Environmental Engineering FOURTH EDITION

378 ENVIRONMENTAL, ENGINEERING

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Detector

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$@$ -70-1

Light Collimator Sample Collimator

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Figure 19-3, Diagram of a nephelometer.

Figure 19-4. A typical bubbler used for measurement of gaseous air pollutants.

Sulfur dioxide may also be measured by impregnating filter papers with chemicals

that react with SO2 and change color. For example, lead peroxide reacts to form dark

lead sulfate, by the reaction

PbOz + SO2 --+ PbSO4.

The extent of dark areas on the filter and the depth of color may be related to the

SO2 concentration. Like the ozone measurement, this type of SO2 measurement takes

several days of exposure to yield measurable results.

Use of a gas bubbler, shown in Fig. 19-4, shortens the time required for sampling

considerably. As shown in Fig. 19-4, the air sample is bubbled through a solution

that reacts chemically with the particular gaseous pollutant being measured. The

concentration is then measured with further wet chemical techniques. For example,