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Federal Register / Vol. 86, No. 156 / Tuesday, August 17, 2021 / Rules and Regulations
The Middle Tennessee Area was in attainment with the most recent effective ozone NAAQS for the entire period. The 20122014 and 20132015 design values were attaining the 2008 8-hour ozone NAAQS of 75 ppb. EPA notes that the 2015 8-hour ozone NAAQS of 70 ppb was not in effect until October 1, 2015, and all design values after this date attained the 2015 standard.
As shown in Table 2, the highest design value for the two ozone monitors in Hamilton County is 69 ppb in 2014 using 20122014 data, 66 ppb in 2015 using 20132015 data, 68 ppb in 2016 using 20142016 data, 67 ppb in 2017 using 20152017 data, 66 ppb in 2018 using 20162018 data, 64 ppb in 2019 using 20172019 data, and 62 ppb in 2020 using 20182020 data. Since the 20132015 design values, the Areas design values do not indicate a strong increasing or decreasing trend and have remained below the 2015 8-hour ozone NAAQS.

TABLE 2HAMILTON COUNTY OZONE MONITOR DESIGN VALUES, ppb Monitor Site Name
Design value 20122014

Eastside Utility
Soddy Daisy High School

Design value 20132015

Design value 20142016

Design value 20152017

Design value 20162018

Design value 20172019

Design value 20182020

69

66

68

67

66

64

62

67

64

65

65

64

64

61

EPA also evaluated the annual 4th maximum daily maximum 8-hour ozone concentrations for each site in both areas shown in Table 3. As discussed
above, it is common for monitors to measure annual variability in ozone concentrations due to several factors.
These annual values do not generally
indicate a strong increasing or decreasing trend at any of the monitors in the Middle Tennessee Area or Hamilton County.

TABLE 3MIDDLE TENNESSEE AREA AND HAMILTON COUNTY: ANNUAL 4TH HIGHEST DAILY MAXIMUM 8-HOUR OZONE
CONCENTRATIONS, 20122020
Monitor Site name
County
AQS ID

East Health

Davidson Middle Tennessee Area.
Davidson Middle Tennessee Area.
Hamilton
Hamilton
Sumner Middle Tennessee Area.
Williamson Middle Tennessee Area.
Wilson Middle Tennessee Area.

470370011

76

65

67

66

64

68

65

60

470370026

60

71

64

68

62

71

63

61

470651011
470654003
471650007

77
77
83

61
64
68

64
67
66

68
68
67

65
69
68

64
65
64

64
64
68

64
65
66

57
58
63

471870106

74

62

63

61

61

58

63

60

57

471890103

77

62

64

61

67

61

64

60

58

Percy Priest Dam
Soddy-Daisy High School
Eastside Utility
Hendersonville
Fairview Middle School
Cedars of Lebanon

2012

2013

2014

2015

2016

2017

2018

2019

2020

Indicates that a monitor did not meet annual data completeness criteria for a given year
Finally, for both areas, EPA evaluated the annual number of days with monitored exceedances of the 2015 8hour ozone NAAQS, where the daily maximum 8-hour ozone concentration at any monitor in the area exceeded 70
ppb. This is equivalent to the number of
the ozone concentrations in both areas, but neither area shows a strong increasing nor decreasing trend in the frequency of days above the 2015 8-hour ozone NAAQS.

days with an ozone AQI above 100 and the number of days with an AQI
category of unhealthy for sensitive groups or worse. The results of this analysis are shown in Table 4. Similar to the data presented above, these values show year to year variability in
TABLE 4MIDDLE TENNESSEE AREA AND HAMILTON COUNTY: ANNUAL COUNT OF DAYS WITH DAILY MAXIMUM 8-HOUR
OZONE CONCENTRATIONS ABOVE 70 ppb, 20122020
Area
2012

Middle Tennessee
Hamilton County

I

31
8

2013

I

2014
0 1

I

2015
6 1

I

2016
1 3

2017
4 2

I

I

2018
1 2

I

2019
6 1

I

2020
1 0

I

0
0

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For consistency, EPA evaluated the number of days above 70 ppb the level of the 2015 8-hour ozone NAAQS for all years. Note that this standard was not effective until October 1, 2015. Some of the days counted in 20122015 were not exceedances of the 2008 ozone NAAQS of 75 ppb, which was effective at the time this data was collected.

Comment A4: Several commenters assert that air quality will worsen by no longer requiring the monitoring of emissions, and therefore the I/M
program should not be removed. One commenter in reference to the Middle Tennessee Area stated that dropping the I/M program will increase NOX by 478 tons per year and VOC by 593 tons per year, and asserts that the analysis likely underestimates the deterioration
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of air quality that will occur, concluding that the emissions increases put Tennessee at risk of violating the standard in the future. At least one commenter also implied that removal of the I/M program would remove the ambient air monitoring requirements for the areas.
Response A4: There is no evidence that air quality will worsen to the point of violating the NAAQS by no longer
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requiring periodic testing of emissions from individual vehicles in Tennessee.
It is important to note that I/M programs require scheduled testing of a vehicles tailpipe and evaporative emissions to determine the effectiveness of existing emission controls on that individual vehicle. Emissions controls are not specifically required by I/M programs but rather are required for all light-duty vehicles pursuant to EPAs vehicle
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