Page 104 - Fundamentals of Air Pollution

74 6. Sources of Air Pollution

Fig. 6-2. Uncontrolled forest fire. Source: Information and Education Section, Oregon
Department of Forestry.

ings one or two orders of magnitude above ambient air quality standards.
Visibility reduction during major dust storms is frequently the cause of
severe highway accidents and can even affect air travel. The particulate
matter transferred by dust storms from the desert to urban areas causes
problems to householders, industry, and automobiles. The materials re-
moved by the air cleaner of an automobile are primarily natural pollutants
such as road dust and similar entrained material.
The oceans of the world are an important natural source of pollutant
material. The ocean is continually emitting aerosols to the atmosphere, in
the form of salt particles, which are corrosive to metals and paints. The
action of waves on rocks reduces them to sand, which may eventually
become airborne. Even the shells washed up on the beach are eroded by
wave and tidal action until they are reduced to such a small size that they
too may become airborne.
An extensive source of natural pollutants is the plants and trees of the
earth. Even though these green plants play a large part in the conversion
of carbon dioxide to oxygen through photosynthesis, they are still the major
source of hydrocarbons on the planet. The familiar blue haze over forested
areas is nearly all from the atmospheric reactions of the volatile organics