Atmospheric aerosols are particles of 0.001–100 μm that remain suspended in the atmosphere for hours to weeks. They include PM2.5, PM10, sulphuric acid droplets, sea salt crystals, spores, and soot.
Climate effect
Aerosols have a net cooling effect on climate: they scatter solar radiation (direct effect) and act as cloud condensation nuclei that modify cloud properties (indirect effect). Volcanic eruptions inject sulphate aerosols into the stratosphere that can cool the planet by 0.5–1 °C for 1–2 years. Paradoxically, reducing aerosols through clean air policies is accelerating warming.