December 10, 2014 

MEMORANDUM 

SUBJECT: Practicability of SJV 2014 attainment of the 1997 PM2.5 NAAQS 

FROM: Elfego Felix, Air Quality Analysis Office 

Scott Bohning, Air Quality Analysis Office 

TO: San Joaquin Valley Reclassification Docket EPA-R09-OAR-2014-0813 

This memorandum explains the methodology used by EPA to judge the practicability for the San 

Joaquin Valley (SJV) moderate nonattainment area to attain the 1997 PM2.5 NAAQS (annual and 

24-hour) by the end of 2014, which requires data from the 2012-2014 time period. For this 

analysis, EPA obtained data from the U.S. EPA, 2013 Design Value Reports, PM2.5 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 for 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 been fully 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 for 2014 as of early August 2014. 

Annual NAAQS 

For the annual NAAQS of 15.0 μg/m3, the design value is the three-year average of annual mean 

PM2.5 concentrations. Under the rounding conventions of 40 CFR part 50, appendix N, section 

4.3, daily PM2.5 values are reported to one decimal place; in computing the design value, 

intermediate calculation results are not rounded; and in the in final result for comparison to the 

level of the NAAQS, decimals of 0.05 or higher are rounded up. Thus if Cx is the annual mean 

concentration for year x, the 2014 design value D2014 attains the NAAQS when: 

D2014 = (C2012 + C2013 + C2014)/3 ≤ 15.04 

which can be restated as: 

C2014 ≤ 3 * 15.04 – (C2012 + C2013) 

C2014 represents the maximum 2014 annual mean concentration 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 below their corresponding 
historical lows in order to attain by the end 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/m3, the design value is the three-year average of annual 98th 

percentile PM2.5 concentrations. Under the rounding conventions of 40 CFR part 50, appendix N, 

section 4.3, daily PM2.5 values are reported to one decimal place; in computing the design value, 

intermediate calculation results are not rounded; and in the in final result for comparison to the 

level of the NAAQS, decimals of 0.5 or higher are rounded up. Appendix N section 4.5, table 1 

specifies which recorded daily PM2.5 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 Cx is the 98th percentile concentration for year x, the 

2014 design value D2014 attains the NAAQS when: 

D2014 = (C2012 + C2013 + C2014)/3 ≤ 65.4 

which can be restated as: 

C2014 ≤ 3 * 65.4 – (C2012 + C2013) 

C2014 represents the maximum 2014 98th percentile concentration allowed for attainment, given 

known 98th percentiles for 2012 and 2013. 

EPA computed these maximum allowed 2014 concentrations for selected SJV monitors, and 

compared them to estimates of the actual monitored 2014 concentrations. For each monitor, the 

2014 98th percentile was estimated from the 2014 data available in AQS as of early August 

2014, together with two assumptions. It was assumed that the sampling rate observed so far 

would continue throughout the year; this yielded an estimate of the number of total samples 

expected for 2014, and allowed for selection of the corresponding rank of the daily data available 

to use as the 98th percentile. This rank was the 7th high for several sites, and the 3rd high for 

several others. It was also assumed that the concentrations measured during the remainder of 

2014 would be no higher than those already recorded, 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 some concentrations could be higher, the chosen 

98th percentile could be higher, and attainment 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 Bakersfield-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”