ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - AIR POLLUTION SOURCES ppsx

Examples of such direct discharge from an identifiable source into the atmosphere include the complete and incomplete combustion of carbonaceous fuels from industrial processes and bil

Air pollution may be defined as the presence in the atmosphere

of any substance (or combination of substances) that is

detri-mental to human health and welfare; offensive or objectionable

to man, either externally or internally; or which by its presence

will directly or indirectly adversely affect the welfare of man

(“Air Pollution,” Homer W Parker, 1977.) The substances

present in the atmosphere which cause this detriment to health

and welfare are the air pollutants

A considerable quantity of air pollution occurs naturally

as a consequence of such processes as soil erosion and

volca-nic eruptions However, those pollutants which pose a threat

to human health and cause extensive damage to property are

primarily derived from activities associated with the

devel-opment of community living, as well as with the growth of

affluence and living standards in industrial societies These

activities include the burning of fuel for heat and power, the

processing of materials for food and goods, and the disposal

of wastes

Much of the materials which pollute our atmosphere

rep-resent valuable resources which are being wasted We have

available today the technological means of controlling most

sources of air pollution The cost of control however has been

estimated on the order of 10 to 20 percent of the world’s gross

national product Moreover, full implementation of the

con-trol measures that would be necessary to achieve healthful

air quality in many of our large centers of population would

require significant changes in lifestyle in those areas

POLLUTANT CLASSIFICATIONS

Air pollutants are numerous, each with its own peculiar

charac-teristics Therefore it is usual to have these pollutants classified

by some design Classification allows for the study of

pollut-ants in subgroups on the basis of some characteristic of interest

or concern and also provides an ordering which makes it easier

to formulate air pollution control programs Accordingly, the

classification of air pollutants may be based on:

1 How the pollutants are borne into the atmosphere

2 The physical state of the pollutant

3 The molecular composition of the pollutants

4 The nature of the problem or health threat

associ-ated with the pollutants

Classification According to the Method of Entry into the Atmosphere

This classification contains two categories: (1) Primary and (2) secondary

Primary Pollutants Primary air pollutants are emitted into the atmosphere directly from identifiable sources whether from mechanical or chemical reaction processes Examples

of such direct discharge from an identifiable source into the atmosphere include the complete and incomplete combustion

of carbonaceous fuels from industrial processes and bile engines yielding carbon monoxide and carbon dioxide

Secondary Pollutants These pollutants are those which are formed as a result of some reaction in the atmosphere This reaction may occur between any combination of air pollut- ants (including primary pollutants) and natural components

of the atmosphere Some of these reactions require the ence of sunlight and are called photo-chemical reactions An example of such a reaction is the formation of ozone from the interaction of organic and nitrous compounds in the presence

Particulate Pollutants Any pollutant that is not gaseous is defined as a particulate pollutant or particulate whether they exist in the form of finely divided solids or liquids The larger particulates after having been introduced into the air tend

to settle out quickly and affect lives and property near the source The smaller and lighter particles travel further away,

and eventually settle out great distances from the source The

very smallest particulates exhibit certain gaseous

characteris-tics, remaining suspended in the atmosphere for long periods

of time and are readily transported by wind currents

Classification According to Chemical Composition

Pollutants may also be classified according to their

chemi-cal structure The basic classifications are (1) organic and

(2) inorganic

Organic Pollutants Organic compounds may be defined

as those which contain carbon, hydrogen, and may contain

other elements By this definition we exclude the very simple

carbon monoxide and carbon dioxide These contain carbon,

but no hydrogen

Inorganic Pollutants Inorganic pollutants may be defined as

compounds which do not contain compounds of carbon, with

the exception of carbon oxides, like CO and CO 2 , and carbon

disulfide Many of the most commonly encountered

pollut-ants are inorganic You might be asking yourself why CO 2

is considered a pollutant Isn’t CO 2 beneficial in the

mainte-nance of the earth’s ecological system by providing a source

of energy for manufacturing plants? The answer is yes, but the

earth’s ecosystem can utilize only so much carbon dioxide

The surplus of CO 2 in the atmosphere is believed to be one of the contributors to the “Greenhouse Effect.” Excesses of this gas are believed to cause the global heating that is now being experienced The long-term outlook for this phenomenon is the melting of the polar icecaps resulting in the oceans’ levels rising and threatening population areas that are located at the coastline

Classification According to the Nature of the Problem

or Health Threat Posed by the Pollutant

Under the Clean Air Act, the Congress of the United States established a classification system which recognized two dis- tinct categories of air pollutants: those air pollutants which because of their universal nature or ubiquity, presented a threat

to public health and welfare (called criteria pollutants); and those pollutants, while not widespread, contribute to higher mortality rates in humans (called hazardous pollutants)

Criteria Pollutants These are air pollutants for which a national ambient air quality standard has been established

In the selection of these standards, certain criteria are lished using observed levels of air pollution and the associated impacts on human health, vegetation and materials relating air quality level to health and welfare effects Six specific

estab-TABLE 1Classification of Pollutants

Heavy Metals

Other Pollutants Include:

—Pesticides —Aeroallergens

pollutants (nitrogen dioxide, sulfur dioxide, hydrocarbons,

carbon monoxide, particulate matter and ozone) were

identi-fied in 1971 as the most “universal” within the United States

and the most significant pollutants contributing to the

degra-dation of the lower atmosphere or troposphere Once national

air quality standards were established each state was given

the responsibility to make sure that emissions from sources of

air pollution in that state and neighboring states do not violate

these air quality standards by developing and implementing

creative plans for reducing source emissions Recognizing

that hydrocarbons in the atmosphere did not, as a class of

pollutants, create a singular and internally consistent ambient

air quality problem, the class term was dropped and lead was

added as a new pollutant class

Hazardous Pollutants These are air pollutants for which

no air quality standard has been established but nevertheless

cause or contribute to an increase in the mortality rate or

serious irreversible or incapacitating illness The hazardous

pollutants listed by January 1988 are: asbestos, beryllium,

mercury, vinyl chloride, radionuclides, coke oven emissions,

benzene and inorganic arsenic

In November of 1990, the U.S Congress passed Clean

Air Act amendments (CAAA) into law which greatly expand

the list of regulated chemicals—Hazardous Air Pollutants

(HAPs)– to about 190 The EPA’s mandate is to promulgate

standards for the control of HAP emissions from about 100

source categories, employing maximum achievable control

technology (MACT) To date greater than 95% of MACT

standards have been published

Source: http://www.epa.gov/ttn/atw/eparules.html

SOURCE CLASSIFICATIONS

The management and control of air pollution is generally

achieved through the regulation and control of air pollution

sources For convenience, sources of air pollutants may be

classified according to the size or the nature of the pollutant

activity and source type characteristics

Classification According to Magnitude

For convenience of analysis, air pollution sources are divided

into two classes (1) major sources and (2) minor sources

Major sources are sources whose emissions quantities

are large enough to cause them to have a dominant role in the

pollution potential of an area Prior to the 1990 CAAA, the

U.S Environmental Protection Agency classified all sources

that emitted or had the potential for emitting 100 tons/year

of any single pollutant as a major source

Today, the definition has been revised and made more

stringent Depending upon an area’s air quality, emissions of

as little as 10 tons/year would constitute a major source

Major sources are fixed (stationary) and commonly

occupy a limited area relative to a community They include:

1 Major industrial and manufacturing plants

2 Steam—Electric power plants

3 Industrial and Municipal Incinerators

4 Facilities that use solvents (surface coating, degreasing, dry cleaning, plastics manufacture, rubber manufacture) and lose petroleum products

by evaporation

5 Facilities that lose petroleum product from age and marketing (tank farms, service stations) operations.

6 Motor vehicles, aircraft, ships and railroads in which the combustion of fuels for transportation occurs

7 Dumps, incinerators, etc in which combustion of wastes occur

8 Facilities or units in which the decomposition of organic wastes occur

9 Sewage treatment plants

Industrial plants constitute a highly varied and complex chemical system, each industry presenting a unique air pollu- tion problem The characteristics of the emissions produced are directly related to the peculiarities of the operation in question, that is, on the raw materials, the fuels, the process method, the efficiency of the chosen process, the method and the type of air pollution control measures applied

Minor sources are those which cannot be cataloged

prac-tically on a source-by-source basis They may be stationary

or mobile and are commonly spread throughout the nity These sources are associated with:

1 Combustion of fuels in residences and cial buildings and institutions for personal com- fort and convenience

2 Service industries such as laundries, dry-cleaning plants, repair services, etc

Classification According to Nature of Emissions

The U.S Environmental Protection Agency classifies sources depending on both the quantitative and qualitative nature of the emissions The source categories are:

1 NSPS (New Source Performance Standard) sources These are sources for which national emissions standards have been established All sources built subsequent to the date of establishment of these emissions standards must meet NSPS requirements

2 SIP (State Implementation Plan) sources These are sources built prior to the establishment of the new source standards These older SIP sources have no national emissions standards to follow per

se, but rather their level of emissions is determined

on a source-by-source basis and depend on the air quality of the area in which they are located If the

air quality is particularly poor, stricter operating

requirements are imposed

3 NESHAP (National Emission Standards for

Hazardous Air Pollutants) sources These are

sources which emit any of the nine hazardous

pol-lutants which were discussed in the section on air

pollutant classification These sources also have

operating standards imposed on the equipment

4 Transportation sources These are sources of air pollution which do not necessarily remain sta- tionary but are mobile, and include cars, trucks, buses, airplanes, railroad locomotives and marine vessels These sources’ main emissions are car- bon monoxide, carbon dioxide, nitrogen dioxide and lead and result from the internal combustion

of fuel in their engines

TABLE 2Summary of National Emissions (thousand short tons, 1.1 million short tons equals 1 million metric tons)

Year

Carbon

Monoxide

Nitrogen Oxides

Volatile Organic

Particulate Matter (PM-10) (w/o) fugitive dust

Fugitive Dust (PM-10)*

Lead (short tons)

** NAPAP historical emissions. 3,4

*** NA denotes not available

**** Combination of revised transportation values and NAPAP historical emissions

***** There is a change in methodology for determining on-road vehicle and non-road sources emissions (see chapter 6)

****** There is a change in methodology in all sources except on-road vehicles and non-road sources and all pollutants except lead, as reflected by the dotted line

******* 1990 through 1994 estimates are preliminary The emissions can be converted to metric tons by multiplying the values by 0.9072

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 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

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

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

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

Ethane (C2H6), Propane (C3H8), acetylene (C3H4), 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

Part 1 Pollutant Emissions (continued)

1 Oxygenated Hydrocarbons: Like hydrocarbons,

these compounds make up an almost infinite array of

compounds which include alcohols, phenols, ethers,

aldehydes, ketones, esters, peroxides, and organic

acids, like carboxylic acids Oxygenated

hydro-carbons are very commonly used in the paint

industry as solvents, and in the chemical industry as

reactants for many chemical products and

intermediates

Oxygenated hydrocarbons have a two-fold environmental

problem First, they are very reactive thus readily form

photochemical oxidants in the presence of sunlight

(light energy) and oxides of nitrogen; thus adding to

the tropospheric ozone problem

Small amounts of oxygenated hydrocarbons are emitted by industrial processes such as spray paint coating, chemical and plastics industry

The large majority of emissions of these chemicals are associated with the internal combustion engine Table 6 shows some typical concentrations, (parts per million), of simple hydrocarbon fuels The aldehydes are the predominant oxygenates (these compounds will be discussed in greater detail

in the following section) in emissions, but are emitted in minor amounts when compared to aliphatics and aromatics, carbon dioxide, carbon monoxide, and nitrogen oxide emissions

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 sources These controls usually involve pressurized vacuum hoses and tighter seals at the filler pipe

TABLE 3 Summary of U.S Methane Emissions by Source Category, 1990 to 1994 Preliminary Estimates (thousand short

Note(s): Totals presented in this table may not equal the sum of the individual source categories due to

rounding

Source(s): Inventory of U.S Greenhouse Gas Emissions and Sinks, 1900–1994 Draft Report, U.S

Environmental Protection Agency September 1995

TABLE 4 Total National Emissions of Volatile Organic Compound Emissions, 1940 through 1994 (thousand short tons)

Light-Duty Gas Vehicles and

Motorcycles

Note(s): Categories displayed below Tier 1 do not sum to Tier 1 totals because they are intended to show major contributors

1994 emission estimates are preliminary and will be updated in the next report

Tier 1 source categories and emissions are shaded

TABLE 5Oxygenates in Exhaust from Simple Hydrocarbon Fuel*

On-Road Vehicles Chemicals & Allied Product Mfg.

Waste Disposal & Recycling Miscellaneous (primarily tires)

Non-Road Sources Remaining Categories

Year

0 5 10 15 20 25 30 35

FIGURE 1 Trend in volatile organic compound emissions by seven principal source categories, 1990

to 1994

Part 1 Pollutant Emissions (continued )

Many of the oxygenated hydrocarbons are themselves

toxic, many of them are known human carcinogens

and some, especially esters, ketones, and alcohols

are known to cause central nervous system disorders

(narcosis, etc…)

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

(continued )

Part 1 Pollutant Emissions (continued )

2 Aldehydes: Aldehydes are one of a group of

organic compound with the general formula R-CHO

which yield acids when oxidized and alcohols when

reduced They are products of incomplete

combustion of hydrocarbons and other organic

materials

Formaldehyde and Acrolein-Acetaldehyde cause

irritation to the mucous membranes of the eyes,

nose, and other portions of the upper respiratory

tract Formaldehyde has also been cited as a potential

Among its many uses are as an intermediate

in the production of phenolic and amino resins and also in the production of slow release fertilizers Annual worldwide

metrics tons (calculated as 37% solution)

In general, aldehydes are produced by the combustion of fuels in motor vehicles, space heating, power generation, and in other combustion activities (such as the incineration

of wastes) In addition aldehydes are formed

in photochemical reactions between nitrogen oxides and certain hydrocarbons

Natural sources of aldehydes do not appear to be important contributors to air pollution Some aldehydes are found in fruits and plants

c) Use materials which have a higher boiling point or are less photo-chemically active

d) Use control equipment and recycling of organic solvents to reduce emissions

e) Control by absorption, adsorption and condensation

Control methods include more effective combustion as may be obtained in direct flame and the use

of catalytic afterburners

volume organic chemical produced today Ethylene

is a colorless hydrocarbon gas of the olefin series, it

is generally not toxic to humans or animals, but it is

the only hydrocarbon that has adverse effects on

vegetation at ambient concentrations of 1 ppm or

less It therefore represents a considerable air

pollution problem, for two reasons:

1 it is significantly harmful to plants,

Ethylene may form as a by-product of incomplete combustion of hydrocarbons and other organic substances Thus, ethylene has been found to be one of the components of automobile and diesel combustion emissions (exhaust and blow by emissions), incinerator effluents, and agricultural waste combustion gases Ethylene is not normally found in deposits of petroleum or natural gas

Ethylene poses no peculiar control problem in these emissions and this can be controlled by methods generally used for hydrocarbons These methods include combustion techniques, absorption techniques, absorption methods, and vapor recovery systems

TABLE 6 Emissions of Hydrofluorocarbons and Prefluorinated Carbon, 1990 to 1994 Preliminary Estimates

(thousand short tons; molecular basis)

Source(s): Inventory of U.S Greenhouse Gas Emissions and Sinks, 1900–1994 Draft Report, U.S

Environmental Protection Agency September 1995

Part 1 Pollutant Emissions (continued )

2 it contributes to photochemically produced air

pollution Ethylene is the most abundant (based on

mole volume) of the photoreactive hydrocarbons in

the lower atmosphere

In the chemical process industry, virtually all ethylene is consumed as feedstock for a variety of petrochemical products Ethylene has been known to be used as a ripening agent for fruits and vegetables

4 Organic Carcinogens: These are carbon compounds

which cause cancer in experimental animals and are

therefore suspected of playing a role in causing

human cancer, particularly cancer of the lungs There

is some question as to the carcinogenicity of selected

compounds Polynuclear aromatic hydrocarbons

(PAH) in our environment evolve from

high-temperature reactions under pyrolytic conditions

during incomplete combustion contained in some air

pollution source effluents in automobile exhaust

fumes, and in moderate concentrations in the air The

major classes of organic carcinogens are as follows:

1 Polynuclear aromatic hydrocarbons (PAH);

Benzo-(a)-pyrene (BAP)-substance found in

3 Polynuclear imino-heterocyclic compounds

4 Polynuclear carbonyl compounds

Organic carcinogens are primarily unwanted by-products of incomplete combustion

However, a few sources of organic carcinogens might be defined as naturally occurring

Bituminous coal contains certain organic carcinogens

From Motor Vehicle Sources: (Same Controls as Hydrocarbons)From Stationary Sources:

1 Design equipment to use or consume completely the processed material

2 Use of materials which have a higher boiling point or are less photochemically reactive

3 Use of control equipment to reduce emissions

4 Stop open burning of waste by use

of multiple-chamber incinerators or disposing of waste in sanitary landfills

5 Halogenated Hydrocarbons: Halogenated

hydrocarbons are carbon and hydrogen compounds

with one or more of the halide elements of fluorine,

chlorine, bromine, or iodine Of these elements, the

most common halogenated hydrocarbons are those

containing fluorine and chlorine

Halogenated hydrocarbons were once thought to solve

the ozone problem because of their low reactivity

However, many of these compounds are very toxic and

thus cause a more immediate threat to human health

Also, there is a great concern of damage caused by

these compounds to the stratospheric ozone layer

which protects us from the harmful ultraviolet

radiation of the sun These compounds tend to degrade

into their elemental components, which include radical

alogen, which have a great affinity for ozone

Halogenated hydrocarbon solvent vapors

tetrachloride (CCl4), trichloroethylene (C2HCl3), perchloroethylene (C2Cl4), etc

From vapors (CFCl3, C3FCl3) are very widely used as refrigerants and were once used as propellants Except for the vicinity of major urban areas, atmospheric halogen concentrations are very low

The same controls apply for halogenated hydrocarbons as for non-halogenated hydrocarbons These are adsorption, absorption, etc However, combustion may be undesirable since free halogen radical combining with water vapor may cause an acid problem This may damage equipment as well as create a serious environmental problem

6 Pesticides: Pesticides are economic poisons used to

control or destroy pests that cause economic losses or

adverse human health effects These chemicals can be

grouped as insecticides, herbicides (weed and brush

killers, defoliants, and desiccants), fungicides,

iscaricides, nematocides, repellants, attractants, and

plant growth regulators

In the United States, 300–400 pesticides are registered

for use in the production of food These chemicals

The primary source of pesticides in air is from the application process; a certain amount of drift is unavoidable, even under normal conditions

Pesticides can evaporate into the air from soil, water and treated surfaces Pesticides contained

in dust from the soil can enter the air and be transported for considerable distances before falling back to the earth Chemical plants manufacturing pesticides also produce pollutant emissions

Improved application equipment and methods:

Improved formulas for pesticides (higher density or use water soluble oils)Wider distribution and use of weather data in area where pesticides are used

(continued )

Part 1 Pollutant Emissions (continued )

have served quite well in the past years in the

prevention of famine and disease However, it must

be realized that some pesticides, especially

chlorinated hydrocarbons, are metabolized very

slowly thus, accumulate in adipose tissue DDT for

example, has been shown to cause tumors in

FUEL COMB -ELEC UTIL

FUEL COMB -INDUSTRIAL

FUEL COMB -OTHER

443514,890

11054910,656

1106616,250

2377703,625

3227506,230

3146774,072

3226703.961

3256713,888

PETROLEUM and RELATED

WASTE DISPOSAL and

(continued )

Part 1 Pollutant Emissions (continued )

B INORGANIC GASES: The chemistry of the lower

atmosphere is controlled by the reactivity of oxygen

forms of almost all of the elements are oxides, with

the notable exception of nitrogen Thus, many of the

major pollutants are oxides (i.e., CO, SO2, SO3, NO,

1 Carbon Oxides

Significant amounts of carbon oxides, carbon monoxide

natural and anthropogenic (man made) sources CO

is considered a major atmospheric pollutant because

of its significant health effects, whereas, CO2 is a

relatively non-toxic, normal tropospheric (lower

atmospheric) constituent and is, therefore, not

usually described as a major atmospheric pollutant

contribute to global climatic warning

a Carbon Monoxide:

Carbon monoxide (CO) is a colorless, odorless, tasteless gas formed by the incomplete combustion of fossil fuels and other organic matter During combustion, carbon is oxidized to CO by the following reactions:

CO, formed as an intermediate in the combustion process, is emitted if there is insufficient O2 present for reaction (2) to proceed CO is produced naturally by volcanic eruptions, forest fires, lightning and photochemical degradation of various reactive organic compounds Biologically,

CO is formed by certain brown algae, decomposition of chlorophyll in leaves of green plants, various micro-organisms and microbial action in the oceans Major anthropogenic sources include transportation, industrial processing, solid waste disposal and agricultural burning it also is present in high concentrations in cigarette smoke

Background concentrations of CO average 0.1 ppm, with peak concentrations in the northern hemisphere during the autumn months due to the decomposition of chlorophyll associated with the color change and fall of leaves The residence time for CO

in the atmosphere is estimated to be 0.1 to 0.3 years

Because CO has a higher affinity (approximately

oxygen, and also tends to remain more tightly bound, oxygen transport throughout the body

CO can be removed from the atmosphere by the actions of soil micro-organisms which convert it to

CO2 The soil in the U.S alone is estimated to remove approximately

is far in excess of the anthropogenic emission rate However, little CO is removed in urban areas since emissions of CO are large and soil is scarce In automobiles, catalytic convertors are used to reduce CO emissions by combusting the exhaust gases over a catalyst This

Similar after-burner processes are used in controlling emissions from stationary sources

Note(s): Categories displayed below Tier 1 do not sum to Tier 1 totals because they are intended to show major contributors

1994 emission estimates are preliminary and will be updated in the next report

Tier 1 source categories and emissions are shaded

Part 1 Pollutant Emissions (continued )

of an individual exposed to CO can be greatly reduced CO is highly toxic at concentrations greater than 1000 ppm Death results from asphyxiation since body tissues, especially the brain, are deprived of a sufficient supply of oxygen Because it is colorless, odorless and tasteless, individuals exposed to toxic concentrations are unaware of its presence

However, the concentrations of CO commonly encountered in urban environments are usually only a fraction of those levels which cause asphyxiation Low-level CO exposure affects the central nervous system with typical behavioral changes including decreased time interval recognition, impairment of brightness, delayed reaction time to visual stimuli, decrease in drying performance and, at concentrations of 100 ppm, dizziness, headache, fatigue and loss of coordinatation

Cigarette smoke contains especially high levels

of CO (15,000 to 55,000 ppm) which bind to approximately 3 to 10% of a smoker’s hemoglobin The effects of these high levels would be extremely harmful if it were not for the intermittent nature of the exposure The inhalation of air between drags greatly reduces the toxic dose The major effect of CO in cigarette smoke appears to be to increase the risk of angina pectoris patients to myocardial infarcation and sudden death However, cigarette smoke contains many harmful substances and it is difficult to specifically assess the harmful effects of CO and its exact role in cardiovascular diseases

emitted air contaminant It is a product of the complete combustion of carbon in the

(2) previously

decomposition, weathering and combustion of organic matter Human and animal respiration

combustion of coal, oil and natural gas in both stationary and mobile sources is responsible

throughout the world Solid waste disposal and agricultural burning account for the remaining 10% Coke ovens and smelters emit

basis

The oceans absorb approximately

soluble in water Green plants also

use in photosynthesis The use of alternate sources of energy such as nuclear, solar or chemically derived energy is the preferred method to

Part 1 Pollutant Emissions (continued )

CO2 is not typically considered a pollutant in air pollution regulations, however, its role in the

heat up the earth’s surface by a phenomenon commonly called the “greenhouse effect.” This

“greenhouse effect” is caused primarily by water

absorbers of infrared radiation When radiation is absorbed by CO2 and water, it is reemitted in all directions with the net result being that part of the radiation returns to the earth’s surface and raises

levels have increased from about 290 to 322 ppm

25% of this increase has occurred in the past

have increased at a rate of approximately 0.7 ppm

levels could double by the year 2035a.d This doubling could result in the warming of surface temperatures by 2.4ºC in the midlatitudes, with a greater warming in the polar regions

Sulfur Oxides

a Sulfur Dioxide:

and taste can be detected in the concentration range of 0.3 to 0.1 ppm Above 3 ppm, it has a

(and sulfur trioxide, SO3) is due to the burning of

In order to reduce the levels of sulfuric acid aerosols in urban air, power plants are often built with tall smokestacks which

This reduces the local problem but increases the problem for areas

FIGURE 2 Comparison of Per Capita Carbon Dioxide emissions

Note(s): U.S per capita emissions data is not presented for 1990 or 1991 See section 10.1 for a discussion of

Sources(s): Marland, G., R.J Andres, and T.A Boden 1994 Global, regional and national CO 2 emissions, pp

9–88 In T.A Boden, D.P Kaiser, R.J Sepanski, and F.W Stoss (Eds.), Trends ’ 93: A Compendium

of Data on Global Change ORNL/CDIAC-65 Carbon Dioxide Information Analysis Center, Oak

Ridge National Laboratory, Oak Ridge, Tenn., U.S.A

Part 1 Pollutant Emissions (continued)

coal and crude oils for electric power and heating The sulfur content of refined petroleum is usually quite low At the high temperatures of combustion, the sulfur in these fuels is converted to SO2 by the reaction:

1 ppb In urban areas maximum concentrations vary from less than 0.1 to over 0.5 ppm SO2 itself is a lung irritant and is known to be harmful to people who suffer from respiratory disease However, it is the sulfuric acid aerosol formed from the

damaging health effects in urban areas The sulfuric acid aerosol is formed by the following reactions which in the atmosphere are photochemically and catalytically accelerated:

The sulfuric acid aerosols formed are usually less than 2 microns in diameter and can quite effectively penetrate the innermost passages

of the lung, known as the pulmonary region

CO in the blood Sulfuric acid aerosols irritate the fine vessels of the pulmonary region, causing them to swell and block the vessel passages Severe breathing impairment may occur The effect is cumulative, with older people suffering the most severe respiratory problems

spinach, turnip, beets, alfalfa and oats Trees such as the white pine, white birch and trembling aspen, as well as, ornamental plants such as gladiolus, tulip and sweet pea, can also be damaged

which are far from the source of the pollutant

The sulfuric acid aerosol is washed out in either rain or snowfall and increases the acidity of local waters downwind from the plant This condition is known as acid rain

to substitute low sulfur coal, sulfur free coals (produced by screening crushed coal) and other sulfur free fuels for high sulfur to low sulfur fuels This can be seen in urban areas where coal has largely been displaced by petroleum and natural gas An alternative approach is to

of the plant by using chemical scrubbers In the chemical scrubber, the stack gas is passed through a slurry of limestone (calcium

sulfite which can be collected and disposed of More commercially valuable abatement processes include catalytic oxidation to produce usable sulfuric acid and reaction with alkalized alumina which allows the recovery of usable sulfur

TABLE 8 Total National Emissions of Sulfur Dioxide 1940 through 1994 (thousand short tons)

PETROLEUM and RELATED

WASTE DISPOSAL AND

Note(s): Categories displayed below Tier 1 do not sum to Tier 1 totals because they are intended to show major contributors

1994 emission estimates are preliminary and will be updated in the next report

Tier 1 source categories and emissions are shaded

Part 1 Pollutant Emissions (continued )

known by its characteristic rotten egg odor

eruptions, geothermal wells and chemical

or bacteriological decomposition of mineral sulfates in springs and lakes In these natural occurances, other sulfur compounds are nearly

Anthropogenic sources include the combustion of coal, natural gas and oil The refining of petroleum products, coke production, sulfur recovery operations and the kraft process for producing chemical pulp from wood are all

The typical rotten egg odor can be detected at very low concentrations, 0.025 to 0.2 ppm, but at these concentrations it has little or no effect upon human health However, at higher concentrations,

human olfactory apparatus becomes paralyzed, effectively preventing any olfactory warning signal H2S is life threatening at 300 ppm since it causes pulmonary edema At 500 ppm, there is strong stimulation to the nervous system Above

1000 ppm, there is immediate collapse and respiratory paralysis

gas streams with a suitable absorbent and then remove the absorbed gas from the absorbent for disposal by burning or conversion to usable by-products Different types of scrubbers can be used such as spray towers, plate towers and venturi scrubbers

is subsequently removed from the atmosphere through precipitation and absorption by surfaces and vegetation

3 Nitrogen Compounds: There are five major

gaseous forms of nitrogen in the atmosphere:

atmosphere and counts for 78% of the

pollutants of the lower atmosphere and because

of their interconvertibility in photochemical

reactions, are usually collectively grouped as

source of any nitrogen oxide on a worldwide basis It is present in the atmosphere at an average concentration of 0.27 ppm It is quite inert in the lower atmosphere, but it can react with oxygen atoms that are available in the stratosphere to produce nitric oxide

a Nitrous Oxide:

relatively non-toxic gas Natural sources include anaerobic biological processes in soil and water, combustion processes and photochemical destruction of nitrogen compounds in the stratosphere On a worldwide basis, natural emissions of NO are estimated at approximately

sources include automobile exhaust, fossil fuel fired electric generating stations, industrial boilers, incinerators, and home space heaters

All of these sources are high temperature combustion processes which follow the reaction:

Background concentrations of NO are approximately 0.5 ppb In urban areas, one hour average concentrations of NO may reach 1 to 2 ppm Atmospheric levels of CO are related to the transportation and work cycle, with the highest

(continued )

Part 1 Pollutant Emissions (continued )

concentrations observed during the morning and evening rush hours Emissions of NO are also greater in the winter months since there is

an increase in the use of heating fuels

NO is a relatively non-irritating gas and is considered to pose no health threat at ambient levels It is rapidly oxidized to nitrogen dioxide, which has a much higher toxicity

TABLE 9 Total National Emissions of Nitrogen Oxides, 1940 through 1994 (thousand short tons)

Note(s): Categories displayed below Tier 1 do not sum to Tier 1 totals because they are intended to show major contributors

1994 emission estimates are preliminary and will be updated in the next report

Tier 1 source categories and emissions are shaded

Part 1 Pollutant Emissions (continued )

light yellowish orange at low concentrations and reddish brown at high concentrations It has a pungent, irritating odor It is relatively toxic and has a rapid oxidation rate which makes it highly

follows the reaction:

This reaction is slow at low atmospheric levels and accounts for about 25% of all NO conversion The major NO conversion processes are photochemical, involving hydrocarbons, ozone, aldehydes, carbon monoxide, and other compounds

approximately 0.5 ppb with one hour average concentrations in urban areas of 0.5 ppm Peak morning concentrations of NO are followed

produced by the chemical and photochemical oxidation of the NO Since the conversion of

photochemically oxidized to nitrates which are subsequently removed by precipitation, dry deposition and surface absorption

In motor vehicles, current methods for

retardation of spark timing, increasing the air/fuel ratio (i.e., less fuel to air), injecting water into the cylinders, decreasing the compression ratio, and recirculating exhaust gas All these methods reduce the combustion chamber temperature (which reduces

increasing the emissions of hydrocarbons and CO Catalytic convertors which reduce NO to elemental nitrogen (N2) can also be used The use of alternative fuels, such

as methyl and ethyl alcohol, which combust at a lower temperature than

emissions

For stationary sources, one abatement

fuel; emissions are highest from coal, intermediate with oil and lowest with natural gas For the numerous methods

of control see the article “Nitrogen Oxides” in this Encyclopedia

4 Photochemical Oxidants: Photochemical oxidants

are secondary pollutants which result from a

complex series of atmospheric actions involving

the section on nitrogen compounds) and, to a lesser

extent, peroxyacetylnitrate

reported of the photochemical oxidants It is a bluish gas that is 1.6 times heavier than oxygen and is normally found at elevated levels in the stratosphere where it functions to absorb harmful ultraviolet radiation Ground level ozone is one

of the major constituents of photochemical

“smog” which is a widespread, urban phenomenon It is formed when nitrogen dioxide absorbs ultraviolet light energy and dissociates into nitric oxide and an oxygen atom:

Abatement is achieved through the control

of hydrocarbons and nitrogen oxides as discussed in other sections of this chapter

Part 1 Pollutant Emissions (continued )

These oxygen atoms, for the most part, react with oxygen to form ozone:

In addition, the oxygen atoms can react with certain hydrocarbons to form free radical intermediates and various products such as peroxyacetylnitrate (PAN)

Since photochemical oxidants are secondary pollutants formed in the atmosphere as the result of primary pollutants reacting, their concentration in the atmosphere will vary proportionally to the amount of hydrocarbons and NO2 in the air and the intensity of sunlight

PAN is a very potent eye irritant in addition to being a strong lung irritant like O3 O3 is relatively insoluble in respiratory fluids and can be transported into the pulmonary system where it can damage the central airways and terminal pulmonary units such as the respiratory bronchioles and alveolar ducts

Exposure in excess of ambient levels affects lung function causing increased respiratory rates and decreased lung capacity These effects are more pronounced in smokers and during exercise Prolonged low-level exposure may result in decreased lung elasticity Studies

on micro-organisms, plants mutagenic, that is,

it can cause permanent, inheritable changes in genes Since mutagens and carcinogens appear

to be related, it is possible that O3 is also carcinogenic

TABLE 10 Summary of U.S Nitrous Oxide Emissions by Source Category, 1990 to 1994 Preliminary Estimates

(thousand short tons)

Note(s): Totals presented in this table may not equal the sum of the individual source categories due

to rounding

Source(s): Inventory of U.S Greenhouse Gas Emissions and Sinks, 1990–1994 Draft Report, U.S

Environmental Protection Agency September 1995

(continued )

TABLE 11 Ozone Levels Generated in Photoxidation* of various Hydrocarbons with

Part 1 Pollutant Emissions (continued )

Halides

a Chlorine:

a distinctive irritating odor The major anthropogenic sources of chlorine emissions include the chemical decomposition of chlorofluorocarbons (CFCs) used as a refrigerant and propellant in consumer goods, the liquifaction of chlorine cell gas, the loading and cleaning of tank cars, barges and cylinders, dechlorination of spent brine solutions and power or equipment failure Due to the high

by atmospheric reactions

The use of propellants which do not contain CFCs Industrial emissions can be controlled by the use of scrubbing systems, i.e., water scrubbers, alkali scrubbers and carbon tetrachloride scrubbers

Since chlorine has strong oxidizing and bleaching properties, it is extremely hazardous to all life forms, as well as corrosive to metals and other materials Chlorine atoms can destroy ozone