rest of Connecticut will also be nonattainment for the 2008 

ozone NAAQS, but part of another nonattainment area called Greater Connecticut. (See separate TSD 

for this area.)

Figure 1. Map of Connecticut Portion of the New York-Newark-Bridgeport, NY-NJ-CT Ozone 

Nonattainment Area