Page 177 - Fundamentals of Air Pollution

I. The Physics of Visibility 143

Fig. 10-7. Scattering and absorption cross-section per unit volume as a function of particle
diameter. Source: Charlson, R. }., Waggoner, A. P., and Thielke, H. F., "Visibility Protection
for Class I Areas. The Technical Basis," Report to the Council on Environmental Quality,
Washington, DC, 1978.

air (maritime or continental), Buma (10) found that at a set relative humidity,
continental air reduced visibility below 7 km more often than did air of
maritime origin. This effect is presumably due to numerous hygroscopic
aerosols from air pollution sources. Some materials, such as sulfuric acid
mist, exhibit hygroscopic growth at humidity as low as 30%.

B. Turbidity

The attenuation of solar radiation has been studied by McCormick and
his associates (11, 12) using the Voltz sun photometer, which makes 'mea-

Fig, 10-8. Single particle scattering to mass ratio for particles of four different compositions.
Carbon particles are also very efficient absorbers of light. Source: U.S. Environmental Protec-
tion Agency, "Protecting Visibility," EPA-450/5-79-008, Office of Air Quality Planning Stan-
dards, Research Triangle Park, NC, 1979.