’ ee oe, . wor dye toe woe gt oe bo Pi foes Stee we AEE net ca atleatdls aAct ottbet MPRpa?ah 131 mediate-sized buildings in the area to obtain sites for additional sensors, so that temperature profiles up to 365 meters can be measured on a continuous basis. It is recognized that it may not be possible to obtain exact temperature profiles in this manner because of heat from buildings, obstructions to wind flow, and the fact that the sensors are not placed vertically; but for the purpose of diffusion analysis, mformation on the lapse rate class (inversion, isothermal, near neutral, or unstable} is probably adequate. The accuracy of building sensor data can be tested by having the instrumented helicopter fly at the height of the sensor but away from the building heat. If these building-mounted sensors prove useful and ac- curate, a significant advance in city meteorological observations will have been achieved. Similar observations could be made at other locations in Chieago, as well as in othercities, at low cost. FUEL SWITCH TESTS The second in a series of fuel switch tests was condueted in Chicago between June 16 and July 4, 1968. A paper published in one of the progress reports‘ and presented at the 62nd Annual Meeting of the Air Pollution Control Association, discusses the design of the experiment and results obtained. An extended abstract of this experiment appears elsewhere in this publication. The third fuel switch test was conducted by DAPC and Argonne between May 20 and May 30, 1969. Re- alistic pollution abatement procedures were used in this test. Analysis of the resulting fuel use, air quality, and meteorological data is contmuing. SULFUR HEXAFLUORIDE TRACER STUDIES In a previous report of this series,“ a series of tracer studies using SF, as the tracer material was proposed to learn more about diffusion rates in Chi- ent kinds of sources, should tell a lot about, the rela- tive importance of different individual sources and classes of sourees, and test the ability of the diffusion equations to accurately simulate nature. The analysis system developed by the Department of Health, Education and Welfare’s National Air Pol- lution Control Administration in Cincinnati for this tracer gas will be used.‘ ® The ultrasensitive de- tectability of this material results from the high re- sponse characteristics of electron capture detectors to halogenated materials. Much of the experimental work to date has been to optimize procedures so that very high sensitivities can be realized. Gas is released at a rate of about 3.5 to 7.0 g/see (1 to 2 cfm) and is collected in plastic bags using samplers borrowed from NAPCA. These samplers contain a small batterydriven pump which fill 16-liter bags at a rate of about 120 ml/min. Instantaneous air samples are also collected in evacuated 1-liter metal cylinders. Argonne’s Industrial Hygiene and Safety Division has modified one of its gas chromatographs to deter- mine concentrations of this tracer material. A Model GC 1500 Micro-Tek unit is being used. The system initially chosen was that designated “System B” by Saltzman, Coleman, and Clemons.‘ The column consists of a 1.2-meter section of 40 to 60mesh 3A molecular sieve which is used to remove interfering water, followed by a 4.2-meter section of 4inch tubing containing 40 to 60-mesh Baymal. The latter material is a colloidal alumina whichis particu- larly useful for halogenated hydrocarbons. The standard inlet in the chromatograph was replaced with a 7-port valve containing a 0.25-ml sample loop. The carrier gas is high purity nitrogen which is cleaned with two 5A molecular sieves. The scavenger gas is 5% hydrogen in argon. A polarizing power supply and a nanoammeter were constructed by Argonne’s IHSinstrument group. A one-millivolt recorder is used to cago. The SOs concentration observed at any location is record the chromatograms, The air in the sample bag is flushed through the sampling loop until approximately 100 ml have passed through. A 0.25-ml sample group of sources in unknown. For pollution abatement The system will be calibrated using standard gas mixtures supplied by NAPCA, tribution of each source in the area. Otherwise, effec- in air has been achieved with this system; it is possi- the sum of the contributions by many individual sources and, with certain assumptions, to estimate their in general, but especially during serious pollution episodes, control authoritics must know the relative contive and economical abatementis not possible. Tracers give one the ability to “see” individual sources and, with certain assumptions, to estimate its contribution to the total SO, levels at the location. Thus, in a given weather situation, we can tag a sus- pected source and see whether the tracer reaches the sensor, and if so, m what amounts. Several experiments under different weather conditions, using differ- is then retained and the SF, concentration measured. A sensitivity better than 0.05 ppb (vol/vol) of SF, ble to improvethis to 0.01 ppb using minor changes. The sensitivity of the system is being greatly increased to better than reported geophysical background levels, one part SF, in 10! parts air, by using changes that have been developed and tested by R. K. Stevens and others in the Cincinnati NAPCA chemistry group. These changes include: (1) using a Nickel-63 detector,