More Information
Estimated particle concentrations and visual range data are derived from real-time light scattering (nephelometer) measurements. Visual range estimates are
calculated directly. Fine particle concentration (PM
2.5; particles less than or equal to 2.5 micrometers in diameter) estimates are based on observed relationships between these variables at each monitoring site.
Estimates provided here most accurately reflect average conditions. They are also useful for evaluating higher particulate matter concentrations, like those associated with smoke from wildland or prescribed fires. Under these conditions, PM
2.5 estimates are likely to be low. (See additional disclaimers below).
Air quality in some parks may at times exceed the primary (human health)
National Ambient Air Quality Standard for fine particulate matter, often during smoke events. The table shown here, taken from
Wildfire Smoke, A Guide for Public Health Officials (2008), provides guidance regarding Air Quality Index (AQI) health advisory categories and the corresponding PM
2.5 levels.