Aerosol

An aerosol is a suspension of fine solid particles or liquid droplets in a gas. Fog, smoke, and airborne dust are familiar examples.

Brownian motion: The irregular movement of small particles suspended in a fluid, caused by collisions with its molecules. Molecular collisions keep the smallest aerosol particles moving unpredictably.
Particulate matter: A mixture of solid particles and liquid droplets suspended in air. Aerosols are the airborne portion of particulate matter.
Cloud condensation nuclei: Airborne particles on which water vapor condenses to form cloud droplets. Aerosols provide many of the seeds from which cloud droplets form.
Gas: A state of matter with no fixed shape or volume, whose particles move freely. A gas is the continuous medium of an aerosol, not its suspended particles.
Coagulation (aerosol science): The merging of suspended particles after collisions, producing larger particles. Collisions can make aerosol particles grow and settle more quickly.
Aerosol particle size: A measure of the dimensions of suspended particles, commonly expressed as an aerodynamic diameter. Size strongly influences how long particles stay airborne and where they deposit.
Aerosol-cloud interactions: The effects of atmospheric particles on cloud formation, properties, and lifetime. Particle abundance can alter cloud brightness and precipitation.
Vapor: A gaseous form of a substance that is liquid or solid under ordinary conditions. Vapor consists of individual molecules, while aerosol particles are condensed-phase material.
Nucleation: The initial formation of a new phase through clusters of atoms or molecules. Vapor condensation onto newly formed clusters can create aerosol particles.
Aerosol optical depth: A measure of how much aerosol in an atmospheric column attenuates light. It captures the combined light-blocking effect of particles along a path through the atmosphere.

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