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To present an overview of problems in air pollution.
Air pollution is one of the most important sources of chemical hazards, especially in highly urbanized and industrialized societies. In the United States, three-quarter of the population is densely packed into 200 urban centers. These days we read and hear about the problems caused by the so called "acid rains". More than 200 million tons of toxic material are released into the air above the United States each year, about 1 ton per person. About 60% of the air pollutants come from approximately 100 million internal combustion engines, the other 40% from sources such as factories, power plants, municipal dumps and private incinerators.
Most Scientist assume "air" to be a mixture of the gases listed in Table I.
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Air pollutants may be defined as those substances which exist in such concentrations as to cause an unwanted effect. These pollutants can be natural (such as smoke from forest fires) and can be in the form of gases or particulates. (liquid or solid particles larger than 1 micron).
In the context of air pollution control, gaseous pollutants include substances that are gases are normal temperature and pressure as well as vapors of substances that are liquid or solid at normal temperature and pressure. Among the gaseous pollutants of greatest importance in terms of present knowledge are carbon monoxide, hydrocarbons, hydrogen sulfide, nitrogen oxides, ozone and other oxidants and sulfur oxides. carbon dioxide should be added to this list because of its potential effect on climate.
Particulate pollutants are classified as follows:
Solid particles which are:
A solid particle, frequently a metallic oxide, formed by the condensation of vapors by sublimation, distillation, calcination or chemical reaction processes. Examples of fumes are zinc and lead oxide resulting from the condensation and oxidation of metal volatilized in a high-temperature process. The particles in fumes are quite small, with diameters from 0.03 microns.
A liquid particle formed by the condensation of a vapor and perhaps by chemical reaction. An illustration of this process is the formation of sulfuric acid mist:
- SO (gas) 22 C SO (liquid)- SO (liquid) + H 0 H S0
- Sulfur trioxide gas becomes a liquid since its dew point is 22 C and SO particles are hydroscopic. Mists typically range from 0.5 to 3.0 microns in diameter.
Solid particles formed as a result of incomplete combustion of carbonaceous materials. While hydrocarbons, organic acids, sulfur oxides, and nitrogen oxides are also produced in combustion processes, only the solid particles resulting from the incomplete combustion of carbonaceous materials are smoke. Smoke particles have diameters ranging from 0.05 to approximately 1 micron.
A liquid particle formed by the atomization of a parent liquid.
The key to the realm of air pollution control is the effect on the health and welfare of people, property and environment. The air pollution loss syndrome is depicted in Table 2.
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Much of our knowledge of the effects of air pollution on people comes from the study of acute air pollution episodes. The three most famous episodes occurred in the Meuse Valley of Belgium, in Donora, Pennsylvania, and in London, England. Some of the essential features of these episodes are in Table 3. Features common to these episodes are of particular interest. In all three the illness appeared to be chemical irritation of the respiratory tract. The weather circumstances were also similar in that a high pressure system with an inversion layer was present.
In all three episodes, the pollutants affected a specific segment of the public those individuals already suffering from diseases of the cardiorespiratory system. Another observation of great importance is that upon investigation it was not possible to blame the adverse effects upon any one pollutant. Today, after many years of study it is thought that the health problems during the Donora, Meuse and London episodes were attributed to the combined action of a particulate matter (solid or liquid particle) and sulfur dioxide, a gas.
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Effects on human health may be acute due to short high level exposures-increased mortality among the elderly and the persons ill with chronic diseases (like bronchitis asthma and heart attacks). Air pollutants in asthma patients have been shown to increase levels of globulins in their blood.
Long-term effects of low-level exposures to polluted air may lead to chronic disease such as cancerous growths and genetic mutations; general body defense mechanisms are impaired, and physiologic function interfered with. Lung cancer has been correlated with air pollution as well as with certain other factors such as smoking habits.
The mechanism by which an animal can become affected by air pollution is entirely different from that of humans. With animals, we are concerned with a two-step process: the accumulation of airborne contaminants in vegetation and forage which serves as cattle food and the subsequent effect of the ingested contaminated herbage on the animal. Air pollutants that present a hazard to livestock are those which are taken up by vegetation and react in the plant to form toxic substances.
Table 4 contains a list of the major pollutants with respect to animals. Arsenic and lead have been pollutants which affected animals in the past and are no longer of importance because emissions have been controlled. As the effects of some pollutants are reduced because of air pollution control, new pollutants take the place of the old.
The report of organic phosphates (nerve gas) killing 6200 sheep is a rarity (Chemical and Engineering News, 1968). Although this type of air pollution episode may never occur again, it clearly points out the result of an accidental emission of a dangerous chemical on the living objects in the area. Findings of high mercury levels in tuna and swordfish have shocked the public and complacent governmental agencies.
Some 75% of phosphate are in the United States is in Polk and Hillsborough Counties in Florida. Fluoride emissions from industries producing phosphate fertilizers or phosphate derivatives are detrimental to the growth of cattle, citrus, and commercial row crops. The affected area in Florida covers some 600 sq miles; the cattle population decrease by 30,00 head between 1953 and 1960 (Special Subcommittee Hearings on Air and Water Pollution, 1964). Although much remains to be done to reduce the fluoride emissions in Florida, research has diagnosed fluorosis in cattle and has published safe ingestion levels (Greenwood et al., 1964). No adverse effects on cattle were found at 15-30 ppm fluorine and chronic fluorosis was noted at 60-109 ppm; acute fluorosis occurred when the fluoride content of forage exceeded 250 ppm fluorine in the moisture-free diet.
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Vegetation damage is not a major problem in urban areas; vegetation damage normally results from emissions from and industrial plant located away from crowded areas. Major pollutants affecting vegetation are presented in Table No. 5.
Sulfur Usually
interveinal necrotic blotches bleached dioxide white to
straw color. Spongy parenchymal cells initially affected.
Oldest leaves less resistant. Insect, injury, winter and
drought conditions may show similar markings. Alfalfa,
barley, cotton, etc. sensitive at 0.25-0.3 ppm; plant
cells have capacity to detoxify SO2 or SO3 at a definite
rate. Sulfur levels in leaf varies from
0.1-0.6%
(dry). Oxidant Silvered
or bronzed appearance usually on underside of smog gases
leaf, Initial collapse in spongy parenchyma. Youngest
leaves react first, insect and "sun scald" may show
similar markings. Ozone Upper
surface stipple or flecking with small irregular
collapsed areas bleached white to straw color. Initial
effect in palisade layer, Tomato, tobacco, bean sensitive
at 0.2 ppm. Nitrogen Brown
margins and brown to black spots on
leaves. oxides Mature
and middle-aged leaves most sensitive. Fluorides Pinto
beans symptoms at 3 ppm. Necrotic "burned" tip or on
edges of leaf. Narrow brown-red band separates necrotic
from green tissue. Fungal diseases, wind and high
temperatures, drought and cold temperatures may show
similar markings. Ethylene
Epinasty and/or abcission without markings. Young leaves
recover rapidly; older leaves do not
recover fully. Water
stress may produce similar effects. Orchids sensitive at
0.005 ppm; tomatoes sensitive at 0.1 ppm Acetylene,
olefinic hydrocarbons and carbomonoxide produce similar
effects at higher concentrations. ------------------------------------------------------------------
Pollutant
Leaf markings, injury levels
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Air pollution effects on inert materials depend on the type and concentration of the pollutant and the type and time exposed of the materials involved. Some of these effects are:
Air pollution effects on inert materials depend on the type and concentration of the pollutant and the type and time exposed of the materials involved. Some of these effects are:
In order to achieve the standards set by 1970 Federal Clean Air Act in an orderly manner, the following tasks were undertaken:
In order to develop an adequate control strategy, considerable information is necessary regarding air quality and air pollutant emissions.
Ideally, control strategy development evolves as a series of interrelated efforts:
Regulations assume many forms - all aimed at limiting the amount of pollutants being emitted into the atmosphere.
Control techniques also assume many forms such as fuel switching, prohibition of certain practices such as open burning, process modifications, reduction of vehicle miles or improved traffic flow and installation of control devices. The type of air pollution control device depends on the pollutant to be captured, the process involved, and the regulations to be met.
Mechanically collectors are usually only used as per-cleaners, since their efficiency on small particles is low. Wet collectors come in many forms and are used to collect gases and particulates. Baghouses are normally thought of as having the highest efficiency for particulates. Electrostatic precipitators are also considered as a high efficiency control device. Afterburners are often used for gas (CO) and vapor (hydrocarbons) carbons control. Many control systems employ a combination of control and gas conditioning devices. Meteorology also plays a significant role in air pollution control activities. Inversions and stagnant air masses cause abnormal accumulation of pollutants. If you consider just a long vertical column of the atmosphere, you can reduce the atmospheric pressure is the weight exerted on a parcel of air by the column above it. Therefore, pressure decreases as altitude increases. This one reason smoke rises - it is actually being pushed from a high pressure area to a lower pressure. Another reason smoke rises is temperature. Hot air is lighter than cold air. Therefore, pollutants emitted at ground level where temperature is normally higher than it is at elevated altitudes tend to rise. However, an inversion reverses this normally temperature profile of the atmosphere and actually "traps" the pollutants.
InversionAloft
Surface
Inversion
Increasing T
(Normal -54° F/1,000 ft.)
Horizontal air movement also effects pollution levels by increasing or decreasing the diffusion of pollutants.
In order to develop additional strategies, we must better understand the causes of the violations and the relative contributions of various sources.
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