Chemistry
How Aerosol Particles Nucleate Cloud Droplets and Affect Climate
Quick fact
Most clouds could not form without aerosol particles acting as seeds; pure water vapor needs extreme supersaturation to condense by itself. Ship tracks—bright, narrow clouds along ship exhaust plumes—are visible evidence that human-made aerosols nucleate cloud droplets and change cloud reflectivity.
Why this is interesting
Every cloud you see was born on a tiny particle of dust, salt, or pollution. But how does such an invisible speck grow into a water droplet that can rain on you?