WAC 173-433-140   Impaired air quality criteria.  Impaired air quality shall be determined by ecology or an authority in accordance with the following criteria:

     (1) "First stage impaired air quality" - the first stage indicates the presence of:

     (a) Particulate matter ten microns and smaller in diameter (PM₁₀) at or above an ambient level of seventy-five micrograms per cubic meter; or

     (b) Carbon monoxide at or above an ambient level of eight parts of contaminant per million parts of air by volume (ppm).

     (2) "Second stage impaired air quality" - the second stage indicates the presence of particulate matter ten microns and smaller in diameter (PM₁₀) at or above an ambient level of one hundred five micrograms per cubic meter.

     (3) On or after July 1, 1995, if an authority has geographically limited the use of solid fuel burning devices as specified under WAC 173-433-150(6), a single stage of impaired air quality will apply within the geographical area defined by the authority. A single stage of impaired air quality indicates the presence of:

     (a) Particulate matter ten microns and smaller in diameter (PM₁₀) at or above an ambient level of ninety micrograms per cubic meter; or

     (b) Carbon monoxide at or above an ambient level of eight parts of contaminant ppm.

     (4) Acceptable ambient air quality measurement methods.

     (a) Particulate matter ten microns and smaller in diameter (PM₁₀).

     (i) Procedures specified by the EPA in "40 CFR 50, APPENDIX J - REFERENCE METHOD FOR THE DETERMINATION OF PARTICULATE MATTER AS PM₁₀ IN THE ATMOSPHERE" as amended through July 1, 1990, shall be used to gather reference ambient PM₁₀ data on a twenty-four-hour average.

     (ii) More timely ambient PM₁₀ measurement methods may be utilized to evaluate air quality impairment if accepted and approved by ecology. Any alternative method for evaluating air quality impairment for the purpose of curtailing solid fuel burning device use must be done at the same location and in parallel to the reference method, and must be related to the reference method by a mathematical relationship with a correlation coefficient of no less than 0.85.

     (b) Carbon monoxide (CO) must be measured on an eight-hour average in accordance with procedures specified by the EPA in "40 CFR 50, APPENDIX C - REFERENCE METHOD FOR THE DETERMINATION OF CARBON MONOXIDE IN THE ATMOSPHERE (NON-DISPURSIVE INFRARED PHOTOMETRY)" as amended through July 1, 1990.

     (c) All monitors used to measure PM₁₀ for evaluation of air quality impairment due to solid fuel burning device use must be sited in accordance with EPA siting criteria in or near affected residential areas.



[Statutory Authority: Chapter 70.94 RCW. 91-07-066 (Order 90-58), § 173-433-140, filed 3/20/91, effective 4/20/91.]