The Environmental Protection Agency (EPA) approved the Massachusetts Department of Environmental Protection (MassDEP) State Implementation Plan (SIP) revisions on November 13, 2019. The rule is effective December 13, 2019. The revisions addressed the interstate transport requirements of the Clean Air Act (CAA) for the 2010 1-hour sulfur dioxide (SO2) national ambient air quality standards (NAAQS). The CAA requirements for this standard are referred to as the good neighbor provision because they address the air pollution transport across state borders and the downwind states' ability to attain and maintain NAAQS.
EPA has determined that Massachusetts does not pose a threat to downwind states' ability to attain and maintain the 1-hr SO2 NAAQS.