AP Environmental Science - Unit 7: Atmospheric Pollution

7.1 Intro to Air Pollution

• air pollution - introduction of chemicals, PM, or microorganisms into atm at concentrations high enough to harm plants, animals, and materials such as buildings, or to alter ecosystems

  • FRQ TIP! → write about air pollutants specifically, don’t just write “pollution”

  • air pollutants

    • clean air act identified 6 criteria air pollutants that the epa is required to set acceptable limits for, monitor, and enforce

      • SO₂ → sulfur dioxide

        • coal combustion

      • NO_x → nitrogen oxides (NO & NO₂)

        • all FF combustion

      • CO → carbon monoxide

        • incomplete combustion

      • PM → particulate matter

        • FF/biomass combustion

      • O₃ → ozone (tropospheric)

        • photochemical oxidation of NO₂

      • Pb → lead

        • metal plants, waste incineration

• greenhouse gases

  • CO₂ is NOT an air pollutant according to the clean air act

    • not included on FRQ guides for air pollutants

    • does not directly lower air quality from a human health standpoint

      • not toxic to organisms to breathe

      • not damaging to lungs/eyes

      • does not lead to smog or decreased visibility

    • CO₂ is a ghg; it does lead to earth warming → env and human health consequences

• sources of pollution

  • combustion

    • factories/power plants (energy)

      • coal releases more air pollutants than other FFs

      • releases CO, CO₂, SO₂, NO_x, toxic metals (mercury, arsenic, lead), and PM (often carries the toxic metals)

    • vehicles

    • natural resources (volcano, forest fire, lightning, plants, decaying matter, etc.)

• primary air pollutants - polluting compounds that come directly out of a smokestack, exhaust pipe, or natural emission source

  • NO_x, CO, CO₂, VOCs, SO₂, PM, hydrocarbons

• secondary air pollutants - primary pollutants that have undergone transformation in the presence of sunlight, water, oxygen, or other compounds

  • tropospheric O₃ (ozone)

  • sulfuric acid (H₂SO₄) and sulfate (SO₄ ^2-)

  • nitric acid (HNO₃) and nitrate (NO₃^-)

7.2 Photochemical Smog

• photochemical smog

  • forms when NO_x chemicals mix with VOCs

  • mix with heat and sunlight to produce smog and other secondary pollutants

    • NO₂ (+ sunlight) → NO + O → O + O₂ → O₃ (ozone)

• volatile organic compounds - chemicals that vaporize quickly (go from liquid to gas)

  • common VOCs → benzene, ethylene glycol, formaldehyde, gasoline, trees (natural)

• other contributing factors

  • time of day → nitrogen oxides are produced in the morning from vehicle combustion

    • ozone tends to peak in the afternoon

  • season → summer is sunniest, so more reactions

  • location → urban areas

    • heat island effect → higher temps = faster evaporation of VOCs

    • more VOCs - gas stations, laundromats, factories

    • more NO_x emissions - more vehicles, power plants

• impacts of smog

  • env → reduces sunlight, limits photosynthesis; ozone damages plant stomata (opening to take in CO₂) and animal respiratory tracts

  • human → respiratory irritant; worsens asthma; COPD; irritates eyes

• reduction of smog

  • decreasing the number of vehicles on the road decreases NO₂ emissions

    • fewer vehicles = less gas = fewer VOCs

      • carpooling, public transport, biking, walking, working from home

  • increased electricity production from renewable sources that don’t emit NO_x (solar, wind, hydro)

    • natural gas power plants release far less NO_x than coal

7.3 Thermal Inversion

• thermal inversion

  • under normal conditions, where temperatures decrease with increasing altitude, emissions rise into the atmosphere

  • the warm layer of air trapped between the two cooler layers in known as an inversion layer

  • inversions occur because the ground cools quicker than the air above

    • due to this layer, convection doesn’t carry pollutants away

    • inversion layer traps smog, pm, and smoke

• effects of thermal inversion

  • air pollutants trapped closer to earth (smog, PM, SO₂, NO_x)

  • respiratory irritation

  • env effects - decreased photosynthesis rate

  • econ effects - decreased tourism revenue

7.4 Atmospheric CO₂ & PM

• natural sources of air pollutants

  • lighting strikes

    • convert N₂ in atm to NO_x

  • plants

    • plants emit VOCs

      • ex) terpenes and ethylene from pine, fir, spruce trees

    • forms natural photochemical smog in smoky mnts

  • forest fires

    • CO, PM, NO_x

    • combustion of biomass also releases CO₂ and H₂O vapor (GHGs)

  • volcanoes

    • SO₂, PM, CO, NO_x

• natural sources of CO₂ & PM

  • respiration

    • all living things release CO₂ through respiration

  • aerobic decomposition

    • decomposition of organic matter by bacteria and decomposers in the presence of oxygen → releases CO₂

  • natural PM sources

    • sea salt, pollen, ash from forest fires and volcano dust (windborne soil)

    • leads to haze (scattering of sunlight and reduced visibility

  • anaerobic decomposition

    • decomposition of organic matter by bacteria and decomposers in low or oxygen-free conditions → releases CH₄

• PM₁₀ vs PM_2.5

  • particulate matter - solid/liquid particles suspend in air (also referred to as “particulates”)

    • PM₁₀ (<10 micrometers)

      • particles or droplets like dust, pollen, ash, or mold

      • too small to be filtered out by nose hairs and trachea cilia; can irritate respiratory tract and cause inflammation

    • PM_2.5 (<2.5 micrometers)

      • particles from combustion (especially vehicles)

      • more likely to reveal deep into the lungs due to smaller size

      • associated with chronic bronchitis and increased risk of lung cancer

7.5 Indoor Air Pollutants

• developing vs developed countries

  • developing

    • use more subsistence fuels such as wood, manure, charcoal (biomass)

    • often combusted indoors with poor ventilation, leading to high concentrations

      • about 3.5 - 4.3 million of 3 billion people who use subsistence fuels die annually

  • developed

    • use more commercial fuels (coal, oil, natural gas) supplied by utilities

      • typically burned in closed, well ventilated furnaces, stoves, etc.

    • many indoor air pollutants in developed nations come from chemicals in products

      • adhesives in furniture

      • cleaning supplies

      • insulation

      • lead paint

• classes of indoor air pollutants

  • natural

    • radon-222

    • mold

    • dust

  • anthropogenic

    • VOCs

    • formaldehyde

    • lead

    • major indoor air pollutants in developed nations come from chemicals in products: adhesives in furniture, cleaning supplies, insulation, lead paint

• indoor pollutants - description - effects

7.6 Reduction of Air Pollutants

• general methods

  • regulatory practices

    • clean air act → allow epa to set acceptable levels for criteria air pollutants

    • cafe vehicle standards

      • corporate average fuel economy → standards requiring the entire united states “fleet” of vehicles to meet certain average fuel

    • emissions inspections (VA)

  • conservation methods and practices

    • drive less, walk, bike, bus, etc.

  • alternative fuels/energy

    • solar, wind, hydro

• reducing vehicle emissions

  • vapor recovery nozzle

    • capture hydrocarbon VOCs released from gasoline fumes during refueling

      • separate tube inside nozzle captures vapors and returns them to underground storage tank beneath the gas station

      • reduces VOCs

      • reduces benzene (carcinogen) released from gasoline vapors

  

  • catalytic converter (cc)

    • cc converts NO_x, CO, and other hydrocarbons released by internal combustion engines into CO₂, N₂, O₂, and H₂O

• scrubbers

  • dry scrubbers (NO_x, SO_x, VOCs)

    • large column/tube/pipe filled with chemicals that absorb or neutralize oxides (NO_x, SO_x, VOCs) from exhaust streams (emissions)

    • calcium oxide is a common dry scrubber additive which reacts with SO₂ to form calcium sulfite

  • wet scrubbers (NO_x, SO_x, VOCs + PM)

    • may involve chemical agents that absorb or neutralize NO_x, SO_x, VOCs, but also include mist nozzles that trap PM in water droplets as well

    • mist droplets with pollutants and PM trapped in them fall to bottom of scrubber or get trapped at top by mist eliminator

    • sludge collection systems traps polluted water for disposal

• electrostatic precipitator

  • power plant/factory emissions passed through device with a negatively charged electrode, giving particles a negative charge

  • negatively charged particles stick to positively charged collection plates, trapping them

  • plates discharged occasionally so particles fall down into collection hopper for disposal in landfills

7.7 Acid Rain

• acid rain/deposition

  • NO_x and SO₂ are primary pollutants that cause most acid precipitation

    • NO_x and SO₂ react with O₂ and H₂O in the atm, forming nitric and sulfuric acid (secondary pollutants)

    • sulfuric and nitric acid dissociate in the presence of water into sulfate, nitrate, and hydrogen ions (H⁺)

      • acidic rain water (higher H⁺ concentration) decreases soil and water pH, limiting tree growth in forests

  • reducing NO_x and SO₂ emissions reduces acid deposition

    • higher cafe standards

    • more public transit

    • renewable energy sources

    • more efficient electricity use

    • acid rain has decreased significantly since the passage of the clean air act

• effects of acid deposition

  • acidity = higher H⁺ ion concentration, lower pH

  • effects of acid deposition may be direct, such as a decrease in the pH of lake water, or indirect

    • often difficult to determine whether an effect is direct or indirect

    • greatest effect of acid deposition is on aquatic ecosystems

    • soil pH can also drop

    • corrosion of man-made structures

  • indicator species can be surveyed and used to determine conditions of an ecosystem (soil, water, etc.)

    • ex) high white moss/filamentous algae population indicated pH < 6.0

    • high crustacean population indicates pH > 6.0

• mitigating acid rain

  • limestone

    • calcium carbonate (CaCO₃) reacts with H⁺ ions, forming HCO₃ and giving off Ca²⁺

    • this “neutralizes” acidic water/soil, moving it closer to a pH of 7

    • regions with limestone bedrock have some natural buffering of acid rain

    • humans can also add crushed limestone to soils/waters to neutralize

7.8 Noise Pollution

• sources of noise pollution

  • any noise at great enough volume to cause physiological stress (difficulty communicating, headaches, confusion) or hearing loss

    • construction

      • ex) jack hammers, trucks, concrete pouring

    • transportation

      • ex) cars, busses, trains

    • industrial activity

      • ex) manufacturing plants

    • domestic activity

      • ex) neighbor’s music, lawn mowing, home projects

• effects of noise pollution

  • noise pollution can disrupt animal communication, migration, and damage hearing

    • effects on wildlife (land)

      • causes physiological stress

        • ex) caterpillar hearts beat faster when exposed to simulated highway noise pollution → could drive pollinator species to decline

      • masks natural sounds

        • ex) mating calls, prey/predator noises

    • effects on aquatic organisms

      • aquatic noise pollution comes from the noise of ship engines, military sonar, and seismic air blasts from oil and gas surveying ships

        • causes physiological stress

          • ex) hearing loss, disrupted communication, mating calls, predator/prey navigation

        • disrupts migration (especially whales, as communication underwater can be disrupted)