Smoke School Information in Wisconsin

Wisconsin Acceptance Status for VirtualOpacity^® — EPA ALT-152A

Pending Acceptance.

Wisconsin Acceptance Letter »

Wisconsin Visible Emissions / Opacity Standard

The opacity limit for Wisconsin is General/pre-1972: 40% opacity (Ringelmann 2); post-April 1, 1972 construction or modification: 20% (Ringelmann 1); SE Wisconsin and Lake Michigan subregion 1 sources after July 31, 1975: 20% regardless of age; fire-cleaning/new-fire exception: up to 80% for 6 min/hr, <=3x/day; alternate opacity limits via NR 431.07, as established under Wis. Admin. Code NR 431.04(1) (general 40%/Ringelmann 2); NR 431.04(2) (SE Wisconsin & Lake Michigan subregion 1 after July 31, 1975: 20%); NR 431.05 (post-April 1, 1972 construction/modification: 20%).

Compliance is demonstrated via Ringelmann Chart or equivalent opacity percentage observation; EPA Method 9 (continuous emission monitor or certified observer for alternate opacity limit procedures in NR 431.07).

Averaging period: Not specified as 6-minute average in NR 431 general standard; Ringelmann Chart Number 1 = 20%, Number 2 = 40%

Wisconsin uses the Ringelmann Chart framework: Ringelmann No. 2 (40%) for pre-1972 sources statewide; Ringelmann No. 1 (20%) for post-1972 sources and for all sources in the Lake Michigan / SE Wisconsin areas. NR 431.05 provides exceptions for fire-starting/cleaning (up to 80% for 6 minutes/hr). An alternative opacity limit process (NR 431.07) is available for sources that comply with mass PM limits. Wisconsin DNR administers its own smoke school.

Last verified July 8, 2026

Note: Regulations change — always verify current requirements with your state's air quality agency before making compliance decisions. This page is for informational purposes and is not legal advice; consult a qualified attorney or environmental compliance professional for guidance specific to your facility.