Air Quality Demonstration: 

SIP Revision for CPV Sentinel Energy Project 

Air Quality Impacts 

The impacts to regional air quality resulting from the proposed Sentinel power plant were 

analyzed for three primary criteria air pollutants: ozone, PM2.5 and PMl 0. This analysis 

examines the regional impacts for two air basins for which the District has jurisdiction 

including the South Coast Air Basin and the Coachella Valley portion of the Salton Sea Air 

Basin. More specifically, the impacts of the project are analyzed for 8-hour average ozone, 

24-hour and annual average PM2.5 and PMI 0. U.S. EPA has designated the South Coast 

Air Basin as extreme non- attainment for ozone and the Coachella Valley as Severe-1 5. 

This means that the South Coast Air Basin must attain the federal standard by 2024 and the 

Coachella Valley by 201 8. In addition, both air basins are designated as severe nonattainment for 24-hour average PM10. Furthermore, the South Coast Air Basin is one of 

two regions in California that is designated as non-attainment for annual average PM2.5 

with an attainment date of 201 5. In contrast, the Coachella Valley has been in compliance 

with the federal PM2.5 standards with observed concentrations typically at values of only 

.a- two thirds of the NAAQS. 

The South Coast Air Basin and Coachella Valley have been in compliance with the federal 

air quality standards for SO2 and NO2 for more than a decade. The South Coast Air Basin 

and Coachella Valley are both expected to continue to be in compliance with the recent 

proposed revisions to the federal standard for each criteria pollutant. California has 

recently lowered the state annual NO2 air quality standard (below the corresponding 

federal level) and the Basin was designated in February 20 10 as non-attainment. It is 

important to note that the degree the Basin was found to in excess of the standards was 

fractional and is expected to be remedied shortly due to oxide of nitrogen controls 

scheduled to be implemented to meet the 2015 PM2.5 attainment date. 

Regional Simulation Methodology 

To determine the air quality impact due to the Sentinel project, future-year concentrations 

of ozone and PM2.5 were simulated using the project emissions and then compared to the 

predicted baseline future year air quality. The simulated impacts to future year air quality 

were determined using the 2007 AQIVIP air quality modeling methodology. The years 

selected for simulations included 2014 for PM2.5 and 2023 for ozone. 

Briefly, the regional impacts are simulated by using National Weather Service (NWS) 

numerical meteorological model data to provide the characterization of the hourly weather 

-. that is coupled with a peer reviewed regional air quality dispersion platform that reacts and 

transports emissions throughout a modeling domain. The 2007 AQMP modeling domain 

extends from 100 kilometers west of Palos Verdes Peninsula east through Joshua Tree 

National Monument. The southern boundary of the modeling domain extends into Mexico 

and the northern extent of the domain touches the San Joaquin Valley. Air quality impacts 
were simulated for a 5 X 5 kilometer grid. The South Coast Air Basin and Coachella 

Valley are both fully represented in the modeling domain. 

The 2007 AQMP used a the state-of-the art modeling platform which utilized the 

combination of the Comprehensive Air Quality Model with Extensions (CAMx) dispersion 

model with the "one atmosphere" chemistry mechanism to simulate annual average 

particulate air quality and CAMx with the SAPRC99 chemistry mechanism to simulate 

episodic gaseous ozone air quality. The MM5 meteorological model provided critical 

meteorological inputs for the daily and annual simulations. The simulations utilized 

mobile source emissions provide by CARB7s EMFAC~M~ and the growth and planning 

assumptions provided by SCAG from their Interim 2007 Regional Transportation Plan. 

Point and areas source emissions profiles were developed jointly by the District and 

CAW. A comprehensive discussion of the modeling techniques, input data and model 

performance is provided in Appendix V of the 2007 AQMP, available at 

www.aqmd. govlaq mp/07aqmp/aq mp/Appendix V.pdf. 

As described in Appendix V of the 2007 AQMP, the regional numerical air quality 

projections followed U.S. EPA guidance using relative response factors (RRF) to estimate 

future year ozone and PM2.5 design values to determine future year attainment of the 

respective 8-hour average and annual average standards. The RRFs were used to adjust 

simulated future year air quality by accounting for variance in the model performance. 

The ozone simulations were conducted using the CAMx/MM5/SAPRC99 platform for a 

series of meteorological episodes identified in the 2007 AQMP attainment demonstration. 

Two indices are presented in the air quality analysis to characterize the impact of the 

projects: the ozone air quality impact to the area in each air basin having the projected 

maximum concentration; and, the average ozone impacts predicted throughout each of the 

basins. The ozone simulations were conducted for the 2023 baseline and the baseline plus 

the Sentinel power plant emissions. The impact of the project was estimated by calculating 

the difference in the simulated impacts for the two emissions scenarios. 

The annual PM2.5 simulations were generated for the CAMx/MM5/One-Atmosphere 

platform for every hour in the year for 2014 for the 2007 AQMP baseline emissions and 

those for the Sentinel project. The emissions from the proposed source are combustion 

related and almost exclusively in the fine particulate size distribution. Similarly, the 

projected secondary formation of particulates is expected to be concentrated in the fine size 

scale as well. As a consequence, this analysis assumes that the PM2.5 and PM10 impacts 

are the same. Future year annual average PMlO concentration impacts were assumed 

equivalent to the PM2.5 impact for both the annual and 24-hour averaging periods. 

Visibility 

Visibility impacts to nearby Joshua Tree, San Gorgonio, San Jacinto Class I wilderness . 

areas were estimated using the CAMx predicted PM2.5 and gaseous air quality coupled 
with the Interagency Monitoring of Protected Visual Environments (IMPROVE) 

methodology. The EPA sponsored IMPROVE program was established to provide 

background measurements and visual range calculation in support of the federal Regional 

Haze Rule visibility standard attainment. The IMPROVE technique utilizes empirical 

relationship visibility-air quality equations to provide visual range in miles which can be 

converted into deciviews. 

The deciview is an index that scales humanly-perceived changes in visual air quality. The 

deciview increases as haze increases (and visual range decreases). In general, perception 

of visibility beyond 8-10 miles is very subjective and subtle changes in range are not easily 

detected by the eye. (Until recent upgrades in automated monitoring, many military 

airports would not report range more than 8 miles). The deciview index is directly used as 

the metric for visibility assessment in the federal Regional Haze Rule criterion. A 

deciview is approximately a 10% change in the light extinction reading. Impacts from 

sources that result in a 0.5 deciview reduction are considered by EPA to be significant. 

Air Quality Impacts 

Table 1 summarizes the predicted 8-hour ozone and PM2.51PM10 impacts to the Coachella 

Valley and Basin. 

Ozone 

The maximum increase in 8-hour average ozone concentrations predicted for the Coachella 

Valley was at 0.3 ppb. The predicted increase to maximum ozone in the South Coast Air 

Basin due to the Sentinel power plant was 0.1 ppb. The predicted average Coachella Valley 

ozone impact was valued at 0.1 ppb and the average South Coast Air Basin impact at less 

than 0.1 ppb. 

The 2007 AQMP Basin ozone attainment demonstration indicated that with full 

implementation of the control strategy the Basin would meet the federal NAAQS in 2024 

with a predicted maximum 8-hour concentration of 83 ppb and remain in attainment 

through 2030. The additional maximum ozone impact due to the Sentinel plant (0.1 ppb) 

would not jeopardize the Basin ozone attainment. 

The 2007 AQMP Coachella Valley ozone attainment demonstration projected attainment 

of the NAAQS in 201 8 with a predicted maximum average concentration of 8 1 ppb. The 

projected maximum 8-hour average concentration increase (0.3 ppb) due to the Sentinel 

power plant would not result in a delay of the observed ozone attainment. 
Table 1 

Simulated Total Sentinel Project Regional Air Quality Impacts 

Averaging 

Period 

p Annual PM2.5 

I I I I I 

&Hour 

Basin 

Average 

Scenario ~ Impact 

I I I I I Ozone 

24-Hr 

PM2.5 and PMlO 

Basin 

Maximum 

Station 

Impact 

PMlO 1 0.01 < pg/m3 1 

Annual 

As previously discussed, this analysis assumes that -the PM2.5 and PM10 impacts are the 

same. The maximum impact to the Coachella Valley annual average PM2.5 due to the 

Sentinel project was predicted at 0.03 pg/m3in 2014. The average valley impact was 

predicted to be less than 0.02 pg/m3. The proposed project would result in a 0.01 pgim3 of 

increase to the South Coast Air Basin annual average PM2.5 with an average impact of 

less than 0.01 throughout the area. 

I I I 

PMlO 1 0.01 < pdm3 ( 0.01 pg/m3 0.015 pg/m3 1 0.03 pg/m3 1 

The project was predicted to generate a maximum 24-hour PM2.5 impact of 0.07 pg/m3 in 

the Coachella Valley. The maximum predicted 24-hour average in the Basin from the 

project is valued at 0.1 pg/m3 in 2014. The average predicted PM2.5 concentration 

impacts to the Coachella Valley and Basin were predicted to be less than 0.5 pg/m3 and 

0.01< pg/m3 respectively. The predicted particulate impacts would not result in a delay of 

the 2014 Basin PM2.5 attainment or impact the Coachella Valley and Basin 24-hour 

average PM 10 federal standard attainment demonstrations. 

Coachella 

Valley 

Average 

Impact 

I 

Visibility Impact 

Coachella 

Valley 

Maximum 

Station 

Impact 

0.1< ppb 0.1 ppb 

Table 2 summarizes the proposed Sentinel power plant's impact to visibility at the nearby 

Class-I areas (San Gorgonio, San Jacinto and Joshua Tree National Monument). The 

baseline values of deciview for the three Class I areas range from 1 1.3 to 14.0. The 

average baseline visual range for the Class I areas is more than 60 miles. The Sentinel ... power plant would result in a minor increase in deciviews (0.006 deciview or less in all 

cases). These impacts, however, would not be significant based on U.S. EPA criteria. 

When translated to miles of visual range, the power plant would lower visual range to the 

Class I areas by less than 3 one hundredths of a mile. 

0.2 ppb 0.3 ppb ~ 
Table 2 

Impacts to Visibility at Class-I Wilderness Areas 

Measured in Deciview and Visual Range (miles) 

- 

13.037 0.004 67.7 17 P -0.026 

San Jacinto -0.03 1 

Area Impacted 

Baseline 

Deciview 

Joshua Tree 

Difference in 

Deciviews 

11.251 

Baseline 

Visual Range 

(miles) 

0.006 

Difference in 

Miles 

90.694 -0.035 1