Visualizing Environmental Science

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Summary 213

air pollutant in the lower atmosphere (troposphere) but

an essential part of the stratosphere. Tropospheric ozone

reduces visibility, causes health problems, stresses plants,

and is associated with global warming. Some air pollutants are

called air toxics, or hazardous air pollutants, because they

are potentially harmful and may pose long-term health risks to

people who are exposed to them; chlorine, lead, hydrochloric

acid, formaldehyde, radioactive substances, and fluorides

are examples. Air pollutants come from transportation, fuel

combustion, industrial processes, and other sources.

Summary

1

The Atmosphere 192

1. Oxygen (21 percent) and nitrogen (78 percent) are the main
   gases in the atmosphere, the gaseous envelope surrounding
   Earth. Argon, carbon dioxide, other gases, water vapor, and
   trace amounts of various air pollutants are also present.


2. The troposphere, the layer of atmosphere closest to Earth’s
   surface, extends to a height of approximately 12 km (7.5 mi).
   Temperature decreases with increasing altitude, and weather
   occurs in the troposphere. In the stratosphere, there is a
   steady wind but no turbulence. The stratosphere contains an
   ozone layer that absorbs much of the sun’s UV radiation. The
   mesosphere, directly above the stratosphere, has the lowest
   temperatures in the atmosphere. The thermosphere has
   steadily rising temperatures and gases that absorb x-rays and
   short-wave UV radiation. The thermosphere reflects outgoing
   radio waves back toward Earth without the aid of satellites.


3. The Coriolis effect is the tendency of moving air or water to be
   deflected from its path and swerve to the right in the Northern
   Hemisphere and to the left in the Southern Hemisphere.

2

Types and Sources of Air Pollution 196

1. Air pollution consists of various chemicals (gases, liquids,
   or solids) present in the atmosphere in high enough levels
   to harm humans, other organisms, or materials. Primary air
   pollutants are harmful chemicals that enter the atmosphere
   directly due to either human activities or natural processes;
   examples include carbon oxides, nitrogen oxides, sulfur
   dioxide, particulate matter, and hydrocarbons. Secondary air
   pollutants are harmful chemicals that form in the atmosphere
   when primary air pollutants react chemically with each other
   or with natural components of the atmosphere; ozone and
   sulfur trioxide are examples.


2. Particulate matter—solid particles and liquid droplets
   suspended in the atmosphere—corrodes metals, erodes
   buildings, soils fabrics, and can damage the lungs. Nitrogen
   oxides are gases associated with photochemical smog,
   acid deposition, global warming, and stratospheric ozone
   depletion; they also corrode metals and fade textiles. Sulfur
   oxides are gases associated with acid deposition; they
   corrode metals and damage stone and other materials.
   Carbon oxides include the gases carbon monoxide, which
   is poisonous, and carbon dioxide, which is linked to global
   warming. Hydrocarbons are solids, liquids, or gases
   associated with photochemical smog and global warming;
   some are dangerous to human health. Ozone is a secondary

✓✓THE PLANNER

3

Effects of Air Pollution 201

1. Exposure to low levels of air pollutants irritates the eyes
   and causes inflammation of the respiratory tract. Many
   air pollutants suppress the immune system, increasing
   susceptibility to infection. Exposure to air pollution during
   respiratory illnesses may result in the development of chronic
   respiratory diseases, such as emphysema and chronic
   bronchitis.


2. Industrial smog refers to smoke pollution. Photochemical
   smog is a brownish-orange haze formed by chemical
   reactions involving sunlight, nitrogen oxides, and
   hydrocarbons. Ozone is a principal component of
   photochemical smog. A temperature inversion is a layer of
   cold air temporarily trapped near the ground by a warmer
   upper layer; during a temperature inversion, polluting
   gases and particulate matter remain trapped in high
   concentrations close to the ground. An urban heat island is
   local heat buildup in an area of high population. Urban heat
   islands affect local air currents and weather conditions and
   contribute to the buildup of pollutants, especially particulate
   matter, in the form of a dust dome, a dome of heated air that
   surrounds an urban area and contains a lot of air pollution.