This print ISBN is the U.S. Federal Government official edition. 40CFR, Pt. 81, continues coverage of Protection of Environment, Environmental Protection Agency (EPA)--Air Programs. This includes designation of areas for air quality planning purposes.Related items: The Annual CFR Print Subscription can be found here: https: //bookstore.gpo.gov/products/code-federal-regulations-subscription-service-2017-paperback-0CFR Title 40, Protection of Environment publications can be found here: https: //bookstore.gpo.gov/catalog/cfr-title-40-protection-environmentEnvironment and Nature resources collection is available here: https: //bookstore.gpo.gov/catalog/environment-nature