Understanding Carbon Offsets
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Particulate Emissions from Aviation: Sulfates & Soot Aerosols

Aircraft also emit soot (black carbon) and sulfate aerosols. Dark soot particles absorb solar radiation and therefore have a warming effect. This effect is particularly strong when soot is deposited on snow and ice, thus darkening the light surface and decreasing its albedo effect (dark surfaces absorb more radiation than light surfaces).

Sulfate aerosols lead to direct cooling, as they reflect sunlight. On the other hand, sulfate particles can also lead to cloud formation. Water vapor in saturated air can condense on these particles, resulting in contrails and cirrus clouds. This in turn leads to warming because additional heat is stored in this way.

The direct effect of particles from aircraft is short (hours to days), fairly well understood, and is estimated to be small. Indirect effects on clouds, however, are still poorly understood (Lee, 2018).