State of California

Air Resources Board

Method 8

Determination of Sulfuric Acid Mist and Sulfur Dioxide

Emissions from Stationary Sources

Adopted: June 29, 1983

Amended: July 1, 1999
July 1999 CARB Method 8 Page 1

Method 8 - Determination of Sulfuric Acid Mist and Sulfur Emissions from Stationary

Sources

1. PRINCIPLE AND APPLICABILITY

1.1 Principle.

A gas sample is extracted isokinetically from the stack. The sulfuric acid mist (including

sulfur trioxide) and the sulfur dioxide are separated, and both fractions are measured

separately by the barium-thorin titration method.

1.2 Applicability.

This method is applicable for the determination of sulfuric acid mist (including sulfur

trioxide (SO3) in the absence of other particulate matter) and sulfur dioxide (SO2)

emissions from stationary sources. Collaborative tests have shown that the minimum

detectable limits of the method are 0.05 mg/m3 (0.03 x 10C7 lb/ft3) for SO3 and 1.2 mg/m3

(0.74 x 10-7 lb/ft3

) for SO2. No upper limits have been established. Based on theoretical

calculations for 200 ml of 3 percent hydrogen peroxide solution, the upper concentration

limit for SO2 in a 1.0 m3 (35.3 ft3) gas sample is about 12,500 mg/m3 (7.7 x 10C4 lb/ft3). The

upper limit can be extended by increasing the quantity of peroxide solution in the

impingers.

Possible interfering agents of this method are fluorides, free ammonia, and dimethyl

aniline. If any of these interfering agents are present (this can be determined by

knowledge of the process), alternative methods, subject to the approval of the Executive

Officer, are required.

Any modification of this method beyond those expressly permitted shall be considered a

major modification subject to the approval of the Executive Officer. The term Executive

Officer as used in this document shall mean the Executive Officer of the Air Resources

Board (ARB), or his or her authorized representative.

Filterable particulate matter may be determined along with S03 and S02 (subject to the

approval of the Executive Officer) by inserting a heated glass fiber filter between the probe

and isopropanol impinger (see Section 2.1 of Method 6). If this option is chosen,

particulate analysis is gravimetric only; H2SO4 acid mist is not determined separately.

2. APPARATUS

2.1 Sampling.

 A schematic of the sampling train used in this method is shown in Figure 8-1; it is similar

to the Method 5 train, except that the filter position is different, and the filter holder does not

have to be heated. Commercial models of this train are available. For those who desire to

build their own, however, complete construction details are described in APTD-0581

(Construction Details of Isokinetic Source-Sampling Equipment, EPA, 1971, document

#PB-203-060, available from NTIS). Changes from the APTD-0581 document and

allowable modifications to figure 8-1 are discussed in the following subsections. 

The operating and maintenance procedures for the sampling train are described in APTD0576 (Maintenance, Calibration and Operation of Isokinetic Source Sampling Equipment,

EPA, 1972, document #PB-209-022, available from NTIS). Since correct usage is
July 1999 CARB Method 8 Page 2

important in obtaining valid results, all users should read the APTD-0576 document and

adopt the operating and maintenance procedures outlined in it, unless otherwise specified

herein. Further details and guidelines on operation and maintenance are given in Method

5 and should be read and followed whenever they are applicable.

2.1.1 Probe Nozzle.

Same as Method 5, Section 2.1.1.

2.1.2 Probe Liner.

Borosilicate or quartz glass, with a heating system to prevent visible condensation

during sampling. Do not use metal probe liners.

2.1.3 Pitot Tube.

Same as Method 5, Section 2.1.3.

2.1.4 Differential Pressure Gauge.

Same as Method 5, Section 2.1.4.

2.1.5 Filter Holder.

Borosilicate glass, with a glass frit filter support and a silicone rubber gasket. Other

gasket materials, e.g., Teflon or Viton, may be used subject to the approval of the 

Executive Officer. The holder design shall provide a positive seal against leakage

from the outside or around the filter. The filter holder shall be placed between the

first and second impingers. Note: Do not heat the filter holder.

2.1.6 Impingers. 

Four, as shown in Figure 8-1. The first and third shall be of Greenburg-Smith design

with standard tips. The second and fourth shall be of Greenburg-Smith design

modified by replacing the insert with an approximately 13-mm (0.5-in.) ID glass tube,

having an unconstricted tip located 13 mm (0.5 in.) from the bottom of the flask. 

Similar collection systems, subject to the approval of the Executive Officer, may be

used.

2.1.7 Metering System.

Same as Method 5, Section 2.1.8.

2.1.8 Barometer. 

Same as Method 5, Section 2.1.9.

2.1.9 Gas Density Determination Equipment.

Same as Method 5, Section 2.1.10.

2.1.10 Temperature Gauge.

Thermometer, or equivalent, to measure the temperature of the gas leaving the

impinger train to within 1EC (2EF).

2.2 Sample Recovery.

2.2.1 Wash Bottles. 

Polyethylene or glass, 500-ml (two).
July 1999 CARB Method 8 Page 3

2.2.2 Graduated Cylinders. 

250-ml, 1-liter. (Volumetric flasks may also be used.)

2.2.3 Storage Bottles. 

Leak-free polyethylene bottles, 1-liter size (two for each sampling run).

2.2.4 Trip Balance. 

500-g capacity, to measure to "0.5 g (necessary only if a moisture content analysis is

to be done).

2.3 Analysis.

2.3.1 Pipettes.

Volumetric 25-ml, 100-ml.

2.3.2 Burette.

50-ml.

2.3.3 Erlenmeyer Flask.

250-ml (one for each sample, blank, and standard).

2.3.4 Graduated Cylinder.

100-ml.

2.3.5 Trip Balance.

500 g capacity, to measure to " 0.5 g.

2.3.6 Dropping Bottle.

To add indicator solution, 125-ml size.

3. REAGENTS

Unless otherwise indicated, all reagents are to conform to the specifications established by the

Committee on Analytical Reagents of the American Chemical Society, where such

specifications are available. Otherwise, use the best available grade.

3.1 Sampling.

3.1.1 Filters.

Same as in Method 5, Sections 3.1.1.

3.1.2 Silica Gel.

Same as Method 5, Section 3.1.2.

3.1.3 Water.

Deionized, distilled to conform to ASTM Specification D1193-77, Type 3. At the

option of the analyst, the KMnO4 test for oxidizable organic matter may be omitted

when high concentrations of organic matter are not expected to be present.
July 1999 CARB Method 8 Page 4

3.1.4 Isopropanol, 80 Percent.

Mix 800 ml of isopropanol with 200 ml of deionized, distilled water. 

Note: Experience has shown that only A.C.S. grade isopropanol is satisfactory. 

Tests have shown that isopropanol obtained from commercial sources occasionally

has peroxide impurities that will cause erroneously high sulfuric acid mist

measurement. Use the following test for detecting peroxides in each lot of

isopropanol: Shake 10 ml of the isopropanol with 10 ml of freshly prepared 10

percent potassium iodide solution. Prepare a blank by similarly treating 10 ml of

distilled water. After 1 minute, read the absorbance on a spectrophotometer at 352

nanometers. If the absorbance exceeds 0.1, the isopropanol shall not be used. 

Peroxides may be removed from isopropanol by redistilling, or by passage through a

column of activated alumina. However, reagent grade isopropanol with suitably low

peroxide levels is readily available from commercial sources; therefore, rejection of

contaminated lots may be more efficient than following the peroxide removal

procedure.

3.1.5 Hydrogen Peroxide, 3 Percent.

Dilute 100 ml of 30 percent hydrogen peroxide to 1 liter with deionized, distilled water.

Prepare fresh daily.

3.1.6 Crushed Ice.

3.2 Sample Recovery.

3.2.1 Water. 

Same as in Section 3.1.3.

3.2.2 Isopropanol, 80 Percent.

Same as in Section 3.1.4.

3.3 Analysis. 

3.3.1 Water.

Same as 3.1.3.

3.3.2 Isopropanol, 100 percent.

3.3.3 Thorin Indicator. 

1-(o-arsonophenylazo) 2-naphthol-3, 6-disulfonic acid, disodium salt, or equivalent. 

Dissolve 0.20 g in 100 ml of deionized, distilled water.

3.3.4 Barium Perchlorate (0.0100 Normal). 

Dissolve 1.95 g of barium perchlorate trihydrate (Ba(Cl04)2$3H2O) in 200 ml

deionized, distilled water, and dilute to 1 liter with isopropanol; 1.22 g of barium

chloride dihydrate (BaCl2$2H2O) may be used instead of the barium perchlorate. 

Standardize with sulfuric acid as in Section 5.2. This solution must be protected

against evaporation at all times.

3.3.5 Sulfuric Acid Standard (0.0100 N). 

Purchase or standardize to " 0.0002 N against 0.0100 N NaOH that has previously
July 1999 CARB Method 8 Page 5

been standardized against primary standard potassium acid phthalate.

3.3.6 Quality Assurance Audit Samples.

Same as in Method 6, Section 3.3.6.

4. PROCEDURE

4.1 Sampling.

4.1.1 Pretest Preparation. 

Follow the procedure in Method 5, Section 4.1.1; filters should be inspected but need

not be desiccated, weighed, or identified. If the effluent gas can be considered dry,

i.e., moisture free, the silica gel need not be weighed.

4.1.2 Preliminary Determinations. 

Follow the procedure in Method 5, Section 4.1.2.

4.1.3 Preparation of Collection Train. 

Follow the procedure in Method 5, Section 4.1.3 (except for the second paragraph

regarding impinger solutions and other obviously inapplicable parts), and use Figure

8-1 instead of Figure 5-1. Replace the second paragraph with: Place 100 ml of 80

percent isopropanol in the first impinger, 100 ml of 3 percent hydrogen peroxide in

both the second and third impingers; retain a portion of each reagent for use as a

blank solution. Place about 200 g of silica gel in the fourth impinger.

Note: If moisture content is to be determined by impinger analysis, weigh each of the

first three impingers (plus absorbing solution) to the nearest 0.5 g, and record these

weights. Weigh also the silica gel (or silica gel plus container) to the nearest 0.5 g,

and record.

4.1.4 Pretest Leak-Check Procedure. 

Follow the basic procedure in Method 5, Section 4.1.4.1, noting that the probe heater

shall be adjusted to the minimum temperature required to prevent condensation, and

also that verbiage such as "....plugging the inlet to the filter holder...." shall be

replaced by "...plugging the inlet to the first impinger...." The pretest leak-check is

optional.

4.1.5 Train Operation.

Follow the basic procedures in Method 5, Section 4.1.5, in conjunction with the

following special instructions. Record the data on a sheet similar to the one in Figure

8-2.(or use Figure 5-2 in Method 5) The sampling rate shall not exceed 0.030 m3/min

(1.0 cfm) during the run. Periodically during the test, observe the connecting line

between the probe and first impinger for signs of condensation. If it does occur,

adjust the probe heater setting upward to the minimum temperature required to

prevent condensation. If component changes become necessary during a run, a

leak-check shall be done immediately before each change, according to the

procedure outlined in Section 4.1.4.2 of Method 5 (with appropriate modifications, as

mentioned in Section 4.1.4 of this method); record all leak rates. If the leakage

rate(s) exceeds the specified rate, the tester shall either void the run or shall plan to

correct the sample volume as outlined in Section 6.3 of Method 5. Immediately after
July 1999 CARB Method 8 Page 6

component changes, leak-checks are optional. If these leak-checks are done, the

procedure in Section 4.1.4.1 of Method 5 (with appropriate modifications) shall be

used.

After turning off the pump and recording the final readings at the conclusion of each

run, remove the probe from the stack. Conduct a post-test (mandatory) leak-check

as in Section 4.1.4.3 of Method 5 (with appropriate modifications), and record the

leak rate. If the post-test leakage rate exceeds the specified acceptable rate, the

tester shall either correct the sample volume, as in Section 6.3 of Method 5, or shall

void the run.

Drain the ice bath and, with the probe disconnected, purge the remaining part of the

train by drawing clean ambient air through the system for 15 minutes at the average

flow rate used for sampling.

Note: Clean ambient air can be provided by passing air through a charcoal filter. At

the option of the tester, ambient air (without cleaning) may be used.)

4.1.6 Calculation of Percent Isokinetic.

Follow the procedure in Method 5, Section 4.1.6.

4.2 Sample Recovery.

4.2.1 Container No. 1.

If a moisture content analysis is to be done, weigh the first impinger plus contents to

the nearest 0.5 g, and record this weight. 

Transfer the contents of the first impinger to a 250-ml graduated cylinder. Rinse the

probe, first impinger, all connecting glassware before the filter, and the front half of

the filter holder with 80-percent isopropanol. Add the Rinse Solution to the cylinder. 

Dilute to 250 ml with 80 percent isopropanol. Add the filter to the solution, mix, and

transfer to the storage container. Protect the solution against evaporation. Mark the

level of liquid on the container, and identify the sample container.

4.2.2 Container No. 2.

If a moisture content analysis is to be done, weigh the second and third impingers

(plus contents) to the nearest 0.5 g, and record the weights. Also, weigh the spent

silica gel (or silica gel plus impinger) to the nearest 0.5 g, and record.

Transfer the solutions from the second and third impingers to a 1-liter graduated

cylinder. Rinse all connecting glassware (including back half of filter holder) between

the filter and silica gel impinger with water, and add this rinse water to the cylinder. 

Dilute to 1 liter with water. Transfer the solution to a storage container. Mark the

level of liquid on the container. Seal and identify the sample container.

4.3 Analysis. 

Note the level of the liquid in Containers No. 1 and 2, and confirm whether any sample was

lost during shipment; note this on the analytical data sheet. If a noticeable amount of

leakage has occurred, either void the sample or use methods, subject to the approval of

the Executive Officer, to correct the final results.
July 1999 CARB Method 8 Page 7

4.3.1 Container No. 1. 

Shake the container holding the isopropanol solution and the filter. If the filter breaks

up, allow the fragments to settle for a few minutes before removing a sample. Pipette

a 100-ml aliquot of this solution into a 250-ml Erlenmeyer flask, add 2 to 4 drops of

thorin indicator, and titrate to a pink endpoint using 0.0100 N barium perchlorate.

Repeat the titration with a second aliquot of sample, and average the titration values.

 Replicate titrations must agree within 1 percent or 0.2 ml, whichever is greater.

4.3.2 Container No. 2. 

Thoroughly mix the solution in the container holding the contents of the second and

third impingers. Pipette a 10-ml aliquot of sample into a 250-ml Erlenmeyer flask. 

Add 40 ml of isopropanol, 2 to 4 drops of thorin indicator, and titrate to a pink

endpoint using 0.0100 N barium perchlorate. Repeat the titration with a second

aliquot of sample, and average the titration values. Replicate titrations must agree

within 1 percent or 0.2 ml, whichever is greater.

4.3.3 Blanks. 

Prepare blanks by adding 2 to 4 drops of thorin indicator to 100 ml of 80 percent

isopropanol. Titrate the blanks in the same manner as the samples.

4.4 Quality Control Procedures. 

Same as in Method 5, Section 4.4.

4.5 Audit Sample Analysis. 

Same as in Method 6, Section 4.4.

5. CALIBRATION

5.1

Calibrate equipment using the procedures specified in the following sections of Method 5: 

Section 5.3 (metering system), Section 5.5 (temperature gauges), and Section 5.7

(barometer). Note that the recommended leak-check of the metering system, described in

Section 5.6 of Method 5, also applies to this method.

5.2 

Standardize the barium perchlorate solution with 25 ml of standard sulfuric acid, to which

100 ml of 100 percent isopropanol has been added.

6. CALCULATIONS

NOTE: Carry out calculations retaining at least one extra decimal figure beyond that of the

acquired data. Round off figures after final calculation.

6.1 Nomenclature. 

An = Cross-sectional area of nozzle, m2 (ft2).

Bws = Water vapor in the gas stream, proportion by volume.

CH2SO4= Sulfuric acid (including SO3) concentration, g/dscm (lb/dscf).

CSO2 = Sulfur dioxide concentration, g/dscm (lb/dscf).
July 1999 CARB Method 8 Page 8

I = Percent of isokinetic sampling.

N = Normality of barium perchlorate titrant, g-equivalents/liter.

Pbar = Barometric pressure at the sampling site, mm Hg (in. Hg).

Ps = Absolute stack gas pressure, mm Hg (in. Hg).

Pstd = Standard absolute pressure, 760 mm Hg (29.92 in. Hg).

Tm = Average absolute dry gas meter temperature, (see Figure 8-2), EK (ER).

Ts = Average absolute stack gas temperature, (see Figure 8-2), EK (ER).

Tstd = Standard absolute temperature, 293EK (528ER).

Va = Volume of sample aliquot titrated, 100 ml for H2SO4 and 10 ml for SO2.

V1c = Total volume of liquid collected in impingers and silica gel, ml.

Vm = Volume of gas sample as measured by dry gas meter, dcm (dcf).

Vm(std)= Volume of gas sample measured by the dry gas meter corrected to standard

conditions, dscm (dscf).

vs = Average stack gas velocity, calculated by Method 2, equation 2-9, using data

obtained from Method 8, m/sec (ft/sec).

Vsoln = Total volume of solution in which the H2SO4 or SO2 sample is contained, 250 ml

or 1000 ml, respectively.

Vt = Volume of barium standard solution titrant used for the sample, ml.

Vtb = Volume of barium standard solution titrant used for the blank, ml.

Y = Dry gas meter calibration factor.

ΔH = Average pressure drop across orifice meter, mm (in.)H2O.

θ = Total sampling time, min.

13.6 = Specific gravity of Mercury.

60 = sec/min.

100 = Conversion to percent.

6.2 Average Dry Gas Meter Temperature and Average Orifice Pressure Drop.

See data sheet (Figure 8-2).

6.3 Dry Gas Volume. 

Correct the sample volume measured by the dry gas meter to standard conditions (20EC

and 760 mm Hg or 68EF and 29.92 in. Hg) by using Equation 8-1. 

T

13.6

Ä H

P +

 =K V Y

P

13.6

Ä H

P +

T

T

V = V Y 

m

bar

1 m

std

bar

m

std

m(std) m









































Eq. 8-1

Where:

K1 = 0.3858 EK/mm Hg for metric units.

= 17.65 ER/in. Hg for English units.

Note: If the leak rate observed during any mandatory leak-checks exceeds the specified

acceptable rate, the tester shall either correct the value of Vm in Equation 8-1 (as described

in Section 6.3 of Method 5), or shall invalidate the test run.
July 1999 CARB Method 8 Page 9

6.4 Volume of Water Vapor and Moisture Content.

Calculate the volume of water vapor using Equation 5-2 of Method 5; the weight of water

collected in the impingers and silica gel can be converted directly to milliliters (the specific

gravity of water is 1 g/ml). Calculate the moisture content of the stack gas, using Equation

5-3 of Method 5. The Note in Section 6.5 of Method 5 also applies to this method. Note

that if the effluent gas stream can be considered dry, the volume of water vapor and

moisture content need not be calculated.

6.5 Sulfuric Acid Mist (Including SO3) Concentration.

V

V

V N(V - V )

C =K

m(std)

a

soln

t tb

H2SO4 2

















Eq. 8-2

Where:

K2 = 0.04904 g/milliequivalent for metric units,

= 1.081 x 10-4 lb/meq for English units.

6.6 Sulfur Dioxide Concentration.

V

V

V N(V - V )

C =K

m(std)

a

soln

t tb

SO2 3

















Eq. 8-3

Where:

K3 = 0.03203 g/meq for metric units,

= 7.061 x 10-5 lb/meq for English units.

6.7 Isokinetic Variation. 

6.7.1 Calculation from raw data. 

60 è v P A

13.6

ÄH

P +

T

V Y 100 T K V +

I=

s s n

bar

m

m

s 4 lc 











































Eq. 8-4

Where:

K4 = 0.003464 mm Hg- m3/ml-EK for metric units.

= 0.002676 in. Hg-ft3/ml-ER for English units.

6.7.2 Calculation from intermediate values.

P v A è (1- B )

T V

=K

T v è A P 60 (1-B )

T V P 100

I=

s s n ws

s m(std)

5

std s n s ws

s m(std) std

Eq. 8-5
July 1999 CARB Method 8 Page 10

Where:

K5 = 4.320 for metric units.

= 0.09450 for English units.

6.8 Acceptable Results. 

If 90 percent < I < 110 percent, the results are acceptable. If the results are low in

comparison to the standards and I is beyond the acceptable range, the Executive Officer

may opt to accept the results. Otherwise, reject the results and repeat the test.

6.9 Stack Gas Velocity and Volumetric Flow Rate.

Calculate the average stack gas velocity and volumetric flow rate, if needed, using data

obtained in this method and equations in Sections 5.2 and 5.3 of Method 2.

6.10 Relative Error (RE) for QA Audit Samples. 

Same as in Method 6, Section 6.4.

7. BIBLIOGRAPHY

1. EPA Method 8, Determination of Sulfuric Acid Mist and Sulfur Dioxide Emissions from

Stationary Sources, CFR40, Part 60, Appendix A

2. ARB Method 5, Determination of Particulate Matter Emissions from Stationary Sources

3. ARB Method 6, Determination of Sulfur Dioxide Emissions from Stationary Sources

4. ARB Method 2, Determination of Stack Gas Velocity and Volumetric Flow Rate (Type S

Pitot Tube)
July 1999 CARB Method 8 Page 11

Figure 8-1 Sample Train Schematic

Dry Gas

Meter

Ice

Water

Bath

Vacuum

Line

Vacuum

Gauge

By-pass

Valve

Air-Tight

Pump

Orifice

Temperature

Sensors

Filter 

Holder

Check 

Valve

Impingers

Temperature 

Sensor

Main

Valve

Stack

Wall

Heat Traced

Glass-lined 

Probe

Manometer

Type S Pitot Tube

Type S

Pitot Tube

Probe

Temperature

Sensor
July 1999 CARB Method 8 Page 12

Plant______________________________ Ambient Temperature ______________________________

Location ___________________________ Barometric Pressure _______________________________

Operator ___________________________ Assumed Moisture, % ______________________________

Date ______________________________ Probe Length, (ft.) _________________________________

Run No. ___________________________ Nozzle Identification No. ____________________________

Sample Box No. ____________________ Average Calibrated Nozzle Diameter, (in.) _______________

Meter Box No. ______________________ Probe Heater Setting _______________________________

Meter ΔH@ ________________________ Leak Rate, (cfm) __________________________________

C Factor ___________________________ Static Pressure, (in. Hg) ____________________________

Pitot Tube Coefficient, Cp _____________ Probe Liner Material _______________________________

Filter No. ________________________________________

Gas Sample

Temperature At Day

Gas Meter

Traverse

Point

Number

Sampling

Time

min.

Vacuum

(in. Hg)

Stack

Temperature

(Ts) (°F)

Velocity Head

(ΔPs)(in. H2O)

Pressure

Differential

Across

Orifice Meter

(in. H2O)

Gas Meter

Reading

(ft3)

Inlet

(°F)

Outlet

(°F)

Filter

Temperature

(°F)

Temperature

Of Gas

Leaving

Condenser

Or Last

Impinger

(°F)

Total Avg. Avg.

Average Avg.

Figure 8-2 Data Sheet

SCHEMATIC OF STACK CROSS