Attachment A

The State of Wyoming 2008 8-Hour Ozone Infrastructure SIP

Element 110(a)(2)(D)(i)(I) Support Documents
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Attachment A

Interstate and International Transport Provisions for the 2008 8-Hour Ozone NAAQS

The Wyoming Department of Environmental Quality-Air Quality Division (AQD) has identified 

nearby nonattainment areas from the U.S. Environmental Protection Agency’s (EPA’s) map of 8-

Hour Ozone Nonattainment Areas (Figure 1) and evaluated the potential likelihood of impact 

from emissions in Wyoming to those nonattainment areas. The only ozone nonattainment area 

identified is the Denver-Boulder-Greeley-Ft. Collins-Loveland, Colorado nonattainment area 

(Denver NAA). The Denver NAA is designated as “marginal” nonattainment for the 2008 8-

hour ozone National Ambient Air Quality Standard (NAAQS). A “marginal” rating is the least 

significant rating of nonattainment possible. 

The primary objective of the Cheyenne NCore Multi-Pollutant Monitoring Project is to obtain 

ambient air quality and meteorological data for the purposes of incorporating it into the EPA’s 

National Core (NCore) Monitoring Network. NCore monitoring methods and strategies focus on 

the deployment of instrumentation to target air pollutants originating from the Cheyenne area, 

their concentrations, and their direction and extent of travel. As seen in Figure 2, the Cheyenne 

NCore ambient air and meteorological monitoring station is centrally located in the city of 

Cheyenne, Wyoming in the extreme southeastern portion of the State. Cheyenne is also the 

closest capital city in Wyoming with an approximate county-wide population of 91,000 citizens 

(Figure 3) within proximity to the Denver NAA that hosts an expansive approximate population 

of 3 million (Figure 3). The Denver NNA is located approximately 30 miles directly south of the 

southeastern Wyoming border (Figures 4 and 5). 

Meteorological data collected along with air quality parameters at the Cheyenne NCore 

monitoring station are used to better understand the local conditions and transport of air 

pollutants. The 2011 annual and quarterly wind roses produced for the Wyoming Air Quality 

Monitoring Network Annual Summary at the Cheyenne NCore Soccer Complex monitoring 

station (Figures 6 and 7), and a composite wind rose from Cheyenne for the years 2006 through 

2010 (Figure 8), show that prevailing winds in Cheyenne, Wyoming come from the west, 

northwest indicating that the transport of air pollutants is away from the Denver NAA. 

The Cheyenne NCore monitoring station became operational June 2010, and provides two years 

of ambient air quality data to assess. Ozone data for the year 2011 and three (3) quarters of the 

year 2012 gathered from the Cheyenne NCore station shows relatively low concentrations of 

ozone, where no one (1) day in either year exceeded the 2008 8-hour ozone NAAQS (Table 1). 

The combination of prevailing wind flow and low 8-hour ozone concentration values indicate 

that the Denver NAA is not, and has not been, significantly influenced by the transport of ozone 

and/or its precursors from Wyoming. 

Other downwind, or potentially downwind States such as North Dakota, South Dakota, Nebraska

and Kansas do not have any areas designated as nonattainment for the 2008 8-hour ozone 

standard. Based on this information, the State of Wyoming believes that ozone and ozone 

precursor emissions from Wyoming do not contribute to nonattainment or interfere with 

maintenance of the 2008 8-hour ozone NAAQS in another State. 
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Figure 1.
WDEQ-AQD 2008 8-Hour Ozone Infrastructure SIP (Attachment A)

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 Figure 2.
WDEQ-AQD 2008 8-Hour Ozone Infrastructure SIP (Attachment A)

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Figure 3.
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Figure 4.
WDEQ-AQD 2008 8-Hour Ozone Infrastructure SIP (Attachment A)

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 Figure 5.
WDEQ-AQD 2008 8-Hour Ozone Infrastructure SIP (Attachment A)

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Figure 6.
WDEQ-AQD 2008 8-Hour Ozone Infrastructure SIP (Attachment A)

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Figure 7.
WDEQ-AQD 2008 8-Hour Ozone Infrastructure SIP (Attachment A)

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Figure 8.
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Table 1. Cheyenne NCore Rolling 8-Hour Ozone Summary

NAAQS/WAAQS1 Measured Value

2012 

Jan. 1 – Sept. 30, 20122

Running 3rd Quarter

75 ppb3 Highest Daily Max: 73 ppb

4

th Highest Daily Max: 68 ppb

2011 Annual 75 ppb Highest Daily Max: 70 ppb

4

th Highest Daily Max: 67 ppb

 

1 National Ambient Air Quality Standards/Wyoming Ambient Air Quality Standards.

2 The 2012 4th Quarter and Annual reports are being finalized and unavailable at this time.

3 To attain the O3 standard, the 3-year average of the fourth-highest daily maximum 8-hour average O3

 concentrations must not exceed the standard.