ultrafine particles

Very small atmospheric particles, less than 10 nm in diameter.

Such particles are thought to be formed by binary nucleation of compounds, such as sulfuric acid and water, and lead to an increase in the total number of particles present. The increased particle number density has consequences for climate effects such as light scattering.

An aggregation of sufficiently many atoms or molecules that it can be assigned macroscopic properties such as volume, density, pressure, and temperature.