Air Pollution

Air Pollution General

Definition Air pollution may be defined as the presence in the air (outdoor atmosphere) of one or more contaminants or combinations thereof in such quantities and of such durations as may be or tend to be injurious to human, animal or plant life, or property, or which unreasonably interferes with the comfortable enjoyment of life or property or conduct of business.

Air Pollutant It is a substance or effect dwelling temporarily or permanently in the air , which adversely alters the environment by interfering with the health, the comfort, or the food chain, or by interfering with the property values of people. A pollutant can be solid (large or sub-molecular), liquid or gas . It may originate from a natural or anthropogenic source (or both). It is estimated that anthropogenic sources have changed the composition of global air by less than 0.01%. However, it is widely accepted that even a small change can have a significant adverse effect on the climate, ecosystem and species on the planet. Examples of these are acid rain, ozone in the lower atmosphere, and photochemical smog.

Comp dry atmosph

ppmv: parts per million b

Gas Nitrogen (N2) Oxygen (O2)

V 7 2

N

Pollutant

Carbon M

Index Value

D

Health Effects of Nitrogen Oxides • Short-term exposure at concentrations greater than 3 parts per million (ppm) can measurably decrease lung function. • Concentrations less than 3 ppm can irritate lungs. • Concentrations as low as 0.1 ppm cause lung irritation and measurable decreases in lung function in asthmatics. • Long-term lower level exposures can destroy lung tissue, leading to emphysema. • Children may also be especially sensitive to the effects of nitrogen oxides.

Other Effects • Seriously injure vegetation at certain concentrations. Effects include: – Bleaching or killing plant tissue. – Causing leaves to fall. – Reducing growth rate.

• Deteriorate fabrics and fade dyes. • Corrode metals (due to nitrate salts formed from nitrogen oxides). • Reduce visibility.

Other Effects (Continued) • Oxides of nitrogen, in the presence of sunlight, can also react with hydrocarbons, forming photochemical oxidants or smog. • Also, NOx is a precursor to acidic precipitation, which may affect both terrestrial and aquatic ecosystems.

Sulfur Dioxide Ninety-five percent of pollution related sulfur oxide emissions are in the form of sulfur dioxide (SO2), a heavy, colorless gas with an odor like a struck match. This gas combines easily with water vapor, forming aerosols of sulfurous acid (H2SO3), a colorless, mildly corrosive liquid. This liquid may then combine with oxygen in the air, forming the even more irritating and corrosive sulfuric acid (H2SO4).

Other sulfur-containing compounds • Hydrogen sulfide (H2S) gas - rotten eggs. • Mercaptans - skunk spray or decayed garbage. (Added in trace amounts to natural gas, providing a leak-detecting warning odor.) Note: The amount of SO2 released from coal fired power plants depends on the sulfur content of coal, normally 0.7% to 2% by weight. High sulfur coal sometimes contains as much as 6% sulfur by weight. In India, sulfur content is quite low.

Health Effects of Sulfur Oxides • Sulfur dioxide not only has a bad odor, it can irritate the respiratory system. • Exposure to high concentrations for short periods of time can constrict the bronchi and increase mucous flow, making breathing difficult. • Children, the elderly, those with chronic lung disease, and asthmatics are especially susceptible to these effects.

Sulfur dioxide can also: • Immediately irritate the lung and throat at concentrations greater than 6 parts per million (ppm) in many people. • Impair the respiratory system's defenses against foreign particles and bacteria, when exposed to concentrations less than 6 ppm for longer time periods. • Apparently enhance the harmful effects of ozone. (Combinations of the two gases at concentrations occasionally found in the ambient air appear to increase airway resistance to breathing.)

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Sulfur dioxide tends to have more toxic effects when acidic pollutants, liquid or solid aerosols, and particulates are also present. (In the past, thousands of excess deaths occurred in areas where SO2 concentrations exceeded 1 ppm for a few days and other pollutants were also high.) Effects are more pronounced among mouth breathers, e.g., people who are exercising or who have head colds.

These effects include: • Health problems, such as episodes of bronchitis requiring hospitalization associated with lower-level acid concentrations. • Self-reported respiratory conditions, such as chronic cough and difficult breathing, associated with acid aerosol concentrations. (Asthmatic individuals are especially susceptible to these effects. The elderly and those with chronic respiratory conditions may also be affected at lower concentrations than the general population.) • Increased respiratory tract infections, associated with longer term, lower-level exposures to SO2 and acid aerosols. • Subjective symptoms, such as headaches and nausea, in the absence of pathological abnormalities, due to long-term exposure.

Sulfur oxides Effects on Plants • Sulfur dioxide easily injures many plant species and varieties, both native and cultivated. Some of the most sensitive plants include various commercially valuable pines, legumes, red and black oaks, white ash, alfalfa and blackberry. The effects include: • Visible injury to the most sensitive plants at exposures as low as 0.12 ppm for 8 hours. • Visible injury to many other plant types of intermediate sensitivity at exposures of 0.30 ppm for 8 hours. • Positive benefits from low levels, in a very few species growing on sulfur deficient soils.

Other Effects • Increases in sulfur dioxide concentrations accelerate the corrosion of metals, probably through the formation of acids. (SO2 is a major precursor to acidic deposition.) Sulfur oxides may also damage stone and masonry, paint, various fibers, paper, leather, and electrical components. • Increased SO2 also contributes to impaired visibility. Particulate sulfate, much of which is derived from sulfur dioxide emissions, is a major component of the complex total suspended particulate mixture.

Health Effects of Ozone • Ozone acts as a powerful respiratory irritant at the levels frequently found in most of the nation's urban areas during summer months. • Ozone exposure may lead to: – Shortness of breath. – Chest pain when inhaling deeply. – Wheezing and coughing.

Long-term, repeated exposure to high levels of ozone may lead to large reductions in lung function, inflammation of the lung lining, and increased respiratory discomfort.