Aerosols interact with light by scattering it and absorbing it, a combined process known as light extinction. This interaction is the primary reason that aerosols in the atmosphere reduce visibility, creating haze.

The key insight is that this effect is highly size-dependent. The most effective particle size for scattering visible light is approximately 0.5 μm in diameter. This is because this particle size is perfectly matched to the wavelengths of visible light (which are around 0.4 to 0.7 μm), causing the strongest possible interaction. Particles of this size are the main culprits behind hazy and smoggy conditions.

The impact can be dramatic. For example, a concentration of just 10,000 of these 0.5 μm particles per cubic centimeter—a tiny amount of mass—can reduce the daylight visual range to only 0.6 kilometers (about 0.37 miles).