Encyclopedia of Environmental Science and Engineering, Volume I and II

822 PARTICULATE EMISSIONS

In addition to new source performance standards, major

new stationary sources and major modifications are usually

subject to a “Prevention of Significant Deterioration” review.

If a particulate source of more than 25 tons/year is located

in an area which attains NAAQS or is unclassifiable with

respects to particulates, the owner must demonstrate that the

source will not violate NAAQS or PSD concentration incre-

ments. This requires modelling and preconstruction moni-

toring of ambient air quality. If the new or expanded source

is to be located in an area which does not meet NAAQS, then

emission from other sources must be reduced to offset the

new source. The regulation regarding emission offsets and

prevention of significant deterioration are relatively recent.

A summary of federal regulations as of 1981 has recently

been published as a quick guide to this rapidly changing

field.^18

In recent years, regulation of particulate emissions from

mobile sources has been initiated. The burden is essentially

on manufacturers of diesel engines. Because the emission

requirements and test procedures are quite complex and

because the target is highly specific, a comprehensive discus-

sion is beyond the scope of this article. Some representative

standards are: Diesel engines for urban buses, 0.019 grams/

megajoule, and other diesel engines for road use, 0.037 grams/

megajoule:^19 Non-road diesel engines, 1 gram/kilowatt-hour

for sizes less than 8 kilowatts in tier 1 down to 0.2 grams/

kilowatt-hour for units larger than 560 kilowatts in tier 2.^20

Locomotives, 0.36 grams/bhp-hr for switching service in tier

1 down to 0.1 grams/bhp-hr for line service in tier 3.^21 Marine

diesel engines, 0.2 grams/KwH to 0.5 grams/KwH, depending

on displacement and tier.^22 Note that the emission units above

are as specified in the printed regulation.

Particulate emission standards are also being promulgated

by agencies other than the Environmental Protection Agency.

In general, these are workplace standards. An example

would be the standard for mobile diesel-powered transporta-

tion equipment promulgated by the Mine Safety and Health

Administration. This specifies that the exhaust “shall not con-

tain black smoke.”^23

MEASUREMENT OF PARTICULATE EMISSIONS

As a first step in any program for control of particulate emis-

sions, a determination must be made of the quantity and

nature of particles being emitted by the subject source. The

quantity of emissions determines the collection efficiency

and size of required cleanup equipment. The particle size and

chemical properties of the emitted dust strongly influence

the type of equipment to be used. Sampling for this purpose

has been mainly a matter of industrial concern. A last step

in most control programs consists of measuring pollutants

in the cleaned gas stream to ensure that cleanup equipment

being used actually permits the pertinent emission targets to

be met. With increasing public concern and legislation on air

pollution, sampling for this purpose is increasingly required

by statute to determine compliance with the pertinent emis-

sion regulations. To this end the local pollution control

authority may issue a comprehensive sampling manual

which sets forth in considerable detail the procedures to be

used in obtaining raw data and the computations involved in

calculating the pertinent emission levels.

Complete and comprehensive source testing procedures

are beyond the scope of this paper. References 24–28 give

detailed instruction for performance of such tests.

Sampling of gas streams, especially for particulates, is

simple only in concept. Actual measurement require special-

ized equipment, trained personnel, careful experimental and

computational techniques, and a considerable expenditure

of time and manpower. Matters of technique and equipment

are covered in source testing manuals as mentioned above

and are briefly summarized later in this paper. Two addi-

tional complicating factors are usually present. First is the

frequent inaccessibility of sampling points. These points are

often located in duct work 50–100 ft above ground level.

Scaffolding must often be installed around the points, and

several hundred pounds of equipment must be lifted to that

level. Probe clearances are often critical, for in order to make

a sample traverse on 12 ft dia. stack, a 14 ft probe is needed,

and clearance must be available for insertion into the sam-

pling port as well as a means for suspending the probe from

above. At least one professional stack sampler is an ama-

teur mountain climber and puts his hobby to good use on

the job. A second complicating factor is the adverse physical

conditions frequently encountered. A somewhat extreme but

illustrative example is a refinery stream recently sampled. Gas

temperature was 1200°F requiring special probes and gas-

kets and protective clothing for the workers. The gas stream

contained 10% carbon monoxide creating potential hazards

of poisoning and explosion especially since duct pressure

was slightly above that of the atmosphere. Temperature in

the work area was in excess of 120°F contributing further to

the difficulty of the job.

In preparation for a sampling program, work platforms

or scaffolding and valved sample ports must be installed.

All special fittings for adapting the sampling probes to the

ports should be anticipated and fabricated. Arrangements

must be made with plant operating personnel to maintain

steady operating conditions during the test. The test must

be carefully planned as to number and exact location of tra-

verse sample points, and probes should be premarked for

these locations. Flow nomographs for sampling nozzles

should be made; and all filters, impingers, and other ele-

ment of sampling trains should be tared. With that advance

preparation a 3 man sampling team would require 1–2 days

to position their equipment and make gas flow measure-

ments and 2 sample transverses at right angles in a large

duct or stack.

Measurement of Gas Flow Rates

A preliminary step in determination of emission rates from

a stack is measurement of the gas flow rate. Detailed pro-

cedures in wide use including the necessary attention to

technique have been published by the ASME,^20 ASTM,^19

the Environmental Protection Agency, referred to as EPA,^21

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