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Air Quality & Conformity

Intro to Air Quality

Air pollution is harmful to both public health and the natural environment. The Clean Air Act of 1970 was enacted to reduce air pollution while, in the same year, the Environmental Protection Agency (EPA) was established to carry out the Act and other environmental laws. The EPA has since worked with state and local governments to improve air quality through regulation and policy.

Image showing current Air Quality Status

In the Alamo Area, ground-level ozone, commonly known as smog, is the only pollutant currently regulated under the Clean Air Act. In 2018, after demonstrating ozone levels exceeded regulatory standards, the EPA designated the San Antonio area/Bexar County as a “Marginal Nonattainment” area for ozone. Subsequently, in 2022, this same area was redesignated as “Moderate Nonattainment” for failing to meet regulatory standards. Other counties, within the AAMPO study area, remain “in attainment” of ozone standards and are not included in EPA’s air quality regulation of the region. AAMPO’s part, in meeting EPA’s air quality standards, is called Transportation Conformity. Before AAMPO adopts or amends the region’s transportation plans, the transportation investments in those plans must be studied and shown to meet, conform with, EPA air quality standards. This test of conformity is limited to the Bexar County area projects and programs only.

Transportation Conformity

Transportation Conformity ensures future transportation projects, programs, plans and policies will cause no further harm to air quality. The transportation conformity process is required of all MPOs with air quality nonattainment areas.

Bexar County (aka the San Antonio Area) was originally designated as a Marginal nonattainment area for ozone in 2018. Since Bexar County did not attain air quality standards within three years, EPA redesignated the nonattainment area as Moderate Nonattainment effective November 7, 2022. This change requires additional regulations, to be developed by the State of Texas, in order to fulfill the requirements of the Clean Air Act, in the Bexar County area.

AAMPO developed its initial draft 2023 Transportation Conformity Determination document (TCD) based on Bexar County’s Marginal Nonattainment status for air quality. The Transportation Policy Board approved it at the June 2022 meeting. Thereafter, once staff was notified of the pending air quality reclassification, AAMPO revised the TCD to reflect additional EPA requirements for Moderate Nonattainment in the Bexar County area. The revised TCD was made available and open for public comment from October 30, 2022 to December 1, 2022. Responses to public comments have been incorporated into the final draft document. The AAMPO Transportation Policy Board locally approved the 2023 Transportation Conformity Determination document on December 12, 2022. As of early 2023, the TCD document is currently pending Federal and State approval.

Public Feedback Introduction Video

Recorded Public Meeting Presentation

Click below to visit the Transportation Conformity Document page for more information.

Transportation Conformity Document


The Environmental Protection Agency (EPA) monitors air pollution around the country through a nationwide network of monitors maintained by each state. The Texas Commission on Environmental Quality (TCEQ) manages the state’s network, called Continuous Air Quality Monitoring Systems (CAMS). CAMS record pollutant levels daily within the AAMPO study area. Three of the CAMS are regulatory monitors used by the EPA to measure and track the area’s air quality. These CAMS are: San Antonio Northwest (C23), Camp Bullis (C58), and Calaveras Lake (C59).

Ozone is measured in parts per billion (ppb), and levels are averaged over 8-hour periods. The highest 8-hour average for each day is recorded, and the fourth-highest daily average for each year is averaged over three years to determine the Design Value for each year. This is done for each monitoring site. Under the most current 2015, 8-hour EPA standard for ozone, design values over 70ppb indicate nonattainment. Ozone levels would need to be reduced dramatically for both the Northwest and Camp Bullis monitors in order for Bexar County to attain the 2015 standard. The ozone levels at the Calaveras Lake CAM (C59) has stayed within the 2015 attainment standard.

Map data provided by the Environmental Protection Agency (EPA).

Congestion Mitigation and Air Quality & Other Funding

The Congestion Mitigation and Air Quality Improvement (CMAQ) Program awards transportation projects and programs, that generate air quality benefits in the form of emissions reductions for criteria pollutants, in nonattainment areas. Funding is available for eligible activities that help meet the requirements of the Clean Air Act. Added capacity (added lanes) projects are not eligible. A calculation of each project's expected emission reduction benefits must also be submitted as part of the competitive funding process.

Examples of eligible activities for CMAQ funding include:

  • Establishment or operation of a traffic monitoring, management, and control facility, including advanced truck stop electrification systems, if it contributes to attainment of an air quality standard;
  • Projects that improve traffic flow, including projects to improve signalization, improve intersections, add turning lanes, improve transportation systems management and operations that mitigate congestion, and implement Intelligent Transportation Systems (ITS);
  • Projects that improve incident and emergency response;
  • Travel Demand Management projects and programs that shift traffic demand to nonpeak hours or other transportation modes, increase vehicle occupancy rates, or otherwise reduce demand;
  • Purchase of diesel retrofits or conduct of related outreach activities;
  • Facilities utilizing electric or natural gas-fueled vehicles;
  • Transit improvements;
  • Bicycle and pedestrian facilities and programs; and
  • Workforce development, training, and education activities.

Federal legislation requires a CMAQ performance plan for MPOs that serve one million or more population and that represent a nonattainment or maintenance area. This plan documents three CMAQ-related federal performance measures: Annual Hours Peak Hour Excessive Delay (PHED), Percent Non-Single-Vehicle-Occupancy Travel, and Total Emissions Reduction. These performance measures are a subset of the Federal Highway Administration’s (FHWAs) System Performance Measures. A copy of AAMPO’s CMAQ Performance Plan can be viewed and downloaded here, and a list of the region’s CMAQ projects can be found below. Projects in the AAMPO nonattainment area, Bexar County/San Antonio Area, are the only eligible projects to be considered and awarded CMAQ funds.

Educational Info

In 2018, the U.S. Environmental Protection Agency (EPA) designated Bexar County in marginal nonattainment for the pollutant ozone. Levels of ground-level ozone in Bexar County were exceeding National Ambient Air Quality Standards (NAAQS) set by the EPA in 2015. These standards are designed to protect human and environmental health, and ground-level ozone is monitored and targeted for reductions due to its potentially harmful effects. The Alamo Area Metropolitan Planning Organization (MPO) works in cooperation with federal, state, and local partners to ensure our community is meeting air quality requirements for on-road transportation sources.

The Clean Air Act requires that every five years, the Environmental Protection Agency (EPA) set National Ambient Air Quality Standards (NAAQS) for six criteria pollutants:

  1. Ground-level Ozone (O3)
  2. Particulate matter (PM)
  3. Carbon Monoxide (CO)
  4. Sulfur Oxides (SO2)
  5. Nitrogen Oxides (NO2)
  6. Lead (Pb)
Along with setting the pollutants, EPA evaluates whether or not the thresholds set for the pollutants are adequately protective of human health and the environment, based on the most recent scientific evidence. Locally, the Texas Commission on Environmental Quality (TCEQ) is responsible for monitoring air quality and reporting those findings to the EPA.

Of the six criteria pollutants, the one that poses the greatest challenge to our region is ground level ozone. When ozone, a naturally occurring gas, resides in the upper atmosphere, it serves as a shield from the harmful ultraviolet radiation emitted by the sun. Unlike the “good ozone” in the upper atmosphere, ozone in the lower atmosphere is a pollutant and a primary component of smog, which is why scientists and experts frequently say, “ozone good up high, bad nearby.” Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors and chemical solvents are some of the major sources of the pollutants that when under certain meteorological conditions, can mix to form ground level ozone.

Transportation's Contribution to Ozone

Emissions from industrial facilities, electric utilities, motor vehicle exhaust, gasoline vapor and chemical solvents are some of the major sources of the air pollutants nitrogen oxides (NOx) and volatile organic compounds (VOC). When these pollutants react together in sunlight and heat, ozone is formed.

The chart below shows the emission sources that contribute to Ground Level Ozone and their total contribution by percentage in 2017.

image of graph showing transportation's contribution to ozone

Why is Ground Level Ozone Dangerous?

Ground level ozone, more commonly known as smog, is the brown haze that rests upon the region on hot, sunny days. Ozone forms when certain pollutants mix with sunlight. Ozone formation is most likely during the months of April, May, June, July, August, September and October, when heat and sunlight are at their hottest and brightest in the region. In high ozone conditions, people can experience a number of different health problems, including chest pain, coughing, throat irritation, and congestion. People with lung disease, children, older adults, and people who are active outdoors may be particularly sensitive to ozone.

Ozone season is a period of time in which ground-level ozone, the primary air pollution in the Alamo Area, reaches its highest concentration levels in our air. In our region, ozone season stretches from the month of April through October.

Ground-level ozone reaches its highest concentrations during these months because it forms when nitrogen oxides mix with volatile organic compounds in intense sunlight, and sunlight is strongest from April through October. It is during this time that we are most likely to have exceedances of the National Ambient Air Quality Standard for ground-level ozone.

Here are some tips on how to voluntarily reduce your emissions.

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Service your vehicles frequently.

Getting your car serviced regularly will increase your fuel efficiency and add to the car's life. Get your oil changed on time and have your car checked for problems regularly. By ensuring your car is running well you can increase your mileage AND you can save up to $200 a year by increasing your mileage by just 10%.

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Slow down.

Because wind resistance builds up so much with higher speeds, every mile per hour you drive over 55 decreases your fuel economy by 2%. In other words, if you're driving 80 mph you'll cut your fuel economy by half. Accelerating and decelerating abruptly also reduces fuel efficiency and wears down your vehicle.

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Report smoking vehicles.

The next time you see a vehicle anywhere in Texas with dirty smoke coming from its exhaust for more than 10 seconds, write down the license number, date, time, and location and report the smoking vehicle, within 30 days, by calling 1-800-453-SMOG (7664). You do not have to give your name, and the report is free.

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Check your tires.

Under-inflated tires increase the friction between the rubber and the road, and that friction accounts for poor gas mileage as well as increased carbon emissions. Maintaining proper tire pressure is like saving 10 cents per gallon! Tire health not only saves you up to 3% on fuel but also reduces your car’s tailpipe emissions.

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Go in instead of using the drive-thru.

The drive-thru has become a staple of many people’s lives but it also makes us contributors to ground-level ozone. If you spend just 5 minutes in a drive-thru each weekday, that's 1300 minutes or more than 21 hours per year. By skipping the drive-thru and walking into businesses, we can all take the first steps to cleaner air.

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Turn to renewable energy.

Renewable energy is energy that is generated from resources like sunlight, wind, rain, tides, wave and geothermal heat which are continually replenished. Most forms of energy require an energy source that pollutes the air. When renewable energy such as solar power is used, burning does not take place.

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Limit waste.

Reducing the amount of waste you produce and reusing products are best because there is no reproduction process involved. Recycling is good, but it does require energy to break down and reproduce useful products, it still reduces the amount of waste send to break down in landfills.

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Plant a tree.

A healthy tree stores about 13 pounds of carbon annually -- or 2.6 tons per acre each year. An acre of trees absorbs enough CO 2 over one year to equal the amount produced by driving a car 26,000 miles. Shade from trees also helps reduce air conditioning needs up to 30%, thereby reducing the amount of electricity needed.

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Look for eco-friendly items when shopping.

Buying recycled and local projects can help save energy by reducing the amount of energy needed to make and/or transport the product. You can also look for the Energy Star label when buying appliances, electronics, lighting, heating and cooling equipment. Finally, when replacing your car, buy a fuel-efficient vehicle.

Stay Informed!