Appendix C 

PM2.5 Reasonable Further Progress Calculations 

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PM2.5 Reasonable Further Progress Calculations 

The CAA requires SIPs to provide for steady progress in reducing emissions during the 

years leading to the attainment date. This requirement, added as part of the 1990 

amendments, provides a way to measure compliance prior to the attainment date. 

U.S. EPA requires that the RFP plan show linear progress according to emission 

reduction milestones the region establishes for 2009, and every three years thereafter 

until the attainment year. 

For PM2.5, U.S. EPA guidance provides two alternatives for assessing RFP for PM2.5 

strategies. The traditional approach assesses progress for each precursor against the 

required rate of progress without considering how much each precursor contributes to 

ambient PM2.5 concentrations (the “linear” option). The second uses information 

gained from the attainment demonstration modeling to consider how much reductions of 

each pollutant contribute to attainment (the “equivalency” option). In essence, the 

relative contribution approach approximates the progress that will be made in improving 

air quality 

1. Linear RFP Calculation Option 

The following table assesses progress made with the proposed South Coast Plan, 

including the adopted AQMP, and the proposed State Strategy with proposed 

consensus amendments, using U.S. EPA’s linear reasonable further progress option. 

The assessment indicates that reductions of directly emitted PM2.5 and NOx do not 

meet RFP targets in 2009 and 2012 when calculated from a 2002 baseline inventory. 

Reductions of VOC and SOx, however, exceed linear RFP targets in all years. The 

District’s air quality models indicate that SOx and directly emitted PM10 reductions have 

a greater impact on ambient PM2.5 levels than ROG reductions and, to a lesser extent, 

than NOx reductions. The linear approach does not reflect those impacts. 

Table 1

Linear Reasonable Further Progress Calculation 

 

Row Calculation Step PM2.5 NOx SOx VOC

1 2002 Baseline Inventory 99 1093 53 844

2 Control Ratio Needed to Show Linear Progress in 2009 (%) 7/12 

 

7/12 7/12 7/12

3 2009 Target Needed to Show Linear Progress (tpd) 92 720 33 625

4 2009 Remaining Emissions with Plan (tpd) 99 813 28 578

5 Projected Shortfall (tpd) 7 93 0 0

6 Control Ratio Needed to Show Linear Progress in 2012 (%) 5/6 5/6 5/6 5/6 

7 2012 Target Needed to to Show Linear Progress (tpd) 89 561 25 532

8 2012 Remaining Emissions with Plan (tpd) 92 565 21 505

9 Projected Shortfall (tpd) 3 5 0 0

10 2014 Remaining Emissions with Plan (tpd) 87 454 19 469

 
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2. Equivalency RFP Calculation Option 

An RFP evaluation that accounts for the differential impacts that each of the PM2.5 

precursors has on ambient concentrations demonstrates that the proposed strategy also 

allows the South Coast Air Basin to meet RFP targets. The District’s modelers used the 

results of 2014 modeling, using the strategy recommended for approval, to determine 

the PM2.5 reduction value of each of the precursor pollutants and to assess equivalent 

progress against RFP targets. The District’s methodology is described below. 

The PM2.5 attainment modeling simulation was conducted using projected emission 

reductions for control measure implementation for 2014 (CEPA scenario 1). The output 

of the simulation was averaged by component species for the eight validation sites that 

represent the Basin. Since a 2005 base year was used for the PM2.5 modeling, this 

basin average PM2.5 species profile was then compared to the 2005 data and the 

difference in concentration between 2014 with implementation of the plan and 2005 

ammonium sulfate, ammonium nitrate, organic carbon and particulate (metals and 

elemental carbon) concentrations were calculated. The particulate component 

difference concentrations were divided by the emissions reductions for the same period 

to determine species-specific projected concentrations reductions per unit of emission 

reduction. These ratios were then used to compute NOx-equivalent weighting factors 

for converting species-specific inventory values to NOx-equivalent inventory values for 

purposes of comparing RFP targets with projected inventory levels on a NOx-equivalent 

basis. The reason for converting inventories to a NOx-equivalent basis is that 

emissions reductions in some species will exceed RFP targets in 2009 while other 

species will fall short. On the whole, however, the cumulative reductions across all 

species will produce PM2.5 concentration reductions that are generally linear with time 

and that comply with RFP requirements. 

Table 2 summarizes the basin-average conversion factors that relate projected 

emissions reductions with reductions in PM2.5 concentrations. Due to differences in 

particle formation rates, reductions in emissions of SOx and directly-emitted PM2.5

produce much greater reductions in PM2.5 concentrations than occur with reductions in 

emissions of NOx and ROG. Table 3 presents the NOx-equivalent weighting factors 

where the SOx, ROG and PM2.5 basin-average conversion factors are normalized to 

that for NOx. These basin-average conversion factors are then used to convert both 

RFP target emission inventories and plan-projected emission inventories to NOxequivalent inventories for comparison purposes as dictated by RFP requirements. 

Tables 4 and 5 provide the RFP calculations for the 2002- and 2005 base-years 

respectively. The tables convert emission inventories to a NOx-equivalent basis. For 

the 2002 base year, the 2009 plan-projected inventory falls short of the RFP target by 

2.8 percent. For the 2005 base year, the plan-projected inventory in 2009 achieves the 

target reduction and demonstrates compliance with RFP requirements. Under both 

alternatives, RFP requirements are satisfied in 2012. Because the basin-average 

conversion factors were determined from gridded modeling performed for the 2005 
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emission inventory year, this year is the most appropriate base year for the RFP 

analysis. 

Figure 1 plots the emission inventory totals and the RFP targets under the 2005 base 

year alternative. When a best fit line is overlaid, it is clear that the emissions reductions 

are taking place in a linear fashion, not clustered or back loaded. This graphic 

illustrates the intention of the RFP requirement and lends support that a nominal 

shortfall of a few percent in near term reductions in 2009 is not inconsistent with the 

overall annual rate of required emissions reductions. 

Table 2 

Basin-Average Conversion Factors 

Basin-Average Conversion Factors 

Pollutant Species Species Concentration (ug/m3) 

PM2.5 EC & Crustal 0.0345 

NOX Ammonium Nitrate 0.0035 

SOX Ammonium Sulfate 0.0526 

ROG Organic Carbon 0.0015 

Table 3 

Normalized NOx-Equivalent Conversion Factors 

Normalized NOx-Equivalent Conversion Factors 

Pollutant Species NOX Equivalent Factor 

PM2.5 9.8571 

SOX 15.0286 

ROG 0.4286 

Table 4 

 2002 RFP Anchor Year 

 

 Required Required NOx Equivalent 

 2002 2009 2012 2014

Annual 

Change 2002 2009 2012 2014

PM2.5 99 91 88 86 1.0943% PM2.5 976 897 867 848

NOx 1093 719 559 452 4.8872% NOx 1093 719 559 452

SOx 53 34 26 20 5.1887% SOx 797 511 391 301

ROG 844 628 536 474 3.6532% ROG 362 269 230 203

Total 2089 1472 1208 1032 Total 3227 2396 2047 1803

 Projected Projected NOx Equivalent 

 2002 2009 2012 2014 2002 2009 2012 2014

PM2.5 99 99 92 86 PM2.5 976 976 913 848

NOx 1093 819 566 452 NOx 1093 819 566 452

SOx 53 28 21 20 SOx 797 421 313 301

ROG 844 579 505 474 ROG 362 248 214 203

Total 2089 1525 1184 1032 Total 3227 2464 2006 1803
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Table 5 

2005 RFP Anchor Year 

 

 Required Required NOx Equivalent 

 2005 2009 2012 2014

Annual 

Change 2005 2009 2012 2014

PM2.5 102 95 89 86 1.3072% PM2.5 1005 936 877 848

NOx 1033 775 581 452 4.6870% NOx 1033 775 581 452

SOx 61 43 29 20 5.6011% SOx 917 646 436 301

ROG 825 669 552 474 3.5455% ROG 354 287 237 203

Total 2021 1582 1251 1032 Total 3309 2644 2131 1803

 Projected Projected NOx Equivalent 

 2005 2009 2012 2014 2005 2009 2012 2014

PM2.5 102 99 92 86 PM2.5 1005 980 904 848

NOx 1033 819 566 452 NOx 1033 819 566 452

SOx 61 28 21 20 SOx 917 425 311 301

ROG 825 579 505 474 ROG 354 248 216 203

Total 2021 1526 1184 1032 Total 3309 2472 1998 1803

Figure 1 

 RFP Calculations Trend 

Linear and NOx-Equivalent, 2005 Base Year 

RFP Demonstrations: Actual and NOxEquivalent Emissions

0

1000

2000

3000

4000

2004 2006 2008 2010 2012 2014 2016

tons per day

Actual Required NOx-Equivalent Projected

Actual Projected NOx-Equivalent Required

Linear (Actual Projected) Linear (NOx-Equivalent Projected)