MEMORANDUM TO THE FILE

Subject: Temecula Missing Data Analysis for 2011-2013

From: Michael Flagg

U.S. Environmental Protection Agency, Region 9

Date: October 6, 2014

During the following periods during the 2011-2013 time period, ozone data was not reported for 

the Temecula monitoring site (AQS ID: 06-065-0016-1) in Riverside County, California.

 June 4, 2012 – June 21, 2012 (null data code, AY: QC Control Points)

 July 1, 2012 – August 10, 2012 (null data code, AS: Poor QA Results)

 February 20, 2013 – March 17, 2013 (null data code: AY: QC Control Points)

 April 14, 2013 – April 29, 2013 (null data code: AN: Machine Malfunction)

For purposes of the proposed redesignation of Pechanga Reservation to attainment for the 1997 

8-hour ozone National Ambient Air Quality Standard (NAAQS), EPA evaluated whether the 

Temecula ozone monitor met applicable data completeness requirements during the 2011-2013

period. 40 CFR part 50 Appendix I §2.3(b) states: 

“...When computing whether minimum data completeness requirements have been met, 

meteorological or ambient data may be sufficient to demonstrate that meteorological 

conditions on missing days were not conducive to concentrations above the level of the 

standard. Missing days assumed less than the level of the standard are counted for 

purpose of meeting the minimum data completeness requirement, subject to the approval 

of the appropriate Regional Administrator.” 

Thus, EPA evaluated whether the conditions on missing days were conducive to concentrations 

above the 1997 8-hour ozone NAAQS of 0.08 ppm1at the Temecula monitoring site. This 

analysis informs EPA’s decision whether to count days between the previously described time 

periods towards meeting the minimum data completeness requirement.

EPA examined the comparability of ozone concentrations nearby ozone monitors in Riverside 

County (Figure 1). Monitors evaluated included:

 Pechanga (AQS ID: 06-065-0009-1): Located 9 miles to the south 

 Lake Elsinore (AQS ID: 06-025-9001-1): Located 20 miles to the northwest 

Evaluation of daily maximum 8-hour ozone concentrations shows that the Temecula monitor 

compares well with the Pechanga monitor while the Lake Elsinore monitor typically measures 

higher concentrations than the Temecula monitor. For example, during high ozone episodes with 

concentrations exceeding the 1997 8-hour NAAQS, the Lake Elsinore monitor consistently 

 

1 Due to rounding conventions, an exceedance of the 1997 8-hour ozone NAAQS occurs when measured concentrations averaged 

over eight hours exceeds 0.084 ppm.
measured higher concentrations (ranging from 0.015 to 0.029 ppm) than the Temecula monitor 

during the 2011-2013 time period. Since the Pechanga monitor provides a more accurate 

prediction than Lake Elsinore of daily maximum 8-hour ozone concentrations at the Temecula 

monitor, data from the Pechanga monitor were primarily relied on for assessing whether missing 

days were not conducive to concentrations above the level of the 1997 8-hour NAAQS.

While there was one exceedance (0.088 ppm) measured during June 4, 2012 – June 21, 2012 and 

three exceedances (0.087, 0.088, and 0.089 ppm) measured during the July 1, 2012 – August 10, 

2012 time period at the Lake Elsinore monitor, the historical relationship between these monitors 

(Figure 2) suggests it is unlikely that the Temecula monitor would have been above the 1997 

8-hour NAAQS.

For the time periods previously mentioned, concentrations at the Pechanga monitor were below 

the 1997 8-hour NAAQS. Based on the relationship between these monitors (Figure 3) and the

8-hour daily maximum concentrations at Pechanga, it is reasonable to conclude that the 

conditions on missing days were not conducive to concentrations above the 1997 8-hour 

NAAQS at the Temecula monitor. EPA also notes that during the February 20, 2013 – March 17, 

2013 and April 14, 2013 – April 29, 2013 time periods both the Pechanga and the Lake Elsinore 

monitors measured concentrations below the 1997 8-hour NAAQS providing further evidence to 

support that conditions were not conducive to concentrations above the 1997 8-hour NAAQS.

Based on these data, EPA concludes that it is appropriate to count the days of June 4, 2012 –

June 21, 2012, July 1, 2012 – August 10, 2012, February 20, 2013 – March 17, 2013, and April 

14, 2013 – April 29, 2013 towards meeting the minimum data completeness requirements.
Figure 1. Map of Nearby Ozone Monitors 
Figure 2. 2011-2013 Daily Maximum 8-hour Ozone: Temecula/Lake Elsinore Linear Regression

Figure 3. 2011-2013 Daily Maximum 8-hour Ozone: Temecula/Pechanga Linear Regression
Figure 2. 2011 Temecula, Pechanga, and Lake Elsinore Daily Maximum 8-hour Concentrations 

Figure 3. 2012 Temecula, Pechanga, and Lake Elsinore Daily Maximum 8-hour Concentrations
Figure 4. 2013 Temecula, Pechanga, and Lake Elsinore Daily Maximum 8-hour Concentrations