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.

Internet Address (URL). http://www.epa.goV
Recycled/Recyclable . Printed with Vegetable Oil Based Inks on Recycled Paper (Minimum 30% PostconsUmer)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