144 CITY OF CHICAGO POLLUTION INCIDENTS: CASE STUDIES* DF. Gatz and £. W. Kiappenbacht Chicago weather phenomena and SO: pollution sources interact In a number of different ways to produce episodes of through the eity may have caused the unusually high pollution of that dav. The two remaining cases involved winds off sented in this paper were a first step in our study of the than the lake surface. The other involved a shift to east severe pollution. The three high-pollution case studies pre- Lake Michigan. One was a lake breeze, with the land warmer weather associated with Chieago pollution. This information 4, % winds aver the whole region In response to a pressure gradient ao a % oe ass<O. a, a o, - “O, “e, Be 4 * Bp “02, On “922> “Ox "02, So 029 1l2 112 sor? 1012 Fie. 105.—19 January 1966 surface weather map, 1200 CST is crucial to our efforts to build an SO: prediction model for the city. The first case examined was evidently a heat-island circulation. Winds converged over the axis of the city heat island reorientation. In this case, the lake surface was warmer than the land. In both cases. observed poliution conditions were generally consistent with theoretical expectations. from northwest and northeast on 2 clear, cold, nearly calm INTRODUCTION winter afternoon. There is evidence that recirculation of air * This paper was prepared for presentation at the Air Pollution Control Association Annual Meeting, New York, June 24, 1969. 7 Senior Meteorologist, City of Chicago Department of Air Pollution Controi. Argonne National Laboratory scientists are developing an SOx pollution prediction model for Chicago. To be useful, the model must be able to predict high concentrations accurately. For the model to predict high concentrations accurately we must provide it