Enduring Understanding:

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

Learning Objective:

• Explain how air pollutants can be reduced at the source.

Essential Knowledge:

• 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.

The Clean Air Act

• The Clean Air Act is a piece of legislation that regulates the emission of air pollutants that affect human health

• Regulation at a national level by cooperating with states and tribes

• The goal is to create and enforce national air quality standards to protect human and environmental health

  • The reduction of automobile emissions can be done by eliminating lead in gasoline and encouraging cleaner technology in transportation

  • The reduction of acid rain can be done by determining levels of how much pollution is permissible by industries and promoting technologies for reductions in sulfur dioxide and nitrogen oxides

Alternative Fuels

• The Clean Air Act supports the development of alternative fuels for transportation

• These fuels reduce pollutants in emissions

• These include natural gas, propane, ethanol, electricity, and biofuels

  • All of these are imperfect and present their own challenges

• The CAA requires the EPA to develop a National Renewable Fuel (RF) program, designed to significantly increase the volume of renewable fuels that can be blended into gasoline

Conservation Actions to Reduce Emissions

• Energy efficiency in appliances and buildings reduces fuel use and emissions

• Water-based, instead of solvent-based, paints and cleaners reduce VOCs

• Improved transportation planning for passengers and freight reduce fuel use and emissions

• Higher fuel standards and cleaner running engines for cars, trucks, and planes also reduce fuel use

• Individual and community actions like composting, recycling, carpooling, no-idle zones, and other actions can have large impacts

Technologies

• Technologies can be very efficient, but all of them create waste

• Scrubbers and precipitators have sludge or ash that is stored at the site of the coal-fired power plants or taken to a landfill

• Managing the waste can cause issues, as it can blow away or contaminate the groundwater

  • There are also ‘ash slides’ that can occur when containment walls fall

Vapor Recovery

• Vapors escape while you put fuel in your car’s gas tank

• The vapor recovery system captures the vapors and sends them to the underground storage tank

• A similar process occurs when gasoline is delivered by a fuel truck

• This is why gas nozzles have the outward facing cup so that fumes are not released

• More efficient nozzles are constantly being designed

• Since 2006, EPA required the auto industry to make vehicles with onboard refueling vapor recovery systems (ORVR)

  • These processes capture vapors and burn them in the car’s own combustion chamber

• After 2013, the EPA no longer required gas pump nozzle systems, but states could choose to continue their use to manage air pollutants

Catalytic Converters

• These converters in cars reduce the toxicity of emissions

• Fumes run through the converter before being released through the exhaust

• Carbon monoxide (CO), nitrogen dioxide (NO2), and VOCs go in

• Oxygen gas (O2), carbon dioxide (CO2), water (H2O), nitrogen, and some nitrous oxide are released

• Catalytic converts can’t catch everything, but the number of original compounds coming out is very low

• Nitrogen oxide pollution is reduced by a catalyst through a reduction reaction (removing oxygen)

  • This breaks up nitrogen oxides into nitrogen and oxygen gases

• Another catalyst works by an opposite chemical reaction called oxidation (adding oxygen) and turns carbon monoxide into carbon dioxide

• Another oxidation reaction turns unburned hydrocarbons in the exhaust into carbon dioxide and water

• Precious metals act as catalysts inside the converter, which is why they are popular targets to be stolen

Scrubbers

• When coal is burned, there are many pollutants that are released as gas and particulates

• These gases are released via the flue, or smokestacks, and enter the atmosphere where they cause air and water pollution

• The Clean Air Act requires scrubber technologies to remove pollutants like sulfur oxides, nitrogen oxides, and particulates

Wet Scrubbers

• Wet scrubbers use liquids in the form of spray or mist to capture or change pollutants

• When particulates and dust are an issue, water alone can be the liquid

• For sulfur oxides, the liquid is often a combination of limestone powder and water that makes a slurry

• The sulfur oxides interact with the limestone (a buffer) and convert it into a synthetic form of gypsum

  • The gypsum can be used as drywall, but not all industries utilize this product

Dry Scrubbers

• Dry scrubbers use dry particles, or reagents, to capture or change pollutants

• Due to the added weight, the particles fall to the bottom of the chamber and be collected by a screen

• Although highly effective, dry scrubbers don’t remove as many pollutants as wet scrubbers

Electrostatic Precipitators

• This technology uses an electrical charge to reduce pollutants

• Gas is forced through a chamber that adds a charge to the pollutants

• As the soot particles move past metal plates or filters that have an opposite charge, the particles stick there

• Clean air can then leave the chamber

• These devices can be used as the first step before the flue gases move into a scrubber chamber