1 

MEMORANDUM 

DATE: May 30, 2013 

FROM: Carol Bohnenkamp, Regional Modeling Contact 

TO: Rulemaking docket # EPA-R09-OAR-2013-0384 

RE: Assessment of projected vs. observed ambient PM2.5

levels for 2012 RFP year 

According to the South Coast Air Quality Management 

District (SCAQMD or District), recent modeling analyses indicate 

that “existing air quality at all monitoring stations is already 

better than it would be if emissions were at the levels 

projected in the plan for RFP, and an additional one year’s 

worth of reductions had been implemented (i.e., simulated 

implementation of contingency measure on top of actually meeting 

RFP).” Contingency Measures SIP at 2. The District states that 

the speciated regional modeling analysis in the South Coast PM2.5

SIP had predicted that implementation of the plan would result 

in a reduction in the basin-wide design concentration from 22.7 

μg/m3 in 2005 to a value of 17.98 μg/m3 in 2010. Id. at 5. The 

maximum observed design value for 2010 at the design value site1

(Rubidoux2), however, was 15.01 μg/m3 according to the District, 

 

1 Consistent with EPA’s definition of “design value” in 40 CFR 58.1, we use 

the term “design value site” to refer to the monitoring site that records the 

highest calculated pollutant concentration (according to the applicable 

appendix of 40 CFR part 50) in the nonattainment area. 

2 Although the current design value site for the area is the Mira Loma (Van 

Buren) monitoring station, this site was not accounted for in the analyses 

underlying the South Coast PM2.5 SIP as it was not operational until 2006. See
2 

17 percent lower than the concentrations projected in the plan. 

See id.; see also id. at 10, Table 2. Accounting for temporary 

reductions in ambient PM2.5 levels due to favorable weather and 

reduced economic activity, the District estimates the PM2.5

design value “improvement” attributable to implementation of its 

plans, compared to previous projections, to be approximately 

1.88 μg/m3 in 2010. Id. at 8-10 and Table 2. If PM2.5 air 

quality at the design site (Rubidoux) were to remain at 2010 

levels through 2012, the difference between the predicted and 

observed design value would show a 1.47 μg/m3 improvement over 

the 2012 projections underlying the South Coast PM2.5 SIP. Id. 

at 5. According to the District, these PM2.5 air quality 

improvements equate to approximately 420 tons per day (tpd) of 

NOx emission reductions in 2012. Id. 

EPA independently reviewed PM2.5 air quality data available 

in EPA’s “Air Quality System” (AQS) for the 2002-2012 period to 

assess the District’s representations regarding PM2.5 air quality 

improvements in the South Coast area.3 PM2.5 air quality data 

collected through the District’s monitoring network and 

available in AQS indicate that ambient PM2.5 levels in the South 

 

Contingency Measures SIP at 5, n. 2. Therefore, the District compared the 

projected and observed values for the Rubidoux monitoring site, which was the 

design value site prior to 2007. 

3 EPA evaluated these data only preliminarily, for purposes of determining 

whether the Contingency Measures SIP satisfies the requirements of CAA 

section 172(c)(9), and is not at this time proposing to make any formal 

determination regarding attainment for the South Coast PM2.5 nonattainment 

area. 
3 

Coast air basin were, in fact, significantly lower in 2012 and 

in the years leading up to 2012 than the levels projected in the 

South Coast PM2.5 SIP for this period. 

Table 1 lists the annual mean PM2.5 concentration at each 

monitor in the South Coast air basin during the 2002-2012 period. 

Table 1. PM2.5 Annual Mean concentrations, 2002-2012 

Site AQS ID 

One-year Annual Mean (μg/m3)

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Azusa 060370002 20.7 19.3 18.3 17.0 15.4 15.7 14.0 13.1 10.8 12.1 10.2

Burbank –

Palm Ave.

060371002 24.0 22.1 19.1 17.8 16.5 16.9 13.9 15.3 12.8 13.5 11.7

LA – North 

Main

060371103 22.0 21.3 19.7 17.8 15.6 16.8 16.1 14.4 12.6 13.5 12.2

Reseda 060371201 18.9 16.5 15.7 13.9 12.8 13.3 11.8 11.4 10.1 10.2 9.8

Lynwood 060371301 23.3 20.3 18.5 17.5 16.7 16.0 14.6 13.0 11.5

Compton 060371302 12.4 14.7 12.5 12.5 11.3

Pico Rivera 

#1

060371601 24.0 20.6 20.0 15.2

Pico Rivera 

#2

060371602 22.3 16.6 16.6 14.9 14.8 12.5 12.5 11.3

Pasadena 060372005 20.3 18.6 16.6 15.1 13.4 14.4 12.8 12.3 10.2 10.8 10.3

Long 

Beach

060374002 19.5 18.0 17.9 15.9 14.1 14.6 14.1 12.8 10.4 11.3 10.0

Long 

Beach – 

PCH

060374004 20.6 16.5 14.7 14.4 13.7 13.7 12.5 10.4 10.7 10.3

Anaheim 060590007 18.6 17.3 17.0 14.7 14.0 14.4 13.1 12.1 10.5 11.1 10.3

Mission 

Viejo

060592022 15.5 13.1 12.0 10.6 11.0 11.1 10.4 9.5 8.0 8.5 7.6

Riverside 060651003 27.1 22.6 20.8 17.9 16.9 18.3 13.3 13.3 11.0 11.8 10.5

Rubidoux 060658001 27.5 24.8 22.1 20.9 18.9 19.0 16.4 15.6 13.3 13.8 13.5

Mira Loma 060658005 20.8 20.9 18.3 17.2 15.5 15.9 15.0

Ontario 060710025 25.4 23.8 20.9 18.8 18.4 18.3 15.8 14.7 13.0 13.3 11.8

Fontana 060712002 24.3 22.1 19.9 18.8 17.5 18.9 15.3 14.2 11.9 12.6 11.9

Big Bear 060718001 11.5 10.6 9.6 12.0 11.3 10.3 9.1 9.9 8.4 8.4 8.0

San 

Bernardino

060719004 25.8 22.2 21.9 17.3 17.6 17.9 13.4 13.0 11.1 12.2 11.7

Source: U.S. EPA, Air Quality System, Preliminary Design Value Report, PM2.5, 

2002-2012 (Report Date: May 10, 2013). 

Table 2 lists the annual PM2.5 design value at each monitor 

in the South Coast air basin for the 2002-2012 period. 
4 

Table 2. Annual PM2.5 Design Values, 2002-2012 

Site AQS ID 

Annual Design Value (μg/m3)

4

2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

Azusa 060370002 20.8 20.6 19.4 18.2 16.9 16.0 15.1 14.3 12.7 12.0 11.0

Burbank –

Palm Ave.

060371002 23.3 23.6 21.7 19.7 17.8 17.1 15.8 15.4 14.0 13.9 12.6

LA – North 

Main

060371103 22.2 22.0 21.0 19.6 17.7 16.7 16.1 15.8 14.4 13.5 12.8

Reseda 060371201 18.4 17.9 17.0 15.4 14.1 13.3 12.6 12.1 11.1 10.6 10.0

Lynwood 060371301 23.6 22.7 20.7 18.7 17.5 16.7 15.8 15.3 14.6

Compton 060371302 12.4 13.5 13.2 13.4 12.3

Pico Rivera 

#1

060371601 24.4 23.3 21.5 18.6 17.6 15.2

Pico Rivera 

#2

060371602 22.3 19.5 18.5 16.0 15.4 14.1 13.3 12.1

Pasadena 060372005 20.2 19.9 18.5 16.8 15.0 14.3 13.5 13.2 11.8 11.1 10.4

Long 

Beach

060374002 20.1 19.6 18.5 17.3 16.0 14.9 14.3 13.9 12.4 11.5 10.6

Long 

Beach – 

PCH

060374004 20.6 18.6 17.3 15.2 14.3 13.9 13.3 12.2 11.2 10.5

Anaheim 060590007 22.0 20.4 17.6 16.3 15.2 14.3 13.8 13.2 11.9 11.2 10.6

Mission 

Viejo

060592022 15.4 14.8 13.5 11.9 11.2 10.9 10.8 10.3 9.3 8.7 8.0

Riverside 060651003 26.9 25.9 23.5 20.5 18.6 17.7 16.2 15.0 12.5 12.0 11.1

Rubidoux 060658001 28.9 27.8 24.8 22.6 20.6 19.6 18.1 17.0 15.1 14.2 13.5

Mira Loma 060658005 20.8 20.9 20.0 18.8 17.0 16.2 15.5

Ontario 060710025 25.3 25.2 23.4 21.2 19.4 18.5 17.5 16.2 14.5 13.7 12.7

Fontana 060712002 24.6 23.8 22.1 20.3 18.7 18.4 17.2 16.1 13.8 12.9 12.1

Big Bear 060718001 10.9 11.1 10.6 10.8 11.0 11.2 10.3 9.8 9.1 8.9 8.3

San 

Bernardino

060719004 25.9 24.7 23.3 20.5 18.9 17.6 16.3 14.7 12.5 12.1 11.7

Source: U.S. EPA, Air Quality System, Preliminary Design Value Report, PM2.5, 

2002-2012 (Report Date: May 10, 2013). 

Consistent with the District’s explanations in the 

Contingency Measures SIP, these monitoring data show that actual 

ambient PM2.5 levels in the South Coast area in 2010 were, in 

fact, lower than the levels projected in the South Coast PM2.5

SIP for this timeframe. Specifically, the modeling analyses in 

 

4 Most but not all of these design values are based on data that meet EPA’s 

completeness criteria in 40 CFR part 50, appendix N, section 4.0. See

Memorandum from Meredith Kurpius to File dated May 10, 2013. 
5 

the South Coast 2007 AQMP indicated that implementation of 

existing control requirements would reduce ambient PM2.5 levels 

at the Rubidoux monitoring site from 22.7 μg/m3 in 2005 to 17.9 

μg/m3 in 2010. See South Coast 2007 AQMP, Appendix V at V-2-10, 

Table V-2-4 (showing 2003-2005 annual design concentrations) and

V-2-48 (discussing “future air quality”).5 The observed design 

value at the Rubidoux monitor for 2010, however, is 15.1 μg/m3

(see Table 2 above), 2.8 μg/m3 lower than the 17.9 μg/m3

projected in the plan for that year. If we subtract from this 

difference the 1.09 μg/m3 that the District attributes to 

favorable weather and temporary economic conditions in 2010 (see 

Contingency Measures SIP at 8-10 and Table 2), the design value 

“improvement” compared to the plan’s projected ambient PM2.5

level at the Rubidoux site in 2010 would be approximately 1.71 

μg/m3. Further assuming, conservatively, that PM2.5 levels at the 

Rubidoux site remain at 2010 levels through 2012, the design 

value “improvement” compared to the plan’s projected ambient 

PM2.5 levels for 2012 would be approximately 1.35 μg/m3. Finally, 

 

5 The Contingency Measures SIP, as supplemented in 2013, references portions 

of a 2007 CARB Staff Report as the source of the “predicted” PM2.5 design 

values (i.e., the ambient PM2.5 levels projected for future years in the South 

Coast PM2.5 SIP). See Contingency Measures SIP at 5, n. 1 and 2013 Supplement, 

Attachments 1 and 2 (referencing Appendix C of CARB Staff Report entitled 

“2007 State Implementation Plan for the South Coast Air Basin PM2.5 and 8-

Hour Ozone NAAQS,” September 21, 2007) (hereinafter “2007 CARB Staff 

Report”). EPA independently evaluated the District’s calculations, however, 

by also reviewing the District’s previous technical analyses in Appendix V of 

the South Coast 2007 AQMP (“Modeling and Attainment Demonstration”), which 

provides the technical basis for the attainment demonstration in the South 

Coast PM2.5 SIP. 
6 

if we take into account the higher PM2.5 levels recorded at the 

Mira Loma monitoring site,6 the design value “improvement” for 

2012 would be reduced to approximately 0.95 μg/m3. 

EPA also independently reviewed the District’s evaluation 

of NOx-equivalent emission reductions to assess its conclusion, 

in the Contingency Measures SIP, that the observed design value 

“improvement” in the South Coast area should be equated to 

approximately 420 tpd of NOx-equivalent reductions which are 

available for contingency measure purposes. See Contingency 

Measures SIP at 5. Specifically, EPA evaluated the District’s 

assessment in the South Coast 2007 AQMP of total precursorspecific emission reductions needed to bring the area into 

attainment of the annual PM2.5 NAAQS by the attainment date of 

April 5, 2015.7 See South Coast 2007 AQMP, Appendix V at V-2-19, 

V-2-53, V-2-61, and V-2-62. As part of this analysis, the 

District developed estimates of NOx-equivalent emissions 

 

6 The Mira Loma monitor, which is currently the PM2.5 design value site in the 

South Coast area, has also recorded significant declines in ambient PM2.5

levels since becoming operational in 2006. See tables 1 and 2. Although the 

District was unable to directly compare observed data with projected plan 

levels for the Mira Loma monitor, given that this monitor was not operational 

during the development of the South Coast 2007 AQMP, the District identified 

the higher PM2.5 levels recorded at the Mira Loma site in 2010 (see Contingency 

Measures SIP at 5-6) and EPA has taken these higher ambient levels into 

account to develop a more conservative assessment of the design value 

“improvement” compared to the plan’s projected ambient levels for 2012. 

7 The Contingency Measures SIP and 2013 Supplement reference Appendix C of the 

2007 CARB Staff Report. See Contingency Measures SIP at 5, n. 1 and 2013 

Supplement, Attachments 1 and 2. As explained above in n. 5, however, EPA 

independently evaluated the District’s calculations by also reviewing the 

District’s previous technical analyses in Appendix V of the South Coast 2007 

AQMP (“Modeling and Attainment Demonstration”), which provides the technical 

basis for the attainment demonstration in the South Coast PM2.5 SIP. 
7 

reductions based on precursor-equivalent ratios provided in 

Appendix V of the South Coast 2007 AQMP, at Table V-2-14, 

“Relative Contributions of Precursor Emissions Reductions to 

Simulated Controlled Future Year PM2.5 Concentrations.” See id.

at V-2-52. These ratios provide an indication of the level of 

NOx-equivalent reductions (in tons) needed to achieve a 

particular level of air quality improvement (in μg/m3). We find 

the District’s conclusions regarding the level of NOx-equivalent 

emission reductions needed to achieve the observed design value 

“improvement” in the area (i.e., in the range of 0.95 to 1.47 

μg/m3) to be generally consistent with the technical analyses 

provided in the South Coast PM2.5 SIP, and we believe these 

assessments provide a reasonable basis for concluding that the 

level of air quality improvement observed for 2012 equates to an 

amount of NOx-equivalent emission reductions that exceeds both 

the amount needed to achieve 1 year’s worth of RFP and the 

amount needed to meet the 2012 RFP benchmarks in the South Coast 

PM2.5 SIP.8 

These assessments of the level of NOx-equivalent emission 

reductions needed to achieve an air quality “improvement” in the 

 

8 EPA approved the 2012 RFP benchmarks in the South Coast PM2.5 SIP, which 

were based on the plan’s emissions projections for 2012. See 76 FR at 41578, 

Table 8 (“Revised RFP Calculations”) and 76 FR 69928 at 69952 (final rule). 

Given our conclusion that ambient PM2.5 levels projected in the plan for 2012 

were consistent with RFP for that year, it follows that a lower ambient PM2.5

level observed for 2012 also represents an emission level consistent with RFP 

in 2012. 
8 

range of 0.95 to 1.47 μg/m3 also support a conclusion that the 

attainment demonstration in the South Coast PM2.5 SIP contains 

some amount of “surplus” emission reductions. Specifically, 

because the District demonstrated attainment using 15.00 μg/m3 as 

the target emission level in its modeling analyses, rather than 

15.04 μg/m3 as provided in EPA guidance, the “additional” 0.04 

μg/m3 of air quality improvement accounted for in the 

demonstration may be characterized as “surplus” to attainment 

needs. The precursor-equivalent ratios provided in Appendix V 

of the South Coast 2007 AQMP, at Table V-2-14 (“Relative 

Contributions of Precursor Emissions Reductions to Simulated 

Controlled Future Year PM2.5 Concentrations”), and the 

District’s broader assessment of the level of emission 

reductions needed for attainment in the South Coast Basin,9

provide an indication of the level of NOx-equivalent or SOxequivalent reductions (in tons) needed to achieve this level of 

“additional” air quality improvement (in μg/m3). See id. at V-2-

52. 

 

9 See South Coast 2007 AQMP, Appendix V at V-2-19, V-2-53, V-2-61, and V-2-62.