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Federal Register / Vol. 86, No. 183 / Friday, September 24, 2021 / Proposed Rules
model choice and performance, modeling emissions inventory preparation procedures, model performance, attainment test procedure, adjustments to baseline air quality for modeling, the 2020 attainment test, and an unmonitored area analysis. CARBs supplemental weight of evidence analysis further supports the Plans demonstration of attainment by the end of 2020. These analyses are generally consistent with the EPAs recommendations in the Modeling Guidance.
The model performance evaluation in Appendix K includes statistical and graphical measures of model performance. The magnitude and timing of predicted concentrations of total PM2.5, as well as of its ammonium and nitrate components, generally match the occurrence of elevated PM2.5 levels in the measured observations. A
comparison to other recent modeling efforts shows good model performance on bias, error, and correlation with
measurements, for total PM2.5 and for most of its chemical components. The Weight of Evidence Analysis shows the downward trend in NOX emissions along with a 70 percent decrease between 1999 and 2017 in the number of days above the 1997 24-hour PM2.5
NAAQS.184 The analysis also shows decreases in daily PM2.5 concentrations during winter, and in the frequency of high PM2.5 concentrations generally.185
Available ambient air quality data show that total PM2.5 and ammonium nitrate concentrations have declined over the 20042017 period, despite some increases from time to time.186 These trends show that there has been an improvement in air quality due to emissions reductions in the San Joaquin Valley, although that point is not fully reflected in the 98th percentile statistic, which is the basis for the regulatory design value.
The State conducted three CMAQ 187
simulations: 1 A 2013 base year simulation to demonstrate that the
model reasonably reproduced the observed PM2.5 concentrations in the San Joaquin Valley; 2 a 2013 baseline year simulation that was the same as the 2013 base year simulation but excluded exceptional event emissions, such as wildfire emissions; and 3 a 2020 future year simulation that reflects projected emissions growth and reductions due to controls that have already been adopted and implemented.188
Table 4 shows the 2013 base year and 2020 projected future year 24-hour PM2.5 design values at monitoring sites in the San Joaquin Valley. As recommended by the EPAs guidance, the 2013 base year design value for modeling purposes is a weighted average of three monitored design values, to minimize the influence of year-to-year variability. The highest 2020 projected design value is 47.6 mg/
m3 at the BakersfieldCalifornia monitoring site, which is below the 65
mg/m3 level of the 1997 24-hour PM2.5
NAAQS.

TABLE 4PROJECTED FUTURE 24-HOUR PM2.5 DESIGN VALUES AT MONITORING SITES IN THE SAN JOAQUIN VALLEY g/
m 3
2013 Base design value
Monitoring site BakersfieldCalifornia
Fresno-Garland
Hanford
Fresno-Hamilton & Winery
Clovis
Visalia
Bakersfield-Planz
Madera
Turlock
Modesto
Merced-M. Street
Stockton
Merced-S Coffee
Manteca
Tranquility

64.1
60.0
60.0
59.3
55.8
55.5
55.5
51.0
50.7
47.9
46.9
42.0
41.1
36.9
29.5

2020
Projected design value 47.6
44.3
43.7
45.6
41.1
42.8
41.2
38.9
37.8
35.8
32.9
33.5
30.0
30.1
21.5

Source: 2018 PM2.5 Plan, Table 55.

3. The EPAs Review of the States Submission The EPA must make several findings in order to approve the modeled attainment demonstration in an attainment plan SIP submission. First, we must find that the attainment demonstrations technical bases, including the emissions inventories and air quality modeling, are adequate. As discussed in section IV.A of this preamble, we are proposing to approve the emissions inventories on which the SJV PM2.5 Plans attainment demonstration and related provisions 184 Weight of Evidence Analysis, 2728, Figure 14, and Figure 24.

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are based. Furthermore, the EPA has evaluated the States choice of model and the extensive discussion in the Modeling Protocol about modeling procedures, tests, and performance analyses. We find that the analyses are consistent with the EPAs guidance on modeling for PM2.5 attainment planning purposes. Based on these reviews, we find that the modeling in the Plan is adequate for the purposes of supporting the RFP demonstration and demonstration of attainment by 2020
and are proposing to approve the air 185 Id.
186 Id.

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at Figure 16 and Figure 17.
at Figure 21.

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quality modeling. For further detail, see the EPAs February 2020 Modeling TSD.
Second, we must find that the SIP
submittal provides for expeditious attainment through the timely implementation of the control strategy.
As discussed in section IV.C of this preamble, we are proposing to approve the control strategy in the SJV PM2.5
Plan, including the BACM/BACT
demonstration and the five percent emissions reduction requirement under CAA sections 189b1B and 189d, respectively.
187 CMAQ
188 2018

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