### 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 PM 2.5



### 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 PM 2.5



### SIP had predicted that implementation of the plan would result

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

μg/m 3 

### in 2005 to a value of 17.98 μg/m 3 

### in 2010. Id. at 5. The

maximum observed design value for 2010 at the design value site 1



### (Rubidoux 2 

### ), however, was 15.01 μg/m 3 

### 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 PM 2 .5 SIP as i t 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 PM 2.5 

### levels due to favorable weather and

reduced economic activity, the District estimates the PM 2.5



### design value “improvement” attributable to implementation of its

plans, compared to previous projections, to be approximately

1.88 μg/m 3 

### in 2010. Id. at 8-10 and Table 2. If PM 2.5 

### 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/m 3 

### improvement over

the 2012 projections underlying the South Coast PM 2.5 

### SIP. Id.

at 5. According to the District, these PM 2.5 

### air quality

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

NOx emission reductions in 2012. Id.

EPA independently reviewed PM 2.5 

### air quality data available

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

assess the District’s representations regarding PM 2.5 

### air quality

improvements in the South Coast area. 3 

### PM 2.5 

### air quality data

collected through the District’s monitoring network and

available in AQS indicate that ambient PM 2.5 

### 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 PM 2.5 

### SIP for this period.

Table 1 lists the annual mean PM 2.5 

### concentration at each

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

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

Sit e A Q S I D One

- y e a r A nnu a l M e a n ( μg /m 3 )

2 002 2 003 2 004 2 005 2 006 2 007 2 008 2 009 2 010 2 011 2 012

A z u sa 0 60 3 70 0 02 20 .7 19 .3 18 .3 17 .0 15 .4 15 .7 14 .0 13 .1 10 .8 12 .1 10 .2

B u r b a n k

– P a lm A ve. 0 60 3 71 0 02 24 .0 22 .1 19 .1 17 .8 16 .5 16 .9 13 .9 15 .3 12 .8 13 .5 11 .7

LA

– N o r t h

M a in 0 60 3 71 1 03 22 .0 21 .3 19 .7 17 .8 15 .6 16 .8 16 .1 14 .4 12 .6 13 .5 12 .2

Re s e da 0 60 3 71 2 01 18 .9 16 .5 15 .7 13 .9 12 .8 13 .3 11 .8 11 .4 10 .1 10 .2 9 .8 Ly n w ood 0 60 3 71 3 01 23 .3 20 .3 18 .5 17 .5 16 .7 16 .0 14 .6 13 .0 11 .5

C om p ton 0 60 3 71 3 02 12 .4 14 .7 12 .5 12 .5 11 .3

P ico R i v e r a
#1 0 60 3 71 6 01 24 .0 20 .6 20 .0 15 .2

P ico R i v e r a
#2 0 60 3 71 6 02 22 .3 16 .6 16 .6 14 .9 14 .8 12 .5 12 .5 11 .3

P a s a d e na 0 60 3 72 0 05 20 .3 18 .6 16 .6 15 .1 13 .4 14 .4 12 .8 12 .3 10 .2 10 .8 10 .3

L o n g
B e a ch 0 60 3 74 0 02 19 .5 18 .0 17 .9 15 .9 14 .1 14 .6 14 .1 12 .8 10 .4 11 .3 10 .0

L o n g
B e a ch – P CH 0 60 3 74 0 04 20 .6 16 .5 14 .7 14 .4 13 .7 13 .7 12 .5 10 .4 10 .7 10 .3

A n a h e im 0 60 5 90 0 07 18 .6 17 .3 17 .0 14 .7 14 .0 14 .4 13 .1 12 .1 10 .5 11 .1 10 .3

Mi ss ion

V i e jo 0 60 5 92 0 22 15 .5 13 .1 12 .0 10 .6 11 .0 11 .1 10 .4 9 .5 8 .0 8 .5 7 .6

R i v e r s ide 0 60 6 51 0 03 27 .1 22 .6 20 .8 17 .9 16 .9 18 .3 13 .3 13 .3 11 .0 11 .8 10 .5

R ubid o ux 0 60 6 58 0 01 27 .5 24 .8 22 .1 20 .9 18 .9 19 .0 16 .4 15 .6 13 .3 13 .8 13 .5

Mi r a L om a 0 60 6 58 0 05 20 .8 20 .9 18 .3 17 .2 15 .5 15 .9 15 .0

On t a r io 0 60 7 10 0 25 25 .4 23 .8 20 .9 18 .8 18 .4 18 .3 15 .8 14 .7 13 .0 13 .3 11 .8

Fo n t a na 0 60 7 12 0 02 24 .3 22 .1 19 .9 18 .8 17 .5 18 .9 15 .3 14 .2 11 .9 12 .6 11 .9

B i g B e ar 0 60 7 18 0 01 11 .5 10 .6 9 .6 12 .0 11 .3 10 .3 9 .1 9 .9 8 .4 8 .4 8 .0

S a n
B er n a r dino 0 60 7 19 0 04 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, PM 2 .5 , 2002-2012 (Report Date: May 10, 2013). 

### Table 2 lists the annual PM 2.5 

### 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

Sit e A Q S I D A nnu a l D e s i g n Va l u e ( μg /m 3 ) 4

2 002 2 003 2 004 2 005 2 006 2 007 2 008 2 009 2 010 2 011 2 012

A z u sa 0 60 3 70 0 02 20 .8 20 .6 19 .4 18 .2 16 .9 16 .0 15 .1 14 .3 12 .7 12 .0 11 .0

B u r b a n k

– P a lm A ve. 0 60 3 71 0 02 23 .3 23 .6 21 .7 19 .7 17 .8 17 .1 15 .8 15 .4 14 .0 13 .9 12 .6

LA

– N o r t h

M a in 0 60 3 71 1 03 22 .2 22 .0 21 .0 19 .6 17 .7 16 .7 16 .1 15 .8 14 .4 13 .5 12 .8

Re s e da 0 60 3 71 2 01 18 .4 17 .9 17 .0 15 .4 14 .1 13 .3 12 .6 12 .1 11 .1 10 .6 10 .0 Ly n w ood 0 60 3 71 3 01 23 .6 22 .7 20 .7 18 .7 17 .5 16 .7 15 .8 15 .3 14 .6

C om p ton 0 60 3 71 3 02 12 .4 13 .5 13 .2 13 .4 12 .3

P ico R i v e r a
#1 0 60 3 71 6 01 24 .4 23 .3 21 .5 18 .6 17 .6 15 .2

P ico R i v e r a
#2 0 60 3 71 6 02 22 .3 19 .5 18 .5 16 .0 15 .4 14 .1 13 .3 12 .1

P a s a d e na 0 60 3 72 0 05 20 .2 19 .9 18 .5 16 .8 15 .0 14 .3 13 .5 13 .2 11 .8 11 .1 10 .4

L o n g
B e a ch 0 60 3 74 0 02 20 .1 19 .6 18 .5 17 .3 16 .0 14 .9 14 .3 13 .9 12 .4 11 .5 10 .6

L o n g
B e a ch – P CH 0 60 3 74 0 04 20 .6 18 .6 17 .3 15 .2 14 .3 13 .9 13 .3 12 .2 11 .2 10 .5

A n a h e im 0 60 5 90 0 07 22 .0 20 .4 17 .6 16 .3 15 .2 14 .3 13 .8 13 .2 11 .9 11 .2 10 .6

Mi ss ion

V i e jo 0 60 5 92 0 22 15 .4 14 .8 13 .5 11 .9 11 .2 10 .9 10 .8 10 .3 9 .3 8 .7 8 .0

R i v e r s ide 0 60 6 51 0 03 26 .9 25 .9 23 .5 20 .5 18 .6 17 .7 16 .2 15 .0 12 .5 12 .0 11 .1

R ubid o ux 0 60 6 58 0 01 28 .9 27 .8 24 .8 22 .6 20 .6 19 .6 18 .1 17 .0 15 .1 14 .2 13 .5

Mi r a L om a 0 60 6 58 0 05 20 .8 20 .9 20 .0 18 .8 17 .0 16 .2 15 .5

On t a r io 0 60 7 10 0 25 25 .3 25 .2 23 .4 21 .2 19 .4 18 .5 17 .5 16 .2 14 .5 13 .7 12 .7

Fo n t a na 0 60 7 12 0 02 24 .6 23 .8 22 .1 20 .3 18 .7 18 .4 17 .2 16 .1 13 .8 12 .9 12 .1

B i g B e ar 0 60 7 18 0 01 10 .9 11 .1 10 .6 10 .8 11 .0 11 .2 10 .3 9 .8 9 .1 8 .9 8 .3

S a n
B er n a r dino 0 60 7 19 0 04 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, PM 2 .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 PM 2.5 

### levels in the South Coast area in 2010 were, in

fact, lower than the levels projected in the South Coast PM 2.5



### 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 PM 2.5 

### levels

at the Rubidoux monitoring site from 22.7 μg/m 3 

### in 2005 to 17.9

μg/m 3 

### 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/m 3



### ( see Table 2 above), 2.8 μg/m 3 

### lower than the 17.9 μg/m 3



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

difference the 1.09 μg/m 3 

### 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 PM 2.5



### level at the Rubidoux site in 2010 would be approximately 1.71

μg/m 3 

### . Further assuming, conservatively, that PM 2.5 

### levels at the

Rubidoux site remain at 2010 levels through 2012, the design

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

PM 2.5 

### levels for 2012 would be approximately 1.35 μg/m 3 

### . Finally,

5 The Contingency Measures SIP, as supplemented in 2013, references portions of a 2007 CARB Staff Report as the source of the “predicted” PM 2 .5 design values ( i.e., the ambient PM 2 .5 levels p r ojected for future years in the South

Coast PM 2 .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 PM 2 .5 SIP

.

### 6

if we take into account the higher PM 2.5 

### levels recorded at the

Mira Loma monitoring site, 6 

### the design value “improvement” for

2012 would be reduced to approximately 0.95 μg/m 3



### .

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 PM 2.5 

### 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 PM 2 .5 design v alue site in the South Coast area, has also recorded significant declines in ambient PM 2 .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 PM 2 .5 lev e ls 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 PM 2 .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/m 3 

### ). 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/m 3 

### ) to be generally consistent with the technical analyses

provided in the South Coast PM 2.5 

### 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

PM 2.5 

### 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 PM 2 .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 PM 2 .5 l evels projected in the plan for 2012 were consistent with RFP for that year, it follows that a lower ambient PM 2 .5 level observed for 2012 also represents an emission level consistent with RFP

in 2012.

### 8

range of 0.95 to 1.47 μg/m 3 

### also support a conclusion that the

attainment demonstration in the South Coast PM 2.5 

### SIP contains

some amount of “surplus” emission reductions. Specifically,

because the District demonstrated attainment using 15.00 μg/m 3 

### as

the target emission level in its modeling analyses, rather than

15.04 μg/m 3 

### as provided in EPA guidance, the “additional” 0.04

μg/m 3 

### 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/m 3 

### ). 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.