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Contact information
For information on sulfur dioxide, contact:
Mike Friedlander
Program and planning analyst
608-267-0806

Sulfur dioxide (SO2) National Ambient Air Quality Standard (NAAQS) implementation

Sulfur dioxide (SO2) is one of a group of highly reactive gases known as "oxides of sulfur." The largest sources of SO2 emissions nationally are fossil fuel combustion at power plants (73 percent) and other industrial facilities (20 percent).

The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for criteria pollutants, including sulfur dioxide. The first SO2 air quality standards were set in 1971, including a 24-hour average primary standard at 140 parts per billion (ppb), an annual average primary standard at 30 ppb, and a three-hour, secondary public welfare standard of 500 ppb.

On June 2, 2010, the EPA strengthened the federal SO2 standards, establishing a new one-hour primary standard of 75 ppb. Since the SO2 NAAQS was promulgated, the DNR, in conjunction with the Lake Michigan Air Director Consortium (LADCO), has engaged the EPA on a variety of implementation issues.

Based on recommendations from DNR staff, the consortium and other state agencies, EPA has developed an updated strategy for identifying and addressing unhealthy levels of SO2 in areas of Wisconsin without a monitored violation of the SO2 standard. Accordingly, DNR will develop a process and timetable to characterize air quality through expanded air quality monitoring or air quality modeling techniques.

SO2 NAAQS rule

SO2 guidance and implementation documents

SO2 designation documents

April 2011 meeting and presentation videos

On April 8, 2011, DNR's Air Management Program gave a presentation for interested parties and industrial sources that might be affected by the new SO2 NAAQS. The purpose of the meeting was to share DNR's current understanding of the new SO2 standard, solicit feedback and questions, identify important milestones for EPA compliance, present hypothetical modeling scenarios for SO2 emissions, and underscore remaining uncertainties as they relate to permitting, modeling and enforcement.

Last revised: Tuesday November 29 2016