| Visual Range:
Visual range is defined as the distance at which a black object
can be discerned from a white background on the horizon. For
this application, visual range is measured by instruments
that capture small amounts of air at a fixed location on the
earth’s surface. This method sometimes overestimates
the visual range, especially in foggy or rainy conditions.
Therefore, visual range measurements are shown as “less
than” a particular distance on the FSVISIMAGES website.
The estimated maximum visual range measurements represented
here were derived from hourly ambient nephelometer scattering
measurements. This estimate does not take into account current
particle absorption, which generally contributes less to visibility
impairment than scattering.
Pollutant
PM10: Suspended
particulate matter with an aerodynamic diameter of 10 micrometers
or less and is measured in micrograms per cubic meter. The
PM10 value shown is an hourly average. There is no hourly
ambient air standard.
PM2.5: Suspended
particulate matter with an aerodynamic diameter of 2.5 micrometers
or less and is measured in micrograms per cubic meter. The
PM2.5 value shown is an hourly average. There is no hourly
ambient air standard. The 24-hour standard is 65 micrograms
per cubic meter.
Ozone: A reactive chemical compound of 3
oxygen atoms found at all levels of the atmosphere. Ozone
is measured in parts per million. The ozone value shown is
an hourly average. The hourly ambient air standard is 0.125
parts per million and the 8-hour average ambient air standard
is 0.08 parts per million.
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