Parameter Units
Each measurement is called a parameter. When dealing with air quality, many of the parameters must be given units that relate to how much of the parameter is present in the atmosphere. There are many units that do this, such as the ones below.
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Microgram per cubic meter (μg/m3): how many micrograms (a millionth of a gram) of
the parameter are within a volume of air that is 1m x 1m x 1m.
Often used for particulate matter (PM1, PM2.5, and PM10).
-
Part per million (ppm): How many particles of the parameter there are among a million air
particles.
Often used for the concentration of gases in the atmosphere like carbon dioxide (CO2(g)).
-
Part per billion (ppb): How many particles of the parameter there are among a billion (a
thousand million) air particles.
Often used for the concentration of trace gases in the atmosphere like ozone (O3(g)).
- Percent relative humidity (%RH): The percent of moisture (gaseous water) present in the atmosphere relative to the maximum amount that can be present in the atmosphere.
-
Pressure: How much the atmosphere is pressing down on the Earth. It is commonly measured in
kiloPascals (kPa) or millibars (mbar)
1 mbar = 0.1 kPa
- Lux: How much light is hitting a certain area.
