ASCII - American Standard Code for Information Interchange
Pronounced ask-ee, ASCII is a code for representing English characters as numbers, with each letter assigned a number from 0 to 127. Most computers use ASCII codes to represent text, which makes it possible to transfer data from one computer to another.

Brewer Spectrophotometer
The Brewer is an automated instrument which infers the amount of total column ozone in the atmosphere, and measures the amount of UV radiation that reaches the earth's surface. UV is spectrally resolved between 286.5 - 363 nanometer wavelengths, although measurements below 300nm should not be deemed reliable. The Brewer is manufactured by Kipp and Zonen Instruments, Inc. of Saskatoon, Saskatchewan, Canada.

Diffey Weighting
A weighting function that indicates which UV wavelengths are most efficient at burning human skin. When the weighting is multiplied by spectral irradiance and the product is integrated over all wavelengths, the result is diffey-weighted irradiance, a single number indicating the rate at which fair skin will redden.

Direct Sun
Refers to a measurement based only on direct radiation from the sun's disk and excluding indirect radiation from the remainder of the sky.

Dobson Unit (DU)
The unit of measure for total ozone or other gases. If you were to take all the ozone in a column of air stretching from the surface of the earth to space, and bring all that ozone to standard temperature (0 Celsius) and pressure (1013.25 millibars, or one atmosphere (atm)), the column would be about 0.3 centimeters thick. Thus, the total ozone would be 0.3 atm-cm, or 300 Dobson Units (DU).

Diffey-weighted UV irradiance (watts/m²)

The power transferred to a unit area of a surface by radiation from all directions within a hemisphere, measured in watts per square meter (W/m²).

The energy transferred to a unit area of surface by radiation from all directions within a hemisphere during a specified period of time, (measured in Joules per square meter (J/m2))

Mercury Lamp
The mercury lamp is an internal light source that the Brewer uses to assure that it knows which wavelength it is looking at when doing a scan of the irradiance spectrum.

One billionth of a meter (1 x 10-9 m). A common unit used to describe wavelengths of light or other electromagnetic radiation such as ultraviolet (UV).

Nitrogen dioxide, a brownish, highly reactive gas which is present in urban atmospheres. NO2 is formed in the atmosphere from emissions of oxides of nitrogen (NOx). NOx forms when fuel is burned at high temperatures. The two major NOx emission categories are transportation sources (primarily motor vehicles) and stationary fuel combustion sources, such as electric utilities and industrial boilers.

A molecule consisting of three oxygen atoms. Ozone strongly absorbs short wavelength ultraviolet light and consequently protects life on earth from the damaging effects of this radiation. It is also a very reactive compound, which makes it a harmful air pollutant at the surface. Repeated exposure to ozone can make people more susceptible to respiratory infection and lung inflammation, and can aggravate preexisting respiratory diseases, such as asthma. Sometimes people refer to "good" (stratospheric) ozone and "bad" (surface) ozone.

Optical Density (of the Atmosphere)
The optical density of a material relates to the tendency of its atoms to retain the absorbed energy of an electromagnetic wave before reemitting it. The more optically dense a material is, the slower an electromagnetic wave will move through it.

Ozone layer
That level of the atmosphere which encompasses a peak in ozone concentrations, roughly 12 to 30 km above the surface.

Sulfur dioxide, a non-flammable colorless gas. SO2 is a component in atmospheric air pollution and is one of the factors responsible for acid rain. Coal-fired power plants and volcanoes are major sources of SO2 on a global basis.

Spectral Irradiance
Spectrally resolved irradiance, measured in watts per square meter per nanometer ((W/m²)/nm).

Standard Lamp
The standard lamp is an internal quartz-halogen light source that the Brewer uses to quality assure response to five operational wavelengths involved in the column ozone calculations.

Stratospheric Ozone (O3) Profile
Can be illustrated in a series of graph which measure:
a) O3 molecular density [molecules per cubic meter] as a function of atmospheric altitude;
b) O3 partial pressure as a function of atmospheric altitude;
c) O3 mixing ratio as a function of atmospheric altitude;

Total Column Ozone
The total amount of ozone in a column of air stretching from the earth's surface to space. More than 90% of the ozone is in the ozone layer at high altitude.

Total Column Sulfur Dioxide
The total amount of sulfur dioxide in a column of air stretching from the earth's surface to space.

Ultraviolet (UV)
A portion of the electromagnetic spectrum with wavelengths shorter than visible light. The sun produces UV, commonly split into three bands: UV-A, UV-B, and UV-C.

Ultraviolet-A (UV-A)
UV with wavelengths 315 - 400 nm.

Ultraviolet-B (UV-B)
UV with wavelengths 280 - 315 nm.

Ultraviolet-C (UV-C)
UV with wavelengths less than 280 nm.

UV Radiation
Light having a wavelength greater than 10 nm but less than 400 nm.

The Umkehr (um) measurements can be used to calculate the ozone profile (ozone as a function of height).

Zenith Sky
The zenith sky (zs) measurement is also a measurement of total column ozone (DU), but it is made when the Brewer looks at the zenith.