Air Pollution

Risk Assessment

  1. What is the process of risk assessment?

  2. Why is it important in toxicology?

  3. What is the importance of the threshold effect of environmental toxins?

  4. What is the process of risk assessment in toxicology and how can it be used to evaluate the risk to human health and life?

  5. What controversial issues can develop with the use of risk assessment?

  6. What is the Precautionary Principle and how does it apply to environmental health?

Characteristics of the Atmosphere

  • The atmosphere is made up of major gases, each with its own relative abundance.

  • The layers of the atmosphere are based on temperature gradients and include the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

  • Global wind patterns primarily result from the most intense solar radiation arriving at the equator, resulting in density differences and the Coriolis effect.

    1. What gases are used and expelled by photosynthesis and respiration?

    2. What are the characteristics of Earth's atmosphere?

    3. How does the atmosphere moderate Earth's temperature?

    4. What are the two major atmospheric gases (in the troposphere) and what roles do they play?

    5. Why does more solar radiation of all wavelengths come into the exosphere than reaches Earth's surface?

Air Pollution and Sources

  • Coal combustion releases air pollutants including carbon dioxide, sulfur dioxide, toxic metals, and particulates.

  • The combustion of fossil fuels releases nitrogen oxides into the atmosphere. They lead to the production of ozone, formation of photochemical smog, and convert to nitric acid in the atmosphere, causing acid rain. Other pollutants produced by fossil fuel combustion include carbon monoxide, hydrocarbons, and particulate matter.

  • Air quality can be affected through the release of sulfur dioxide during the burning of fossil fuels, mainly diesel fuels.

  • Through the Clean Air Act, the Environmental Protection Agency (EPA) regulated the use of lead, particularly in fuels, which dramatically decreased the amount of lead in the atmosphere.

  • Air pollutants can be primary or secondary pollutants.

    1. How are primary and secondary pollutants different?

    2. What are the primary pollutants?

    3. What are the secondary pollutants?

  • Photochemical smog is formed when nitrogen oxides and volatile organic hydrocarbons react with heat and sunlight to produce a variety of pollutants.

  • Many environmental factors affect the formation of photochemical smog.

  • Photochemical smog often forms in urban areas because of the large number of motor vehicles there.

    1. How does photochemical smog differ from other types of air pollution?

  • Nitrogen oxide is produced early in the day. Ozone concentrations peak in the afternoon and are higher in the summer because ozone is produced by chemical reactions between oxygen and sunlight.

  • Volatile Organic Compounds (VOCs), such as formaldehyde and gasoline, evaporate or sublimate at room temperature. Trees are a natural source of VOCs.

    1. What is the effect of an increase in particulates on the environment?

    2. What are the effects of ground level ozone?

Thermal Inversion

  • During a thermal inversion, the normal temperature gradient in the atmosphere is altered as the air temperature at the Earth’s surface is cooler than the air at higher altitudes.

  • Thermal inversion traps pollution close to the ground, especially smog and particulates.

Reduction of Air Pollutants

  • Methods to reduce air pollutants include regulatory practices, conservation practices, and alternative fuels.

  • A vapor recovery nozzle is an air pollution control device on a gasoline pump that prevents fumes from escaping into the atmosphere when fueling a motor vehicle.

  • A catalytic converter is an air pollution control device for internal combustion engines that converts pollutants (CO, NOx, and hydrocarbons) in exhaust into less harmful molecules (CO2, N2, O2, and H2O).

  • Wet and dry scrubbers are air pollution control devices that remove particulates and/or gases from industrial exhaust streams.

  • Methods to reduce air pollution from coal- burning power plants include scrubbers and electrostatic precipitators.

Acid Rain

  • Acid rain and deposition is due to nitrogen oxides and sulfur oxides from anthropogenic and natural sources in the atmosphere.

  • Nitric oxides that cause acid deposition come from motor vehicles and coal-burning power plants. Sulfur dioxides that cause acid deposition come from coal-burning power plants.

  • Acid deposition mainly affects communities that are downwind from coal-burning power plants.

  • Acid rain and deposition can lead to the acidification of soils and bodies of water and corrosion of human-made structures.

  • Regional differences in soils and bedrock affect the impact that acid deposition has on the region—such as limestone bedrock’s ability to neutralize the effect of acid rain on lakes and ponds.

    1. Where does most of the acid rain fall and what damage can it do?

Air Pollutants

  • Photochemical smog can harm human health in several ways, including causing respiratory problems and eye irritation.

  • Respiratory problems and overall lung function can be impacted by elevated levels of tropospheric ozone.

Indoor Air Pollutants

  • Carbon monoxide is an indoor air pollutant that is classified as an asphyxiant.

  • Indoor air pollutants that are classified as particulates include asbestos, dust, and smoke.

  • Indoor air pollutants can come from natural sources, human-made sources, and combustion.

  • Common natural source indoor air pollutants include radon, mold, and dust.

  • Common human-made indoor air pollutants include insulation, Volatile Organic Compounds (VOCs) from furniture, paneling and carpets; formaldehyde from building materials, furniture, upholstery, and carpeting; and lead from paints.

  • Common combustion air pollutants include carbon monoxide, nitrogen oxides, sulfur dioxide, particulates, and tobacco smoke.

Noise Pollution

  • Noise pollution is sound at levels high enough to cause physiological stress and hearing loss.

  • Sources of noise pollution in urban areas include transportation, construction, and domestic and industrial activity.

  • Some effects of noise pollution on animals in ecological systems include stress, the masking of sounds used to communicate or hunt, damaged hearing, and causing changes to migratory routes.