Encyclopedia of Environmental Science and Engineering, Volume I and II

817

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PARTICULATE EMISSIONS

EMISSION STANDARDS

Allowable levels of particulate emissions are specified in

several different ways, having somewhat different meth-

odologies of measurement and different philosophies of

important criteria for control. Permissible emission rates are

in a state of great legislative flux both as to the definition

of the suitable measurement and to the actual amount to be

allowed. This section summarizes the various types of quan-

titative standards that are used in regulating particulate emis-

sions. For a detailed survey of standards, the reader should

consult works by Stern,^1 Greenwood et al. ,^2 and the Public

Health Service.^3

A recent National Research Council report proposes

future studies on the nature of particulate emissions, their

effect on exposed populations and their control^4. Friedrich

and Reis^5 have reported the results of a 10-year multinational

European study on characteristics, ambient concentrations

and sources of air pollutants.

The following paragraphs give an overview of standards

for ambient particulate pollution and source emission. The

precise and practical methodology of making accurate and/

or legally satisfactory measurements is beyond the scope of

this article. Books such as those by Katz,^6 Powals et al. ,^7

Brenchly et al. ,^8 and Hawksley et al.^9 should be consulted

for detailed sampling procedures. In the Federal Register

USEPA announced the implementation of the PM-10 regu-

lations (i.e., portion of total suspended particulate matter of

10 μ m or less particle diameter). 40,41^

Ringlemann Number

Perhaps the first attempt at quantifying particulate emis-

sions was developed late in the 19th century by Maximilian

Ringlemann. He developed the concept of characterizing a

visible smoke plume according to its opacity or optical den-

sity and originated the chart shown in Figure 1 as a conve-

nient scale for estimation of opacity. The chart consists of

four grids of black lines on a white background, having frac-

tional black areas of 20, 40, 60 and 80% which are assigned

Ringlemann Numbers of 1–4. (Ringlemann 0 would be all

white and Ringlemann 5 all black.) For rating a smoke plume,

the chart is held at eye level at a distance such that chart lines

merge into shades of grey. The shade of the smoke plume is

compared to the chart and rated accordingly. The history and

use of the Ringlemann chart is covered by Kudlich^8 and by

Weisburd.^9

In actual practice, opacity is seldom determined by use

of the chart, although the term Ringlemann Number persists.

Instead, observers are trained at a “smoke school.”^10 Test

plumes are generated and the actual percentage of light atten-

uation is measured spec-trophotometrically within the stack.

Observers calibrate their perception of the emerging plume

against the measured opacity. Trained observers can usu-

ally make readings correct to 
 1/2 Ringlemann number. 11,13

Thus, with proper procedures, determination of a Ringlemann

Number is fairly objective and reproducible.

The Ringlemann concept was developed specifically for

black plumes, which attenuate skylight reaching the observ-

er’s eye and appear darker than the sky. White plumes, on

the other hand, reflect sunlight and appear brighter than the

background sky so that comparison to a Ringlemann chart is

meaningless. The smoke school approach is quite applicable,

however. Observations of a white plume are calibrated against

the measured light attenuation. Readings of white plumes are

somewhat more subject to variation due to relative locations

of observer, plume, and sun. It has been found that observa-

tions of equivalent opacity taken with the observer facing

the sun are about 1 Ringlemann number higher^13 than those

FIGURE 1 Ringlemann’s scale for grading the density of smoke.

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