Air pollution is nothing new. Ever since the discovery of fire, less-than-desirable substances have been vented into the air. One of the first air-pollution regulations dates back to the fourteenth century, when King Edward I banned the burning of sea coal in lime kilns. U.S. air-pollution regulations have their roots in British Common Law. But regardless of those efforts, air pollution continues to be a serious local and world-wide problem. Pollution is the pressure within the air of one or more substances that are harmful to human health, welfare, animal or plant life, or property. In the past with air pollution we included mainly the outdoor pollutants, although in recent years this is not the case. Today we separate pollutants in to two categories. Primary pollutants, because they come directly from various sources, and secondary which are by-products of chemical interactions of the primary pollutants within the atmosphere.
Although air pollution might be thought of as unwanted gases in the atmosphere, two of five primary pollutants are really solid substances called particulates. Soot has always been a sure indicator of a polluted atmosphere, but other than soiling and a negative psychological effect, soot can’t settle into the lungs and cause serious diseases. Thick ,black smoke coming out of a stack is that what we think causes the pollution, but what really creates the damage is what we can’t see. Particles like this are called suspended particles. They come from many incomplete burning and can consist a variety of substances. The most harmful type of particulate is so small that that it is microscopic. All the particulates are harmful for several reasons. When inhaled, they can damage the interior of the lung; they can also be poisonous. Sometimes gases will glue to their surfaces and in a process called adsorption they can reach the lungs. All these particles are mainly products of combustion. The major sources include industrial processes, power plants that are both coal and oil-fired, residential heating, and transportation. But coal burning is the greatest source.
Table 1 below shows estimates of U.S. particulate emissions from various sources.
National U.S. Emissions Estimates-1990
(Million metric tons/year)
SOURCEPARTICULATESSULFUR OXIDESCARBON MONOXIDES
Stationary fuel combustion
Solid waste disposal0.301.7
Other burning 0.100.6
Misc. Organic solvents000
Only 13% of the total is generated by transportation. Industrial sources account for nearly three times as much as 37%. Fires account for just about as much particulate emissions as transportation. That amount is matched by combustion from sources, which include the generation of all heat and electricity.
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When coal was the main source to generate energy, power plants and homes accounted for much greater contribution. The switch to oil and nuclear power has lowered those concentrations, but it hasn’t been without its own problems. In addition to health-related problems, particles can damage materials through corrosion and erosion, as well as soiling. Particles can also impact the weather, through changes in visibility, and even in enhancing precipitation. Studies around major urban areas show an increase in precipitation and in thunderstorms with hail downwind from downtown areas. The weather modification is localizes but definite, and may be related to an increase in the large condensation nuclei that the particles provide.
Lead particulates are brutal primary pollutant. Their presence in the atmosphere has diminished sharply during the past 29 years. Since 1975, the concentration of lead has decreased by more than 90%, which can be directly linked to the elimination of lead from gasoline. The following table shows that huge drop.
Another primary group of pollutants consists of the surfur oxides(Sox), and the major contributor is SO2, a sulfur dioxide. This is generated whenever sulfur is burned, most often where fuel with a high sulfur content is used. Coal can have very high sulfur concentrations, as can some oil. Overall, coal and oil are the major sources for sulfur oxide pollution. The vast majority of this type of air pollution comes from generation of heat and electricity. These stationary sources account about 80% of all sulfur oxides. Transportation’s contribution is minor, about 5%. The rest comes from industry.
Sulfur dioxides cause damage to vegetation and material. Plants lose their chlorophyll which is the plants food factory. But the most damage appears when sulfur oxides combine with other substances. Because of its solubility, sulfur dioxide becomes a major contributor to acid deposition. Leaves are bleached and show damage. Tree growth is stunted and vegetation dies. Damage to vegetation occurs at concentrations lower than what is harmful to people.
Carbon monoxide (CO)
Carbon monoxide is colorless, odorless , tasteless,non-corrosive, highly poisonous gas of about the same density as that of air. It is very flammable, burns in air with bright blue flame.
Its melting point is at-205.0 C and boiling point is at -191.5 C. There is no way to know if it is around, except we may no feel so well. When a fire burns in an enclosed space, oxygen is gradually depleted and carbon dioxide is increased. The changes in both of the these gases increasingly cause the combustion process to change from one of complete combustion to one of incomplete combustion, resulting in the release of increasing amounts of CO. Thus, even a perfectly designed and adjusted furnace or water heater (or any kind of combustion device) will eventually begin producing toxic/lethal amounts of CO if it operates in a closed space and/or where insufficient fresh air is available. Table three lists some of the effects of CO to humans.
CO concentration in Parts Per Million or as as percentage of air
% of CO in airInhalation time and toxic symptoms developed
0.0001%Normal background levels
0.0009%Maximum allowable concentration short term in living area
0.0025%Maximum exposure TWA (Time Weighted Average)in the workplace.
0.005%Maximum exposure allowed (OSHA) in the workplace.
0.02%Mild headache, fatigue, nausea and dizziness.
0.04% Serious headache – other symptoms intensify. Life threatening after 3 hours.
0.08%Dizziness, nausea and convulsions Dead within 2 to 3 hours
0.16%Headache, dizziness and nausea. Death within 1 – 2 hours.
0.32% Headache, dizziness and nausea. Death within 1 hour.
0.64% Headache, dizziness and nausea. Death within 25 – 30 minutes.
1.28%Death within 1 – 3 minutes.
Control of Air Pollution
The early air pollution laws were passed within small communities and concerned the color and density of the smoke that comes out from the stacks. They first appeared in Chicago and Cincinnati and later on began to show up also in other communities. A special chart determined the level of smoke. The chart showed smoke with different shades of gray and black. At a particular level violations would be set. No national air pollution legislation appeared until the 50’s. The first federal legislation appeared in 1955 when the Air Pollution Control Act was passed. In 1965 the Motor Vehicle Air Pollution Act was passed, establishing national automobile emission regulations for the first time. Then the Air Quality Act of 1967 was passed, providing funds for additional federal research and designating air quality control regions to help establish air pollution criteria. Another goal of this act was to research the cost -effectiveness relation of available engineering control techniques.
Later, during the 70’s National Air Quality Standards were set for the major pollutants. Primary standards were set for health, with secondary standards for vegetation and general environmental welfare. Penalties as high as $25.000 per day and a year in prison were authorized for industries that failed to meet the regulations. Automobiles emission standards were set.
Additional adjustments to the 70’s regulation came along in 1990. Each revised some of the older regulations. Some of which proved to be very strict and unattainable. Overall each new version strengthened and broadened the previous version.
Change of Fuels
The most direct method of pollution control involves changing the fuel. High sulfur coal was responsible for the greatest smog outbreaks of the early twentieth century. Sulfur oxides and particulates reached dangerous levels in many areas, especially in industrial areas. During the 1960s and 1970s a switch to low sulfur oil, natural gas and nuclear power brought the levels of that kind of smog down to relatively low concentrations. Although complex control devices are available, the fuel switch in power plants accounts for most of the improvement.
Of course change can introduce new problems. Natural gas combustion can increase the levels of nitrogen oxides, and nuclear power leads to new problems. Although we know that changing the fuel is not going to stop air pollution, but only reduce it, we are trying to find substitutes which will result to higher efficiency with lower emissions.
Smokestack emissions control
Particles come in assorted sizes and shapes, and a number of control systems have been designed for removing them from the stream of gases that go up the smokestack. The type of device depends on the type of particle and size. Soluble particles can be drained out of an effluent by washing with scrubbers. Sometimes, the particles will simply settle out before being emitted, in what are called settling chambers. Sometimes the gas is pushed through filters of cloth collectors.
Other devices are even more sophisticated. The gas might be whipped around in a circular path, so that centrifugal force separates the particles. Those devices are called centrifugal separators.
An other type of device is the electrostatic precipitators. This device delivers an electrical charge to the particles. An opposite charge is placed on a metal plate, and, because opposites attract, the particles will collect on the plate. Then the plate is cleaned off.
Of course all these devices remove the particles, but once the particles have been removed the problem becomes how to dispose of the sludge. The toxicity of the material and its impact on the environment become new considerations.
Internal Combustion Engine
One of the greatest polluters on Earth is the automobile. Volatile organic compounds, nitrogen oxides and carbon monoxides are the major pollutants that come out of a car’s exhaust. If the air-fuel mix is lean, there is a good deal of air and less fuel. The combustion temperature will be relatively high, which will favor the complete burning of the gases, and hydrocarbons will convert to water vapor and carbon dioxides. However if the mixture is not so lean, but richer with more fuel the temperature will be lower. Instead of completely burning the hydrocarbons with the oxygen, you end up with unburned hydrocarbons and carbon monoxide instead of carbon dioxide.
So the conclusion here should be to have a very lean mix of air and fuel. The problem with that is the high temperature of efficient combustion. The oxygen and nitrogen in the air combine, resulting in a lot of nitrogen oxides. You may reduce the carbon-monoxide pollution in having a transformation to carbon dioxide, but on the other hand, you ‘re going to end up with more nitrogen oxides. Any hydrocarbons that don’t burn can now combine with nitrogen oxides under strong sunlight to deliver photochemical smog. That is one of the major dilemmas of the internal combustion engine.
There are control devices that can eliminate some of the pollutants from the internal combustion engine, most notably the catalytic converter. It raises the temperature of gases that will be exhausted, so there will be further burning of the hydrocarbons. As a result we end with more water vapor and carbon monoxide.
Once exposure levels have been set, steps can be undertaken to reduce exposure to air pollution. These can be accomplished by regulation of man-made pollution through legislation. Many countries have set controls on pollution emissions for transportation vehicles and industry. This is usually done to through a variety of coordinating agencies which monitor the air and the environment.
A significant problem that has to deal with all the changes is the cost. A company that has to install million dollar electrostatic precipitators may have a serious economic problem with pollution control But in general, the overall costs of not controlling air pollution are far greater that the collective costs of pollution control. The problem of course is the concentration of costs within specific industries. Creative techniques of distributing that cost could go a very long way in maintaining our standard of living while having good and healthy air to breath.
Only through the efforts of scientists, business leaders, legislators, and individuals can we reduce the amount of air pollution on the planet. This challenge must be met by all of us in order to assure that a healthy environment will exist for us. In our businesses, communities and as individuals, we can make meaningful reductions of air pollutants and gases. In many cases, one action will reduce both air pollutant and gas emissions. Home energy improvements, ride-sharing, alternative transportation, and tree planting programs are just some of the community-based solutions to reducing air pollutant and gas emissions.
A typical automobile will emit more than 40% of its own weight in common air pollutants in one year, and four times its weight in greenhouse gases. So for those necessary trips by car, make sure that it is a well-tuned, energy-efficient model! Also, avoid idling our engines, as restarting an engine uses less fuel than ten seconds of idling.
Other actions we can take at home and at work include:
Turn off energy-using equipment (lights, computers, or any machinery) when it is not in use. Make your home more energy efficient through improved insulation, caulking and weather-stripping. Recycle, since it takes much less energy to create a new product using recycled materials than using raw materials. Compost kitchen scraps and yard waste, because organic waste in landfills creates gases that contribute to climate change. Plant trees around our home. It’s a natural way to insulate, and trees help clean the air and slow climate change.