148 Fie. 112.—Schematic diagram of heat-island circulation (redrawn from Lowry“) cago area, The weather maps show the broad seale framework sources. We drew SOs isopleths and shaded areas progres- sively darker with mereasing concentration to show pollution patterns at a glance. These are general patterns only—they are not meant to give details. For example, where data were sparse, uniform concentration gradients were drawn. This is an obvious simplification. Others may be evident as we look at the three cases in detail. RESULTS AND DISCUSSION Oo mn 7 fF — t tf a A ua on tf a bo pre of each specific local event. The time sections show the hour-to-hour relationships between SO. and winds. These relationships are clearest in smoothed data; therefore, we plotted hourly averaged winds and SO. concentrations on the time sections. The purpose of the meso-scale charts is to show instantaneousdistributions of SQe, winds, and temperature over Chicago, Thus the winds on these charts are J- to 5-min averages, and temperatures are instantaneous. SOs values are still 1-hr averages, though. to insure that plotted values represent real effects and not nearby — o (3) meso-seale charts showing winds, temperatures and SO. concentrations over the Chi- | MiDWAY ——--—— — O'HARE | ARGONNE ------ a tions of SO. concentrations and winds at selected stations; and r TEMPERATURE, (F ) We studied each case using three graphical aids: (1) a surface weather map for the day; (2) time sec- } DATA AND PROCEDURES {| 2 | 4 | 6 | | jf | f | tf 8 10 12 14 16 I8 20 22 24 19 JANUARY 1966, CST Fic. 113—Diurnal temperature changes at Argonne, Midway. and O’Hare, 19 January 1966. 19 JANUARY 1966 19 o600 CST GRB JANUARY 1966 20 JANUARY [966 1800 CST PIA PIA f fF - eif Ff) fF OC GRB Bal / I f [ —r { fF {/ 7 f VOX \_ \ sunrsce > SN o-2 kt OT FYE A ov] 4 Ld YR XL pe esN err XN PIA fo aw ¢ Cl gir, t 3 > GRB 0600 CST KEY XQ 3-7 kt at RK a-l2kt 13-17 kt 19 January 1966: A Possible Heat-Island Circulation Case Fic. 114—Winds aloft at Peoria and Green Bay, 19-20 January 1966. The 1200 CST* surface weather map (Figure 105) shows an anticyclone covering the Midwest. Its center was just west of Chicago. The pressure gradient over * All times in this paper are CST. Chicago was weak; hence winds were light. The 19th was the third consecutive day that Chicago was in-