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Sulfur dioxide NAAQS implementation

The U.S. Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards (NAAQS) for criteria pollutants, including sulfur dioxide (SO2). On June 2, 2010, EPA revised the SO2 standard, establishing a one-hour primary standard of 75 ppb.

The EPA is completing area designations for this NAAQS in four rounds. The following sections provide information about each round of designations in Wisconsin, the State Implementation Plan (SIP) revisions the DNR has developed to describe how areas will be brought into attainment and other relevant documents.

For general information about SO2, visit Air pollutants and standards.

Round 1

The designations for Round 1 covered areas that violated the one-hour SO2 NAAQS based on certified ambient air quality monitoring data for the years 2009 to 2011. The EPA designated one nonattainment area in Wisconsin in Round 1: a portion of Oneida County including the city of Rhinelander and the towns of Crescent, Newbold, Pine Lake and Pelican.

Area designation documents

State Implementation Plan documents

Round 2

Round 2 designations involved two types of areas: (1) areas that violated the one-hour SO2 NAAQS based on air monitoring data collected from 2013 to 2015, and (2) areas containing sources that emitted SO2 above specified levels in 2012. The EPA designated Columbia County as unclassifiable/attainment in Round 2.

Area designation documents

Rounds 3 and 4

Round 3 and 4 designations affect stationary sources subject to the EPA’s Data Requirements Rule (DRR). The DRR requires states to either model or monitor SO2 concentrations in areas containing sources emitting elevated levels of SO2.

The EPA finalized designations for all areas, except areas where states have established new monitors per the DRR, in December 2017 (Round 3). All remaining areas of Wisconsin were designated unclassifiable/attainment in Round 3, except for Outagamie County, where SO2 concentrations are being monitored.

The EPA must finalize designations for all remaining areas of the country, including Outagamie County, by Dec. 31, 2020 (Round 4).

Area designation documents

State Implementation Plan documents

DNR comments on EPA implementation rules and guidance