December 10, 2014

MEMORANDUM

SUBJECT: Practicability of SJV 20 14 attainment of the 1997 PM 2.5 NAAQS

FROM: Elfego Felix, Air Quality Analysis Office Scott Bohning, Air Quality Analysis Office

TO: San Joaquin Valley Reclassi fication Docket EPA-R09-OAR-2014-0813
This memorandum explains the methodology used by EPA to judge the pract icability for the San Joaquin Valley (SJV) moderate nonatt ainment area to attain the 1997 PM 2.5 NAAQS (annual and 24-hour) by the end of 2014, which requires da ta from the 2012-2014 time period. For this analysis, EPA obtained data from the U.S. EPA, 2013 Design Value Reports, PM 2.5 Detailed Information Updated 8/24/14, available at http://www.epa.gov/airtrends/values.html (“PM25_DesignValues_20112013_FINAL_08_28_14”), and from Air Quality System (AQS) data queries performed on August 7th, 2014 (AQS Combined site values report, AMP355) and August 8th, 2014 (AQS Quicklook Report, AMP450).
Per 40 CFR part 58.15, annual data certification fo r data collected from January 1 to December 31 of the previous year is due on May 1 of the following year. At the time EPA conducted this analysis, 2014 data had not beenfully collected and certified, while 2012 and 2013 data had been certified. For this analysis, EPA was thus able to use certified data from 2012-2013 and preliminary data available fo r 2014 as of early August 2014.
Annual NAAQS
For the annual NAAQS of 15.0 μg/m 3 , the design value is the three-year average of annual mean PM 2.5 concentrations. Under the rounding conventi ons of 40 CFR part 50, appendix N, section 4.3, daily PM 2.5 values are reported to one decimal place; in computing the design value, intermediate calculation results ar e not rounded; and in the in fi nal result for comparison to the level of the NAAQS, decimals of 0.05 or higher are rounded up. Thus if C x is the annual mean concentration for year x, the 2014 design value D 2014 attains the NAAQS when:

D 2014 = (C 2012 + C 2013 + C 2014 )/3 ≤ 15.04

which can be restated as:

C 2014 ≤ 3 * 15.04 – (C 2012 + C 2013 )

C 2014 represents the maximum 2014 annual mean c oncentration allowed for attainment, given known annual mean concentrations for 2012 and 2013. EPA computed these maximum allowed 2014 annual mean concentrations for SJV monitors , and compared them to the lowest valid annual mean concentrations seen since 1999. EPA deemed attainment at a monitoring site impracticable if the maximum allowed 2014 annual mean concentration was substantially lower than has been recorded historically. EPA found that multiple monitoring sites would have to have 2014 annual mean concentrations recorded at 15% or more be low their correspondinghistorical lows in order to attain by the e nd of 2014 with the most extreme example at the Bakersfield-Planz Rd. monitoring site that would require approximately 47% below the previously recorded low.
24-hour NAAQS
For the 24-hour NAAQS of 65 μg/m 3 , the design value is the three-year average of annual 98th percentile PM 2.5 concentrations. Under the rounding conve ntions of 40 CFR part 50, appendix N, section 4.3, daily PM 2.5 values are reported to one decimal place; in computing the design value, intermediate calculation results ar e not rounded; and in the in fi nal result for comparison to the level of the NAAQS, decimals of 0.5 or highe r are rounded up. Appendix N section 4.5, table 1 specifies which recorded daily PM 2.5 value rank is chosen as the 98th percentile; for example, if there are between 301 and 350 daily samples collected in a year, then the 7th highest value is the 98th percentile. The fewer the number of samples collected, the higher the rank used ( e.g. 1st high for between 1 and 50 samples). If C x is the 98th percentile co ncentration for year x, the 2014 design value D 2014 attains the NAAQS when:

D 2014 = (C 2012 + C 2013 + C 2014 )/3 ≤ 65.4

which can be restated as:

C 2014 ≤ 3 * 65.4 – (C 2012 + C 2013 )

C 2014 represents the maximum 2014 98th percentile concentration a llowed for attainment, given known 98th percentiles for 2012 and 2013.
EPA computed these maximum allowed 2014 concen trations for selected SJV monitors, and compared them to estimates of the actual m onitored 2014 concentrations. For each monitor, the 2014 98th percentile was estimated from the 2014 da ta available in AQS as of early August 2014, together with two assumptions. It was assu med that the sampling rate observed so far would continue throughout the year; this yielde d an estimate of the number of total samples expected for 2014, and allowed for selection of th e corresponding rank of the daily data available to use as the 98th percentile. This rank was th e 7th high for several sites, and the 3rd high for several others. It was also assumed that the c oncentrations measured during the remainder of 2014 would be no higher than those already recorde d, so the 98th percentile could be chosen from among the already recorded data. This is a conservative assumption for assessing the impracticability of attainment, since in reality so me concentrations could be higher, the chosen 98th percentile could be higher, and attain ment even more impracticable. EPA deemed attainment at a monitoring site impracticable if the maximum allowed 2014 98th percentile concentration was lower than the estimated 2014 98th percentile concentration. Both the Bakersfield-California Ave. and the Bakersfi eld-Planz Rd. sites yielded estimated 2014 98th percentile concentrations higher than the maximum allowed for attainment by the end of 2014.
Attachment: “SJV PM2 5 1997 std impracticable 2014-12-10.xlsx”