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Breakpoints and Associated Visibility for Particulate Concentrations

Health Effect Categories Visibility
(miles)3
24-Hour BAM
(ug/m3) 1
8-Hour BAM
(ug/m3) 2
1-Hour BAM
(ug/m3) 3
  Hazardous < 1.3 >135.4 > 193.4 > 338.5
  Very Unhealthy 2.1 - 1.3 80.5 - 135.4 115.0 - 193.4 201.1 - 338.5
  Unhealthy 5.0 - 2.2 35.5 - 80.4 50.7 - 114.9 88.6 - 201.0
  Unhealthy for Sensitive Groups
8.7 - 5.1

20.5 - 35.4

29.2- 50.6

51.1 - 88.5
  Moderate 13.3 - 8.8 13.5 - 20.4 19.2 - 29.1 33.6 - 51.0
  Good > 13.4 + 0.0 - 13.4 0.0 - 19.1 0.0 - 33.5
  1. Washington State Department of Ecology, Washington Air Quality Advisory (2007), at https://fortress.wa.gov/ecy/enviwa.
  2. Applied U.S. EPA SCREEN adjustment factor for 8-hour, 0.7, multiplied
    to the 24-hour PM-2.5 Pollutant Standards Index.
  3. John Coefield, Cyra Cain, Montana Department of Environmental Quality empirical study (July 2000) presented at Fire, Smoke and Health Workshop, Seattle, WA, June 5 - 6, 2001.