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Understanding Units of Measurement
Many citizens of Sugar Creek have had the opportunity to read technical reports expressing the amounts of different contaminants in air or water samples taken from the former Amoco refinery and the surrounding area. Units of measurement can be confusing. The explanations in this article are intended to help people understand the measurement units that they may see in technical environmental reports. If you have any questions about the information in this article, please call the TOSC toll-free number, 1-800-798-7796, my direct phone number, 913-780-3328, or send me an email at mboguski@birch.net.
Numbers
Million = 1,000,000
Billion = 1,000,000,000
Trillion = 1,000,000,000,000
28 grams = about 1 ounce
1 milligram (mg) = 1/1,000 gram
1 microgram (ug) = 1/1,000,000 gram
1 nanogram (ng) = 1/1,000,000,000 gram
1 picogram (pg) = 1/1,000,000,000,000 gram
One cubic meter (m3) = 35.31 cubic feet.
One liter (L) = 1.06 quarts
Concentrations in water
Concentrations of chemicals in water are typically measured in units of
the
mass of chemical (milligrams or micrograms) per volume of water (liters).
Mass is weight divided by gravity. Concentrations can also be expressed
as
parts per million (ppm) or parts per billion (ppb). A way to visualize
one
part per billion (ppb) is to think of it as one drop in one billion drops
of water or about one drop of water in a swimming pool. One part per
million is about 1 cup in a swimming pool. Parts per million (ppm) or
parts
per billion (ppb) measurements in water can be changed to milligrams per
liter (mg/L) or micrograms per liter (ug/L). See below.
Parts per million (ppm) = approximately milligrams per liter (mg/L) or
(mg/l)
Parts per billion (ppb) = approximately micrograms per liter (ug/L) or
(ug/l)
1 part per million = 1000 parts per billion
Concentrations in air
Concentrations of chemicals in air are typically measured in units of
the mass of chemical (milligrams, micrograms, nanograms, or picograms)
per volume of air (cubic meters). However, concentrations may also be
expressed as parts per million (ppm) or parts per billion (ppb) by using
a conversion factor. The conversion factors are based on the molecular
weights of the different contaminants and are different for each chemical.
For benzene, the conversion factor for changing micrograms per cubic meter
(ug/m3) to parts per billion (ppb) is 3.25. If the measurement is in micrograms
per cubic meter
(ug/ m3), dividing the value of micrograms per cubic meter (ug/ m3) by
3.25 will
change the value to parts per billion (ppb). For example: 10 ug/ m3 of
benzene is about equal to 3 ppb by volume in air. This is calculated by
dividing 10 by 3.25.
