apes 7.6

Reduction of Air Pollutants

Air Quality Management

• Shade: A method to reduce energy use and air temperature.

• Air Quality Buffer:

  • Description: Shallow basin designed to trap and transform pollutants.

Catalytic Converters

• Purpose: Reduces harmful emissions from internal combustion engines.

• Types of Catalysts:

  • Three-Way Reduction Catalyst: Targets and eliminates nitrogen oxides (NOx).

  • Two-Way Oxidation Catalyst: Aims to remove carbon monoxide (CO) and unburned hydrocarbons (HC).

• Functionality:

  • Inputs: Dirty exhaust from the engine.

  • Outputs: Clean exhaust, which includes carbon dioxide (CO₂), nitrogen (N₂), oxygen (O₂), and water (H₂O).

Unit 7: Atmospheric Pollution

Enduring Understanding STB-2

• Concept: Human activities have direct physical, chemical, and biological consequences for the atmosphere.

Learning Objective STB-2.G

• Task: Explain methods to reduce air pollutants at the source.

Essential Knowledge

• STB-2.G.1:

  • Methods to Reduce Air Pollutants:

  • Regulatory practices.

  • Conservation practices.

  • Alternative fuels.

• STB-2.G.2:

  • Vapor Recovery Nozzle: An air pollution control device attached to gasoline pumps to prevent fumes from escaping into the atmosphere during refueling.

• STB-2.G.3:

  • Catalytic Converter:

  • Definition: Air pollution control device for internal combustion engines that transforms pollutants (CO, NOx, hydrocarbons) in exhaust into less harmful substances (CO₂, N₂, O₂, H₂O).

• STB-2.G.4:

  • Wet and Dry Scrubbers: Air pollution control devices that eliminate particulates and/or gases from industrial exhaust streams.

• STB-2.G.5:

  • Methods for Coal-Burning Power Plants:

  • Utilization of scrubbers and electrostatic precipitators for reducing air pollution.

Strategies for Air Pollution Reduction

Prevention of Air Pollution

• Primary Strategy: The best method to mitigate air pollution emissions is to avoid them altogether.

• Options Available:

  • Use coal and oil with lower sulfur content, although this is more costly.

  • Remove sulfur and impurities during the refining process of oil and coal, also escalating costs.

Energy Efficiency Improvements

• Fossil Fuel Reduction: Minimize reliance on fossil fuel combustion.

• Automotive Efficiency: Enhance automobile efficiency to decrease gasoline usage.

• Home Efficiency: Improve efficiency in home appliances (e.g., air conditioners, washing machines, dryers, electrical heaters).

• Insulation and Solar Energy: Increase home insulation and adopt solar heating/cooling methods to further reduce fossil fuel combustion.

Preferred Energy Sources

• Natural Gas: Recommended over coal or oil due to lower air pollution emissions per energy unit.

• Alternative Energy Sources:

  • Includes hydroelectric, geothermal, solar, and wind energy options that minimize all categories of air pollutants.

Efficiency and Conservation

• Impact on Emissions: Using less fuel results in lower air pollution production, although efficiency and conservation alone may not suffice.

• Behavior Change: Significant reductions in air pollution will also necessitate changes in human habits.

Sulfur Dioxide Pollution Control

• Common Pollutant: Sulfur dioxide (SO₂) is prevalent in the U.S. and contributes to acid deposition.

• Reduction Techniques:

  • Can be addressed at three stages: pre-combustion, during combustion, and post-combustion.

  • Precombustion: Utilize higher-grade coal (e.g., anthracite) and wash coal to eliminate excess sulfur.

Fluidized Bed Combustion

• Mechanism: Burning granulated coal alongside calcium carbonate.

• Chemical Reaction: Heated calcium carbonate absorbs sulfur dioxide (SO₂), producing calcium sulfate, which can be repurposed for gypsum wallboard.

• Post-Combustion Capture: Methods exist to capture escaping sulfur oxides post-combustion.

Post-combustion Control of Sulfur Compounds

• Catalytic Converters: Oxidizes sulfur compounds to mitigate emissions.

• Lime Scrubber: Utilized in smokestacks to capture sulfur through a mixture of lime and water, turning it into calcium sulfate which settles as bottom ash.

Controlling Nitrogen Oxides (NOx)

• Production: Nitrogen oxides are generated in nearly all combustion processes due to atmospheric nitrogen content (78%).

• Reduction Techniques:

  • Control combustion temperatures to lower NOx production.

  • Utilize catalytic converters in automobiles to enhance combustion efficiency, thus reducing NOx, volatile organic compounds (VOCs), and carbon monoxide (CO).

Historical Impact of Catalytic Converters

• Regulatory Requirement: Beginning in 1975, all new U.S. vehicles were mandated to include catalytic converters, resulting in significantly reduced NOx emissions over the past 35 years.

• Material Sensitivity: Precious metals (platinum, palladium) in catalytic converters must not come into contact with lead, hence the shift to unleaded gasoline.

Lead Phase-Out in Gasoline

• Impact of Unleaded Gasoline: Transitioning to unleaded gasoline greatly reduced atmospheric lead levels from vehicle emissions.

New Technologies for NOx Reduction

• Positive Crankcase Ventilation (PCV): Newer vehicles may feature systems reclaiming VOCs and returning them to the combustion chamber.

• Balancing Emission Reductions: Reducing NOx may inadvertently increase VOC emissions, necessitating a balanced regulatory approach.

Motor Vehicle Pollution Control

• Current Needs: Emission control devices are crucial until the complete transition from internal combustion engines.

• Alternative Fuels: Consideration of alcohol, natural gas, and hydrogen as more environmentally friendly options compared to gasoline.

Efficacy of Air Pollution Control Devices

• Impact of Catalytic Converters: Significantly contributed to air pollution reductions, yet broad environmental cleanup post-dispersion remains vastly more challenging.

• NO2 Levels: Documented decline in nitrogen dioxide (NO₂) concentrations from 2005 to 2011.

Control of Particulate Matter

• Common Control Methods: The removal of particulates is a frequent goal of air pollution management.

• Gravitational Settling: Simplest method; relies on gravity to allow particles to settle as exhaust travels through smokestacks.

Ash Disposal

• Management of Ash Residue: Accumulated ash must be disposed of in landfills, sometimes containing high levels of metals that necessitate special handling due to toxicity, especially in coal ash.

Baghouse Filters

• Operational Function: A series of bags function to trap particulates, effectively removing fine hazardous particles with high efficiency (up to nearly 100%).

Electrostatic Precipitators

• Effectiveness: Capable of removing 99% of particulates from coal emissions.

• Mechanism: Operate by charging particulates as emissions pass through charged plates, promoting adhesion to oppositely charged plates.

Cyclone Collectors

• Functionality: Create a vortex within smokestacks, facilitating the collision and descent of particles as bottom ash.

Wet Scrubbers

• Performance: Modern wet scrubbers achieve a removal efficiency of 98% for both sulfur dioxide (SO₂) and particulate matter in emissions, though installation and maintenance costs are significant.

Wet Scrubber Operation

• Description: Utilize a combination of water and air to separate and extract particles, producing slurry while allowing clean gas to exit.

Photochemical Smog Reduction

• Ozone Management: Control efforts target reduction of precursors, primarily focusing on reducing VOC emissions, particularly in urban settings.

Municipal Actions

• Innovative Measures: Some municipalities implement new regulations aimed at supressing smog, such as limiting gasoline spills, regulating dry cleaning vapors, and controlling VOC emissions from products.

Wood-Burning Stoves Regulation

• Air Quality Measures: Calls for reduced wood-burning stove usage to decrease nitrogen oxides, particulate matter, VOCs, and carbon monoxide emissions.

Business Regulation Initiatives

• Specific Regulations: In certain California municipalities, proposals include restricting bakery operations due to VOC emissions from yeast fermentation during rising bread production.

Car Emission Regulations

• Impact in Urban Areas: Cities like Mexico City enforce driving restrictions (for instance, permitting driving on alternate days) to combat high NOx and VOC emissions.

• China's Measures: Expansion of public transport, motor vehicle limitations, and temporary industrial shutdowns to tackle photochemical smog.

Reducing Automobile Use

• Carpool Initiatives: Introduction of carpool lanes encourages vehicle sharing to reduce road congestion.

• Public Transport Improvements: Enhancing public transit options aims to motivate individuals to opt for alternatives to personal vehicles.

Individual User Fees for Road Use

• Examples of Implementation: Some cities in England (like London) trialing road usage fees (tolls) during peak times or in city center zones as a strategy to lower vehicular traffic during high pollution periods.