Encyclopedia of Environmental Science and Engineering, Volume I and II

1108 STACK SAMPLING

2) The isopropanol bubbler or impinger is eliminated.

An empty bubbler is used for the collection of

liquid droplets.

3) The stack gases are extracted from the sampling

point intermittently over the specified period, usu-

ally 24 hours. An industrial timer is used to cycle

the pump on for at least 12 periods of at least two

minutes each. Between 25 and 60 liters of gas

must be collected.

The EPA Test Method 6B write-up contains detailed

instructions, along with a list of references. It should be

read in detail before the Method is attempted. Testing

should be performed only by personnel trained and expe-

rienced with the equipment and titrations specified in this

method. The Method 6 audit samples are also appropriate

for this method.

Test Method 6C

Test Method 6C is an instrumental method for the determi-

nation of sulfur dioxide from stationary sources. No specific

instrument is required by this method. Ultraviolet, nondis-

persive infrared, or fluorescence instruments can be used

providing they meet the performance specifications and the

test procedures are followed.

The following Measurement System Performance

Specification must be passed by the instrument before actual

environmental samples are analyzed:

1) Analyzer Calibration Error must be less than 


2% of the span for the zero, mid-range, and high-

range calibration gases.

2) Sampling System Bias must be less than 
 5% of

the span for the zero, mid-range, and high-range

calibration gases.

3) Zero Drift must be less than 
 3% of the span

over the period of each run.

4) Calibration Drift must be less than 
 3% of the

span over the period of each run.

The analytical range must be selected such that the SO 2

emission limit required of the source is not less than 30% of

the instrument span. Any run in which the SO 2 concentration

in the stack gas goes off-scale must be repeated.

The EPA Test Method 6C write-up contains detailed

descriptions of the calibration gases required, calibration

procedures, sampling procedures in addition to a list of

references. It should be read in detail before the Method

is attempted. The manufacturer’s instructions will provide

instrument specific instructions. Testing should be per-

formed only by personnel trained and experienced with the

equipment being used.

Test Method 7

Test Method 7 is used for the determination of nitrogen oxide

(NO x ) emissions from stationary sources. In this method the

NO x concentration of a grab sample, collected in an evacu-

ated two liter flask, is measured colorimetrically using the

phenoldisulfonic acid procedure.

The apparatus for sample collection consists of probe,

squeeze bulb, vacuum pump, manometer, and a two liter

flask. The probe is heated if necessary to prevent conden-

sation. A one way squeeze bulb is used to purge the probe

before sampling. The vacuum pump is used to evacuate the

flask. A manometer is used to measure the flask pressure.

The two liter flask contains 25 ml of a H 2 SO 4 /H 2 O 2 solution.

This solution will absorb the NO 2. Oxygen from the source

is required for the oxidation of the NO. If less than 1.5%

oxygen is present in the stack gases, the steps described in

the method to introduce additional oxygen must be used.

Once the flask is evacuated 75 mmHg, valves are rotated to

isolate the flask from the pump, and a sample is introduced

into the flask. It should take less than 15 seconds for the

flask to reach ambient pressure. If a longer time is required,

check the probe for plugging.

After sampling, the flask should sit for at least 16 hours

for the NO to oxidize. The flask is then shaken for two min-

utes before checking the pressure of the flask. The liquid

is then transferred to a container, and the flask rinsed with

distilled water. The pH of the liquid is adjusted to between 9

and 12 with 1 normal NaOH. Just prior to analysis the liquid

is transferred to a 50 ml volumetric flask and diluted to

50 ml. A 25 ml aliquot is transferred to an evaporating dish

and evaporated to dryness. Two ml of the phenoldisulfonic

acid solution is added to the evaporating dish along with

1 ml of distilled water and four drops of concentrated sulfu-

ric acid. The solution is again heated for three minutes fol-

lowed by the addition of 20 ml of water. The solution is then

adjusted to pH 10 with ammonium hydroxide. The solution

is filtered if necessary and transferred to a 100 ml volumetric

flask and diluted to 100ml. The absorbance is measured at

the optimum wave length and compared against standards

for quantification. Audit samples are available through the

EPA’s Emissions, Monitoring and Analysis Division.

The EPA Test Method 7 write-up contains detailed

instructions, along with a list of references. It should be read

in detail before the Method is attempted. As with all of these

methods, testing should be performed only by personnel

trained and experienced with the equipment and the spectro-

photometer used in this method.

Test Method 7A

Test Method 7A is man alternative to Method 7 for the deter-

mination of nitrogen oxide (NO x ) emissions from station-

ary sources. The sample is collected with the same sampling

train used in Method 7. However, instead of using the colori-

metric phenoldisulfonic acid procedure, ion chromatography

is used for quantification. Audit samples, available through

the EPA’s Quality Assurance Division, are required for this

method.

The EPA Test Method 7A write-up contains detailed

instructions, along with a list of references. It should be read

in detail before the Method is attempted. As with all of these

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