Module #48

Pollution Control Measures

Module Introduction:

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• In our discussion of energy and energy choices, we saw that sustainability is best achieved by considering conservation and efficiency first.
• Similarly, if we can address the problems of pollution by seeking ways to avoid creating it in the first place, we will require less energy and fewer resources to clean it up.
• Preventing pollution is usually much less expensive and energy intensive then controlling it. Unfortunately, pollution prevention is not always possible.

Module 48: Pollution Control Measures

Essential Knowledge

7.2 Photochemical Smog (Module 47)

• 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.
• 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.
• Photochemical smog often forms in urban areas because of the large number of motor vehicles there.
• Photochemical smog can be reduced through the reduction of nitrogen oxide and VOCs.
• Photochemical smog can harm human health in several ways, including causing respiratory problems and eye irritation.

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Essential Knowledge

7.6 Reduction of Air Pollutants (Module 48)

• 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.

Air Pollution Control Measures

Prevention:

(source reduction)

• Avoiding emissions in the first place (e.g. energy conservation) would be the most effective means to reduce pollution.
• Use cleaner fuel (e.g. switch from coal → natural gas).
• Increase energy efficiency to limit fuel use.
• Control pollutants after combustion (i.e. controlling emissions).

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Mitigation:

(controlling emissions)

• Remove sulfur dioxide from coal by fluidized bed combustion.
• Install catalytic converters on cars to reduce emission of hydrocarbons, carbon monoxide and nitrogen oxides.
• Use baghouse filters.
• Use electrostatic precipitators.
• Install scrubbers on smokestacks.

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Pollution Control Devices

• Pollution Control Device (PCD): A device that is used after combustion to remove harmful air pollutants  such as NO_x, SO_x, and particulate matter.�

Calcium carbonate (CaCO₃) is limestone.

Control of Particulate Matter

• In a wet scrubber, particulate matter is “scrubbed” from the exhaust stream by water droplets. A water-particle “sludge” is collected and processed for disposal.
• Wet scrubbers can be enhanced by using chemicals that neutralize SO_x and NO_x emissions as opposed to plain water (but this is not considered the norm).

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Electrostatic Precipitator

• In this air pollution control device, particles are given a negative charge.
• This causes them to be attracted to a positively charged plate, where they are held.
• Periodically, the particles are removed from the plate and collected for disposal.

Control of Nitrogen Oxides

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• Reducing nitrogen oxide (NO_x) emissions calls for lower burn temperature and reduction of oxygen concentrations.
• This reduces fuel efficiency…unless you use a catalytic converter.
• Catalytic converters are pollution control devices that reduce nitrogen oxide, hydrocarbon and carbon monoxide emissions from cars. They have been required since 1975.
• Catalytic converters use precious metals (e.g. platinum and palladium) that cannot be exposed to lead, which is why leaded gasoline has been phased out (note it was NOT the human health impacts of lead).

Pollution Control Measures

Municipalities around the world have tried a number of innovative pollution control measures and strategies:

• VOCs: Reduce gasoline spilled at the pump, reduce the evaporation rate of dry-cleaning fluids, and restrict the use of lighter fluid.
• PM: Reduce use of wood-burning stoves and fireplaces.
• Carbon Oxides: Limit automobiles to every other day use or charge user fees for roads during heavy commute times. Building better public transportation would also help! �

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Amending the Clean Air Act

• In 1995 the Clean Air Act was amended to incentivize the free market to help determine the least expensive ways to reduce emissions.
• One of the most innovative aspects of these amendments was the provision for buying and selling of allowances that authorized the owner to release specific quantities of sulfur (ie. “Cap and Trade”).
• Utilities are allocated a certain number of sulfur allowances and each allowance gives the holder the right to emit one ton of sulfur. The allowances can be used in that year, traded, or held for future use.
• Sulfur allowances can be bought and sold on the open market by anyone.
• The total SO₂ emissions from all sources in the US have declined from 23.5 million metric tons in 1982 to 10.3 million metric tons in 2008.

First passed in 1970, the Clean Air Act is the comprehensive federal law that regulates air emissions. This law authorizes EPA to establish National Ambient Air Quality Standards (NAAQS) and to regulate emissions of hazardous air pollutants.

Acid Rain Program

• The EPA’s Acid Rain Program (ARP) complements the Clean Air Act Amendments and requires major emission reductions of sulfur dioxide (SO₂) and nitrogen oxides (NO_x), the primary precursors of acid rain, from the power sector.
• The SO₂ program sets a permanent cap on the total amount of SO₂ that may be emitted in the United States.

Acid Rain Program Results

Corporate Average Fuel Economy (CAFE) Standards

• First enacted by Congress in 1975, the purpose of CAFE is to reduce energy consumption by increasing the fuel economy of cars and light trucks.
• The CAFE standards are fleet-wide averages that must be achieved by each automaker for its car and truck fleet, each year, since 1978.
• When these standards are raised, automakers respond by creating a more fuel-efficient fleet, which improves our nation’s energy security and saves consumers money at the pump, while also reducing greenhouse gas (GHG) emissions.

This is a reminder from a previous module.

Do The Math: Calculating Annual Sulfur Reductions

• See page 536 of the textbook.
• Make sure to review the math problem and make sure you understand the set up, especially the dimensional analysis.
• Your Turn answer =
• 23.9% total reduction
• 1.6%/year annual reduction

If you have questions or need further explanation with ‘Do The Math’, you need to come in for extra help before school.

Module Review:

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• In this module, we have seen that the best approach for decreasing air pollution emissions is by avoiding them in the first place.
• This can be done by choosing fuels that contain fewer impurities or by increasing the efficiency of operations.
• After these options have been considered and implemented, a number of pollution control technologies are available to prevent pollutants from entering the air. The baghouse filter physically removes particles and the electrostatic precipitator uses an electrical charge to attract and remove pollutant particles.
• The scrubber literally scrubs the exhaust stream with water droplets, creating a sludge that can be collected and removed.
• Innovative techniques for reducing pollution include putting a price on the right to emit certain pollutants and allowing pollution permits bought and sold on the free market to bring down emissions in the most cost-efficient way possible.