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AIR TEMPERATURE, °C
Fre. 101.—Vertical SQ, and temperature profiles, Argonne National Laboratory, April 16, 1969, 1100 CST
seemed to the observer in the aircraft to originate in
the Ridgeland Power Station and the Chicago Sani-
tary District Plant in Stickney. This airport is about
10 miles from these sources. The SOz and temperature
profiles at this airport are shown in Figure 99. A dry
adiabatic lapse rate 2000 ft thick was observed just
below a weak inversion. The SO. data show that SO.
levels were high and rather uniformly mixed in this
layer, with a very rapid decrease to background levels
above the base of the inversion. This figure rather convincingly demonstrates the importance of the mixing
layer concept and how even a weak inversion aloft
can act as a lid to dispersion and vertical mixing.
The temperature profiles at Midway and Argonne
were quite similar to that of Figure 99; SO. concentrations below the inversion were considerably lower
than those observed at Hinsdale Airport. The sound-
ings at Meigs show near zero SOzat all heights, with a
cool surface layer caused by on-shore winds.
Oneleg of the return flight was going north at con-
stant levels (980 ft, MSL) along County Line Road
from 95th Street (Des Plaines River) to Cermak Road
(2200 South). (County Line Road runs N-S along the
boundary between Cook and DuPage Counties.)
The SOz recorder trace for this leg is shown in Figure 100. SOs levels were quite high (0.25 to 0.33 ppm)
in the visible plume, much lower on either side. The
figure shows that valuable pollution information can
be gained on horizontal as well as vertical flights.
The ragged nature of the interesting SO2 cross section may be due to incomplete horizontal mixing from
several large point sources. A simple diffusion calcula-
tion, using typical SO2 outputs from the two plants
mentioned above, the Gifford™) diffusion parameters,
and the observed weather information, shows that
most of the observed SOs concentration at Hinsdale
Airport could have originated at these two sources.
Not too much should be inferred from this calculation,
as the real SO» emission rates were not known and the
SO, contributions from all the other possible sources
were ignored.
Figure 101 shows the SO. and temperature profiles
at Argonne on April 16, 1969 at 1100 CST. South
winds at 8 mph with clear skies were present when the
sounding was made. The temperature data show the
expected adiabatic layer with a weak (~1° C) inversion at 2000 ft. Even this inversion was enough to
ta
near the center of the visible smoke plume moving to
the SSW along the Expressway. Most of the plume
gh