1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

RESEARCH TRIANGLE PARK, NC 27711



### MEMORANDUM

SUBJECT : Asse ss ment of PM 2.5 

### data to determine the number of sites that would be

potentially required to increase their sample frequency to daily

.
FROM: Tim Hanley (OAQPS /AQAD/AAMG )

TO: Ambient Monitoring Rule Docket (EPA

- HQ

- OAR

- 2013

- 0619)

This memorandum details how PM 2.5 data were assessed to determine the number of PM 2.5 SLAMS stations that would be required to transition to daily sampling if they are not already on d aily sampling as a result of a pro po sed requirement affecting the length of time a site must stay on daily sampling (i.e., proposed to stay on daily sampling for a three year pe riod)

. A s part of a proposed rule

- Revisions to Ambient Monitoring Quality Assurance and Other Requirements

– 79 FR 54356

- OAQPS received

comment s related to the proposed length of time PM 2.5 SLAMS would be expected to operate on a daily sampling freque ncy. Of specific concern was whether clarifying the length of time to operate a PM 2.5 FRM or FEM to run on a daily sampling frequency would resu l t in increased burden to a large number monitoring agencies . To understand the extent of how many sites could potentially be affected by this requirement, we have analyzed site level design values and present our findings below.

BACKGROUND
The existing §58.12 provides that required SLAMS must operate on a daily sampling schedule. The existing requirement is provided below:

“ 58.12 Operating Schedules

– (d)(iii) Required SLAMS stations whose measurements determine the 24

- hour design value for their area and whose data are within plus or minus 5 percent of the leve l of the 24

- hour PM 2.5 NAAQS must have an FRM or FEM operate on a daily schedule if that area's design value for the annual NAAQS is less than the level of the annual PM 2.5 standard. A continuously operating FEM or ARM PM 2.5 monitor satisfies this requirem ent unless it is identified in the monitoring agency's annual monitoring network plan as not appropriate for comparison to the NAAQS. ”

In the proposed rule

- Revisions to Ambient Monitoring Quality Assurance and Other Requirements

– 79 FR 54356, EPA sought to clarify the length of time a site is to maintain the daily sampling frequency

, which was proposed to be 3 years

. 1 In response to this proposed clarification, some commenters believed that this could add a large burden to their workload. To understand the extent to which this clarification may impact monitoring agencies, an assessment of the PM 2.5 site level design values was performed to determine the number of sites not already on a daily sampling frequency that would be expected to operate on a dail y sampling frequency for a three year

- period

.

1 The length of time for the increased sampling frequency was not specified in the existing rule language, providing the potential for inconsistency in interpretation.2

DATA ANALYSIS

PM 2.5 design values were downloaded from EPA’s web site at http://www.epa.gov/airtrends/values.html

. This PM 2.5 file was last updated on August 8 th , 2014 using data downloaded from the EPA’s AQS database . The file include s PM 2.5 design values for the three year period of 2011 through 201 3 by site with design values ca lculated according to EPA’s data interpretation rules 2

. In our data analysis, t he PM 2.5 site le ve l design values were evaluated by looking for the total number of sites , number of valid design value sites, and number of invalid design value sites that meet each of the following criteria:

1. T otal number of sites available to assess ;

2. N umber of sites with a 24

- hour design value 3 of 34, 35, or 36 μg/m 3 ;

3. N umber of s ites additionally having an annual design value of < 12.0 μg/m 3 ;

4. N umber of sites with all the criteria above and without another si te in the same CBSA al ready on a daily sampling schedule ;

5. N umber of sites with all the criteria above and without another site in the same CBSA that is more than 5% above the level of the daily NAAQS.
We considered both sites with design values that are complete as well as those where there was not enough data to provide a valid design value. The results of this assessment are summarized in the following table:

Table of number of PM 2.5 sites according to id e n tif ied crite r i a:

2011

- 2013 PM 2.5 D esign V alue's (DV) sites according to the following criteria Total Number of Sites Number of

Valid Design Values Number of

Invalid Design Values Total n umber of sites in DV listing 980 697 283 Number of sites with a 24

- hour DV of 34, 35, 36 10 9 1 Number of sites with a 24

- hour DV of 34, 35, 36 and annual DV of 12.0 or lower 9 8 1

Number of CBSA's with a 24

- hour DV of 34, 35, 36 and annual DV of 12.0 or lower 7 6 1

Number of CBSA's with a 24

- hour DV of 34, 35, 36 and annual DV of 12.0 or lower, and not already on daily sampling 5 4 1

Number of CBSA's with a 24

- hour DV of 34, 35, 36; annual DV of 12.0 or lower; not already on daily sampling; and no other site in area with DV more than 5% above the 24

- hour NA AQS. 4 3 1

2 Appendix N to 40 CFR Part 50

– Interpretation of the National Ambient Air Quality Stand ards for PM 2.5 3 See http://www.epa.gov/ttnamti1/files/ambient/pm25/NAAQS%20Comparisons

- FAQ

- 010907.pdf3

In the following table we list the four individual sites out of 980 where the requirement to move to daily sampling would potentially 4 be required to be maintained for a three year period . Again, we point out that the requirement to move to daily sampling was already in place.



### Table of Sites with a 24

- hour DV of 34, 35, 36; annual DV of 12.0 or lower; not already on daily sampling; and no other site in area with DV more than 5% above NAAQS.

State CBSA Site ID 2011

- 2013 Annual Design Value (μg/m3) INVALID

2011

- 2013 Annual Design Value (μg/m3) 2011

-

2013 24

- hr Design Value (μg/m3) INVALID

2011

- 2013 24

- hr Design Value (μg/m3) Would

site need to go to daily? California 060631006 10.2 36 Yes Oregon 410250003 9.5 35 Yes

Oregon Portland

Vancouver

Beaverton, OR

- WA 410670004 8.2 34 Yes

Pennsylvania Philadelphia

Camden

Wilmington, PA

- NJ

- DE

MD 421010048 10.9 35 Yes



### SUMMARY

As detailed above using data from 2011 to 2013, there are only four PM 2.5 sites in the country out of 980 sites that are not currently operating on a daily sample frequency that would potentially be required to move to a daily sampling frequency for a three

- year period

. Given the very small number of sites that would potentially be required to go to a daily sampling frequency for a three

- year period

, we believe that likel i hood of such occurances affecting a monitoring agenc y are relatively small

.

4 Note: we are not affirmatively requiring that these sites move to a daily sampling frequency as a result of this memo. This memo was produced to exami ne the potential burden of required daily sampling frequency being maintained for at least a three year period. Sample frequency changes are to be identified and approved as appropriate in each agencies annual monitoring network plan according to §58.10.