Unit 7 - Air Pollution

Unit 7 Air Pollution

7.1 Introduction to Air Pollution (Pollutants)

• Air Pollution Basics

  • Write about air pollutants (specific molecules/particles) not just air “pollution” as an idea

  • Clean Air Act (1980) identified 6 criteria air pollutants that the EPA is required to set acceptable limits for, monitor, and enforce

    • SO₂ - Sulfur dioxide: coal combustion (electricity), respiratory irritation, smog, acid precipitation

    • NO_x – Nitrogen Oxides (NO & NO₂): all fossil fuel combustion, O₃ photochemical smog, acid precipitation

    • CO – Carbon monoxide: incomplete combustion, O₃, lethal to humans

    • PM – Particulate matter: fossil fuel/biomass combustion, respiratory irritation, smog

    • O₃ – Ozone (tropospheric): photochemical oxidation of NO₂, respiratory irritation, smog, plant damage

    • Pb – Lead: metal plants, waste incineration, neurotoxicant

• Air Pollutants vs. Greenhouse Gasses

  • CO₂ is not one of 6 criteria pollutants in Clean Air Act

    • CO₂ does not directly lower air quality from a human health standpoint

      • Not toxic to organisms to breath

      • Not damaging to lungs/ eyes

      • Does not lead to smog, decreased visibility

    • CO₂ is a greenhouse gas; it does lead to earth warming, and thus environment and human health consequences

  • Bottom line: in APES, CO₂ has not typically been included on FRQ scoring guides as an air pollutant (stick to SO₂, NO_x, O₃, PM)

• Coal Combustion

  • Releases more air pollutants than other fossil fuels

    • Releases CO, CO₂, SO₂, NO_x, toxic metals (mercury, arsenic, lead), and PM (0ften carries the toxic metals)

    • Impacts of SO₂

      • Respiratory irritant (inflammation of bronchioles, lungs), worsens asthma and bronchitis

      • Sulfur aerosols (suspended sulfate particles) block incoming sun, reducing visibility and photosynthesis

      • Forms sulfurous (grey) smog

      • Combines with water and O₂ in atmosphere to form sulfuric acid 🡪 acid precipitation

• Nitrogen Oxides (NO_x)

  • Released by combustion of anything, especially FFs and biomass

    • NO_x refers to nitrogen oxides (both NO and NO₂)

    • NO forms when N₂ combines with O₂ (especially during combustion)

    • NO can become NO₂ by reacting with O₃ or O₂

    • Sunlight converts NO₂ back into NO

  • Environment and Human Health Impacts

    • Respiratory irritant

    • Leads to tropospheric ozone (O₃) formation, which leads to photochemical smog

    • Combines with water and O₂ in atmosphere to form nitric acid 🡪 acid precipitation

• EPA and Lead

  • Before CAA< lead was a common gasoline additive; EPA began phaseout of lead from gasoline in 1974. Vehicles made after 1974 are required to have catalytic converters to reduce NO_x, CO, and hydrocarbon emissions (lead damages catalytic converters)

• Primary vs. Secondary Air Pollutants

  • Primary

    • Emitted directly from sources such as vehicles, power plants, factories, or natural sources (volcanoes, forest fires)

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

  • Secondary

    • Primary pollutants that have transformed in presence of sunlight, water, O₂

    • Occur more during the day (since sunlight often drives formation

    • Tropospheric O₃ (ozone)

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

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

7.2 Photochemical Smog

• Photochemical Smog Precursors and Conditions

  • Precursors

    • NO₂ – broken by sunlight into NO + O (free O + O₂ 🡪 O₃)

    • VOCs - volatile organic compounds (hydrocarbons) that bind with NO and form photochemical oxidants

      • Carbon-based compounds that volatize (evaporate) easily (this makes them “smelly”)

      • Sources: gasoline, formaldehyde, cleaning fluids, oil-based paints, even coniferous trees (pine smell)

    • O₃ – forms when NO₂ is broken by sunlight and free O binds to O₂

      • Respiratory irritant in troposphere (at earth’s surface)

      • Damaging to plants stomata, limiting growth

  • Conditions

    • Sunlight - drives O₃ formation by breaking down NO₂ 🡪 NO + O; then free O atom binds with O₂

    • Warmth – hotter atmosphere temperature speeds O₃ formation, evaporation of VOCs and thus smog formation

• Normal O₃ Formation

  • Morning commute leads to high NO₂ levels from car exhaust

  • Sunlight breaks NO₂ into NO + O

  • O bonds with O₂ to form O₃

  • O₃ formation typically peaks in afternoon when sunlight is most direct and NO₂ emissions from morning traffic have peaked

  • At night, O₃ reacts with NO to form NO₂ and O₂ once again; O₃ levels drop overnight

• Photochemical Smog Formation

  • Sunlight breaks NO₂ into NO + O

  • O bonds with O₂ to form O₃

  • VOCs bonds with NO to form photochemical oxidants

  • Without NO to react with, O₃ builds up instead of returning to O₂ and NO₂ overnight

  • O₃ combines with photochemical oxidants (NO + VOCs) to form photochemical smog

• Factors that Increase Smog Form

  • Increased vehicle traffic; increases NO₂ emissions and therefore O₃ formation

  • Higher VOCs emissions (gas stations, laundromats, petrochemicals, and plastic factories)

  • More sunlight (summer, afternoon) = more O₃

  • Warmer temperature, speeds evaporation of VOCs and reaction that lead to O₃

  • Urban areas have more smog due to all of these factors

• Impacts of Smog

  • Environment (reduces sunlight; limiting photosynthesis, O₃ damages plants stomata and irritates animal respiratory tracts)

  • Humans (respiratory irritant; worsens asthma, bronchitis, COPD; irritates eyes)

  • Economic (increased health care costs to treat asthma, bronchitis, COPD, lost productivity due to sick workers missing work or dying, decreased agriculture yields due to less sunlight reaching crops and damage to plant stomata)

• Reduction of Smog

  • Vehicles (decreasing the number of vehicles on road decreases NO₂ emissions, fewer vehicles = less gas = fewer VOCs)

  • Energy (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

• Urban Heat Island Effect

  • Urban areas tend to have higher surface and air temperature than surrounding suburban and rural areas due to:

  • Lower albedo: concrete and asphalt absorb more of sun’s energy than areas with more vegetation (absorbed sunlight is given off as IR radiation – heat)

  • Less evapotranspiration: water evaporating from surfaces and transpiration from plants carries heat from surface into the atmosphere

    • this cools off rural and suburban areas which have more vegetation

• Thermal Inversion

  • Normally the atmosphere is warmest at earth’s surface, and cools as altitude rises. Because warm air rises, air convection carries air pollutants away from earth’s surface and distributes them higher into the atmosphere

  • During a thermal inversion, a cooler air mass becomes trapped near earth’s surface

    • due to a warm front moving in over it

    • or due to hot urban surfaces colling overnight while IR radiation absorbed during the day is still being released

  • because cold air at the surface is trapped beneath the warmer mass above, convection doesn’t carry pollutants up and away.

• Effects of Thermal Inversion

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

  • Respiratory irritation: asthma flare ups leading to hospitalization, worsened COPD, emphysema

  • Decreased tourism revenue

  • Decreased photosynthetic rate

7.4 Atmospheric CO₂ and PM

• Natural Sources of Air Pollutants

  • Lighting strikes (convert N₂ in atmosphere to NO_x)

  • Forest fires (CO, PM, NO_x, combustion of biomass also releases CO₂ and H₂O vapor) (greenhouse gasses)

  • Plants (especially conifers) (plants emit VOCs)

  • Volcanoes (SO₂, PM, CO, NO_x)

• Natural Sources of CO₂ and PM

  • Respiration (all living thins release CO₂ through respiration)

  • Natural PM Sources (sea salt, pollen, ash from forest fires, volcanoes, and dust leads to haze)

  • Aerobic Decomposition (decomposition of organic matter by bacteria and decomposers in the presence of oxygen 🡪 releases CO₂)

  • Anaerobic decomposition (decomposition of organic matter by bacteria and decomposers in low or oxygen-free conditions 🡪 releases CH₄ (methane))

• PM₁₀ vs PM_2.5

  • Particulate matter: solid or liquid particles suspended 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) smaller dust particles

    • More likely to travel deep into the lungs due to smaller size

    • Associated with chronic bronchitis and increased risk of lung cancer

7.5 Indoor Air Pollutants

• Developing Countries

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

  • These biomass fuels release CO, PM, NO₂, VOCs (can also cause deforestation)

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

• Developed Countries

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

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

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

• PM and Asbestos

  • Particulates (PM) are common indoor air pollutant

  • Asbestos is a long, silicate particle previously used in insulations (since been linked to lung cancer and asbestosis)

• CO (Carbon Monoxide)

  • CO is an asphyxiant: causes suffocation due to CO binding to hemoglobin in blood, displacing O₂

  • Lethal to humans in high concentrations, especially with poor ventilation (odorless and colorless – hard to detect)

  • Developed nations: CO released into home by malfunctioning natural gas furnace ventilation

  • Developing nations: CO emitted from indoor biomass combustion for heating/cooking

• VOCs (Volatile Organic Compounds)

  • Chemicals used in a variety of home products that easily vaporize, enter air, and irritate eyes, lungs, bronchioles

  • Adhesives/sealants: chemicals used to glue carpet down, hold furniture together, seals panels

  • Formaldehyde is a common adhesive in particle board and carpet glues

  • Cleaners: common household cleaners and deodorizers such as Febreze

  • Plastics and Fabrics: both can release VOCs themselves, or from adhesives used in production

• Radon Gas

  • Radioactive gas released by decay of uranium naturally found in rocks underground (granite especially)

  • Usually enters homes through cracks in the foundation and then disperse up from basement/foundation through home

  • can also seep into groundwater sources and enter body through drinking water

• Dust and Mold

  • Natural indoor air pollutants that can worsen asthma, bronchitis, COPD, emphysema

  • Dust settles in homes naturally, is disturbed by movement, entering air and then respiratory tract

  • Mold develops in areas that are dark and damp and aren’t well ventilated

• Lead

  • Found in paint in old homes

  • Paint chips off walls/windows and is eaten by small children or inhaled as dust

7.6 Reduction of Air Pollutants

• Reducing Emissions

  • Reducing emissions = reducing air pollutants

• Law/Regulations

  • Clean Air Act

    • Allows EPA to set acceptable levels for criteria air pollutants

      • Monitor emissions levels from power plants and other facilities

      • Tax/sue/fine corporations that release emissions above levels

  • CAFE Vehicle Standards

    • (Corporate Average Fuel Economy) standards require the entire US fleet of vehicles to meet certain average

      • Requires vehicle manufacturers to work to make more efficient vehicles

      • More efficient vehicles burn less gasoline and release less NO_x, PM, CO, and CO₂

  • Pollution Credits

    • Similar to ITQs for fish

    • Companies that reduce emissions below EPA-set levels earn pollution credits

• Reducing Vehicle Air Pollutants

  • Vapor Recovery Nozzle

    • Capture hydrocarbon VOCs released from gasoline fumes during refueling

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

      • Reduces VOCs, which contribute to smog and irritate respiratory tracts

      • Reduces benzene (carcinogen) released from gasoline vapors

  • Catalytic Converter (CC)

    • Required on all vehicles after 1975

    • Contains metals (platinum and palladium) that bind to NO_x and CO

      • CC converts NO­_x, CO, and other hydrocarbons into CO₂, N₂, O₂, and H₂O

• Reducing SO_x­ and NO_x

  • Crushed Limestone (SO₂)

    • Used to reduce SO₂ from coal power plants

    • Crushed coal mixed with limestone (calcium carbonate) before being burned in boiler

    • Calcium carbonate in limestone combines with SO₂ to produce calcium sulfate, reducing the SO₂ being emitted

    • Calcium sulfate can be used to make gypsum wallboard or sheetrock for home foundations

  • Fluidized Bed Combustion (NO_z)

    • Fluidizing jets of air pumped into combustion “bed”

    • Jets of air bring more 0₂ into reaction, making combustion more efficient and bringing SO₂ into more contact with calcium carbonate in limestone

      • Also allows coal to be combusted at lower temperature, which emits less NO_x

• Wet and Dry 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

• Reducing Particulate Matter

  • Electrostatic Precipitator

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

    • Negative charged particles stick to positive charged collection plates, trapping them

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

  • Baghouse Filter (PM)

    • Large fabric bag filters that trap PM as air from combustion/industrial process passes through

    • Shaker device knocks trapped particles loose into collection hopper below

7.7 Acid Rain

• Sources of NO_x and SO₂

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

  • Major Sources

    • SO­₂ – coal fired power plants, metal factories, vehicles that burn diesel fuel

    • NO_x – vehicle emissions, diesel generators, coal power plants

  • Limiting Acid Rain

    • Reducing NO­_x and SO₂ emissions reduces acid deposition

      • Higher CAFE standards

      • More public transit

      • Renewable energy sources

      • More efficient electricity use

    • Since passage of Clean Air Act, acid deposition has decreased significantly

• NO_x and SO₂ react with O₂ and H₂O in the atmosphere, forming nitric and sulfuric acid

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

• Acidic rain water (higher H+ concentration) decreases soil and water pH; can limit tree growth in forests down wind from major SO₂ and NO_x sources

• Environmental Effects of Acid Rain

  • Acidity= higher H+ ion concentration, lower pH

  • Soil/water acidification

    • H+ ions displace or leech other positive charged nutrients (Ca²⁺, K⁺) from soil

    • H+ ions also make toxic metals like aluminum and mercury more soluble in soil and water

  • pH Tolerance

    • as pH decreases (more acidic) outside optimal range for a species, population declines

      • when pH leaves range of tolerance, they cannot survive at all due to aluminum toxicity and disrupted blood osmolarity

  • indicator species can be surveyed and used to determine conditions of an ecosystem

• Mitigating Acid Rain

  • Limestone (calcium carbonate) is a natural base that can neutralize acidic soil/water

  • 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

    • Acid rain can corrode human structures, especially those made from limestone

  • Limiting SO_x and NO_x

    • Decreasing these primary pollutants that drive acid rain can reduce it

      • Renewable energy sources, decreasing coal comb.

      • Fluidized bed combustion and lower burning temperature for existing coal power plants

      • Dry or wet scrubbers

7.8 Noise Pollution

• Urban Noise Pollution

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

  • Construction: jack hammers, trucks, concrete pouring

  • Transportation: cars, busses, trains

  • Industrial activity: manufacturing plants

  • Domestic activity: neighbor’s music, lawn mowing, home projects

• Wildlife Effects (land)

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

  • Physiological stress: caterpillar hearts beat faster when exposed to simulated highway noise pollution

  • Hearing: can prevent predators from hearing prey and vice versa; can prevent mates from locating each other (both decrease chances of survival)

• Wildlife Effects (aquatic)

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

  • Physiological stress: hearing loss, disrupted communication, mating calls, predator and prey navigation

    • whales are especially prone to having migration routes disrupted as their vocal communication is disrupted

  • Seismic surveying: ships send huge air blasts down into the water, searching for oil by recording how the echo is returned from ocean floor

    • So loud that researchers off the coast of Virginia can detect blasts from coast of Brazil