6 linkeam eC ie iee ae meted gl ee te Mae SMede YE Wa et 142 during the nighttime hours. The data show that the mixing depth on the 25th was much deeper than on the previous day. REFERENCES 1. Gifford, F. A. Uses of routine metevcrological observations for estimating atmospheric dispersion. .Vucl. Safely 2, (4), 45-51 (1961). 2. Pasquill, F. The estimation of dispersion of windblown material. Jfeteorel, Mag. 90, (1063), 33-49 (1981). 3. Croke, FE. J., Carson, J. E., Gatz, J}. F., Moses, H., Kennedy, A. S., Norco, J. E., Roberts, J. J.. Croke, K. G., Anderson, J. B., Nelson, 1). 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, ANL/ES-CC-004 (March 1969). PROJECT ITREX—A COOPERATIVE THUNDERSTORM TRACER EXPERIMENT D. F. Gatz The Ulinois Tracer Experiment (ITREN) is a cooperative field research program to study the removal of dust and pollutants from the air by rain. Three research groups are participating in the study, which utilizes two types of tracer materials: some already present in the atmosphere, and some specifically added by the experimenters. The research program runs for several weeks during the summer in a 40-milesquare rain gauge network near Champaign, Illinois. “TTREX” stands for Illinois TRacer EXperiment. It is the code name for the largest field study ever attempted on howrain cleans pollutants from the atmosphere. In some experiments, artificial tracers are released into thunderstorms. Argonne scientists comprise one of three groups participating in the study, which was scheduled for central Illinois during spring and summer 1969. The other groups are from the University of Michigan and the University of Illinois—IIlinois State Water Survey. An aircraft from Weather Science, Ine., Norman, Oklahoma, will participate during the first of two scheduled operational periods. During the second period, an aircraft from the National Center for Atmospheric Research (NCAR), Boulder, Colorado, will participate. Participation in ITREX is a first step in the development of a program in precipitation chemistryat Argonne. This new program, as now planned, will measure the chemical content of rain, air, and airborne particles. Such information will aid the study of two different but related problems of great interest today: air pollution and weather modification. The application to air pollution comes from a desire for a better understanding of the way rain and snowclean the atmosphere. The application of weather modifi- is central IHinois in an area northwest of ChampaignUrbana, where the State Water Survey maintains a network of 196 rain gauges and rain samplers. The field station of the University of Michigan group is located near Clinton, An Argonne automatic rain collector (AARC) will also be located near Clinton, about 1.5 miles from the University of Michigan station. The AARC is an automatie device to collect up to 72 separate 500-ml samples sequentially from rains of up to 1.6 inches. The Water Survey weather radars are at the University of Hlinois Willard Airport, five miles south of Champaign. Both the Michigan and Water Survey groups have radio-dispatched mobile units that carry roof-top and basket-type rain samplers. ILLINOIS CHICAGO RAIN GAUGE NETWORK ~~ CHAMPAIGN URBANA P CLINTON-/ RADAR SITE cation stems from the need to understand hownature makes rain so that man can find ways of modifying the natural processes for his benefit. These two areas are related because of the very real possibility that’ pollutants can interfere with natural processes to produce more—or less—rainfall. The field location for project ITREX (Figure 104) 0 100 SCALE OF KM Fic. 104—Map showing field location of Project ITREX