December 15 , 2014

MEMORANDUM

S UBJECT : Practicability of SJV 201 5 attainment of the 2006 24

- hour PM 2.5 NAAQS

FROM : Elfego Felix , Air Quality Analysis Office

Scott Bohning, Air Quality Analysis Office

T O : San Joaquin Valley 2006 PM 2.5 NAAQS Reclassification Docket EPA

- R09

- OAR

2014

- 0636

This memorandum explains the methodology used by EPA to judge the practicability f or the San Joaquin Valley (SJV) moderate nonattainment area to attain the 2006 PM 2.5 24

- hour NAAQS of 35 μg/m 3 by December 31, 2015 , which requires data from the 201 3

- 2015 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 an Air Quality System (AQS) data query performed on August 7th, 2014 ( AQS Combined site values report, AMP355 ).

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, no data had yet been collected for 2015, 2014 data had not been fully collected and certified, and 2013 data had been certified. For this analysis , EPA was thus able to use certified data f or 2013

, preliminary data available for 2014 as of early August 2014 , and no data from 2015

.
For the 24

- hour NAAQS of 3 5 μg/m 3

, the design value is the three

- year average of annual 98th percentile PM 2.5 concentrations. Under the rounding conventions 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 are not rounded; and in the 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 PM 2.5 value rank is chosen as the 98th percentile; for example, if there are between 301 and 35 0 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 concentration for year x, the 2015 design value D 2015 attains the NAAQS when:

D 2015 = (C 201 3 + C 201 4 + C 2015 )/3 ≤ 35 .4

which can be restated as:

C 2015 ≤ 3 * 3 5.4

– ( C 201 3 + C 201 4 )

C 2015 represents the maximum 2015 98th percentile concentration allowed for attainment, given the known 98th percentile for 201 3 and an estimated 98th percentile for 201 4

.EPA computed these maximum allowed 2015 concentrations for selected SJV monitors, and

compared them to zero, the lowest possible concentration

. (In practice, a concentration of zero is actually not possible since it would require no anthropogenic or natural emissions in the SJV area, and no transport of pollutants into the area from outside. Every area is expected to have some amount of backgroun d PM 2.5. ) 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 yi elded 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 ot hers. 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 asses sing 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 201 5 98th percentile concentration was less than zero ( i.e. negative)

. EPA’s analysis showed that a ll monitoring sites examined

— Bakersfield

- California Ave, Bakersfield

- Planz Rd., Fresno

Garland, Fresno

- Pacific, and Hanford

— would require negative PM 2.5 concentrations to attain the 2006 24

- hour PM 2.5 NAAQS by the end of 2015.

EPA considered the assumption that somehow all sites in this analysis could collect a minimum of 351 daily samples ( i.e. consistent with an everyday s ampling frequency) in 2014 that would allow for select ion of the 8th highest recorded value as the 98th percentile for 2014

. This is particularly an unrealistic assumption for the Bakersfield

- Planz Rd. and Fresno

- Pacific sites that, based on preliminary data as of early August 2014, have operated at a 1:3 sampling frequency ( i.e. one sample is collected every three days) in 2014

. This unrealistic assumption would allow for selection of the lowe st 98th percentile value possible f or 2014 and thus render the easiest attainment scenario conceivable . Even under this assumption, all of the monitoring sites evaluated in this analysis, except Fresno

- Pacific

, would require a negative PM 2.5 98th percentile concentration in 2015 to attain the 2006 24

- hour PM 2.5 NAAQS by the end of 2015 ( Fresno

Pacific would require a 98th percentile concentration of 2.9 μg/m 3 in 2015 , far below expected background concentrations)

. Based on the analysis described in this memorandum, EPA concludes that attainment of the 2006 24

- hour PM 2.5 NAAQS by the end of 2015 would be impracticable for the SJV

.