Atmosphere, Air Quality, and Pollution Control Study Notes

Chapter 17: The Atmosphere, Air Quality, and Pollution Control

Lecture Objectives

• Describe the composition, structure, and function of Earth

• Relate weather and climate to atmospheric conditions.

• Identify major outdoor air pollutants.

• Assess strategies and solutions for control of outdoor air pollution.

• Explain stratospheric ozone depletion and identify steps taken to address it.

• Describe acid deposition, discuss its consequences, and explain how we are addressing it.

• Characterize the scope of indoor air pollution and assess solutions.

The Atmosphere

• The atmosphere is a layer of gases that surrounds the Earth and performs critical functions:

  • Moderates climate

  • Provides oxygen

  • Shields from meteors and hazardous solar radiation

  • Transports and recycles water and nutrients

• Major composition:

  • Nitrogen (approximately 78%)

  • Oxygen (approximately 21%)

  • Other gases and water vapor in smaller amounts.

Layers of the Atmosphere

1. Troposphere

   • Contains the air we breathe and our weather.

   • Temperature decreases with altitude, stabilizing around $-52^{\text{°C}}$ at the tropopause.

2. Stratosphere

   • Drier and less dense than the troposphere with minimal vertical mixing.

   • Temperature increases with altitude due to the absorption of sunlight by the ozone layer.

   • The ozone layer protects living organisms from UV radiation.

Atmospheric Dynamics

• Pressure, Humidity, and Temperature Variability:

  • Air moves due to differences in air pressure, density, relative humidity, and temperature.

  • Gravity pulls air toward Earth

  • Atmospheric pressure is measured as the force per unit area of a column of air; decreases with altitude due to fewer air molecules.

  • Relative humidity is the ratio of water vapor to the maximum capacity of air at a given temperature.

Solar Energy's Role

• Solar energy heating contributes to seasons and air circulation:

  • Sunlight impacts climate when meeting the surface at a perpendicular angle.

  • Intensity of solar radiation is strongest at the equator and decreases towards the poles.

• The Earth is tilted at 23.5 degrees, resulting in seasonal temperature and daylight variations in regions away from the equator.

Weather and Climate

• Weather refers to atmospheric conditions over short periods (weeks or less).

• Climate describes the long-term patterns of atmospheric conditions over years.

• Temperature inversions can significantly affect air quality:

  • A layer of cool air trapped beneath warm air obstructs vertical mixing, causing pollutants to accumulate near the ground.

  • Commonly occurs in valleys shaded by mountains, creating an inversion layer.

Outdoor Air Quality

Outdoor Air Pollution

• Some pollution is from natural sources.

• Air Pollutants affect climate and harm living beings:

  • Primary pollutants are directly released into the air (e.g., ash, sulfur dioxide, carbon monoxide).

  • Secondary pollutants result from reactions among primary pollutants (e.g., ozone formed from urban smog).

• The Clean Air Act (1963; amended in 1970 and 1990):

  • Supports pollution control research, sets air quality standards, and encourages emissions standards for vehicles and specific sources.

Major Outdoor Air Pollutants

1. Carbon Monoxide (CO)

   • Emitted by incomplete combustion of fuels, primarily from vehicles and engines.

   • Binds with hemoglobin, inhibiting oxygen transport in the body.

2. Nitrogen Oxides (NOx)

   • Includes nitric oxide and nitrogen dioxide, produced during combustion.

   • Contributes to smog, acid deposition, and ozone depletion.

3. Volatile Organic Compounds (VOCs)

   • Emitted by vehicle engines and solvents (e.g., methane, propane).

   • React to form secondary pollutants like smog.

4. Particulate Matter

   • Composed of tiny solid or liquid particles in suspension (e.g., dust, soot).

   • Can be either a primary pollutant (e.g., smoke) or a secondary pollutant (e.g., sulfate, nitrates).

5. Lead (Pb)

   • Enters the air as particulate pollutant from burning leaded gasoline or metal smelting.

   • Can cause nervous system dysfunction by accumulating in the body.

6. Nitrogen Dioxide (NO2)

   • A reactive reddish-brown gas contributing to smog and acid precipitation.

   • Ground-level ozone (O3) is unstable and injurious to tissue, resulting from photochemical reactions in sunlight.

Reduction of Air Pollution

• The Clean Air Act amendments resulted in a dramatic decrease in emissions of six principal pollutants since 1970.

• Technological measures to control emissions include:

  1. Bag house filters, Electrostatic precipitators, and Scrubbers that physically remove airborne pollutants from smokestacks.

  2. Catalytic converters in vehicles that convert harmful exhaust components into less harmful substances (e.g., CO, hydrocarbons, NOx to CO2, H2O, and N2).

• The phasing out of leaded gasoline significantly reduced lead levels in the atmosphere.

Toxic Pollutants and Their Risks

• Toxic air pollutants are known to cause:

  • Cancer

  • Reproductive defects

  • Neurological issues

  • Developmental, immune system, or respiratory problems.

• Sources of toxic pollutants include:

  • Mercury (from coal power plants)

  • VOCs (from gasoline)

  • Methylene chloride (found in paint strippers).

Pollution Challenges in Various Areas

• Rural Areas face unique challenges due to:

  • Airborne pesticides from agricultural practices.

  • Industrial pollutants drifting from urban centers.

  • Methane, hydrogen sulfide, ammonia from large livestock operations.

Smog and Its Formation

• Smog, a mixture of air pollutants produced mainly from fossil fuel combustion, is particularly a concern in heavily trafficked urban areas:

  • Industrial smog is common in cities.

  • Photochemical smog forms when chemical reactions occur between primary pollutants in the presence of sunlight, leading to the production of over a hundred different chemicals with ozone as a primary component.

  • Optimal conditions for formation involve warm, windless, and sunny days.

Mitigation Strategies for Smog

• Actions taken to combat smog include:

  • State and federal emission regulations.

  • Regular vehicle inspections to monitor emissions.

  • Technological upgrades to vehicles to enhance emission control.

  • Initiatives like cap-and-trade programs and transitioning from coal to renewable energy sources.

Ozone Layer and Depletion

• Ozone is protective against UV radiation but has been adversely affected by human-made chemicals, specifically ozone-depleting substances (ODS):

  • Halocarbons, including chlorofluorocarbons (CFCs) used extensively until their harmful effects were recognized in the 1980s.

  • CFCs are nonreactive but disintegrate in the stratosphere, releasing chlorine that depletes ozone molecules.

• The ozone hole was first identified in Antarctica in 1985, alarmingly indicating increased UV radiation exposure risks.

• International efforts to phase out CFCs and similar substances have promoted ozone stabilization.

Acid Deposition

• Acid deposition refers to the deposition of acid or acid-forming pollutants (from fossil fuel combustion) on Earth

  • Results primarily from sulfur dioxide and nitrogen oxides reacting with water and oxygen in the atmosphere to form acidic compounds.

• Ecological Impacts:

  • Accelerated leaching of essential nutrients from soil.

  • Increased nitrogen accumulation that can over-fertilize native plants.

  • Elevated aluminum levels that hinder water and nutrient uptake by plants.

  • Detrimental effects on aquatic life diversity.

• The Clean Air Act of 1990 established the Acid Rain Program, significantly reducing SO2 and NO emissions in the U.S.

Indoor Air Quality

• Indoor air pollution generally contains higher concentrations of pollutants compared to outdoor air:

  • Measures taken to reduce energy, like limiting ventilation, can aggravate indoor pollution.

  • Common pollutants include:

  • Tobacco smoke: Irritates respiratory systems; increases cancer risk.

  • Radon: Derived from natural uranium decay; second leading cause of lung cancer, often undetectable without testing.

  • VOCs: Emitted from multiple sources including paints and cleaning products.

Examples of Indoor Pollutants and Their Health Risks:

• Chloroform from treated water can cause nervous system damage.

• Lead from old paint can cause nervous system and organ damage.

• Particulate matter from fireplaces can lead to respiratory issues and lung cancer.

• Asbestos in insulation poses asbestosis risk.

• Nitrogen oxides from unvented stoves correlate with respiratory problems.

• Radon exposure has significant association with lung cancer risk.

• Formaldehyde from furnishings can cause respiratory irritation and cancer.

Improving Indoor Air Quality

• Measures to improve air quality in both developing and developed worlds:

  • Drying fuels before burning.

  • Cooking outdoors when possible.

  • Transitioning to cleaner fuels like natural gas.

  • Ensuring proper ventilation through design and installations.

• In developed nations, strategies focus on minimizing smoke exposure, testing for radon and mold, and limiting VOC exposure sources.

Study Objectives

1. List and briefly describe the layers of the atmosphere.

2. What is the function of ozone in the stratosphere? How is it depleted?

3. List the major classes of outdoor air pollutants; distinguish photochemical from industrial smog.

4. Explain how outdoor air pollution is commonly reduced and how it is commonly increased.

5. Define acid rain and state the primary causes of acid deposition, along with associated difficulties in reduction.

6. Assess the significance of indoor air pollution, noting common pollutants and reduction strategies.

7. Summarize the effects of air pollution on human health, detailing lung defenses against pollutants.