San Antonio Missions National Historical Park is within one of 16 air quality districts in Texas. The Clean Air Act, amended in 1990, provides that emission sources must comply with air quality standards and regulations that have been established by federal, state, and county regulatory agencies. San Antonio is a Class II area as it relates to the Clean Air Act, meaning that it is in an area with less ozone depletion potential than a Class I area. Because the majority of the park is comprised of isolated fragments within the city, the Texas Commission on Environmental Quality provides data in regards to any trends in air quality. The Alamo Area Council of Governments provides air quality information and programs. San Antonio Missions National Historical Park encourages staff and volunteers to take public transportation to assist in maintaining good air quality.