Aerosol optical depth (AOD)

A measure of how much tiny airborne particles — smoke, dust, haze, pollution — dim the sunlight passing through the atmosphere. Higher AOD means hazier, dirtier air.

Why it matters

Aerosols harm air quality and human health, and they nudge the climate by scattering sunlight and seeding clouds, so AOD is a key gauge of both pollution and climate forcing.

Where you’ll meet it

• MODIS and VIIRS produce daily global AOD maps used for air-quality monitoring.
• PACE’s OCI instrument measures aerosols alongside ocean color.
• TEMPO and TROPOMI track aerosols together with pollutant gases.

In plain terms

It’s like rating how smoggy the air looks — clear blue sky is low AOD, while a hazy, smoke-filled horizon you can barely see through is high AOD.