PurpleAir sensors measure airborne particulate matter (PM). Particulate matter describes solid particles suspended in air; this includes dust, smoke, and other organic and inorganic particles. PurpleAir sensors use laser particle counters to count the number of particles by particle sizes 0.3, 0.5, 1, 2.5, 5, and 10 μm, and use the count data to calculate mass concentrations of PM1.0, PM2.5, and PM10. See this graphic.
The unit installed at Sand Point Weather includes an experimental volatile organic compounds (VOCs) sensor. Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. ... VOCs are emitted by a wide array of products numbering in the thousands.
The map above displays the Air Quality Index (AQI) for Particulate Matter <2.5 µm (PM2.5), averaged over 10 minutes, by default. Use the "Map Data Layer" drop-down to select other options.
|Daily AQI Color||Levels of Concern||Values of Index||Description of Air Quality|
|Green||Good||0 to 50||Air quality is satisfactory, and air pollution poses little or no risk.|
|Yellow||Moderate||51 to 100||Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.|
|Orange||Unhealthy for Sensitive Groups||101 to 150||Members of sensitive groups may experience health effects. The general public is less likely to be affected.|
|Red||Unhealthy||151 to 200||Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.|
|Purple||Very Unhealthy||201 to 300||Health alert: The risk of health effects is increased for everyone.|
|Maroon||Hazardous||301 and higher||Health warning of emergency conditions: everyone is more likely to be affected.|