A methodology for determining the effects of fuels and additives on atmospheric visibility has been developed using the smog chamber approach. The methodology involves measuring visibility in a 590 cu m smog chamber after first introducing auto exhaust at a 300:1 detection ratio adding 0.05 ppm SO2 and irradiating the sample for 23 hours. Three 5.7 liter 1972 Chevrolets and one 1973 catalyst-equipped 6.55 liter Ford Galaxie were used in the study. The effects on test results of exhaust dilution ratio, relative humidity, added SO2, primary particulates, evaporative emissions and irradiation time are discussed. The tests show that using commercial grade indolene fuel, the effects on visibility of the additives F-310 and CI-2 are small compared to the effects brought about by variations in engine performance. The presence of primary particulates play an important role in the initial and final visibility noted in the smog chamber. The final visibilities noted in the smog chamber were found to be closely correlated with the initial HC/NO ratio. The correlation for the commercial grade indolene is so good that final visibilities can be predicted from the initial measurement of HC and NO in the chamber. For the fuels and additives tested at a given HC/NO ratio, the sulfur content of the fuel appeared to have the most important effect on visibility.

"EPA-650/2-75-068." "Carlspan Corporation." "EPA contract no. 68-02-0698; ROAP no. 26AAE; program element no. 1A1002." EPA project officer: William D. Conner. "June 1975." "Prepared for Office of Research and Development, U.S. Environmental Protection Agency." PB 245 597--National Technical Information Service. Includes bibliographical references.