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<br />o & .~ OJ. 2 ,") <br /> <br />'More work is needed to substantiate synergistic responses, <br /> <br />especially in the higher altitude low humidity climates of <br /> <br />the Western States, since it is known that climatic condi- <br /> <br />tions markedly affect the response of vegetation to. air <br /> <br />pollutants. " <br /> <br />Visibility <br />"The First Annual Report of the Council on Environmental Quality, "5./ <br /> <br />comments on visibility effects of air pollution to this effect: <br /> <br />" <br /> <br />Particulates, however, are the major villain in reducing <br /> <br />visibility. <br /> <br />Particles (aSh, carbon, dust, and liquid particles, dis- <br /> <br />charged directly to the air scatter and absorb light, reducing the <br /> <br />contrast between objects and their backgrounds. Particles are also <br /> <br />formed in the atmosphere by photochemical reactions and by the con- <br /> <br />version of sulfur dioxide to sulfuric acid mist. Wherever sulfur pol- <br /> <br />lution is significant--which is wherever large amounts of coal and oil <br /> <br />are burned--visibility diminishes as relative humidity rises." <br /> <br />The DHEW publication, '~ir Quality Criteria for Particulate <br />Matter,'Q/ states under the conditions set forth in the studies refer- <br /> <br />enced therein that: "...With a typical rural concentration, such as <br /> <br />30 pg/m3, the visibility is about 25 miles; for common urban concen- <br /> <br /> <br />trations, such as 100 ~/m3o and 200 pg/m3, the visibility would be 7.5 <br /> <br /> <br />miles and 3.75 miles, respectively." <br /> <br />With respect to sulfur dioxide concentrations, the DHEW publica- <br /> <br /> <br />tion, "Air Quality Criteria for Sulfur Oxides, ,,".i/ states that, "Visi- <br /> <br /> <br />bility reduction to about 5 miles was observed at 285 P-g/rr? (0.10 p.p.m.)." <br /> <br />36 <br />