Why do fine particles stay suspended in the air as aerosols?

An aerosol is a suspension of fine solid particles or liquid droplets in a gas like air, generally defined by falling velocities of less than 0.25 m/s. These particles typically have diameters under 10 micrometers. While larger particles have a significant settling speed and create an unstable suspension, smaller particles remain aloft due to these low terminal speeds, and systems like sediment transport also involve fluid motion.

What we know

• An aerosol is defined as a suspension of fine solid particles or liquid droplets in air or another gas with falling velocities broadly less than 0.25 m/s. [2]
• The liquid or solid particles in an aerosol typically have diameters of less than 10 micrometers. [2]
• Sediment transport is the movement of solid particles typically due to a combination of gravity acting on the sediment and the movement of the fluid in which it is entrained. [4]

Still open

• The exact threshold dividing stable aerosol suspensions from unstable mixtures with larger particles is considered somewhat arbitrary.

Where to go next

• a case in pointWhat are common examples of natural and human-made aerosols?
• the bigger pictureHow does wind shape the Earth's surface through aeolian processes?
• how it workedHow do fluid motion and gravity drive sediment transport?
• how we knowWhat meteorological terms define atmospheric phenomena?
• what followedHow are consumer products delivered using aerosol spray cans?
• an unexpected connectionHow do volcanic eruptions and coughing share the same physical classification?Both volcanic gas emissions and human sneezes generate natural aerosols consisting of fine particles suspended in a gas.

Sources

• [1]aerosol (Wikidata Q104541) · CC0 1.0
• [2]Aerosol · CC BY-SA 4.0
• [3]Aeolian processes · CC BY-SA 4.0
• [4]Sediment transport · CC BY-SA 4.0
• [5]Glossary of meteorology · CC BY-SA 4.0