(1) Air Quality Index (AQI). A unitless index used by the U.S. Environmental Protection Agency (EPA) to communicate air quality for several pollutants, including PM2.5. References to the AQI used throughout WAC 296-307-09805 through 296-307-09860 means the "NowCast AQI for PM2.5."

(2) Current PM2.5. The concentration of PM2.5 for the most current hour available, calculated using an hourly average of PM2.5 data.

(3) Emergency response. Rescue, evacuation, utilities, communications, transportation, and medical operations; when such operations are directly aiding firefighting; protecting public health and safety; or actively protecting, restoring, or maintaining the safe and reliable operation of critical infrastructure at risk.

(4) High-efficiency particulate air (HEPA) filter. A filter capable of trapping and retaining at least 99.97 percent of all monodispersed particles of 0.3 micrometers mean aerodynamic diameter or larger.

(5) NIOSH. The National Institute for Occupational Safety and Health of the U.S. Centers for Disease Control and Prevention. NIOSH tests and approves respirators for use in the workplace.

(6) NowCast. The method used by the EPA and the Washington state department of ecology to approximate the air quality for the most current hour available by using a calculation that involves multiple hours of past data. The NowCast uses longer averages during periods of stable air quality and shorter averages when air quality is changing rapidly, such as during a wildfire. The NowCast is generally updated every hour.

(7) PM2.5. Solid particles and liquid droplets suspended in air, known as particulate matter, with an aerodynamic diameter of 2.5 micrometers or smaller. Measured in micrograms per cubic meter (µg/m3).

(8) Wildfire smoke. PM2.5 which includes emissions from planned and unplanned fires in wildlands, wildland urban interface, agricultural operations, or adjacent developed areas. Wildfire smoke contains a complex mixture of gases and particulates. Fine particulates such as PM2.5 are the primary pollutant of public and occupational health concern in wildfire smoke.

(9) Wildlands. Sparsely populated geographical areas covered primarily by grass, brush, trees, crops, or combination thereof.