Air Pollution

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Air Pollution

• General

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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.

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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.

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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.

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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.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

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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.

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