Learning Objective: ERT-4.D - Describe the structure and composition of the Earth's atmosphere.
Essential Knowledge:
ERT-4.D.1: The atmosphere consists of major gases, each with its own relative abundance.
ERT-4.D.2: Layers of the atmosphere are based on temperature gradients, including the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
Atmospheric Composition
Major Gases Abundance:
Nitrogen (N₂): 78.08%
Oxygen (O₂): 20.95%
Argon (Ar): 0.93%
Neon (Ne): 0.0018%
Helium (He): 0.0005%
Hydrogen (H₂): trace
Xenon (Xe): trace
Variable Gases:
Water Vapor (H₂O): 0-4% (varies)
Carbon Dioxide (CO₂): 0.038%
Methane (CH₄): 0.00017%
Nitrous Oxide (N₂O): trace
Ozone (O₃): trace
Chlorofluorocarbons (CFCs): trace
Characteristics of Atmospheric Layers
Exosphere:
Outermost layer; where atmosphere merges with space.
Thermosphere:
Hottest temperature; absorbs harmful X-rays and UV radiation.
Charged gas molecules glow under intense solar radiation, producing auroras (e.g., aurora borealis).
Mesosphere:
Middle layer (60-80 km); even less dense than higher layers.
Stratosphere:
Extends from 16-60 km; less dense due to pressure from layers above.
Ozone (O₃) layer present; absorbs UV-B and UV-C rays which can cause DNA mutations in animals (cancer risk).
Troposphere:
0-16 km; most dense due to pressure of layers above.
Contains most of atmosphere’s gas molecules and is where weather occurs.
High levels of ozone (O₃) in this layer can be harmful to humans (respiratory irritant) and plants (damages stomata, forms smog).
Temperature Gradients in Atmosphere
Graph Data of Altitude vs Temperature:
The graph indicates that temperature typically decreases with altitude in the troposphere and mesosphere; however, it increases in the stratosphere and thermosphere due to the absorption of solar radiation.
Air Pollution Introduction
Learning Objective: STB-2.A - Identify the sources and effects of air pollutants.
Essential Knowledge:
STB-2.A.1: Coal combustion releases pollutants such as CO₂, SO₂, toxic metals, and particulates.
STB-2.A.2: Fossil fuel combustion also emits nitrogen oxides which contribute to ozone formation and acid rain.
STB-2.A.3: Sulfur dioxide (SO₂) impacts air quality negatively when released during fossil fuel burning.
STB-2.A.4: The Clean Air Act regulates lead emissions, significantly reducing atmospheric lead levels.
STB-2.A.5: Air pollutants can be primary (directly emitted) or secondary (formed in the atmosphere).
Detailed Air Pollutants Discussion
Common Air Pollutants Overview:
Sulfur Dioxide (SO₂): Respiratory irritant; forms acid rain.
Nitrogen Oxides (NOx): Respiratory irritants; lead to photochemical smog and acid rain.
Carbon Monoxide (CO): Product of incomplete combustion; lethal in high concentrations.
Particulate Matter (PM): Short for air pollutants can be deadly to human health, causing issues like chronic bronchitis.
Pollution Controls and Effects
Air Quality Control: Identified through the Clean Air Act, emphasizing monitoring pollutants and enforcing limits on lead and other criteria pollutants.
Primary vs. Secondary Pollutants:
Primary pollutants include CO, NOx, SO₂, PM, VOCs. Secondary pollutants include tropospheric ozone and acid rain (nitric & sulfuric acid).
Regulation Measures for Air Pollution: Corporate Average Fuel Economy (CAFE) standards for vehicle emissions control, as well as pollution credits for companies that reduce emissions below regulated levels.
Photochemical Smog
Learning Objective: STB-2.B - Causes and effects of photochemical smog and methods to reduce it.
Formation Conditions: Occurs when nitrogen oxides and volatile organic compounds (VOCs) react with heat and sunlight; mostly seen in urban areas.
Health impacts from photochemical smog: Causes respiratory problems and eye irritation.
Examples of VOCs: Formaldehyde, gasoline vapors, and their sources.
Thermal Inversion
Learning Objective: STB-2.C - Describe thermal inversion and its pollution effects.
Effects: Coal combustion produces pollution trapped in lower atmosphere layers during inversions, resulting in health concerns like asthma flare-ups.
Urban Heat Island Effect: Urban areas maintain higher temperatures due to lower albedo, affecting local climates and furthering pollution effects.
Natural and Indoor Air Pollutants
Natural Sources Include:
CO₂ from respiration, decomposition, and volcanic eruptions.
Particulate matter from natural dust, sea salt, and biological processes.
Indoor Air Pollutants: Includes carbon monoxide, asbestos, VOCs from household products, and radon from soil.
Causes: Resulting from nitrogen oxides and sulfur oxides; often from coal burning and vehicles.
Effects: Can lead to soil and water acidification, harming plants and aquatic systems. Limiting emissions from primary sources reduces acid rain incidence.
Reduction of Air Pollutants Strategies
Key Methods: Regulatory practices, conservation, alternative fuels, and technological advancements in emission reduction such as scrubbers and vapor recovery nozzles.
Public Engagement: Actions like using less personal transportation, energy conservation, and promoting renewable energy sources may contribute to reducing overall air pollution levels effectively.