LaMotte Air Pollution Sampling & Measurement - Manual (Page 4)

Impinger devices are available in various shapes and sizes. The simplest
impinger device consists of a glass vial plus a stopper with a short glass
tube and a longer glass tube. The long tube is immersed into the
absorbing solution. Other types of impingers are more sophisticated and
may meet the specifications set forth by the American Public Health
Association or some other regulatory agency.
In principle, the inexpensive impingers and the precision impingers
operate in a similar fashion. Some precision impingers have a fitted
glass end which is immersed into the absorbing solution. This enables
the impinger to disperse many minute bubbles. The smaller the bubbles,
the more surface contact is permitted between the gas and absorbing
solution and a higher efficiency of gas absorption results. A fritted glass
bubbler of this description is used for nitrogen dioxide determinations.
For other determinations, a plain glass bubbler assembly is used which
usually has a 1 mm opening at the end for dispersing the air sample into
the absorbing solution.
The individual chemical test modules used to analyze the absorbing
solution after impingement are based upon established methods for
testing air pollutants. For convenience and portability these testing units
are furnished in compact carrying cases. All of the necessary apparatus
and reagents needed to conduct a chemical analysis of the air are
included within the testing outfit.
The reagent systems included in the testing units include an absorbing
solution which extracts the chemicals from the atmosphere. In some
systems a single indicator is added to the absorbing solution to cause a
color reaction. In other systems, the absorbing solution is pre-treated
before the indicator is added. The color reaction is measured in a visual
comparator or an electronic colorimeter.
Visual comparators are devices for matching the color of the test sample
to color standards of known value. Each comparator contains eight
permanent color standards. The color standards have an index,
numbered one through eight. The number refers to a calibration chart in
the instructions for each test. After the recommended testing procedure
is completed for a particular test, note which index gave the proper color
match and refer to the calibration chart.
Regardless of whether the air pollution test equipment is used for testing
air pollution levels in confined areas or for monitoring atmospheric
pollutants in the field, significant results are obtained only if correct
analytical techniques are used. Clean glassware and uncontaminated
reagents are important for accurate results. Sampling apparatus should
be checked periodically to insure proper operation.
4 Air Pollution Sampling & Measurement