Analysis of the Interim Year 2019 as a Supplement to the 

2009 MAG Eight-Hour Ozone Redesignation Request and Maintenance 

Plan for the Maricopa Nonattainment Area

June 17, 2013
A supplemental analysis of precursor emissions and eight-hour ozone concentrations for the 

interim year 2019 has been performed1 using the air quality models described in the MAG 

Eight-Hour Ozone Redesignation Request and Maintenance Plan for the Maricopa 

Nonattainment Area, February 2009. The 2019 volatile organic compound (VOC) and nitrogen 

oxide (NOx) emissions were derived by interpolating emissions for 2016 and 2021.2 The 

emissions for the three episodes in June, July and August of 2016 and 2021, as well as the 

interpolated 2019 values, are shown in Tables 1-3. The 2019 VOC and NOx emissions 

summarized in Table 4 were used to estimate eight-hour ozone concentrations for the interim 

year of 2019. 

Table 5a identifies the population and employment projections used in estimating precursor 

emissions for 2016, 2021 and 2025. The socioeconomic projections that were input to the 

travel demand models were adopted by the MAG Regional Council in May 2007. Other inputs 

to the travel demand models include transportation networks that incorporate regionally 

significant highway and transit projects in the MAG FY 2011-2015 Transportation Improvement 

Program (TIP) and Regional Transportation Plan 2010 Update (RTP), adopted by the MAG 

Regional Council in July 2010. The MAG traffic assignments used to estimate onroad mobile 

source emissions for 2016 and 2021 were completed on May 31, 2011.

The socioeconomic projections adopted by the Regional Council in 2007 are based on the 2005 

Special Census for Maricopa County and do not take into consideration the severe economic 

recession that began in 2008. Since the 2010 U.S. Census reveals that population growth in 

Maricopa County slowed considerably between 2005 and 2010, as indicated by the actual 

compound annual growth rate of 0.8% shown in Table 5b, the socioeconomic projections used 

in this analysis are over-estimated and the projected ozone concentrations for 2019 should be 

considered very conservative.

 

The maximum eight-hour ozone concentrations in the interim year of 2019 are shown in Table 

6. Eight-hour ozone design values for 2019, derived from the output of the EPA-approved 

Comprehensive Air Quality Model with Extensions (CAMx), indicate that the maximum 

concentrations will be 0.0810 ppm in June, 0.0800 ppm in July and 0.0796 ppm in August, all at 

the North Phoenix monitor. The Modeled Attainment Test Software (MATS) indicates that the 

maximum unmonitored concentrations in 2019 will be 0.0823 ppm in June, 0.0806 ppm in July, 

and 0.0831 in August. Both the monitored and unmonitored concentrations in 2019 meet the 

1997 eight-hour ozone standard of 0.08 ppm. 

The highest design value at a monitor in 2019, 0.0810 ppm, is identical to the maximum

concentration in 2025, as reported by the 2009 Eight-Hour Ozone Maintenance Plan. Both

occur during the June episode at the North Phoenix monitor.

1

As requested by EPA in a June 4, 2013 e-mail from Anita Lee.

2

In 2011, MAG performed CAMx modeling for the years 2016 and 2021, as requested in a 

March 14, 2011 letter from Colleen McKaughan, EPA.

 
Table 1 - Emissions for the June Episode (June 6) for Eight-Hour Ozone Modeling 

Domain (metric tons/day)

Source

2016 2019 2021

VOC NOx VOC NOx VOC NOx

Point 15.6 58.4 16.7 58.6 17.4 58.7

Area 104.1 25.8 111.4 27.7 116.2 28.9

Onroad 52.6 130.0 48.7 125.8 46.1 122.9

Nonroad 31.0 49.8 30.9 43.9 30.9 39.9

Biogenic 451.3 8.6 451.3 8.6 451.3 8.6

Total 654.5 272.7 659.0 264.4 661.9 258.9

Table 2 - Emissions for the July Episode (July 9) for Eight-Hour Ozone Modeling 

Domain (metric tons/day)

Source

2016 2019 2021

VOC NOx VOC NOx VOC NOx

Point 15.6 58.4 16.7 58.6 17.4 58.7

Area 104.1 25.8 111.4 27.7 116.2 28.9

Onroad 54.0 124.9 49.5 120.8 46.6 118.0

Nonroad 28.3 47.2 28.1 41.4 28.0 37.5

Biogenic 639.9 11.9 639.9 11.9 639.9 11.9

Total 841.8 268.2 845.6 260.2 848.2 254.9

Table 3 - Emissions for the August Episode (August 10) for Eight-Hour Ozone Modeling 

Domain (metric tons/day)

Source

2016 2019 2021

VOC NOx VOC NOx VOC NOx

Point 15.6 58.4 16.7 58.6 17.4 58.7

Area 104.1 25.8 111.4 27.7 116.2 28.9

Onroad 53.3 123.0 49.4 119.7 46.8 117.6

Nonroad 29.8 48.7 29.7 43.0 29.7 39.2

Biogenic 398.4 9.6 398.4 9.6 398.4 9.6

Total 601.2 265.5 605.6 258.5 608.6 253.9

Note: Emissions in 2019 in Tables 1-3 were interpolated using 2016 and 2021 emissions
Table 4 - Emissions in 2019 for the Eight-Hour Ozone Modeling Domain 

(metric tons/day)

Source

June 6 July 9 August 10

VOC NOx VOC NOx VOC NOx

Point 16.7 58.6 16.7 58.6 16.7 58.6

Area 111.4 27.7 111.4 27.7 111.4 27.7

Onroad 48.7 125.8 49.5 120.8 49.4 119.7

Nonroad 30.9 43.9 28.1 41.4 29.7 43.0

Biogenic 451.3 8.6 639.9 11.9 398.4 9.6

Total 659.0 264.4 845.6 260.2 605.6 258.5

Table 5a - Population and Employment Projections for the Maricopa 

Eight-Hour Ozone Nonattainment Area

Resident 

Population

Compound Annual 

Growth Rate

Total 

Employment

Compound Annual 

Year Growth Rate

2005 3,764,712 1,760,200

2016 4,976,262 2005 to 2016 2.6% 2,564,797 2005 to 2016 3.5%

2021 5,508,732 2016 to 2021 2.1% 2,879,077 2016 to 2021 2.3%

2025 5,895,296 2021 to 2025 1.7% 3,121,769 2021 to 2025 2.0%

Table 5b - Census Based Population Estimates for 

Maricopa County

Resident 

Population

Compound Annual 

Date Growth Rate

July 1, 2005 3,681,300

July 1, 2010 3,824,058 2005 to 2011 0.8%
Table 6 - CAMx Eight-Hour Ozone Maintenance Monitored and Unmonitored Area 

Analysis Results for Interim Year 2019 

Site Name Site ID AIRS Design Values (ppm)

June July August

Tonto NM TNM 40070010 0.0785 n/a n/a

West Phoenix WP 40130019 0.0717 0.0708 0.0720

Mesa ME 40131003 n/a n/a n/a

North Phoenix NP 40131004 0.0810 0.0800 0.0796

Falcon Field FF 40131010 0.0739 0.0733 0.0743

Glendale GL 40132001 0.0753 0.0746 0.0743

Pinnacle Peak PP 40132005 0.0753 0.0747 0.0735

Central Phoenix CP 40133002 0.0745 0.0733 0.0726

South Scottsdale SS 40133003 0.0754 0.0744 0.0752

Emergency Management EM 40133004 n/a n/a n/a

Maryvale MV 40133006 n/a n/a n/a

South Phoenix SP 40134003 0.0718 0.0706 0.0719

West Chandler WC 40134004 0.0735 0.0733 0.0731

Tempe TEMP 40134005 0.0745 0.0736 0.0750

Cave Creek CC 40134008 0.0772 0.0768 0.0762

Dysart DY 40134010 0.0656 0.0657 0.0639

Buckeye BE 40134011 0.0628 0.0630 0.0634

Laveen LV 40137003 0.0686 0.0678 0.0701

Humboldt Mountain HM 40139508 0.0794 0.0782 0.0783

Mount Ord MORD 40139701 n/a n/a n/a

Blue Point BP 40139702 0.0715 0.0711 0.0710

Fountain Hills FH 40139704 0.0802 0.0796 0.0790

Rio Verde RV 40139706 0.0800 0.0784 0.0786

Palo Verde PALV 40139993 n/a n/a n/a

Salt River - Pima SRPI 40139994 n/a n/a n/a

Super Site SUPR 40139997 0.0730 0.0720 0.0729

Apache Junction AJ 40213001 0.0711 0.0708 0.0702

Casa Grande CG 40213003 0.0691 n/a n/a

Queen Creek QC 40213009 0.0640 0.0625 n/a

Maricopa MCPA 40213010 0.0624 n/a n/a

Sacaton SAC 40217001 0.0688 n/a n/a

Queen Valley QV 40218001 0.0783 0.0765 n/a

Unmonitored Area Analysis (Max) 0.0823 0.0806 0.0831
Plots of the 2019 design values by episode, based on CAMx output, are provided in Figures 1-3. 

The highest unmonitored concentration occurs during the August episode in both 2019 and 

2025, but the 2019 maximum is 0.0003 ppm less than in 2025.

The socioeconomic projections and air quality models used in performing the supplemental 

analysis for the interim year 2019 are the same as those described in the 2009 MAG Eight-Hour 

Ozone Redesignation Request and Maintenance Plan for the Maricopa Nonattainment Area. 

However, the transportation projects in the FY 2011-2015 TIP and RTP 2010 Update, the truck 

model, and vehicle registrations, were updated between 2009 and 2011. To ensure that these 

changes did not have an impact on the demonstration of maintenance, 2025 concentrations 

were re-estimated using the version of the travel demand models, TIP and RTP projects, and 

vehicle registrations, as of June 2011. Table 7 summarizes the maximum concentrations in 

2025, as reported in the 2009 Eight-Hour Ozone Maintenance Plan, compared with the 2025 

maximum concentrations output by CAMx and MATS modeling performed in June 2011. In 

spite of the changes to the transportation networks, models, and vehicle registrations, the 

maximum monitored concentrations in 2025 are within 0.0004 ppm for all episodes, while the 

unmonitored area values are within 0.001 ppm. This table confirms that the changes to the 

transportation projects and models have an insignificant impact on maintenance of the eighthour ozone standard in 2025 and that the 2019 concentrations shown in this supplemental 

analysis are consistent with the 2025 concentrations reported in the 2009 Eight-Hour Ozone 

Maintenance Plan. 
Figure 1 - Design Values (ppm) at Monitoring Sites in June 2019 
Figure 2 - Design Values (ppm) at Monitoring Sites in July 2019
Figure 3 - Design Values (ppm) at Monitoring Sites in August 2019
Table 7 - Comparison of Maximum Eight-Hour Ozone Concentrations in 2025 -

February 2009 Plan vs. June 2011 Supplemental Modeling

 2025 Monitored Area Maximum1

2025 Unmonitored Area 

Maximum2

Episode 2009 O3 Plan 2011 Modeling 2009 O3 Plan 2011 Modeling

June 0.0810 0.0807 0.0813 0.0816

July 0.0794 0.0798 0.0791 0.0801

August 0.0799 0.0795 0.0834 0.0834

1

Maximum 8-hr ozone concentrations estimated near monitoring sites by CAMx and MATS.

2

Maximum 8-hr ozone concentrations estimated in unmonitored areas by MATS.