Section 285.21 - Ambient air quality standards and increments(1) AMBIENT AIR QUALITY STANDARDS.(a)Similar to federal standard. If an ambient air quality standard is promulgated under section 109 of the federal clean air act, the department shall promulgate by rule a similar standard but this standard may not be more restrictive than the federal standard except as provided under sub. (4).(b)Standard to protect health or welfare. If an ambient air quality standard for any air contaminant is not promulgated under section 109 of the federal clean air act, the department may promulgate an ambient air quality standard if the department finds that the standard is needed to provide adequate protection for public health or welfare. The department may not make this finding for an air contaminant unless the finding is supported with written documentation that includes all of the following:1. A public health risk assessment that characterizes the types of stationary sources in this state that are known to emit the air contaminant and the population groups that are potentially at risk from the emissions.2. An analysis showing that members of population groups are subjected to levels of the air contaminant that are above recognized environmental health standards or will be subjected to those levels if the department fails to promulgate the proposed ambient air quality standard.3. An evaluation of options for managing the risks caused by the air contaminant considering risks, costs, economic impacts, feasibility, energy, safety, and other relevant factors, and a finding that the proposed ambient air quality standard reduces risks in the most cost-effective manner practicable.4. A comparison of the proposed ambient air quality standard with ambient air quality standards in Illinois, Indiana, Michigan, Minnesota, and Ohio.(2) AMBIENT AIR INCREMENT. The department shall promulgate by rule ambient air increments for various air contaminants in attainment areas. The ambient air increments shall be consistent with and not more restrictive, either in terms of the concentration or the contaminants to which they apply, than ambient air increments under the federal clean air act except as provided under sub. (4).(3) CAUSE OR EXACERBATION OF AMBIENT AIR QUALITY STANDARD OR INCREMENT. The department shall promulgate rules to define what constitutes the cause or exacerbation of a violation of an ambient air quality standard or ambient air increment.(4) IMPACT OF CHANGE IN FEDERAL STANDARDS. If the ambient air increment or the ambient air quality standards in effect on April 30, 1980, under the federal clean air act are modified, the department shall alter the corresponding state standards unless it finds that the modified standards would not provide adequate protection for public health and welfare. The department may not make this finding for an ambient air quality standard unless the finding is supported with the written documentation required under sub. (1) (b) 1. to 4.1995 a. 227 ss. 473, 475, 476, 989; 1997 a. 35; 2003 a. 118. The promulgation of emission standards is discussed. Wisconsin Hospital Association v. Natural Resources Board, 156 Wis. 2d 688, 457 N.W.2d 879 (Ct. App. 1990).