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Technical Support Document (TSD)

Michigan

Area Designations For the 

2010 SO2 Primary National Ambient Air Quality Standard

Summary

Pursuant to section 107(d) of the Clean Air Act (CAA), EPA must designate areas as either 

“nonattainment,” “attainment,” or “unclassifiable” for the 2010 one-hour sulfur dioxide (SO2) 

primary national ambient air quality standard (NAAQS). The CAA defines a nonattainment area 

as one that does not meet the NAAQS or that contributes to poor air quality in a nearby area that 

does not meet the NAAQS. Table 1 below identifies the counties or portions of counties (or 

tribal areas) in Michigan that EPA intends to designate “nonattainment” for the primary 2010 

SO2 NAAQS.

Michigan submitted designation recommendations on June 1, 2011. On February 6, 2013, EPA 

sent a letter with intended designations for Michigan. Michigan did not respond to EPA’s 

intended designation. Table 1 below lists Michigan’s recommendations and identifies the 

counties or portions of counties in Michigan for areas that EPA is initially designating

“nonattainment” based on monitored violations. EPA is not yet prepared to designate other areas 

in Indiana, and will address such areas and their sources in a subsequent round of final 

designations.

Table 1. Nonattainment Area Designations for Michigan

Area Michigan’s Recommended 

Designations of Areas/Counties

EPA's Designation of 

Areas/Counties

Detroit, MI

 Wayne County (partial)

 -An area bounded on the east 

 by the Michigan- Ontario 

 border, on the south by the 

 Wayne County-Monroe County

 border, on the west by Interstate

 75 north to Southfield Road, 

 Southfield Road to Interstate 

 94, and Interstate 94 north to 

 Michigan Avenue, and on the

 north by Michigan Avenue to 

 Woodward Avenue and a line 

 on Woodward Avenue extended

 to the Michigan-Ontario border

Nonattainment Nonattainment
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Background

On June 3, 2010, EPA revised the primary SO2 NAAQS (75 FR 35520, June 22, 2010) by 

establishing a new 1-hour standard at a level of 75 parts per billion (ppb), which is met at an 

ambient air quality monitoring site when the 3-year average of the annual 99th percentile of the 

daily maximum 1-hour average concentration at each monitor in an area does not exceed 75 ppb, 

as determined in accordance with Appendix T of 40 CFR part 50. 40 CFR 50.17(a)-(b). EPA 

has determined that this is the level necessary to provide protection of public health with an 

adequate margin of safety, especially for children, the elderly and those with asthma. These 

groups are particularly susceptible to the health effects associated with breathing SO2. The 

Agency is revoking the two prior primary standards of 140 ppb evaluated over 24-hours, and 30 

ppb evaluated over an entire year because the standards will not add additional public health 

protection given a 1-hour standard at 75 ppb. Accordingly, EPA is not designating areas in this 

process on the basis of either of these two prior primary standards. Similarly, the secondary 

standard for SO2 has not been revised, so EPA is not designating areas in this process on the 

basis of the secondary standard.

EPA’s SO2 Designation Approach

Section 107(d) of the CAA provides that not later than 1 year after promulgation of a new or 

revised NAAQS, state Governors may submit their recommendations for designations and 

boundaries to EPA. For the 2010 SO2 NAAQS, this deadline was June 3, 2011. Section 107(d) 

also requires EPA to provide a notification to states of no less than 120-days prior to 

promulgating an initial area designation that is a modification of a state’s recommendation. 

EPA has reviewed the State’s recommendations and has notified the State Commissioner through 

letter signed by the Regional Administrator of any intended modifications. [While language in 

section 107 specifically addresses states, we intend to follow the same process for tribes, 

pursuant to section 301(d) of the CAA and Tribal Authority Rule (40 CFR Part 49). Therefore, 

we intend to designate tribal areas, in consultation with the tribes, on the same schedule as state 

designations.] If a State or Tribe did not submit designation recommendations, EPA is to

promulgate the designations that it deems appropriate. If a state or tribal government disagrees 

with EPA’s intended area designations, it had an opportunity to demonstrate why any proposed 

modification is inappropriate. 

Designations guidance was issued by EPA through a March 24, 2011, memorandum from 

Stephen D. Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air 

Division Directors, U.S. EPA Regions I-X. This memorandum identifies factors EPA intends to 

evaluate in determining boundaries for areas designated nonattainment. These 5 factors include: 

1) Air quality data; 2) Emissions and emissions-related data (location of sources and potential 

contribution to ambient SO2 concentrations); 3) Meteorology (weather/transport patterns); 4) 

Geography/topography (mountain ranges or other air basin boundaries); and 5) Jurisdictional 

boundaries (e.g., counties, air districts, pre-existing nonattainment areas, reservations, 

metropolitan planning organization), among any other information deemed relevant to 

establishing appropriate area designations and boundaries for the 1-hour SO2 NAAQS.
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The March 24, 2011, designations guidance memo recommended that area boundaries be 

defaulted to the county boundary unless additional provided information justifies a larger or 

smaller boundary than that of the county. EPA believes it is appropriate to evaluate each 

potential area on a case-by-case basis, and to recognize that area-specific analyses conducted by 

states, tribes and/or EPA may support a different boundary than a default county boundary.

In this TSD, EPA discusses its review and technical analysis of the recommendations submitted 

by Michigan for designations of the 1-hour SO2 standard and any modifications from these 

recommendations.

Definition of important terms used in this document:

1) Designated nonattainment area – an area which EPA has determined, based on a state 

recommendation and/or on the technical analysis included in this document, has violated the 

2010 SO2 NAAQS, based on the most recent three years of air quality monitoring data from 

2009-2011, or contributes to a violation in a nearby area. 

2) Recommended nonattainment area – an area that a state or tribal government has 

recommended to EPA to be designated as nonattainment.

3) Violating monitor – an ambient air monitor meeting all methods, quality assurance and citing 

criteria and requirements whose valid design value exceeds 75 ppb, as described in Appendix T 

of 40 CFR part 50.

4) 2010 SO2 NAAQS - 75 ppb, national ambient air quality standard for SO2 promulgated in 

2010. Based on the 3-year average of the 99th percentile of the annual distribution of daily 

maximum 1-hour average concentrations

5) Design Value – a statistic computed according to the data handling procedures of the 

NAAQS (in 40 CFR 50 Appendix T) that, by comparison to the level of the NAAQS, indicates 

whether the area is violating the NAAQS.

Technical analysis for the Detroit, MI Area

Introduction

This technical analysis for the Detroit, MI area identifies Wayne County with a monitor that 

violates the 2010 SO2 NAAQS, and evaluates nearby counties for contributions to SO2

concentrations in the area. EPA has evaluated this county and nearby counties based on the 

evidence for the factors recommended in the March 24, 2011 EPA guidance.
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Figure 1 is a map of the area showing the locations and design values of air quality monitors in 

the area, and the counties surrounding any violating air quality monitors. Notably, a monitor at 

Southwest High School in Detroit recorded a 2009 to 2011 design value of 90 ppb. One other 

monitor operates in the area, at Allen Park, also in Wayne County, about 12 kilometers to the 

southwest. The Allen Park monitor recorded a 2009 to 2011 design value of 49 ppb. 

Figure 1. Map of sources and monitors in the Detroit, MI area and the Detroit nonattainment area

Michigan analyzed the sources that might be contributing to the violation at Southwest High 

School. This assessment identified a series of major sources located south of downtown Detroit 

and within a few kilometers of the Detroit River. Based on this assessment, Michigan’s June 1, 

2011, submittal recommended designating a nonattainment area bordered by the MichiganOntario border (in the Detroit River) on the east, the Wayne-Monroe county border on the south, 

Interstate 75, Southfield Road and Interstate 94 on the west, and Michigan Avenue on the north. 

Since Michigan Avenue does not extend fully to the Michigan-Ontario border, Michigan 

subsequently clarified that its recommended nonattainment area should be considered to be 

bounded by Michigan Avenue from Interstate 94 to Woodward Avenue and by Woodward 

Avenue and an extending line as if Woodward Avenue extended to the Michigan-Ontario border. 

Michigan’s recommended nonattainment area averages approximately 6 kilometers east-west 

and about 40 kilometers north-south.

Based on EPA's technical analysis described below, EPA is initially designating a Detroit, MI

nonattainment area for the 2010 SO2 NAAQS with the boundaries recommended by Michigan. 

Areas and sources that we are not yet prepared to conclude are contributing to the monitored 
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violations or to possible other violations are not included in this initial nonattainment area, and 

will be addressed in a subsequent round of designations.

Detailed Assessment

Air Quality Data 

This factor considers the SO2 air quality monitoring data, including the design values (in ppb) 

calculated for all air quality monitors in the Detroit area based on data for the 2009-2011 period.

The 2010 SO2 NAAQS design values for the Detroit, MI area in Michigan are shown in Table 2.

Table 2. Air Quality Data in the Detroit Area

County State Recommended

Nonattainment?

Monitor Air Quality 

System ID

Monitor Location SO2 Design Value, 

2009-2011 (ppb)

Wayne Yes 26-163-0015 42.3028, -83.1065 90

Included in area 26-163-0001 42.2286, -83.2082 49

Monitor in Bold has the highest 2009-2011 design value in the county.

The Southwest High School monitor (Monitor Air Quality System ID 26-163-0015) in Wayne 

County shows a violation of the 75 ppb 2010 SO2 NAAQS. 

Emissions and Emissions-Related Data

Evidence of SO2 emissions sources in the vicinity of a violating monitor is an important factor 

for determining whether a nearby area is contributing to a monitored violation. For this factor, 

EPA evaluated county level emission data for SO2 and any growth in SO2 emitting activities

since the date represented by those emissions data.

Emissions

The most recent year for which national emissions information was compiled was 2008. 

Michigan provided emissions data for 2009 generally showing emissions similar to 2008 

emissions. Therefore, EPA primarily relied on the 2008 National Emissions Inventory (NEI)

emissions data (NEI08V3). 

Table 3 shows total emissions of SO2 (given in tons per year) for major sources in Wayne 

County and for sources emitting over 1000 tons per year in adjoining Monroe and St. Clair 

Counties. Table 3 also shows pertinent information for sources in these counties emitting greater 

than 100 tons per year of SO2 according to the 2008 NEI. 
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Table 3. SO2 Emissions in the Detroit Area (NEI08V3)

County Facility in 

State 

Recommen

ded N.A. 

Area?

Facility Emissions 

NEI08V3

(tons per 

year)

Facility Location Distance 

to SWHS

monitor 

(km)

Total County 

SO2 Emissions 

(tons per year)

Wayne Yes DTE Trenton 

Channel 

27,622 42.1237, -83.1812 21 55,660

Yes DTE River Rouge 14,491 42.2727, -83.1124 3

Yes USS Great Lakes 6,755 42.2817, -83.1102 2

Yes Wyandotte Muni 1,793 42.2082, -83.1456 11

No GM Hamtramck 566 42.3820, -83.0449 10

Yes Severstal 558 42.3032, -83.1655 5

Yes Dearborn Industrial 

Generation

401 42.3026, -83.154 4

Yes Carmeuse 

Lime/River Rough

395 42.2774, -83.128 3

No Detroit WTP 225 42.2217, -83.3622 23

No Detroit Resource 

Recovery

200 42.3686, -83.0517 7

Monroe No DTE Monroe 118,382 41.8917, -83.3461 54 135,789

No J.R. Whiting 9,260 41.7917, -83.4486 63

No Holcim Cement 7265 41.9933, -83.6596 57

St. Clair No Belle River power 

plant

62,114 42.7748, -82.4945 73 64,392

No E.B. Eddy Paper 1,019 42.9865, -82.4415 93

All of the largest sources in Wayne County are located within the recommended nonattainment 

area. Three sources in Wayne County emitting over 100 tons per year are located outside the 

recommended nonattainment area. Based on the emissions from these relatively smaller sources

and their distance from the violating monitor, EPA is not yet prepared to conclude that the 

emissions from these three sources contribute to the monitored violation or to other possible 

violations. These sources will be addressed in a subsequent round of designations.

Monroe County has a power plant with by far the most emissions of any facility in the area based 

on the NEI08V3. This facility is also located at a substantial distance from the violating monitor. 

Using emissions divided by distance as a rough indicator of impacts, this facility is likely to have 

less impact than DTE’s River Rouge plant and USS’ Great Lakes Works but more impact on the 

violating monitor’s design value than other sources in the area. Thus, full consideration of the 

impact of this plant requires consideration of recent emission controls at this plant. The other 

plant in Monroe County and the plant in St. Clair County are at even greater distances and are 

less likely to be contributing to the violating monitor’s design value.

Emissions Controls

The emissions data used by EPA in this technical analysis and provided in Table 3 represent 

emissions levels taking into account any control strategies implemented on stationary sources in 

this area up to and including 2008. Michigan did not provide any additional information on 
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emissions reductions resulting from controls put into place after 2008. However, EPA examined 

emissions data submitted into EPA’s Clean Air Markets database for the Monroe power plant. 

These data show that this facility installed wet limestone scrubbing systems on two of its four 

units in 2009, reducing SO2 emissions from the 2008 level of 118,382 tons to a 2010 level of 

47,608 tons. Emissions in 2011 from this facility were similar to its emissions in 2010. Given 

this decline in emissions, and the distance of the facility from the monitor, the Monroe plant is 

likely to have significantly less impact on the monitor’s design value than sources in Wayne 

County that are much closer to the violating monitor. 

Based on information above for the sources in Monroe County and St. Clair County, we are not 

yet prepared to conclude that the emissions from these sources contribute to the monitored 

violation or that the sources may be considered nearby. We will further address these sources in 

a subsequent round of designations.

Meteorology (weather/transport patterns)

Evidence of source-receptor relationships between specific emissions sources and high SO2

values at violating monitors is another important factor in determining the appropriate 

contributing areas and the appropriate extent of the nonattainment area. Figure 2 shows the 

prevalent wind direction for the Detroit area. 

Figure 2: Wind Rose for Detroit, MI

Source: MDEQ Software: WRPLOT-Lakes Environmental Software

The wind rose above shows that winds are most likely to come from the southwest but also 

frequently come from all the western directions, and occasionally from the other directions. This 

shows that a source from any direction could contribute to the violation at the monitor. All of 

the largest emitters in the area, including DTE Trenton Channel, DTE River Rouge, and USS 
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Great Lakes, are located to the south and southwest of the monitor, which are the most frequent 

wind directions. 

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

The Detroit area does not have any geographical or topographical barriers significantly limiting 

air pollution transport within its airshed. Therefore, this factor did not play a significant role in 

determining the nonattainment boundary.

Jurisdictional boundaries 

Once the geographic area associated with the area violating the SO2 standard and the nearby 

areas contributing to the monitored violations are determined, we considered existing 

jurisdictional boundaries for the purpose of providing a clearly defined legal boundary for 

carrying out the air quality planning and enforcement functions for the area. Michigan does not 

have any pre-existing SO2 nonattainment area boundaries under the prior NAAQS. 

Nonattainment areas in Michigan for other pollutants have often been defined on the basis of 

roadways, and roadways in Michigan have well established locations and are a suitable basis for 

defining nonattainment areas. Therefore, EPA used roadways in defining the nonattainment 

boundary for the Detroit area. The boundary for the Detroit nonattainment area is provided in 

Table 1 above.

Other Relevant Information

EPA did not receive additional information relevant to establishing a nonattainment area 

boundary for this area.

Conclusion

The air quality monitor located at Southwest High School shows a violation of the 2010 SO2 

NAAQS, based on 2009-2011 air quality data. The nonattainment area recommended by 

Michigan includes the violating monitor and sources that are likely to be contributing to the 

violating monitor’s design value. While a large source is located in Monroe County south of the 

recommended nonattainment area, this source has recently installed significant emission 

controls, and the source is sufficiently distant from the violating monitor to warrant not including 

it in the initial nonattainment area based on the monitored violation, as we are not yet prepared to 

conclude that it is a nearby source contributing to that violation. This source will be further 

addressed in a subsequent round of designations.

Other sources outside Michigan’s recommended nonattainment area are also less likely to be 

having a significant impact on the violating monitor’s design value, and we are similarly not yet 

prepared to conclude that these sources are contributing to the monitored violation. We will also 

further address these sources in a subsequent round of designations. Therefore, EPA is initially 

designating a Detroit, MI nonattainment area using the boundaries recommended by Michigan.

In a subsequent round of designations, we will make final designation decisions for areas in 

Michigan not included in the nonattainment area designation addressed in this TSD.