Section 8: Air Quality

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The subject of air quality, conformity, nonattainment, and required corrections is complex, convoluted, and rapidly changing. It is extremely difficult to prepare a generalized description that covers all aspects of this subject. For detailed information and/or source documents, please contact TPP, ENV, TNRCC, or FHWA for additional information.

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1969 -1980. The National Environmental Policy Act (NEPA) of 1969 and the 1970 Federal-Aid Highway Act required TxDOT as the state transportation agency to consider the “…environmental impacts of federal projects.” The 1970 Clean Air Act (CAA) established National Ambient Air Quality Standards (NAAQS) for six pollutants. Of these six pollutants, three are closely associated with mobile sources. These three pollutants are ozone (smog), carbon monoxide (CO), and particulate matter (PM-10). The CAA also dealt with precursors of these pollutants. Those precursors are volatile organic compounds (VOCs) and nitrogen oxides (NOx) in areas that are nonattainment for ozone; NOx in areas that are Nonattainment for NO2; and VOC and NOx in areas that are Nonattainment for PM‑10.

The 1977 Clean Air Act Amendments (CAAA) strengthened the original CAA and established deadlines for reaching air quality attainment status. The CAAA also required the development and implementation of SIPs to bring air quality nonattainment areas into compliance with the NAAQS.

1990-2000. The 1990 CAAA established specific criteria that must be met for air quality nonattainment areas. The criteria are based on the severity of the air pollution problem and include:

  1. specific timetables for implementing mobile source emission control strategies
  2. requirement for meeting mobile source emission reduction goals
  3. development and implementation of SIPs in order to meet the NAAQS
  4. requirement for the EPA to sanction all or part of a state Sanctions are defined as stricter industrial controls and the withholding of federal highway funds. Sanctions may be levied against the state for:
    1. failing to develop and submit SIPs
    2. failing to implement all aspects of SIPs
    3. failing to meet any of the air quality progress or attainment deadlines.

ISTEA of 1991 and associated federal planning regulations strengthened the role of the MPO in transportation planning and programming. Furthermore, ISTEA linked transportation and environmental goals by providing funding flexibility and the Congestion Mitigation and Air Quality Improvement Program (CMAQ).

TEA-21 and associated federal planning regulations reaffirmed ISTEA’s commitment to the continued protection of public health and the environment.

TNRCC is the state agency charged with preparing those documents and rules enacted by Congress and EPA. Prior to the formation of TNRCC in 1993, air quality issues were handled by the Texas Air Control Board. In 1993, the Texas Air Control Board (TACB) and the Texas Water Commission (TWC) merged into TNRCC, the overall environmental agency for Texas.

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As the responsible agency, TNRCC operates monitoring stations at various locations. At least one site is located in each urbanized area with a population of 200,000 or greater. Certain selected urbanized areas with populations less than 200,000 have received monitoring sites. There are three types of monitors. The monitors measure the level of ozone; ozone and carbon monoxide; or ozone, carbon monoxide, and VOCs.

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Nonattainment Designation

An urbanized area is declared as being in “nonattainment” when the readings at one or more monitoring sites show the urbanized area has persistently exceeded the current NAAQS for one or more pollutants. The CAAA established the “one-hour” standard for each pollutant. The “one‑hour” standard for ozone is 12 parts per million (PPM) by volume; for carbon monoxide, the standard is 35 PPM; for nitrogen dioxide, the standard is 0.053 PPM; and for PM-10 the standard is 50 micrograms (μg/m3). These one-hour standards apply to nonattainment areas that were designated prior to July 1997. In Texas, the one-hour standard applies to the four current nonattainment areas in Texas (Dallas-Fort Worth, Houston, Beaumont-Port Arthur, and El Paso).

In 1997, EPA announced a new NAAQS for ozone. The new NAAQS was for an “eight‑hour” standard of 85 parts per billion (PPB) or 0.08 parts per million (PPM). Under the old NAAQS for ozone, if an area exceeded the one-hour NAAQS four or more times within a three-year period, the area was declared in nonattainment. Under the new NAAQS for ozone, if the three-year average of the area’s fourth highest eight-hour reading exceeds 85 PPB the area is declared in nonattainment.

NOTE: As of December 1999, due to current ongoing lawsuits, the eight-hour standard for ozone is not being enforced.

When EPA declared areas as nonattainment under the CAAA of 1990, the boundaries of the areas were drawn along county lines. Whole counties were included in the nonattainment areas. For example, the Beaumont–Port Arthur nonattainment area included all of Jefferson, Orange, and Hardin counties. In general, federal rules required the MPO to expand its Metropolitan Area Boundary (MAB) or Metropolitan Planning Area Boundary (MPAB) to take in the entire nonattainment area. Under TEA-21, newly declared nonattainment areas (as under the eight-hour standard for ozone, if the courts allow) could petition the Governor, with EPA approval, not to expand their boundaries. Because the eight-hour standard is currently on hold due to lawsuits, no formal boundary changes have occurred, so it is uncertain if EPA will hold to the full-county boundary standard.

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Transportation Conformity

Once an area has been declared a nonattainment area for one or more pollutants, several actions must take place. Section 176(c) of the CAA requires a demonstration of “transportation conformity.” That is, the nonattainment area MPO(s) must demonstrate, through regional emissions analysis, that the estimated on-road motor vehicle emissions of projects included in the Metropolitan Transportation Plan (MTP) from which the three-year TIP is drawn will be less than the allowable estimated on-road motor vehicle emissions listed in the SIP. If an area cannot show that the planned projects in the MTP (and TIP) will allow the area to meet or be less than the emission levels required by the SIP, then the MPO must modify its TIP and MTP by removing projects or adding other controls/programs until the SIP emission requirements are met. Failure to comply with this requirement can result in the freezing of all federal funds (both FHWA and FTA) and possibly more severe restrictions.

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Conformity Demonstration

The MPO must demonstrate “transportation conformity” on its MTP and TIP every three years. Any revision to the TIP or MTP requires the MPO to resubmit transportation conformity documentation to EPA for review and approval. Several other conditions require the MPO to demonstrate transportation conformity. Conformity must be demonstrated:

  • within 18 months of a state’s initial submission of a control strategy SIP or a maintenance plan that contains a Motor Vehicle Emissions Budget (MVEB);
  • within 18 months of EPA approval of a control strategy SIP revision or maintenance plan that establishes or revises a MVEB or adds, deletes, or changes Transportation Control Measures (TCMs); or
  • within 18 months of EPA promulgation of an implementation plan that establishes a MVEB or adds, deletes, or changes TCMs.

Transportation conformity is demonstrated for an area by using two computer models. The Travel Demand Model is a computer model for the nonattainment area that uses forecasted demographics and job information to estimate future vehicle miles traveled (VMT) over the proposed roadway network that included the project improvements in the MTP and TIP. The information from the Travel Demand Model is used as input information to the Emission Model. The Emission Model is currently “Mobile 5.” This model was developed and released by EPA. New upgraded computer model programs are approved and released periodically by EPA, such as “Mobile 5a,” etc. The total emissions predicted by the Emission Model for each required year must not exceed the limits established in the SIP.

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State Implementation Plan

Just as the STIP consists of the MPO TIPs and rural TIPs plus some statewide programs, the SIP consists of an individual part or plan for each nonattainment area plus some statewide initiatives to reduce pollutants. The CAA requires each state to develop a SIP that addresses each pollutant for which the state fails to meet the NAAQS and to describe how the state and the individual areas will meet the NAAQS on schedules prescribed in the CAA. Emissions are generally classified in one of three categories: stationary sources, area sources, and mobile sources. There are also natural emissions, called biogenic. The SIP assigns emission reduction targets to each source category. For the mobile source category, the emission reduction target is further refined into a regulatory limit on emissions, referred to as a Motor Vehicle Emissions Budget (MVEB). Emission reduction targets for mobile sources may be achieved through Transportation Control Measures (TCMs). TCMs are strategies designed to reduce vehicle emissions. Some examples of TCMs and the programs that result are:

  • high occupancy vehicle (HOV) lanes
  • flexible work hours for employees to shift peak travel hours
  • improved public transit or rideshare programs
  • and traffic flow improvement programs such as signal timing.

If adopted in the SIP, these strategies/programs have legal requirements. Failure to comply can result in federal sanctions against the area and/or the state.

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TIP/STIP Coordination

In order to demonstrate transportation conformity, the area must run the Travel Demand Model for each of the required years. Depending on the regulations, this process may require five to seven model years. Once a project timeframe is determined in the transportation conformity process, in order for the MPO or district to move a project (either accelerate it or delay it), the MPO may be required to demonstrate transportation conformity again. This process is an intensive computer modeling process. EPA approval of each transportation conformity demonstration may take up to six months. Therefore MPOs and districts must consider all proposed completion dates carefully.

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