136 Since vertical lapse rate data are so important in pollution work, the City of Chicago Department of Air Pollution Control purchased an airborne instrument package designed to measure SOz, pressure altitude, and wet bulb depression and temperature. The instrument was purchased from Sign X Laboratories, routine observations. The balloons also give wind in- formation in the zone of transport over the city, data not observable from the helicopter. The first helicopter flight using this instrument was made on March 5, 1969. On this flight, only the Midway temperature profile was complete and showed an adiabatic lapse rate to the top of the sounding at 2600 ft above ground at 1045 CST. The winds were southwest at 8 to 10mph. Clouds at Midway were thin, broken cirrus above 20,000 feet with scattered Inc., Essex, Connecticut. This package, mounted on a Chicago Fire Department helicopter, has been used to measure SO. and temperature profiles over the city since March 1969. Several examples of the types of information that can be obtained from this system are cumulus at 900 meters. By far the most interesting of the helicopter flights given below. DAPC personnel operate the equipment on most flights. was made on March 19, 1969. The 0600 CST weather map on this date showed an east-west stationary front across Wisconsin, Lake Michigan, and Michigan just The U. S. Weather Bureau, using funds from NAPCA, began a balloon program in Chicago in April to the north of Chicago. Winds were mostly light and 1969 to provide wind and temperature data from the variable south of the front and weak north to north- surface to 10,000 feet. Slow-rising radiosondes are used to obtain temperature and humidity data; the east behind it. This frontal zone pushed to the south during the morning hours, passing Meigs Airport be- balloons are followed optically to give wind speed and direction. An over-inflated 100-g pilot balloon is used fore the helicopter started its flight program and Argonne after the sounding there. The three tempera- to lift the package. Two flights are made each normal work day at 0500 CST and 1000 CST (none on week- ture soundings are shownin Figure97. All three soundings show the same temperature at ends or holidays). As originally planned, the helicopter system was to 2600 ft (MSL) and above; it is assumed thatall three soundings were madein the same air mass abovethis be used both to obtain routine vertical temperature and SO2 soundings and to study in detail these profiles in the city and how they vary horizontally and with time during “typical” weather and pollution situ- level. The data indicate that the fresh polar air mass behind the front was still very shallow at Meigs and Midway. The Meigs temperature profile was made at 1030 ations. The balloon program frees the helicopter from 1000 | | | ] O b Oo a | | | | | 19 MARCH 1969 ° 4, MIDWAY Y © ARGONNE © _ O MEIGS SURFACE AIR FLOW v 2 = 500/— _ x | 00 L 2 = | 2.5-5 m/sec = o oO A oO Lo oO LAKE SURFACE - TEMPERATURE :|°¢¢ 0 4 | 5 ANL A oO | 6 —o— MEIGS GROUND | 9 1100 CST 1050 CST O km-LAKE FRONT | B —O— ARGONNE GROUND MIDWAY GROUND [030 CST | 7 TOWER ‘A az km ISkm - CITY | IO | i | 2 | 13 SUBURBAN /RURAL | 4 | I5 | 6 7 (7 TEMPERATURE , °C Fia. 97.—Vertical temperature profiles, Meigs and MidwayAirports and Argonne National Laboratory, March 19, 1969 ap aE . owe UE