Atmospheric Aerosol

:: Section 4

Urban Aerosol

II. Accumulation Mode

The accumulation mode (0.1 μm < particle size < 2.5 μm) includes combustion particles, smog particles, and coagulated nuclei-mode particles . The smog particles are formed in the atmosphere by photochemical reactions. Particles in this mode are small but they coagulate too slowly to reach the coarse-particle mode. Hence, they have a relatively long lifetime in the atmosphere and they account for most of the visibility effects of atmospheric aerosols. The nuclei and accumulation modes together constitute “fine” particles.