Have you ever heard us talk about air quality conformity? It’s a bit of transportation jargon that’s incredibly important for our region. But what does it mean?
Every time the TPB has a new Transportation Improvement Program (TIP) or an update to its long-range plan, these plans and programs must show that the transportation system meets air quality requirements.
Air quality conformity is a federal requirement that requires TPB staff to test the draft plans and TIPs to ensure that the projects, when considered collectively, contribute to the air quality improvement goals embodied in the Clean Air Act Amendments of 1990. Staff perform a series of tests with computer models that estimate air pollution levels from mobile sources over the next 25 years. Once the TPB finds that the plan meets the regional air quality goals, federal agencies certify that the plan is “in conformity.” In other words, the TPB ensures that its plan and TIP conform to air quality improvement goals.
How are regional air quality improvement goals set?
The Metropolitan Washington Air Quality Committee (MWAQC) is the entity certified by the mayor of the District of Columbia and the governors of Maryland and Virginia to prepare air quality plans for the Washington region. MWAQC includes local elected officials, representatives of the state and DC air management and transportation agencies, state legislators, and the TPB Chair. Like the TPB, MWAQC is housed and staffed by the Metropolitan Washington Council of Governments.
Transportation and air quality
Transportation planning is integral to air quality planning. Air quality plans include emissions ceilings called “mobile budgets” for vehicle or mobile sources. They also have emissions reduction requirements for other sources of air pollution like power plants. The TPB must show that its transportation plans will conform to the mobile budgets for specific milestone years.
How do you predict emissions 25 years from now?
Future emissions levels are estimated using computer models. First, a travel demand model is used to estimate travel patterns and congestion levels from the transportation system laid out in the plan. Then, an Air quality model, using data output from the travel demand model, estimates the amount of emissions from vehicles, measured in tons per day that will be produced in future years. The air quality model incorporates many factors including the number and types of vehicles that will be on the road, the speeds at which they will travel, and the effects of technology on vehicles and fuels.
What kinds of pollution does the air quality analysis measure?
As required in the Clean Air Act, the Environmental Protection Agency (EPA) must set limits on certain (criteria) pollutants that are harmful to public health and the environment. In the Washington metropolitan region, the types of emissions included in the air quality conformity analysis are ozone season pollutants, Volatile Organic Compounds (VOC), and Nitrogen Oxides (NOx).
State air agency staff monitor the six “criteria” pollutants (ground level ozone, particulate matter, carbon monoxide, lead, sulfur dioxide, nitrogen dioxide) commonly found in the air and defined in the Clean Air Act as harmful to public health and the environment. These pollutants are related to transportation because some of them are caused by emissions from mobile sources.
What does it mean to be in a “non-attainment” area?
The EPA sets limits on each of the six criteria pollutants in National Ambient Air Quality Standards (NAAQS or standard). When each standard is set, the EPA defines geographic areas (generally counties clustered around a metropolitan area) that will be evaluated for each pollutant. Meanwhile, data are continually collected from monitors set all around the country that read the level of the criteria pollutants. If, based on a very specific definition, an area’s data show levels above the standard, the area is designated as “non-attainment.” Based on the monitor levels, each non-attainment area is given a level of severity (marginal, moderate, serious, severe, or extreme) which defines how long the area has to attain the standard.
The Clean Air Act also requires that the EPA must review the NAAQS at least once every 5 years to determine if the limit set in the standard still protects public health and the environment. This review has led to updates to the standards, which is why there are multiple standards for each pollutant (i.e. the 2008 ozone standard, the 2015 ozone standard). Some areas around the country, including the Washington metropolitan region, are meeting requirements for multiple standards for multiple pollutants.
Learn more about Air Quality Conformity