An Improved Gas Sampler for Air Pollutant Analysis Arthur F. Wartburg, John B. Pate, and James P. Lodge, Jr. Laboratory of Atmospheric Sciences, National Center for Atmospheric Research, Boulder, Colo. 80302
H A gas sampling bubbler, consisting of easily assembled and replaceable glass and Teflon components, has been designed to replace prior designs, which are both expensive and fragile. The new bubbler has proved to be rugged, and easy to handle in the field. It is far less subject to damage than allglass designs, but equally efficient in pollutant collection. Instructions for its use in the field are presented.
P
robably the most widely used form of fritted glass bubbler for sampling gaseous air pollutants is a form derived from designs by (Cauer, 1935) through modifications by (Haagen-Smit, 1958) and Kinosian (Calif. State Dept. of Public Health, Air and Indus. Hygiene Laboratory, 1967). Kinosian's design had a very long bottom tube to accommodate reagents prone to serious foaming. The present iorm was developed in the U S . Public Health Service laboratories between 1957 and 1960, but was not reported in the literature until 1965 (U.S. Dept. of Health, Education, and Welfare, 1965). This all-glass bubbler is adequately efficient for collecting nearly all polar gases at an air flow rate of 0.5 to 2 liter min.-l, and requires only 10 ml. of collecting solution. The design, though excellent, has three major drawbacks. First, the configuration is too fragile to withstand damage in the field and during washing. Breakage of the central stem inside the cap is frequent and expensive to repair. Second, the upper and lower parts of the bubbler are not interchangeable unless built with great precision. Finally, a separate bubbler is required for each sample to be taken, since there is no easy way to transfer exposed samples to another container in the field. The improved glass and Teflon design, now available commercially at a cost comparable to the all glass version, shown in Figure 1 eliminates all three of these problems. Its geometry and dimensions are the same as the glass version, since these are satisfactory in the latter; the identical dimensions permit the same holders, connectors, etc., to be used interchangeably on either version. Details of the new bubbler are shown in Figure 2 . The top is accurately machined from a single block of Teflon (Type TFE) and grooved on the inside to accept a silicone rubber O-ring. A Teflon straight union is modified by removing one cap and machining a groove to take a smaller silicone rubber O-ring. The bubbler's top is bored and threaded for this part, and for a Teflon male connector. Both the tube fittings are screwed in place and secured with epoxy cement. The two ball joint members are cut to length and bent. The stem which may be any kind of gas disperser desired such
Figure 1. Bubble with Teflon top
MALE 1 2 / 5 BALL JOINT
/FEMALE
12/5
\KNURLED ALUMINUM C A P
KNURLED ALUMINUM CAP
BUBBLER BODY
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O-RING S E A L TEFLON TUBE FITTING TEFLON
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O-RING SEAL
Y
F R I T STEM
Figure 2. Detail of Teflon top Volume 3, Number 8, August 1969 767
as a fritted or a capillary glass tube, is cut to length. The bottom of the bubbler is shaped as in the earlier model. None of the sections in the upper part should be seriously out of round. The only critical dimensions are the overall length, which must allow inserting the fritted tube to 2 mm. from the bottom; and the diameter of the upper part of the bottom section, where an O-ring seals it with the top part. Both O-ring seals are easily disassembled, yet leakage through them is negligible. Assembled bubblers, with the knurled aluminum caps tightened, will routinely maintain an internal vacuum of one-half atmosphere for 24 hours without noticeable loss. After a sample has been collected in the field, the top of the bubbler is removed. The fritted tube is slipped out, and the reagent is blown out of it with a rubber bulb. A polyethylene cap is placed on the bottom part, making an airtight closure that protects the reagent from contamination. The fritted tube is put into a plastic bag and is not reused until thoroughly washed. The Teflon top is rinsed, fitted with a fresh fritted tube, and attached to a new bottom. (The bottom sections can be conveniently filled with reagent in advance in the laboratory and sealed with the polyethylene tops.) Thus, only bottoms and fritted tubes, both relatively inexpensive, are needed in large numbers.
The bubblers may be completely disassembled for transporting or cleaning. This decreases breakage substantially. Even when fully assembled, the bubblers are less fragile, since the protruding parts are set in somewhat yielding plastic. Finally, if the entire glass portion does break, its replacement costs less than 25 of the total cost of the bubbler. Tests made to compare the new bubbler with the all-glass version have shown that no pollutant is lost during its very brief contact with Teflon in the inlet. None of the usual sampling reagents attack Teflon. In brief, the plastic-topped bubbler offers advantages with no loss of sampling performance. Literature Cited California State Department of Public Health, Air and Industrial Hygiene Laboratory, “Recommended Methods in Air Pollution Measurements.” Method No. 3.. Berkelev. -, Calif., 1967. Cauer, H., 2. Anal. Chern. 103, 166-80 (1935). Haagen-Smit, A. J., Brunelle, M. F., Internatl. J . Air Pollution 1, 51-9 (1958). U. S. Department of Health, Education, and Welfare, Public Health Service. Cincinnati, Ohio. “Selected Methods for Measurement of Air Pollutants,” 1965. Received for review December 23, 1968. Accepted April 21, 1969.
A Modification of the Bausch and Lomb Aerosol Dust Counting System to Automatically Measure Aerosol Size Distributions Paul M. Brown National Center for Atmospheric Research, Boulder, Colo. 80302
’Circuitry has been added to a Bausch and
Lamb Dust Counting System to allow unattended, automatic measurementS from which Size distributions O f airborne particles Can be determined. The system has been tested and operated up to altitudes of 20,000 feet MSL.
C
ircuitry has been added to a Bausch and Lomb Dust Counting System consisting of the Dust Counter 40-1, Printer, and Digital Readout to allow unattended, automatic measurements from which size distributions of airborne particles can be determined. The Bausch and Lomb Aerosol Dust Counting System (as described in the Dust Counter 40-1 operation manual) is used to monitor airborne particle concentrations. Particle detection is done by light scattering, and the system is capable of detecting particles 0.3pn-diameter and larger. Light scattered by aerosol particles is concentrated by an optical system onto a photomultipler tube. The signal, in the form of pulses, from the photomultiplier tube is then amplified and the pulses counted and recorded. The pulse rate is also displayed by a meter on front of the Dust Counter 40-1. Sample times of 102, lo3,or 104 seconds can be selected on the digital readout; and, at the end of the sample time, the printer records on paper the total count. The printer then resets to zero and begins to accumulate counts, the total of which will be printed at the end of the sample time, etc. 768 Environmental Science & Technology
On front of the Dust Counter 40-1 is a size selector switch which may be set at one of several size ranges, and only particles equal to or larger than the range selected will be detected and counted. T~ determine the size distribution of airborne particles, the size selector switch must be manually changed to the various size ranges. In this note, a simple, inexpensive circuit is described which can carry out the switching function from size range to size range automatically and continuously. A diagram of the switching circuit which allows automatic (or manual) operation is shown in Figures 1 and 2 and works as follows: A solenoid plunger is energized in the printer when it prints the accumulated count at the end of the sampling time. This signal is used to energize a relay (24 VDC, 1000 ohm coil), the contacts of which are used to furnish power to a
115 VAC 1
1
TO COIL OF SOLENOID PLUNGER IN PRINTER
Figure 1. Diagram of the switching circuit
