UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 4 

ATLANTA FEDERAL CENTER 

61 FORSYTH STREET 

PROW ATLANTA, GEORGIA 30303-8960 

Ms. Susan Zimmer-Dauphinee, Manager 

Ambient Monitoring Program 

Georgia Environmental Protection Division 

2 Martin Luther King, Jr. Drive, SE 

Suite 1152 East 

Atlanta, Georgia 30334-4100 

Ms. Zimmer-Dauphinee: 

This is in response to the Georgia Environmental Protection Division’s (GA EPD) May 5, 

2010, letter regarding the particulate matter less than 2.5 microns (PM2.5) data completeness 

issues at the Rossville, Georgia air monitor site during the second and third quarters of 2007. 

The supporting documentation provided a technical analysis of why the U.S. Environmental 

Protection Agency (EPA) should consider an attainment determination for PM 2 .5 in the 

Chattanooga, Tennessee metropolitan statistical area (MSA). The EPA has reviewed your 

demonstration and agrees that the Chattanooga MSA qualifies for a clean data determination. 

Below is a summary of the issue, GA EPD’s analysis, and EPA’s basis for the clean data 

determination. 

On June 11, 2007, the original Rossville site was shut down due to the renovation of the 

building and roof on which it was located. The flat roof was replaced with a pitched roof that 

would no longer physically support ambient air monitors. While a new site was sought, no data 

were collected from June 12November 13, 2007. GA EPD followed appropriate shutdown and 

startup protocols for this site relocation. GA EPD worked with EPA to evaluate a proposed site, 

finalize site details, place purchase orders, build a deck and fence, and complete electrical work. 

Because of the work needed to relocate the site, data collection for the 2007 calendar year was 

incomplete and, therefore, the 2007-2009, design value does not meet the 75 percent data 

completcness requirement. 

There are three other PM2.5 sites in the Chattanooga MSA: Tombras Avenue, TN (East 

Ridge); Siskin Drive, TN (UTC) and Soddy Daisy, TN. A valid design value must be 

determined at each site in the MSA. Forty (40) Code of Federal Regulations (CFR) Part 50, 

Appendix N describes the data handling conventions and computations necessary for 

determining when the annual and 24-hour national ambient air quality standards (NAAQS) for 

PM2,5 specified in 40 CFR Part 50.7 and 50.13 are met. The Rossville site is the only site where 

a valid design value cannot be computed. 

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The analysis provided by GA EPD developed a weight of evidence for an alternative 

method of data substitution to determine attainmentinonattainment. The analysis used data from 

the Siskin Drive and Tombras Avenue sites to determine the attainment status of the Rossville 

site. It revealed several interesting and notable statistics. Appendix N to 40 CFR Part 50 

requires a quarterly correlation coefficient of at least 0.9 between the site where data substitution 

is being attempted and the site(s) from which the substituted data came. The PM25 federal 

reference method (FRM) data comparing Rossville to both the Tombras Avenue and Siskin 

Drive sites in Tennessee over a nine year period, January 1, 2000, through December 29, 2008, 

showed Pearson Product-Moment correlations of 0.91362 and 0.9 1609, respectively. Further 

evidence of the strong relationship between the sites is provided through a comparison of the 

FRM means with each pair of data. The spatial averaging requirements in 40 CFR Part 50, 

Appendix N require that the means reflect a percent difference of no greater than 10%. For the 

same nine year time period mentioned above, the percent differences in FRM means between 

Rossville and Siskin Drive and between Rossville and East Ridge were 2.50% and 0.20%, 

respectively. 

After receiving GA EPD’ s data completeness request, EPA Region 4 asked EPA’s Office 

of Air Quality Planning and Standards (OAQPS) to conduct a data completeness analysis of the 

Rossville PM2.5 site using a new OAQPS statistical tool. The tool, while still in draft form, has 

been used to analyze several cases across the country. The tool seeks to make a defensible 

determination on whether an MSA [and its previously violating site(s)] can be called "clean" in 

lieu of missing data. Unlike most other approaches, this analysis uses past patterns (the 

regression relationship) combined with new information (the current tendencies in the area as 

shown by the still-operating site). Per the protocol, the missing data at a previously violating site 

with incomplete data in the current period are imputed using the recent-past day-to-day 

relationship with another site in the area, and the current period data for that other site. If, 1) the 

imputed data combined with available real data produce a valid design value that meets the 

NAAQS and 2) the re-estimation of the current data confirms the result, then the area is deemed 

"clean" for the current period. The Rossville site passed this analysis. 

In summary, GA EPD’s analysis successfully demonstrated a strong correlation between 

the PM2.5 data from the Rossville site (the missing data site) and the other two sites. GA EPD’s 

analysis is bolstered by an OAQPS regression analysis using imputed data. As a result, EPA 

Region 4 agrees that the Chattanooga MSA would qualify for a clean data determination. You 

should consult with Dick Schutt, the Air Planning Branch Chief, on the ramifications of this 

determination. 
If you have questions, please call me at 404-562-9097 or Darren Palmer of my staff at 

404-562-9052. 

Sincerely, 

R. Douglas eley~Chief 

Air Toxics and Monitoring Branch 

cc: Jack Capp, GA EPD 

Barry Stephens, TN DEC 

Robert Colby, CHCAPCB 

Archie Lee, EPA SESD 

Dick Schutt, EPA APTMD