NOX Reductions Established Under the NOX SIP Call and CAIR

June 1, 2010

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TENNESSEE DEPARTMENT OF ENVIRONMENT AND CONSERVATION

DIVISION OF AIR POLLUTION CONTROL

NASHVILLE, TENNESSEE 37243-1531

Memorandum

To: Public Depository, Knoxville Ozone Redesignation Request

From: Travis Blake

Date: June 1, 2010 (Revised and Corrected July 16, 2010)

Subject: NOX Reductions Established Under the NOX SIP Call and CAIR

Due to the remand of the Clean Air Interstate Rule (CAIR) NOX Ozone Season Trading Program and other CAIR rules, questions 

have arisen as to whether or not Tennessee’s use of CAIR constitutes a “permanent and enforceable” measure for ozone 

attainment in the Knoxville area. Review of these issues indicates that, while CAIR will ultimately be replaced by a new 

interstate transport rule, the NOX reductions established under the NOX SIP Call remain in effect, regardless of whether CAIR, 

the NOX Budget Trading Program, or other applicable requirements are used to attain those reductions. Tennessee also notes 

that most future NOX reductions in the Knoxville area occur in the mobile source sector, and these emission reductions are 

expected to contribute to additional reductions in ambient ozone concentrations.

The NOX SIP Call requires States to make significant, specific emissions reductions. It also provided a mechanism, the NOX

Budget Trading Program, which States could use to achieve those reductions. When EPA promulgated CAIR, it discontinued 

(starting in 2009) the NOX Budget Trading Program, (40 CFR §51.121(r)), but created another mechanism—the CAIR NOX

ozone season trading program—which States could use to meet their SIP Call obligations. 

EPA is not currently administering the NOX Budget Trading Program, but all States remain subject to all of the requirements in 

the NOX SIP Call, even if the existing CAIR ozone season trading program is withdrawn or altered. In addition, the antibacksliding provisions of 40 CFR §51.905(f) specifically provide that the provisions of the NOX SIP Call, including the statewide 

NOX emission budgets, continue to apply after revocation of the 1-hour standard.

EPA has noted in other rulemaking actions that all NOX SIP Call States have SIPs that currently satisfy their obligations under 

the SIP Call, and that the SIP Call reduction requirements are being met. EPA has also indicated that the Agency will continue 

to enforce the requirements of the NOX SIP Call after any response to the CAIR remand. Regardless of the status of the CAIR 

program, the NOX SIP call requirements can be relied upon in demonstrating maintenance. 

Tennessee has reviewed the projected changes in NOX emissions for the greater Knoxville area between 2007 and 2024. 

Summary of NOX Emissions (tons/day)

Year Point Area Onroad Nonroad 

(excluding 

MLA)

Nonroad 

(MLA)

Total Safety 

Margin

Change 

from 

2007

2007 42.69 2.07 71.84 13.16 5.44 135.2

2010 42.65 2.14 63.09 12.17 5.03 125.08 10.12 -7.5%

2013 42.94 2.29 54.35 10.51 4.34 114.43 20.77 -15.4%

2016 43.56 2.50 45.61 8.74 3.61 104.02 31.18 -23.1%

2020 44.30 2.61 33.95 7.21 2.98 91.05 44.15 -32.7%

2024 45.11 2.68 22.29 6.37 2.63 79.08 56.12 -41.5%

Note: Emissions are for Anderson, Blount, Jefferson, Knox, Loudon, Sevier and onroad emissions for Cocke County.

MLA = Commercial Marine Vessels, Locomotives and Aircraft.
NOX Reductions Established Under the NOX SIP Call and CAIR

June 1, 2010

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NOX emissions from all categories are projected to decrease in the region by 56.1 tons/day between 2007 and 2024 (41.5% 

reduction). Total point source NOX emissions are projected to increase slightly (2.42 tons/day), while Electricity Generating 

Unit (EGU) NOX emissions are projected to remain unchanged between 2007 and 2024. 

Onroad mobile sources, the largest emitting category in 2007, are expected to decrease from 71.84 tons/day to 22.29 tons/day 

(69% decrease), and provide the bulk of NOX reductions in the emission inventory. Thus, in the absence of additional NOX

reductions from EGUs, total NOX emissions are projected to continually decrease throughout the maintenance period. Since 

motor vehicle and non-road emissions continue to decrease as the engine population is gradually replaced by newer engines, 

it is reasonable to expect that the projected decrease in NOX emissions from mobile and non-road sources assure that ozone in 

the Knoxville region will continue to decline.