Atmosphere

‘Atmosphere’ refers to the layer of gases surrounding a planet; each planet has its own atmosphere.

International standards and resources

The International Union of Pure and Applied Chemistry (IUPAC), Chemistry and the Environment Division, Commission on Atmospheric Chemistry, has published a Glossary of atmospheric chemistry terms(Opens in a new tab/window). (Note that use of initial capitals for terms in this glossary reflects the style of the publication; most terms do not require initial capitals.)

Earth’s 5 principal atmospheric layers are (with distance from Earth’s surface):

  • troposphere (<12 km)
  • stratosphere (12–50 km)
  • mesosphere (50–80 km)
  • thermosphere (80–700 km)
  • exosphere (>700 km).

These 5 layers are delineated according to temperature; other layers may be named for other properties, such as ozone layer, ionosphere and magnetosphere. Use lower case for atmospheric layers in any context.

Related terms also take lower case:

biosphere     middle atmosphere

Use lower case for terms related to atmospheric chemistry unless they include a proper noun:

acid rain     air pollution index     haze horizon

See also:

Stratospheric ozone

Stratospheric ozone limits the amount of harmful ultraviolet light that reaches Earth.

See Wavelengths for information on how to write about ultraviolet light.

Use lower case for terms relating to atmospheric ozone, even if they have capitalised abbreviations, but add an s to abbreviations:

ozone-depleting substances (ODSs)     chlorofluorocarbons (CFCs)     photochemical oxidants

Reminder. Just because the abbreviation of a term is made up of capitals, it does not mean that the term has initial capitals when it is spelt out.

Ambient air quality

Use lower case for the names of air pollutants:

nitrogen dioxide     sulfur dioxide     carbon monoxide     lead

See Chemical compounds for more information on presenting names of chemical compounds.

Benzene, toluene and xylene are collectively known as BTX.

‘Particulate matter’ refers to particles of dust resulting from combustion and other processes, including vegetation burning, bushfires, windblown dust, road dust, motor vehicle exhaust, fuel burning and mining. Indicate the size of particulate matter by a superscript denoting the particle size in micrometres:

PM10 [coarse particulate matter; less than 10 micrometres in diameter] 

PM2.5 [fine particulate matter; less than 2.5 micrometres in diameter] 

Concentrations of air pollutants can be given in parts per million (ppm), parts per billion (ppb) or, preferably, micrograms per cubic metre (µg/m3; for ppm) or nanograms per cubic metre (ng/m3; for ppb).

Use lower case for terms relating to air pollution, even if they have capitalised abbreviations:

volatile organic compounds (VOCs)     air quality index (AQI)     ambient air quality (AAQ)     monitoring investigation level (MIL)

Use initial capitals for the names of Australia’s formal environmental protection measures:

National Environmental Protection Measure (Ambient Air Quality) [AAQ NEPM]