Encyclopedia of Environmental Science and Engineering, Volume I and II

74 AIR POLLUTION SOURCES

The NSPS, SIP and NESHAP sources are further classified

depending on their actual and potential emissions.

Presuming that a certain area’s major-source cutoff is

100 tons/year, for that area:

1. Class A sources are sources, which actually or
   potentially, can emit greater than 100 tons per
   year of effluent.


2. Class SM sources, can emit less than 100 tons per
   year of effluent, if and only if the source complies
   with federally enforceable regulations.


3. Class B sources are sources, which at full capac-
   ity, can emit less than 100 tons per year of efflu-
   ent, products, and by-products.

Miscellaneous

The group is used to include such air environmental prob-

lems as aeroallergens, biological aerosols, odorous com-

pounds, carbon dioxide, waste heat, radioactive emissions,

and pesticides. In many cases they are not normally charac-

terized as air pollutants.

The remainder of this chapter is divided into two parts.

Part 1 deals with emissions from three major classes of

pollutants: hydrocarbons, inorganic gases and particulates.

Typical pollutants in these major classes are described, along

with their sources and the method of abatement or control.

Part 2 discusses the nature of the activity and the types

of air pollutant problems associated with sources identified

under standard categories of industries.

Part 1. Pollutant Emissions

Pollutant types Sources and abundance Abatement and control

A. HYDROCARBONS: Hydrocarbons are

compounds containing the elements of carbon

and hydrogen. The gaseous compounds of

carbon found in nature and polluted

atmospheres make up a broad spectrum of the

compounds of organic chemistry.

Carbon atoms bond readily to one another to

form the stable carbon–carbon link. It is this

link which forms the great number of organic

molecules in existence (
1,000,000). By

linking together in various ways, carbon

atoms form a great assortment of chain and

ring molecules (Aliphatics and Aromatics).

The most significant hydrocarbons when

considering air pollutants are known as volatile

compounds (VOCs), that exist in the

atmosphere primarily as gases because of their

low vapor pressures. However, it is important to

note that solid hydrocarbons can cause an

environmental and health threat as well. For

example, Benzo-(a)-pyrene, a well known

carcinogen, exists in the air as a fine particulate.

Hydrocarbons by themselves in air have

relatively low toxicity. They are of concern

because of their photochemical activity in the

presence of sunlight and oxides of nitrogen

(NOx). They react to form photochemical

oxidants. The primary pollutant is ozone,

however, other organic pollutants like per-

oxyacetal nitrate (PAN) have been identified

as the next highest component. Table 11

shows ozone levels generated in the photo-

chemical oxidation of various hydrocarbons

with oxides of nitrogen.

The immediate health effects associated with

ozone is irritation to the eyes and lungs. Long-

term health effects include scarring of the lung

tissue. The long-term welfare effects include

damage to architectural surface coatings as

well as damage to rubber products. Ozone can

also damage plants and reduce crop yields.

More hydrocarbons (HC) are emitted from

natural sources than from the activities of

man. The one in greatest abundance is

methane which has an average background

concentration of 1.55 ppm. This is produced

in the decomposition of dead material, mostly

plant material. Methane is joined by a class of

compounds of a more intricate molecular

structure known as terpenes. These substances

are emitted by plants, and are most visible as

the tiny aerosol particulates or the “blue haze”

found over most forested areas. Other

hydrocarbons found in large concentrations in

the ambient air besides methane (CH 4 ), are

Ethane (C 2 H 6 ), Propane (C 3 H 8 ), acetylene

(C 3 H 4 ), butane and isopentane.

Methane gas is one of the major greenhouse

gases See Greenhouse Gases Effects, B.J.

Mason. As can be inferred from Table 3,

landfill emissions are the primary source of

methane. About 15 percent of all atmospheric

hydrocarbon is due to man’s activity. However,

the impact of man-made hydrocarbons to

human health is out of proportion to their

abundance since they are emitted in urban

areas which have a high population

concentration.

FROM MOBILE SOURCES: Emissions

resulting from the evaporation of gasoline

from fuel tanks and carburetors can be limited

by storage of the vapors (within the engine

itself or in a carbon canister which absorbs the

fuel vapors) and then routs the vapors back to

the tanks where they will be burned. Controls

also exist in the refueling of automobiles and

other mobile sources. These controls usually

involve pressurized vacuum hoses and tighter

seals at the filler pipe.

FROM STATIONARY SOURCES:

a) Design equipment to use or consume

completely the processed material.

b) In the surface coating industry, use a higher

percent solids paint to reduce the amount

of VOC.

c) Use materials which have a higher boiling

point or are less photochemically active.

d) Use control equipment and recycling or

organic solvents to reduce emissions.

e) Control by adsorption, absorption and

condensation.

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