Atmospheric Aerosol

:: Section 4

Urban Aerosol

I. Nuclei Mode

The Nuclei mode (particle size < 0.1 μm) consists primarily of combustion particles emitted directly into the atmosphere and particles formed in the atmosphere by gas-to-particle conversion. They are usually found near highways and other sources of combustion. Because of their high number concentration, especially near their source, these small particles coagulate rapidly. Consequently, nuclei particles have relatively short lifetimes in the atmosphere and end up in the accumulation mode.

Examples of Gas-to-Particle Conversion

Gas-phase species that are individually volatile may react and form low-vapor-pressure solids. Some examples are listed as follows.

1. Inorganic aerosol formation:

2. Secondary organic aerosol (SOA) formation: