Pollution,Dust and Smoke Measurement 2

All credit for this post goes to my student Sridhar C. who did an excellent work in collecting all the required details.

4. DICHOTOMOUS SAMPLER SYSTEM

To carry out the urban air analysis two air-sampling systems were required to provide representative urban air to the instruments. A semi-high volume dichotomous air sampling system constructed in 1999 was used to provide urban air to the APS, DMPS and LAMS in room 132. A second air sampling system, which collected air and PM with a cut point of 2.5 µm (PM2.5) for the instruments in room 123 was designed and developed by the group in June 2001.

Description of Semi-high Volume Dichomotous Air Sampler

The semi-high volume dichotomous air sampler located in room 132 was designed and developed to collect particulate matter at a flow rate up to 280 L/min from downtown Toronto. The in-house sampler consisted of a 4" sampling duct located 4 m off the ground, a multi-nozzle PM10 impactor, six sampling outlets, six isokinetic probes, a PM2.5 commercial impactor, a filter distributor and holder and a flow controller (Figure).
In the first stage of the sampler an inertial impactor removed particles larger than 10 µm. Small portions of this air stream were then diverted to different instruments within the laboratory such as the APS, DMPS and an on-line LAMS. At the second stage a No. 2 plate from a Sierra-235 five-stage cascade impactor removed PM that was less than 10 µm and greater than 2.5 µm. The bulk PM2.5 was then collected on a 8" x 10" Whatman 41 cellulose after filter for subsequent elemental analysis.

The air sampler, consisted of a 4-inch sampling duct with six sampling outlets, a cyclone, a .3.5 inch diameter ABS pipe, plastic tubing which served as a barometer and a hi-volume motor blower (see Figure 8a. & 8b). The entire duct, located 2.6 metres above the ground, was made of aluminum except for a 2 metre ABS section connected to the motor blower. Aluminum was used to construct the duct in order to minimize wall losses due to charging of the duct surface.

Tape Sampler

THE USE OF FILAMENT TAPE IN RAISING LONG CORES FROM SOFT SEDIMENT

This note describes the advantages of using filament tape to line the inside of athe variety of heavier piston samplers suitable for work in soft sediment in water of sediment coring tube. Such tape has been used with a hand-driven aluminum samplerany depth (Wright, Cushing, and Livingstone 1965 ) .(Livingstone 1955) weighing 10 or 20 kg It is desirable for cores from the soft and suitable for use by one man from a skiff in 10 or 20 m of water. It should be sediments of lakes or the ocean to be long, equally valuable when used with any of

complete, and undisturbed. The principal barrier to obtaining such cores is the frictional force between a sample of sediment and the tube in which it is taken. Becauseof this frictional force a simple tube will take a sample only 10 or 20 times its diameter,but the sample length can be increased somewhat by adding an airtight piston to

the sample tube. Where the hydrostatic pressure is great, such a piston sampler is highly effective and cores 20 m in length are commonly raised with it. In shallow water, however, piston samplers are less effective, and piston cores are usually taken in sections of 1 m. The troublesome frictional force is removed completely in the Swedish foil sampler ( Kjellman, Kallstenius, and Wager l%O), but it is heavy and expensive to construct. The availability of fiberglass-reinforced polyester tapes with the tensile strength of steel, but much more flexible, permits application of the foil principle to standard equipment at moderate cost. The new method is immediately applicable to raising mud cores from glacial lakes with standard equipment, but its fullest advantage is likely

to be realized in work with older lakes using especially designed equipment.A length of flexible Mylar tape slightly longer than the sample tube, and of a width equal to the inside circumference of the tube, is wrapped longitudinally around the outside of a piece of thin-walled metal tubing of the sort commonly used by paleolimnologists.

Rubber bands or cellophane tape may be used to hold the tape in place.The extra length of tape, which overlaps the lower end of the tube, is firmly attached to a piston. The piston is then pulled into the tube by the piston cable, so that the

tape wraps around the edge of the tube and up the inside.The sample tube wrapped with tape islowered into a lake using a Lichtwardt drill rod. When the bottom is reached, the piston cable is clamped, fixing the piston in place, and the sample tube is pushed down aroundit by the rod. This part of the operation does not differ from ordinary piston sampling(Deevey 1965), but it has a different result: As the tube penetrates the mud, the Mylar tape slides down the outside and up the inside, lining it smoothly. There is no motion between the sample of sediment entering the tube and the Mylar liner, so the frictional force is absent, as in the Swedish foil sampler. There are, of course, frictional forces in other parts of the system, and these may be great enough to rupture an unsupported tape of Mylar. For that reason, the Mylar is reinforced with Scotch filament tape ( No. 890), which is strong and stretches very little. Samples were raised successfully with Mylar carrying only one %-inch (1.9

cm) strip of this filament tape, but more strips may be added for extra strength.A 4.5inch ( 11.4 cm) width of 0.0005-inch (0.001 cm) Mylar that is completely covered with No. 900 tape will have a breaking strength of about 1,000 kg Trials were made with 0.005inch (0.01 cm) thick Mylar, which was too stiff to bend smoothly around the end of the sample tube, and with uncovered 0.0005-inch ( 0.001 cm) Mylar, which was too flimsy to stand the vicissitudes of fieldwork. A piece of 0.0005-inch ( 0.001 cm) Mylar that was completely covered on one side with filament tape was quite serviceable. An even more satisfactory tape can be prepared by painting the sticky surface of a filament tape of suitable width with a single coat of shellac and dispensing with Mylar, other

than that forming an integral part of the filament tape. Excellent samples 3.8 cm in diameter and almost 3.6 m long were taken with it. Longer sample tubes were not available for more exhaustive tests. On one occasion a lightly reinforced tape of 0.002-inch ( 0.005 cm) Mylar tore on the cutting edge of the sample tube as it penetrated clayey silt with sharp angular granite granules and struck the rocky bottom of the lake basin. Similar breakage occurred in the clean, coarse sand of a Carolina bay lake. Breakage might be avoided by using a cutting shoe to bear the brunt of the shock. Two tapes would have to be used instead of a single one, and passed through offset slits in the wall of the shoe. Fig. A is a diagrammatic sketch of the sampler in operation, and Fig. B shows details of a piston for holding the tape. This type of piston works well, but more convenient designs may be possible.