133 The highest SF. value measured was 0.60 ppb, with values about half as large as 10° on either side of the plume centerline. One sample again failed to collect any alr. PROPOSED SFs PROGRAM, SUMMER AND FALL 1969 More SF, experiments will be made at Argonne, using both ground level and stack releases. These will continue until the system is operational. Simultaneously, additional SF, background measurements will be made both in Chicago and at Argonne. Someof the Argonne releases will be made from the Argonne heating plant. If these tests are satisfactory, and if background levels are acceptably low and uniform, full-scale re- leases in Chicago will begin. Arrangements have been made to introduce the SF, into one of the stacks of the Commonwealth Edison Company’s Crawford and Will County plants. Gas samplers will be placed next to the TAM SOzsensor inlets to determinethe relative contribution of this one stack to total SOs levels. A series of gas collectors will also be placed across the expected plume axis one or more miles downwind to define the plume center-line and to measure actual dispersion coefficients (sigmas) in the urban environment. Other experiments are being planned, including the use of other power plant stacks and ground and roof-level releases. REFERENCES 1. Croke, E., Carson, J. E., Clark, F., Kennedy, A., and Roberts, J. Chicago Air Pollution System Model, First Quar- terly Progress Report. Argonne National Laboratory Report ANL/ES-CC-001 (February 1968). 2. Croke, E. J., Carson, J. E., Gatz, D. F., Moses, H., Clark, F, L., Kennedy, A. 8., Gregory, J. A., Roberts, J. J., ’ Carter, R. P., and Turner, D. B. Chicago Air Pollution System Model, Second Quarterly Progress Report. Argonne National Laboratory Report ANL/ES-CC-002 (May 1968). 3. Croke, E. J., Carson, J. E., Gatz, D. F., Moses, H., Kennedy. A. 8., Gregory, J. A., Roberts, J. J., Croke, K., Anderson, J., Parsons, D., Ash, J., Norco, J., and Carter, R. P. Chicago Air Pollution System Model, Third Quarterly Progress Report. Argonne National Laboratory Report ANL/ES-CC-003 (October 1968). 4. Croke, E. J., Carson, J. E., Gatz, D. F., Moses, H., Kennedy, A. 8., Noreo, J. E., Roberts, J. J., Croke, K. G., Anderson, J. B., Nelson, D. M., Ash, J. E., Carter, R. P., Lin, J.-W., and Votruba, R. J. Chicago Air Pollution System Model, Fourth Quarterly Progress Report. Argonne National Laboratory Report ANL/ES-CC-004 (March 1969). 5. Carson, J. E. and Gatz, D. F. Chicago Air Pollution Meteorological Studies. Argonne National Laboratory Radiological Physies Division Annual Report, July 1967-June 1968 ANL-7489, pp. 87-93. 6. Carson, J. E., Votruba, R. J., and Lin, J.-W. Chicago’s Air Pollution Incident Control Test, Summer 1968. Paper presented at 62nd Annual Meeting, Air Pollution Control Association, New York City, June 25, 1969. 7. Saltzman, B. E., Coleman, A. I., and Clemons, C. A. Halogenated Compounds as Meteorological Tracers. Anal. Chem. 38, 753-758 (1966). 8. Niemeyer, L. E. and McCormick, R. A. Some Results of Multiple Tracer Diffusion Experiments at Cincinnati. J. Air Poilution Conirel Assoc. 18, 403-405 (1968). 9. Turner, D. B. Workbook of Atmospheric Dispersion Estimates. Public Health Service Publication, No. 999-AP26, Environmental Health Series, Department of Health, Edueation and Welfare, 1967. CHICAGO'S AIR: POLLUTION INCIDENT CONTROL TEST, SUMMER 1968*. + J. E. Carson, R. J. Votrubat§ and J.-W. Lint One method for reducing pollution concentrations during periods of weak winds and poor diffusion conditions without turning industry off is to convert as many of the large sources to alternate fuels as possible. Sulfur dioxide is a major pollutant in Chicago; unfortunately, sufficient supplies of low-sulfur fuels are not available to replace the usualfuels at all times. The City of Chicago’s Department of Air Pollution Control, in cooperation with Argonne National Laboratory, is developing an air pollution abatement strategy to use the limited * Summary of paper presented at the 62nd Annual Meeting, Air Pollution Control Association, June 25, 1969, New York City. t This work was partially supported by the Chicago Department of Air Pollution Control and the National Air Pollution Control Adiministration, Department of Health, Education and Welfare. +t Department of Air Pollution Control, City of Chicago. § Deceased, October 16, 1969. quantities of low-sulfur fuels with maximum effect on air quality. This technique consists of asking major SO: producers to convert to such fuels during periods of poor ventilation, especially those sources within and upwind of the polluted areas and population centers. A full-scale dress rehearsal of this technique was tested during a three-week period in June and July, 1968. This paper discusses the results of this outdoor experiment, including changesof air quality due to fuel switches. The second in a series of fuel-switch tests was conducted in the City of Chicago between 16 June and 6 July 1968. Industry and the power generating plants cooperated with the city’s Department of Air Pollution Control (DAPC) in conducting this unique and valuable experiment in air quality control. Chicago is the first and to date the only majorcity