On July 12, 2016, EPA published the final designations for areas included in the second round of designations for the 2010 one-hour sulfur dioxide (SO₂) national ambient air quality standard (NAAQS). 81 Fed. Reg. 45039 (July 12, 2016). For this NAAQS EPA is designating areas in multiple rounds. The first round was completed in 2013 when EPA designated 29 areas in 16 states as being in nonattainment with the standard. A Consent Decree entered by EPA and environmental groups set a schedule for the remaining second through fourth rounds of designations. The second round was completed with this final action. Two groups of areas were designated: 1) areas with newly monitored violations of the 2010 SO₂ NAASQ and 2) areas with sources not announced for retirement as of March 2, 2015 and that emitted in 2012 either more than 16,000 tons of SO₂ or more than 2600 tons of SO₂ with an annual average emission rate of at least 0.45 lbs SO₂/mmBtu. EPA designated 61 areas in 24 states as either unclassifiable/attainment, unclassifiable or nonattainment. Forty-one areas were designated as unclassifiable/attainment, 16 areas were designated as unclassifiable and four areas were designated as nonattainment. Alton Township, Illinois, Williamson County, Illinois, Anne Arundel and Baltimore Counties Maryland and St. Clair, Michigan were designated as nonattainment.

In Kentucky, Pulaski County and Ohio County were designated as unclassifiable. In Ohio, Gallia County and part of Miegs County were designated as unclassifiable. Clermont County, Ohio, excluding Pierce Township, was designated as unclassifiable attainment. No areas in West Virginia were designated during this round.

By December 31, 2017, EPA is required to complete the third round of designations for any remaining undesignated areas where states did not install and begin operation by January 1, 2017 of a new SO₂ monitoring network according to the specifications in the Data Requirements Rule. The fourth round must be completed by December 31, 2020 and must designate all remaining areas.