isibility or visual range can be seriously reduced by polluting gases and fine particles called aerosols that absorb or scatter light. This reduces clarity, color, texture, and form and can even completely obscure objects.

Some light scattering and absorption is natural--the sky is blue because of the scattering effect of naturally-occurring gases. But, human activities also create fine organic particles as well as tiny nitrate, sulfate, and nitrogen dioxide particles close to the size of the wavelength of light. These are very efficient at reducing visibility. The aerosols obscuring our view can be in the form of a general regional haze, a layered haze with distinct layers of pollutants or in coherent plumes with specific identifiable sources.

Emissions from power plants and industrial facilities, soot from fires and diesel engines, and dust from farming and dirt roads all contribute. As well, sulfates and nitrates from burning fuels, and organic particles from trees to gas stations scatter or absorb the light. Stagnant weather conditions trap air in valleys and canyons creating haze-filled inversions blocking our view.

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