Encyclopedia of Environmental Science and Engineering, Volume I and II

44

Advances in pollutant monitoring techniques and instrumen-

tation have progressed significantly in the past several years

to the point where noteworthy confidence in instrumentation-

generated data has been established. Most systems, whether

manual or automatic, have been designed to determine the

quality of pollutants present per unit volume of air. These

determinations can be made either in a duct/stack or in the

outside atmosphere for the purpose of either ensuring adher-

ence to published air quality regulations or for defining air

pollution control device design criteria.

Air pollution instrumentation is utilized in the two major

air quality areas of source and ambient monitoring with

a further breakdown in the source monitoring category to

the manual, and continuous type of instrumentation. Each

of the three categories presents various types of monitoring

problems which must be overcome, and each program is per-

formed for a different reason.

MANUAL MONITORING—SOURCE

INSTRUMENTATION

Instrumentation is utilized in this type of monitoring to

provide a means to determine compliance with existing

regulations and for developing design criteria for control

of air pollution. The systems must be durable and allow for a

certain amount of flexibility due to the many different situa-

tions which are encountered during the evaluations of station-

ary sources. This is emphasized by the fact that there are more

than 25 different Environmental Protection Agency (EPA)

sampling methods which, all except Method 9, require

some type of instrumentation to complete the evaluation.

(See Stack Sampling. ) The most familiar procedure, “Method

5,” has been the basis for the development of most of the

other procedures. Method 5, shown in Figure 1, utilizes the

basic equipment and sampling procedures (i.e., imping-

ers, dry gas meter, pump, etc.) which with minor modifi-

cations or additions can be utilized to perform other EPA

methods. As an example, Method 17 shown in Figure 2,

utilizes the same components from the EPA 5 “sampling

train” with a change in the filter location, and Method 8 for

sulfuric acid mists presents even other changes. The EPA

methodology and equipment were developed specifically to

improve the accuracy of the source testing programs, and

supplement the “ASME Train” (the “ASME” or American

Society of Mechanical Engineers Train was developed

to allow the determination of stack gas concentrations

primarily in the electric utility area). The major reason for

the testing methodology change (ASME to EPA) was to

improve the capture efficiency of smaller (submicron) par-

ticles, and allow for gaseous concentration determinations.

Due to thimble porosity the alundum thimble utilized in

the “ASME Train” did not allow for the determination of

representative data when sampling after a control device

for either the determination of regulatory compliance or

control efficiency. In addition, the use of an entirely glass-

lined sampling system (“EPA Five Train”) minimized the

introduction of outside contamination to the samples being

collected.

Such theories as isokinetic sampling for particulates 
 1.0

micron and proportional testing for gaseous determinations

remain unchallenged. Only the equipment for manual monitor-

ing has changed and will continue to change as improvements

are made.

Manual source testing (stack sampling) equipment is

available through several manufacturers, some of which

are presented in the “Product Line Profiles” developed by

Pollution Equipment News.

CONTINUOUS MONITORING—SOURCE

INSTRUMENTATION

There are two basic types of source emission monitoring

instrumentation—opacity monitors and gaseous emission

monitors. Opacity monitors, which measure the transmit-

tance of light through the gas stream, are called transmis-

someters, and are of two basic types; single-pass systems

and double pass systems. Gaseous emission monitors on the

other hand, are utilized to measure the concentration of spe-

cific gaseous components of the exhaust gas, such as O 2 , CO,

SO 2 , NO 2 , NO x , etc. These instruments are divided into three

basic types: extractive systems, in-situ systems, and remote

systems. The in-situ systems can be further sub-divided into

either in-stack or cross-stack monitors.

Opacity Monitors

Opacity monitors, also known as transmissometers, serve

the purpose of providing information relative to combustion

conditions, or control device efficiency. Transmissometers,

although required by the EPA for various stationary sources

AIR POLLUTION INSTRUMENTATION

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