Gases that occur at low concentrations in the atmosphere are known as trace gases. Trace gases make up only 1% of the atmosphere's gases, while nitrogen, oxygen, and argon make up 99%. Water vapour, ozone, nitrogen oxides, sulphur dioxide, carbon dioxide, ammonia, formaldehyde, methane, and ozone are among the 1% of gases that make up the atmosphere. Because of their highly reactive nature or because they are produced or emitted at such a low rate, they are only found in trace levels in the atmosphere.

Despite their low concentration in the atmosphere, trace gases have an important role in climate change since many of them are greenhouse gases like methane and carbon dioxide, as well as air quality because many of them are pollutants like nitrogen dioxide and sulphur dioxide.

Satellites can be used to measure trace gases in the atmosphere through sunlight (UV/Vis) backscattered by the atmosphere and/or measuring the atmospheric spectra in the infrared. We can then analyse its spectrum of "colours" from infra-red to UV, as we know the distinct absorption spectra of each trace gas. Retrieval algorithms can then be used to infer physical quantities such as density, vertical distribution, and column amount.

Featured Educator

• Dr Pepijn Veefkind, Senior Scientist, KNMI

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