Understanding Scientific Units

Earth science data parameters have very specific definitions and units. The links below will access some definitions for science parameter units by the topic of interest.
Temperature | Pressure | Radiation | Aerosols | Air Quality | Clouds | Surface
All Unit Definitions | Full Science Glossary | The Metric System

C
column number density:
A unit often used in remote sensing. The number of something (particles, atoms, molecules, …) in an atmospheric column over an area. The area could be a square centimeter, square meter, square kilometer, etc… This provides information about the total amount of that substance in the column, but does not provide any information about how it is distributed: uniformly mixed in the atmosphere (i.e., CO2), vs concentrated near the surface (i.e. pollution), vs concentrated at some other level (i.e., the ozone layer). Because the number of atoms or molecules is usually large, scientific notation is used. For example: 1.e15 NO2 molecules in a column over one square centimeter of the surface (1,000,000,000,000,000 NO2 molecules in an atmospheric column)..  
  Related MY NASA DATA Activity:  Parts Per Billion Activity (PowerPoint)
Illustration of molecules within an atmospheric column
Image courtesy MY NASA DATA Team
D
dobson unit:
a standard unit measure for ozone in a column of air.  
Graphical explanation
M
mole:
a standard unit of measure for the amount of a substance. One mole (mol) of a substance is numerically equal to the molecular weight of that substance. For gases, one mole is equal to Avogadro’s number of molecules (6.022e23). In atmospheric chemistry, moles are sometimes used to quantify atmospheric constituents or pollutants.  
N
number density:
A unit often used in chemistry and physics. The number of something (particles, atoms, molecules, …) in a given volume. The volume could be a cubic centimeter, cubic meter, or some other volume. This can be used in atmospheric science to describe the concentration of aerosols or trace gases. Because the number of atoms or molecules is usually large, scientific notation is used. For example: 3.e12 ozone molecules in a cubic centimeter inside the ozone layer (3,000,000,000,000 ozone molecules in a cubic centimeter).  
  Related MY NASA DATA Activity:  Parts Per Billion Activity (PowerPoint)
P
parts per billion volume:
one method of expressing chemical concentration, usually of a gas. For example, 20 ppbv of ozone means that, if a sample of gas contained one billion units, then 20 of the units would be ozone.  
  Related MY NASA DATA Activity:  Parts Per Billion Activity (PowerPoint)