Environmental Chemistry
Raymond J. Suplinkas
University N e w Haven, Connecticut 06520
Air Pollution Measurements
Yale
in the Freshman Laboratory
Recently we have initiated a new freshman laboratory program to accompany a course entitled "Chemical Cycles and the Environment." Briefly, the program consists of
Power
Vacuum
1) four experiments on water quality illustrating titrimetric,
grrwimetric, and colorimetric analysis and the use of the pH meter 2) trace analysis for mercury in food, a two-week experiment 3) three experiments on the mertsurement of gaseous pollutants in the ambient air near the campus area 4) identification and estimation of pesticide in treated seed corn involving thin-layer chrometography.
The air analysis experiments required the most extensive equipment preparations but proved to be one of the most valuable portions of the course. The typical method for air pollution analysis involves drawing a known volume of air through a solution which absorbs by chemical reaction the pollutant of interest.' Subsequent analysis of the solution permits the calculation of pollutant concentration in the air sample. Equipment needs include an absorbing train consisting of gas bubblers and traps, a flow-measuring device, a means of controlling flow-rate, a small vacuum pump and power source and a timer. Ambient temperature and pressure are also needed to correct volumes to standard conditions; however, these corrections are generally so small that area-wide figures (such as from the U.S. Weather Service) are sufficient. It was our intention to have equipment which was readily portable and independent of an outside power source so that we could send out students into a 1-mi radius area (20 min walking time) which includes both the campus and nearby commercial district. These needs were met by the equipment illustrated in block diagram in Figure 1. The NI-Cd battery shows little voltage drop even at high current rates and is small and lightweight among rechargable batteries for its rating. We assembled both the charger and transistorized power STERN,A. C., "Air Pollution" (2nd. ed.), Academic Press, New Pork, 1968, Vol. 11, p. 3. U S . Public Health Service, "Selected Methods for the Measurement of Air Pollotants," Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio, 1 0R9 L"",,.
LEIGHTON, P . A., "Photochemistry of Air Pollution," AcaA. P., AND demic Press, New York, 1961, p. 273. ALTSAULLER, B U F A L IJ. NJ., ~ Envi~on.SCI.Technol., 5, 39 (1971).
24 / Journol o f Chemical Education
Flowmeter with VDIYC
Train
Figure 1.
Block diagram of oir rampling appardur.
inverter ourselves although commercial units are available. The inverter must have adequate power capacity to operate the vacuum pump which in our case is a modified aquarium pump. The flowmeter with regulating valve is an easily available commercial item as are the bubblers and U-tube traps in the absorbing train. The pump and power source were mounted in one carrying case while the flowmeter, absorbing train, and a timer were mounted in another. We chose to measure the levels of SO2,photochemical oxidants, NO, and NOa. The detailed analytical techniques for these tests are given in a variety of sources.' For the SO2 and oxidant determinations, the students first assembled for a 30-min discussion of the chemistry involved in the test and then dispersed in pairs to 12 assigned locations. Sampling took from 30 min to an hour. They then returned to the laboratory to analyze the contents of the bubblers. This last step generally could be completed in well under an hour. The chemistry involved in these two tests is the type that can he treated at a number of levels of sophistication. For example, SO2 is initially trapped as the dichloro-sulfito mercurate ion HgCIF
+ SO2(.,,
$ HgCLSO,
+ 2 C1-
(1)
The tetrachloromercurate ion used is square planar, in contrast to the linear dithizone mercury complex used in the trace analysis in food. This can provide the starting point for a general discussion of complex ion structure. The mode of attachment of the SO2 can open up a discussion of its detailed structure (dipole moment, bond dipoles, bond angle, electronic structure, etc.).
Environmental Charnietry
The chemistry of the oxidant analysis can be illustrated in terms of ozone, the predominant oxidant. The test involves the oxidation of iodide ion to iodine in either neutral or alkaline buffered solution. The solution chemistry of iodine in its various oxidation states is a natural discussion topic. Given that the and that NOz gives a 20% response oxidation stops at 1% in the test, it is interesting to ask whether these conditions are determined by equilibrium thermodynamics (oxidat,ion potentials) or whether they are kinetic effects. For the third experiment, the equipment was set up so that NO and NO2 could be determined separately and simultaneously. The reactions involved in these tests are rather complex organic dye reactions and of less general interest than in the two cases above. The NO-NO2 system itself provides for an interesting study, however. The typical concentrations of various components of an urban atmosphere as a function of time are shown in Figure 2. The photochemical con12
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NO"
0
l4
Figure 2.
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6
8 A.M.
10
12 Noon
I 2
I 4 P.M.
1
6
Typical potlerns of air pollutant consenhations during the day.
version of NO to NO2 and the subsequent series of reactions leading to ozone have been intensively studied2 and provide, a wealth of material. I n order to demonstrate this typical diurnal behavior, we asked students to sign up for one of a series of time slots ranging from before 8 A.M. to 4 P.M. The number of sampling locations was reduced to two for this experiment. The sampling sites must be chosen to be relatively remote from direct sources of nitrogen oxides. For example, readings at a busy intersection or a bus stop will reflect traffic levels much more than they will the overall atmospheric photochemistry. One extraordinary bonus in these experiments is the interaction of the students with other students or with townspeople at the sampling sites. The experiment in progress nearly always attracted onlookers and queries. Most students were eager to explain the equipment and the experiment. The fact that they were experimenting in "the real world" rather than at a "sterile" lab bench was also a strong motivating factor to some. I n any case, one could be sure that the students were very well prepared and enthusiastic when they set out to collect a sample. The apparatus also allows for interesting and valuable term or summer projects. For example, a nearby town contains three major north-south highways (Interstate 91, U.S.5 and Conn. 15), thirty industries including steel and chemicals, and lies almost entirely within a valley. Yet, there had never been a survey of gaseous atmospheric pollutants made in the town. It was a relatively simple matter for a dozen students working for a week to perform a preliminary air quality survey. It was our experience that the initial difficulties in setting up instrumentation were amply compensated for by pedagogic value and student interest and enthusiasm.
Volume 49, Number
I,
January 1972
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