Encyclopedia of Environmental Science and Engineering, Volume I and II

STACK SAMPLING 1107

the sulfuric acid mist that collected on the filter. Once the ace-

tone from the probe wash has been evaporated, the residue is

also dried at high temperature to remove the sulfuric acid.

Test Method 5D

The purpose of this method is to select appropriate alternate

locations and procedures for sampling emissions from posi-

tive pressure fabric filters. Many times these air pollution

control devices were not designed with emission sampling

in mind. This method should be consulted if a source using

fabric filters does not met the criteria specified in Method 1.

Test Method 5E

Test Method 5E is used for the determination of particu-

late emissions from the wool fiberglass insulation industry.

Method 5 has been modified to include the measurement of

condensable hydrocarbons in this method. A 0.1N NaOH

solution is used in place of distilled water in the impingers.

The particulates condensed in this solution are analyzed with

a Total Organic Carbon (TOC) analyzer. The sum of the fil-

tered particulates and the condensed particulates is reported

as the total particulate mass.

Test Method 6

Test method 6 is used for determining the sulfur dioxide

(SO 2 ) emissions from stationary sources. The sulfuric acid

mist and the sulfur trioxide are separated from the SO 2 , and the

SO 2 quantified using the barium-thorium titration method.

In this method, the use of midget impingers is recom-

mended. However, the standard size impingers as used in

Method 5 or 8 can be used if the modifications required by

Method 6 are implemented. SO 2 can be determined simul-

taneously with moisture and particulates by making the

required modifications.

The train for Method 6 is similar to Method 5 except

for the size of the impingers and the use of a glass wool

plug in the probe tip, replacing the particulate filter. The

first impinger or bubbler (fritted glass tip) contains 15 ml of

80% isopropanol and a glass wool plug at the exit. The first

impinger will collect SO 3 in the isopropanol solution and the

glass wool will prevent the carry-over of sulfuric acid mist.

The isopropanol should be checked for the presence of per-

oxides with potassium iodide. Peroxides would prematurely

oxidize the SO 2 and capture it along with the SO 3. The next

two midget impingers each contain 15 ml of 3% hydrogen

peroxide. This will oxidize the SO 2 to sulfuric acid for analy-

sis. The hydrogen peroxide should be prepared daily from

30% hydrogen peroxide. A drying tube containing silica gel

is used to protect the vacuum pump and dry gas meter. The

dry gas meter must be capable of 2% accuracy for a 20 liter

sample. The vacuum pump should be a leak-free diaphragm

pump. A surge tank should be used to eliminate pulsations.

Sampling for SO 2 is not done isokinetically since the gas

is assumed to be uniformly dispersed in the stack. Sampling

is done at one point and at a constant rate (+ 10%). Crushed

ice should be added as necessary to maintain 68ºF at the last

impinger.

After sampling, the train is leak checked, then the ice

drained and the train purged with clean air for 15 minutes

at the sampling rate. This will remove any SO 2 dissolved n

the isopropanol and carry it over to the peroxide solution for

oxidation and analysis. The isopropanol solution is then dis-

carded. The peroxide solution containing the oxidized SO 2 is

transferred to a graduated cylinder and diluted to 100 ml with

distilled water. A 20 ml aliquot with four drops of thorium

indicator is titrated with barium perchlorate. The solutions

should be standardized as described in the method. The end

point for this titration can be difficult to catch. It is possible,

however, to get replicate titrations within 1% or 0.2 ml as

required by the method. Audit samples are available through

the EPA’s Emissions, Monitoring and Analysis Division.

The EPA Test Method 6 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 experienced with

the equipment and titrations specified in this method.

Test Method 6A

Test Method 6A is used for the simultaneous determina-

tion of SO 2 and CO 2 from fossil fuel combustion source.

Moisture may also be determined by this method. The train

for Method 6A is very similar to Method 6 with the following

exceptions:

1) The probe is heated to prevent moisture

condensation.

2) The fourth impinger contains 25 grams of anhy-

drous calcium sulfate to remove the water. This is

weighed after sampling to determine the moisture

content.

3) In place of the drying tube in Method 6, there is a

CO 2 absorber tube containing Ascarite II. This is

weighed to determine the CO 2 concentration.

As with Method 6, the EPA Test Method 6A write-up con-

tains 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

experienced with the equipment and titrations specified in

this method. The Method 6 audit samples are also appropri-

ate for this method.

Test Method 6B

Test Method 6B is used for the simultaneous determination

of SO 2 and CO 2 daily average emissions from fossil fuel

combustion sources.

The train for Method 6B is very similar to Method 6A

with the following exceptions:

1) The probe is heated to 20ºC above the source but

not greater than 120ºC.

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