APES Unit 7 Notes: Controlling Atmospheric Pollution Through Technology and Policy

Primary pollutants

Air pollutants emitted directly from a source (e.g., SO2 from burning coal, particulate matter from diesel exhaust).

Secondary pollutants

Air pollutants formed in the atmosphere through chemical reactions of precursor pollutants (e.g., tropospheric ozone formed from NOx and VOCs in sunlight).

Source reduction (pollution prevention)

Preventing pollution before it is created (e.g., changing fuels, improving efficiency, redesigning industrial processes).

Fuel switching

Replacing a higher-polluting fuel with a cleaner one to reduce emissions (e.g., using natural gas instead of coal to lower SO2 and particulate emissions).

Energy efficiency and conservation

Reducing energy demand so less fuel is burned and multiple pollutants decrease at once; sometimes called “invisible control technology.”

End-of-pipe controls

Technologies that remove pollutants from exhaust after they form but before release (often requiring energy/maintenance and creating waste).

Pollution transfer

When pollution control captures pollutants in one form but creates another waste stream (e.g., scrubber sludge or captured dust requiring disposal).

Particulate matter (PM; PM2.5)

Tiny solid or liquid particles suspended in air; fine particles (PM2.5) are especially harmful because they can penetrate deep into lungs.

Electrostatic precipitator (ESP)

Particulate-control device that uses an electric field to charge particles and collect them on oppositely charged plates (common on coal power plants).

Baghouse filter

Particulate-control device that forces exhaust through fabric filters that trap particles; very high removal but filters must be cleaned/replaced and dust disposed.

Cyclone separator

Particulate-control device that spins air so heavier particles fall out by inertia; often a pre-cleaner and less effective for very fine particles.

Flue-gas desulfurization (scrubber)

SO2 control technology that sprays a basic slurry (often limestone/CaCO3) into exhaust to chemically remove SO2, producing a solid byproduct (e.g., gypsum).

Nitrogen oxides (NOx)

Gases formed mainly during high-temperature combustion; contribute to acid deposition (nitric acid) and photochemical smog (ozone formation).

Selective catalytic reduction (SCR)

NOx control system using a catalyst and a reducing agent (often ammonia or urea) to convert NOx into nitrogen (N2) and water (H2O).

Catalytic converter

Vehicle exhaust device that uses catalysts to reduce CO, NOx, and unburned hydrocarbons (VOCs) by converting them to less harmful products (e.g., CO2, N2, H2O).

Emission standards

Legal limits on how much of a pollutant a source may emit (can apply to stationary sources like power plants and mobile sources like vehicles).

Ambient air quality standards

Limits on pollutant concentrations in outdoor air to protect health and welfare (standards for the air people breathe, not the emissions rate from a source).

Cap-and-trade

Market-based policy where total emissions are capped and allowances can be bought/sold, encouraging reductions where they are cheapest while meeting the overall cap.

Clean Air Act (CAA)

Major U.S. federal law that authorizes the EPA to set and enforce air quality regulations, including national standards for key pollutants.

Criteria pollutants

Six common pollutants with EPA national ambient standards: CO, Pb, NO2, O3 (tropospheric), PM, and SO2.

Acid deposition (acid rain)

Wet (rain/snow/fog) and dry deposition that is more acidic than normal precipitation, mainly driven by SO2 and NOx forming sulfuric and nitric acids.

Buffering capacity

An ecosystem’s ability to neutralize added acids and resist pH change; carbonate-rich geology (e.g., limestone) generally increases buffering.

Aluminum mobilization

Process where acidic conditions make aluminum more soluble in soils, allowing it to enter waterways and harm aquatic life (e.g., damaging fish gills).

Liming

Adding limestone (calcium carbonate) to acidified lakes/soils to raise pH; a temporary remediation that does not reduce SO2/NOx emissions.

Decibel (dB) scale

Logarithmic measure of sound intensity; a 10 dB increase corresponds to a tenfold increase in intensity (not a linear “twice as loud” change).