Air Pollution

• Sources of Air Pollution

Air pollution can be arised from air, forest and plants or human activities. Incomplete combustion, burning of oil and fat, use of gasoline and diesel fuel, use of coal or oil in power plants, mining, nuclear weapon development etc. are examples of human activities that cause air pollution.

Recently, more attention is focused on the indoor air pollutants such as formaldehyde from building materials. Consumer products also produce volatile organics such as benzene. However, the most serious problem is the exposure of non-smokers to environmental tobacco smoke(ETS) and second-hand smoke.

• Dispersion and Transport of Air Pollutants

Cigarette smoking creates pollutants near the point of release. Concentration and distribution of pollutants in workplaces depends on:
--- level of airbourne materials;
--- source of pollutants;
--- size of particles and;
--- ventilation.
Filters and chemical analyzers can be used to collect and monitored air pollutants.

For air pollutants farther away from the source, dispersion depends on how and where they are emitted. The pattern of regional and global dispersion and transport is influenced by the nature of the surroundings, meteorology and chemistry of the released materials, for example, a chemically stable compound will travel farther than a higher reactive compound.

Air pollutants like fluoride and lead usually deposit on forage or soil. Resuspension of soil lead in higher contaminated area increase the concentraton of lead in air. And deposition of acids in air may reduce the pH of soil and ground water. Although these ecological effects are very large, they are often overrided by the concern of the direct human health.

• Intake of Air Pollutants by People
The concentration of air pollutants determines its impact on human. Glass fibers deposit on skin causing skin irritation. Ozone gases cause eye irritation.

However, most concerns related to pollutants being inhaled and deposited in the respiratory tract. The quantity of deposit depends on:
--- quantity in the air;
--- physical and chemically properties and ;
--- individual breathing characteristics, i.e. an exercise individual inhales more than a sedentary one.
Depending on the chemical properties of the pollutants, it can be deposited on all parts of the respiratory tract. A highly reactive gas, such as formaldehyde, will deposit in the naval cavity while a less reactive gas, such as the Ozone, will deposite in the airway. A non-reactive gas, such as O2, CO, will reach the alveoli and move into the blood of the capillaries. Through the blood, some will reach the liver, bone marrow and othe organs.

The deposition of inhaled particles are strongly affected by their size and shape. The means of deposit include diffusion, impaction, sediment and interception. Particles and fibers can be blown out, moved to the mouth and be swallowed. Those deposit in larynx may be cleared by cilia in the mucous membrane. But most are `eaten' by macrophages which carry them through the airway to the lung. Some may move within the lung to the pheura on the peripheral surfaces.

• Health Responses of the Respiratory Tract to the Air Pollutants

As a result of molecular, biochemical, structural and functional alternations in our body, health responses are very complex.

Some air pollutants enter the respiratory tract but have effects elsewhere. An examples will be a reduction in cardiac or nervous tissue function due to the binding of carbon monoxide to hemoglobin in blood.

Air pollutants can also cause inflammation, i.e. kill body cells or their function temporarily or permanently. Rhinitis will result if it occurs in nose; bronchitis in bronchi and pneumonitis in pulmonary region. If inflammation continued in the alveolar portions of the lung, not enough oxygen is transported into the bloodstream and emphysema will be resulted.

Continued cell injury can alter cell type. For example, ciliated cells change to squamous epithelium will cause an uncontrollable growth of cells and destruction of adjacent normal tissue by compression and invasion and finally causes cancer. Cigarette smoking is the best known cause of lung cancer.

Studies using animal cells can indicate the ability of a new materials to cause mutation. However, questions arise whether these results can be applied to human.

• Regulations of Air Pollutants

In U.S., air pollutants are regulated by:
1. OSHA (Occupational Health and Safety Adminstration)-- sets workplace exposure limits and draw heavily on threhold limit values(TLC) for compound set by American Conference of Governmental Indoustrial Hygienists(ACGIH);
2. MSHA (Mine Safety and Health Administration)-- sets limits for miners to dust;
3. EPA (Environmental Protection Agency)-- regulates environmental esposures to air pollutants under the Clean Air Act(1990) which
   -- set limits on air pollutant to protect health in sensitive populations by using human data from epidemiological studies. The current standard of ozone pollutants is 120 parts per billion.
   -- set standard based on welfare considerations such as damage to crops or buildings.
   The initial phase is technological-based by using the maximum achievable control technology(MACT) within a specified period of time. Risk potecy will be estimated quantitatively in the second phase and decisions will be made on whether further controls are needed.

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