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424 GEORGE D. CLAYTON 2. The control of rare metals by a mint paid for itself in one year;-;g1g 3. The sale of sulfur dioxide recovered by a Canadian smelter yieif profit than the original product. Whether or not there is a profit or loss in the control of air poiia, incidental to the fact that the day is fast approaching when managelfir consider the control of sources of pollution as an integral part of the cj struction and maintenance of a plant. IV. Sources and Kinds of Air Pollution Sources of pollution may be divided into two major classificatic "natural" and (8) man-made contaminants. Three outstanding ex natural air pollution in recent times are: the Katmai volcanic erujjj; emissions clouded the Northern Hemisphere in 1902 and 1903; the Jt. forest fire of 1951, which obscured the sun across a great swath of ^CiL the United States, causing street lights to be turned on at 9 a.m. in P|iifP Baltimore, and Cleveland; and the devastating dust storms that lagcd-sts Texas, Oklahoma, and Kansas in the 1930's, as well as the dust storm?5! past few years. -f'| }* TABLE 2 `i Estimated Emissions of Aerosols, Acid Gases, and Aldehydes to the Atrro'-r'L'Te liil County ~ " ......... (IBTBfis'pef'day).............. 3 Ji Source Chemical, paint, roofing, rubber, soap; food, fertilizer, metal & mineral industries . Fuel oil burning* Transportation, diesel Transportation, gasoline Petroleum refining Incineration, domestic Incinerationy-commercialy'indus trial; milnicipaliand'diimps Aero sols* Oxides of nitrogen* Sulfur dioxide Mdo- , h-vd(.elf,-i / 27 85 170 10 2 132 21 -- 80 21 / IDr'-'gSS 34 7 / 1 -V- Total 225 255 300 0 Iccludcs snroke, dusts, fumes and mists. `'Reported-asmitrogen'dtetiite---------------* Reported as formaldehyde. 4 Reported as acetic acid. Includes fuel oil burned in all categories except transportation. All value s1 fuel oil usage, which is approximately one half of the winter usage. ' Less than one ton. 4A AIR POLLUTION 425 been estimated that in Detroit approximately 40 per cent of the follution would remain in the area if all human activity stopped, lution of the air from man-made activities ranges from the cooking home to the effluents from large metal-smelting plants. It is unfortuifeept in Los Angeles, little is known of the relative amounts from I'e sources. Table 2 gives an estimate of the amounts of emissions i Angeles in 1951.18 r A. POLLUTION IN VARIOUS CITIES i'oxide is probably the most common of the contaminant gases found ^riupity atmosphere, being formed in the combustion of most fuds, aiffpSla having a very high percentage of sulfur content.14 Certain |ocesses emit several tons of sulfur dioxide per day.10 Henderson and jtate that the least detectable odor of sulfur dioxide is from 3 to wever, it may be "tasted" in much lower atmospheric concentrations. |ipxide is of interest to air hygienists because, in sufficient concenferyodes building materials, destroys cloth and leather, and affects fil'd human health. The economic effects of sulfur dioxide have been Ssinuch discussion. In London it is reported that the sulfur gases defaced-the stone and other building material, as well as statues jiTOCl^vornaments used to beautify the city. Also in London, library leather'm^^ks^eteriorate as the result of sulfur dioxide.17 . {ev^rer'iBfiereffect-of-sulfur-dioxide-on-buman.bealth,.There are po. acceptable jlpajfjSi psent time that incriminate it as the responsible agent in concen- .lonSsujhoient to cause sickness resulting in death. ifflhi^ffccrapfi sulfur dioxide on plant life is much better known. Setterstr'om18 influencing the effect of sulfur dioxide on plants are: (1) *^ci^Ssgreater at 40 F. or below; (2) resistance decreased with increases u&idity; (3) ample water supply made them.-more susceptible; and IJjBjjS were more resistant than old ones." ^^liage; sulfur dioxide concentrations found in various cities10,18-21 range B St,. ^^I'^lp.ljuPon.CoDtrol Dist., Co. of Los Angeles, Calif., Second Tech. and Admin. Kept., t?Ied^Barkleyroncentration..of.sulphur-cbmpounds,iacity...air,,.U..S, 'C"* ,?*. No. 7066, April, 1939. jjjfeSlffl KHKlltV . .. Industrial __ - Toxicology. ____ Williams and Wilkins, Baltimore, 1949. and H. W. Haggard, Noxious Oases. 2nd ed.. Reinhold, New' Y(ork, 1943. jclflibrary atmosphere, Atmos. Poll. Bull., 16, No. 1 (1948): ' om|Effects--of-Aulfur dioxide on plants and animals, Ind,. Eng.,Chem., 32, '^S8l'7'le measurement and survey of atmospheric pollution, J. Roy. Sanil wfl? ^pollution in Leicester--a Scientific Survey. H. M. S. O., London,-1945. ^^^j^yBulphur dioxille content of air at Boyce Thompson Institute, Contribsi 10, No. 2, 183-187 (1939). ,