From July to November 2016, Delaware and Maryland respectively (and together) filed Clean Air Act (CAA) 126(b) petitions to the Environmental Protection Agency (EPA) alleging that upwind states such as Pennsylvania, West Virginia, Indiana, Kentucky and Ohio were significantly contributing to their nonattainment of eight-hour ozone national ambient air quality standards (NAAQS). On June 8, EPA published its notice of proposed action denying each of these 126(b) petitions. Section 126(b) petitions relate to the CAA’s “good neighbor” provision, which requires states to factor in their potential contributions to downwind state nonattainment of NAAQS when developing and submitting state implementation plans (SIP). Section 126(b) petitions allow individual states to ask that EPA set emissions limits for specific sources of air pollution significantly contributing to the nonattainment. Most recently, New York filed a 126(b) petition with EPA alleging that nine downwind states significantly contribute to its nonattainment of the 2008 and 2015 ozone NAAQS. The deadline for EPA to act on the petition has been extended through early November. EPA has already finalized its denial of a similar 126(b) petition made by Connecticut in 2016. EPA is accepting comments on its proposed denial of Delaware and Maryland’s 126(b) petitions through July 23. The agency also proposes to hold a public hearing on the matter.