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Columbus, Ohio

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

Summary

The table below identifies the areas in Ohio that EPA is designating as “nonattainment” for the 

2008 8-hour ozone National Ambient Air Quality Standard (NAAQS)1 as part of the Columbus, 

Ohio (OH) nonattainment area. In accordance with section 107(d) of the Clean Air Act (CAA), 

EPA must designate an area (county or part of a county) as “nonattainment” if it is violating the 

2008 8-hour ozone NAAQS or if it is contributing to a violation of the 2008 ozone NAAQS in a 

nearby area. The technical analysis supporting the boundary for this ozone nonattainment area is 

provided below.

Table 1. Areas in Ohio Included in the Columbus, OH Ozone Nonattainment Area

Area Ohio Recommended 

Nonattainment Counties

EPA’s Nonattainment 

Counties

Columbus, OH Delaware

Fairfield

Franklin

Knox

Licking

Madison

Delaware

Fairfield

Franklin

Knox

Licking

Madison

EPA is designating as “unclassifiable/attainment” for the 2008 8-hour ozone NAAQS the 

remaining counties in Ohio that are not included in the table above or in the Cincinnati, OH-KYIN or Cleveland-Akron-Lorain, OH nonattainment areas (see separate Technical Support 

Documents for these areas).

The analysis below provides the basis for the Columbus, OH nonattainment area boundary. It 

relies on our analysis of whether and which monitors are recording violations of the 2008 ozone 

NAAQS, based on certified air quality monitoring data from 2008-2010 and on 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. 

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 designation recommendations to EPA.2

 

1 The primary 8-hour ozone standard, set to protect human health was revised on March 27, 2008 (73 FR 16436) 

from 0.08 parts per million (ppm) to 0.075 ppm. The secondary ozone standard, set to protect human welfare and 

the environment, was revised to be consistent with the primary ozone standard.

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-Related Data,” which results in 5 categories of 

factors.
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1. Air quality data (including the ozone design value calculated for each Federal Reference 

Method (FRM) or Federal Equivalent Method (FEM) monitor in the area);

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

of emissions and emission controls, and growth patterns);

3. Meteorology (weather/transport patterns);

4. Geography and topography (mountain ranges and other basin boundaries affecting ozone 

levels and ozone precursor transport); and,

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

Indian country, Metropolitan Planning Organization (MPOs) and their covered area).

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

reactions involving Nitrogen Oxides (NOx) and Volatile Organic Compounds (VOC) in the 

presence of sunlight.3

 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).4

 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. Congress required a similar approach in 1990 for areas classified as 

serious and above for the 1-hour ozone standard and EPA used the same approach in the 

designation process for the 1997 ozone NAAQS. Where a violating monitor is not located in a 

CSA or CBSA, EPA’s September 4, 2008 guidance recommends using the boundary of the 

county containing the violating monitor as the starting point for considering the nonattainment 

area’s boundary.

Technical Analysis for Columbus-Marion-Chillicothe, OH

Figure 1 is a map of the intended Columbus, OH ozone nonattainment area for the 2008 ozone 

NAAQS. The map provides other relevant information, including the locations and ozone design 

values of air quality monitors recording violations of the 2008 ozone NAAQS, county and other 

jurisdictional boundaries, existing maintenance boundary for the 1997 ozone NAAQS, 

Columbus-Marion-Chillicothe, OH CSA boundary and major transportation arteries.

 

3 Peak ozone concentrations generally occur downwind of source areas on relatively sunny days with high 

temperatures and relatively low wind speeds.

4 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).
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Figure 1. Columbus, OH Area

For purposes of the 1997 ozone NAAQS, as noted in Figure 3, portions of this area were 

designated nonattainment and subsequently redesignated to attainment (maintenance). The 

boundary for the nonattainment area for the 1997 ozone NAAQS included only a portion of the 

Columbus-Marion-Chillicothe, OH CSA. In March 2009, Ohio recommended that the same 

counties (the same counties included in the nonattainment area for the 1997 ozone NAAQS) in 

Ohio be designated as nonattainment for the 2008 ozone NAAQS based on air quality data from 

2006-2008 and other considerations. The 2006-2008 ozone data are from monitors sited and 

operated in accordance with 40 CFR part 58.

After considering these recommendations and based on EPA’s technical analysis described

below, EPA is designating the same 6 counties in Ohio (identified in Table 2 below) as 

“nonattainment” for the 2008 ozone NAAQS as part of the Columbus, OH nonattainment area.
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Table 2. EPA’s Selected Nonattainment Counties for the Columbus, OH Ozone 

Nonattainment Area

State-Recommended Nonattainment 

Counties in Columbus, Ohio

EPA Intended Nonattainment Counties in 

Columbus, Ohio

Delaware

Fairfield

Franklin

Knox

Licking

Madison

Delaware

Fairfield

Franklin

Knox

Licking

Madison

Factor Assessment

Factor 1: Air Quality Data

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

counties in the Columbus-Marion-Chillicothe, OH CSA based on data for the 2008-2010 period, 

which are the most recent years with fully-certified air quality data. As discussed above, a 

monitor’s design value is the metric or statistic that indicates whether that monitor attains a 

specified air quality standard. The 2008 ozone NAAQS are met at a monitor when the annual 

fourth-highest daily maximum 8-hour ozone concentrations, averaged over 3 years is 0.075 ppm 

or less. A design value is valid only if minimum data completeness requirements are met. See

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

designated nonattainment area or maintenance area), the design value for the county or area is 

determined by the monitor with the highest individual design value.

The ozone design values for ozone monitors in the Columbus-Marion-Chillicothe, OH CSA are 

shown in Table 3.

Table 3. Ozone Air Quality Data for the Columbus-Marion-Chillicothe, OH CSA

County Site Number 2008-2010 8-

Hour Ozone 

Design 

Values 

(ppm)

Delaware 390410002 0.073
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Franklin 390490081 0.069

Franklin 390490037 0.071

Franklin 390490029 0.078†

Knox 390830002 0.071

Licking 390890005 0.072

Madison 390970007 0.070

† Monitored violation of the 2008 ozone NAAQS.

From Table 3, it can be seen that Franklin County is the only county in the Columbus-MarionChillicothe, OH CSA with a monitored violation of the 2008 ozone NAAQS for the period of 

2008-2010. Therefore, at minimum, Franklin County must be included in the ozone 

nonattainment area. As noted above, a county (or partial county) must also be designated 

nonattainment if it contributes to an air quality violation in a nearby area (to the violation of the 

2008 ozone NAAQS recorded in Franklin County). Each county in the Columbus-MarionChillicothe, OH CSA has been evaluated, as discussed below, based on the five factors 

discussed above and other relevant information to determine whether it contributed to the 

violation of the 2008 ozone NAAQS in Franklin County.

Please note that the State of Ohio, in its March 9, 2009 area designation recommendations and 

accompanying technical support documentation, based its area recommendations on 2006-2008 

ozone data. Since these data no longer cover the most recent 3-year period with quality-assured, 

state-certified data and have been supplanted by the more current 2008-2010 ozone data, we are 

not reviewing the older ozone data covered by the state of Ohio.

Factor 2: Emissions and Emissions-Related Data

EPA evaluated emissions for VOC and NOx and other emissions-related data (primarily county 

population, population density, and traffic levels, and projected growth rates for these emissionsrelated data) that provide information on area contributions to local ozone standard violations.

EPA’s Accumulated Emissions and Emissions-Related Data

Emissions Data

EPA evaluated county-level emission data for NOx and VOC derived from the 2008 NEI, 

version 1.5. These are the most recently available NEI emissions data. (See 

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

area (in a county near to a county with a violating ozone monitor) indicate the potential for the 

area to contribute to the observed ozone standard violation. 

Table 4 shows the 2008 emissions of NOx and VOC (in tons per year) for all counties in the 

Columbus-Marion-Chillicothe, OH CSA. This table also indicates which of the counties were 

recommended to be nonattainment for the 2008 ozone NAAQS by the State of Ohio.
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Table 4. Total 2008 VOC and NOx Emissions (tons/year) in the Columbus-MarionChillicothe, OH CSA

State/County State Recommended 

Nonattainment?

VOC Emissions

(tpy)

NOx Emissions

(tpy)

Ohio:

Delaware Yes 5,686 5,655

Fairfield Yes 4,459 4,915

Fayette No 1,887 1,981

Franklin Yes 38,690 32,092

Knox Yes 2,324 1,539

Licking Yes 7,016 6,008

Madison Yes 2,373 2,809

Marion No 3,588 3,509

Morrow No 1,983 2,190

Pickaway No 2,969 3,919

Ross No 3,292 5,010

Union No 3,404 2,413

CSA Total 77,671 72,041

From the emissions data in Table 4, it can be seen that the VOC and NOx emissions in the 

Columbus-Marion-Chillicothe, OH CSA are dominated by those in Franklin County. The VOC 

emissions in Franklin County are 49.8 percent of the CSA total, and the NOx emissions in 

Franklin County are 44.5 percent of the CSA total. All other counties in this CSA have 

significantly lower and similar (to each other) VOC and NOx emissions. However, the 

accumulative VOC and NOx emissions in these remaining counties is a significant portion of the 

total VOC and NOx emissions in the CSA. 

The high emissions in Franklin County, along with the monitored violation of the 2008 ozone 

NAAQS in this county, implies that Franklin County should be part of the nonattainment area for 

the 2008 ozone NAAQS. In addition, the VOC and NOx emissions in Delaware, Fairfield, and 

Licking Counties are moderately high, which, coupled with the proximity of these counties to the 

violating ozone monitoring site, favors the inclusion of these counties in the ozone nonattainment 

area.

Population, 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 ozonecreating 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, which 

can contribute to local and downwind high ozone concentrations. Rapid population or VMT 

growth in a county on the urban perimeter signifies increasing integration with the urban core 
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area, and indicates that it may be appropriate to include this county in the ozone nonattainment 

area, particularly if this county already has moderate or higher VOC and/or NOx emissions.

Table 5 shows the 2010 population, population density, and population growth information for 

each county in the Columbus-Marion-Chillicothe, OH CSA.

Table 5. Population and Population Growth in the Columbus-Marion-Chillicothe, OH 

CSA

State/County State 

Recommended 

Nonattainment?

2010 

Population

2010 

Population 

Density 

(1,000 per 

square mile)

Change in 

Population 

(2000-2010)

Population 

Percent 

Change 

(2000-2010)

Ohio:

Delaware Yes 174,214 0.38 62,504 56

Fairfield Yes 146,156 0.29 22,736 18

Fayette No 29,030 0.07 595 2

Franklin Yes 1,163,414 2.14 91,127 8

Knox Yes 60,921 0.12 6,278 11

Licking Yes 166,492 0.24 20,421 14

Madison Yes 43,435 0.09 3,223 8

Marion No 66,501 0.16 351 1

Morrow No 34,827 0.09 3,033 10

Pickaway No 55,698 0.11 2,882 5

Ross No 78,064 0.11 4,614 6

Union No 52.300 0.12 11,105 27

CSA Totals 2,071,052 0.34 228,869 12

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

(http://factfinder2.census.gov/faces/tableservices/jsf/pages/productview.xhtml?pid=DEC_10_PL

_GCTPL2.STO5&proType=table)

The population data show that half of the 2010 population and almost half of the 2000-2010 

population growth in the Columbus-Marion-Chillicothe, OH CSA can be found in Franklin 

County. Comparatively large 2010 populations and 2000-2010 population growths can also be 

found in Delaware, Fairfield, and Licking Counties. The 2010 populations in the remaining 

counties in the CSA are comparatively smaller. Union County has a comparatively high 

population growth percentage, however, its 2010 population is small compared to those of 

Delaware, Fairfield, Franklin, and Licking Counties. Finally, the 2010 populations and 2000-

2010 population growths of Fayette and Marion Counties are comparatively lower than those of 

other counties in the Columbus-Marion-Chillicothe, OH CSA.

Traffic and Commuting Patterns
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EPA evaluated the commuting patterns of residents in the Columbus-Marion-Chillicothe, OH 

CSA. In combination with the county-specific population/population density data and the 

locations of the main transportation arteries (see above), this information helps identify the 

probable locations of non-point source emissions. A county with high VMT and/or a high 

number of commuters is generally an integral part of an urban area and indicates the presence of 

relatively high motor vehicle emissions that may significantly contribute to ozone standard 

violations in or downwind of the urban area. Rapid population or VMT growth in a county on 

the urban perimeter signifies increasing integration with the urban core area, and indicates that 

this county should be included in the ozone nonattainment area, particularly if the VOC and/or 

NOx emissions in this county are a significant portion of the total emissions in the nonattainment 

area.

Table 6 shows the traffic levels, 2008 VMT, in each county in the Columbus-Marion-Chillicothe, 

OH CSA.

Table 6. Traffic Levels in the Columbus-Marion-Chillicothe, OH CSA

State/County State Recommended 

Nonattainment?

2008 VMT (million miles)

Ohio:

Delaware Yes 1,530

Fairfield Yes 1,035

Fayette No 505

Franklin Yes 10,645

Knox Yes 397

Licking Yes 1,780

Madison Yes 704

Marion No 629

Morrow No 605

Pickaway No 648

Ross No 772

Union No 630

CSA Total 19,881

The VMT data show that county-specific VMT levels are the highest in Delaware, Franklin, 

Fairfield, and Licking Counties. These VMT account for 75.4 percent of the total VMT in the 

Columbus-Marion-Chillicothe, OH CSA. 

The VMT data plus the population data in Table 19 indicate that Delaware, Fairfield, Franklin, 

and Licking Counties are relatively urbanized with significant population- and traffic-related 

emissions that contributed to the ozone standard violation in Franklin County. This contribution 

is much smaller for the remaining counties in the Columbus-Marion-Chillicothe, OH CSA.
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Additional Emissions-Related Data Discussed in Ohio’s March 9, 2009 Designation 

Recommendation Submittal

OEPA has provided typical daily, county-specific total VOC and NOx emissions for 2005 and 

2009 for each of the counties in the Columbus-Marion-Chillicothe, OH CSA. These data 

confirm the conclusions we have drawn above using county-specific annual emissions. 

OEPA has provided population projections through 2030 for each of the counties in the CSA. 

Populations are projected to increase significantly in Delaware, Fairfield, Franklin, Licking, 

Medina, Morrow, Pickaway, Ross, and Union Counties. Populations are projected to increase 

moderately in Fayette and Marion Counties. Populations are expected to decline in Knox 

County.

OEPA provided graphs of daily VMT levels plotted for the period of 1990-2007 for each of the 

counties in the CSA. This visual VMT trend information shows that daily VMT grew 

significantly during the 1990-2007 period for Delaware, Fairfield, Franklin, Licking and Morrow 

Counties. The VMT trend information shows that daily VMT grew moderately during the 1990-

2007 period for Knox, Marion, Pickaway (VMT levels remained substantially unchanged after 

1999 in this county), and Ross Counties.

OEPA provided inter-county commuter numbers and percentages for each of the counties in the 

Columbus-Marion-Chillicothe, OH CSA. These numbers show a moderate to high inter-county 

commuting pattern between Franklin County and other counties (with the exceptions of Fayette, 

Knox, Ross, Marion, and Morrow Counties) in the Columbus-Marion-Chillicothe, OH CSA. 

Inter-county commuter numbers between other counties (other than Franklin County) in the CSA 

are moderate to small.

Collectively, the OEPA-supplied population and traffic/commuter data show moderate 

integration between Franklin, Delaware, Fairfield, Licking, Medina, Morrow, Pickaway, Ross, 

and Union Counties. Less integration is apparent between Franklin, Fayette, Knox, and Marion 

Counties. 

Factor 3: Meteorology (Weather/Transport Patterns)

EPA’s Accumulated Meteorological Data

EPA evaluated available meteorological data to help determine how meteorological conditions, 

particularly transport conditions, affect the fate and transport of ozone and ozone precursors 

contributing to ozone formation in the Columbus-Mario-Chillicothe, OH CSA. EPA examined 

the frequency distribution of wind directions for the four seasons of the year by averaging 

National Weather Service direction-sorted wind directions for each county for a 30-year period. 

To apply the results of this data analysis to the Columbus-Marion-Chillicothe, OH CSA, we have 

considered the wind direction (direction from which winds are blowing, reflecting directions to 

potential source areas) frequencies during the summer months (June-August) for Franklin 

County, which is the only county in the CSA with a monitored violation of the 2008 ozone 

NAAQS (See Table 17). 
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Table 7 shows the summertime 30-year averaged percentages of wind directions (winds blowing 

into the subject county from the specified wind direction sector) for Franklin County.

Table 7. Averaged Summertime Wind Direction Percentages For Franklin County

Wind Direction Franklin County

North-Northeast 15.3

East-Northeast 9.6

East-Southeast 11.4

South-Southeast 12.0

South-Southwest 22.0

West-Southwest 11.0

West-Northwest 9.7

North-Northwest 9.0

The wind direction percentages show that there is no single “preferred” wind direction during the 

summertime, when the highest ozone concentrations are generally monitored. Winds from 

south-southwest may be more prevalent than the winds from other wind directions during the 

summertime.

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 airshed and, therefore, the distribution of ozone over the area.

The Columbus-Marion-Chillicothe, OH CSA does not have any geographical or topographical 

barriers significantly limiting air pollution transport within its air shed. Therefore, this factor did 

not play a significant role in this evaluation.

Factor 5: Jurisdictional Boundaries

Once we identified the general area that we anticipated we would recommend as nonattainment 

for the 2008 ozone NAAQS, we then considered existing jurisdictional boundaries for the 

purposes of providing a clearly defined legal boundary and to help identify the area appropriate 

for carrying out the air quality planning and enforcement functions for an ozone nonattainment 

area. Examples of jurisdictional boundaries include existing/prior nonattainment boundaries for 

ozone or other urban-scale pollutants, county boundaries, air district boundaries, township 

boundaries, areas covered by metropolitan planning organizations, state lines, and Reservation 

boundaries. Where existing jurisdictional boundaries are not adequate or appropriate to describe 

the nonattainment area, other clearly defined and permanent landmarks or geographic 

coordinates may be considered.

The portion of the Columbus-Marion-Chillicothe, OH CSA that we have selected for designation 

as nonattainment for the 2008 ozone NAAQS has a previously established nonattainment 

boundary associated with the 1997 8-hour ozone NAAQS. The State of Ohio has recommended 
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the same counties (as included in the 1997 8-hour ozone nonattainment area) in Ohio be included 

in the boundary of the nonattainment area for the 2008 ozone NAAQS. The prior inclusion of 

these counties in the ozone nonattainment area for the 1997 ozone NAAQS forms the primary 

jurisdictional basis for the inclusion of these counties in the nonattainment area for the 2008 

ozone NAAQS.

Conclusion

Based on the assessment of factors described above, EPA has concluded that the following Ohio 

counties should be included in the Columbus, OH ozone nonattainment area because they are 

either violating the 2008 ozone NAAQS or are contributing to a violation of the 2008 ozone 

NAAQS within this intended ozone nonattainment area: Delaware; Fairfield; Franklin; Knox; 

Licking; and, Madison.

The results of our factor review above show that Delaware, Fairfield, Franklin and Licking 

Counties should be included in the Columbus, OH ozone nonattainment area on the bases of a 

violation of the 2008 ozone NAAQS and/or significant emissions that contribute to the violation 

of the 2008 ozone NAAQS.

We note that the State of Ohio has also recommended the inclusion of Knox and Madison 

Counties in the ozone nonattainment area for the 2008 ozone NAAQS. We accept the State’s 

recommendation and have included these counties in the ozone nonattainment area.