Learning Objective: STB-2.A: Identify the sources and effects of air pollutants.
Essential Knowledge:
STB-2.A.1: Coal combustion releases air pollutants including carbon dioxide, sulfur dioxide, toxic metals, and particulates.
STB-2.A.2: The combustion of fossil fuels releases nitrogen oxides into the atmosphere. They lead to the production of ozone, formation of photochemical smog, and convert to nitric acid in the atmosphere, causing acid rain. Other pollutants produced by fossil fuel combustion include carbon monoxide, hydrocarbons, and particulate matter.
STB-2.A.3: Air quality can be affected through the release of sulfur dioxide during the burning of fossil fuels, mainly diesel fuels.
STB-2.A.4: Through the Clean Air Act, the Environmental Protection Agency (EPA) regulated the use of lead, particularly in fuels, which dramatically decreased the amount of lead in the atmosphere.
STB-2.A.5: Air pollutants can be primary or secondary pollutants.
Air Pollution Basics
Coal combustion (electricity): Responsible for respiratory irritation, smog, and acid precipitation.
Fossil fuel/biomass combustion: Responsible for respiratory irritation and smog.
SO_2 (Sulfur dioxide).
Nitrogen Oxides (NO & NO_2).
Carbon Monoxide (CO).
Particulate Matter (PM).
Ozone (tropospheric) (O_3).
Lead (Pb ).
All FF combustion (gas esp.): Ozone, photochemical smog, and acid precipitation.
Incomplete combustion: Ozone, lethal to humans.
Photochemical oxidation of NO_2: Respiratory irritation, smog, and plant damage.
Metal plants, waste incineration: Neurotoxicant.
Clean Air Act (1970): Identified 6 criteria air pollutants that the EPA is required to set acceptable limits for, monitor, and enforce.
Air Pollutants vs. Greenhouse Gasses
CO_2 is NOT one of 6 criteria pollutants in Clean Air Act (although 07’ SC ruling found EPA could regulate greenhouse gases and it began doing so in 09’)
CO_2 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
CO_2 is a greenhouse gas; it does lead to earth warming, and thus env. and human health consequences (basis for SC ruling in 07’)
Bottom line: In APES, CO2 has not typically been included on FRQ scoring guides as an air pollutant (stick to sure fire air pollutants on FRQs: SO2, NOx, O3, PM)
Coal Combustion
Releases more air pollutants than other FFs; ~35% of global electricity.
Releases CO, CO2, SO2, NO_x, toxic metals (mercury, arsenic, lead), and PM (often carries the toxic metals).
Impacts of SO_2
Respiratory irritant (inflammation of bronchioles, lungs), worsens asthma & bronchitis.
Combines with water & O_2 in atmosphere to form sulfuric acid → acid precipitation.
Nitrogen Oxides (NO_x)
Released by combustion of anything, especially FFs & biomass.
NOx refers to nitrogen oxides (both NO, and NO2).
NO forms when N2 combines with O2 (esp. during combustion).
NO can become NO2 by reacting with O3 or O_2.
sunlight converts NO_2 back into NO.
Env. & Human Health Impacts
Resp. irritant.
Leads to tropospheric ozone (O_3) formation, which leads to photochemical smog.
Combines with water & O_2 in atm. to form nitric acid → acid precipitation.
EPA & 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).
Also a known neurotoxicant (damages nervous systems of humans).
Primary vs. Secondary Air Pollutants
Primary
Emitted directly from sources such as vehicles, power plants, factories, or natural sources (volcanoes, forest fires).
NOx, CO, CO2*, VOCs, SO_2, PM, hydrocarbons.
Secondary
Primary pollutants that have transformed in presence of sunlight, water, O_2.
Occur more during the day (since sunlight often drives formation).
Tropospheric O_3 (Ozone).
Sulfuric acid (H2SO4) & sulfate (SO_4^{2-}$).
Nitric acid (HNO3) & nitrate (NO3^-$).
7.2 Photochemical Smog
Learning Objective: STB-2.B: Explain the causes and effects of photochemical smog and methods to reduce it.
Essential Knowledge:
STB-2.B.1: Photochemical smog is formed when nitrogen oxides and volatile organic hydrocarbons react with heat and sunlight to produce a variety of pollutants.
STB-2.B.2: Many environmental factors affect the formation of photochemical smog.
STB-2.B.3: 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.
STB-2.B.4: Volatile Organic Compounds (VOCs), such as formaldehyde and gasoline, evaporate or sublimate at room temperature. Trees are a natural source of VOCs.
STB-2.B.5: Photochemical smog often forms in urban areas because of the large number of motor vehicles there.
STB-2.B.6: Photochemical smog can be reduced through the reduction of nitrogen oxide and VOCs.
STB-2.B.7: Photochemical smog can harm human health in several ways, including causing respiratory problems and eye irritation.
Precursors
NO2 | Broken by sunlight into NO + O (free O + O2 → O_3)
VOCs | Volatile organic compounds (hydrocarbons) that bind with NO & form photochemical oxidants
O3 | Forms when NO2 is broken by sunlight & free O binds to O_2
Sunlight | Drives O3 formation by breaking down NO2 → NO + O; then free O atom binds with O_2
Warmer temperature, speedes evap. of VOCs and rxn that lead to O_3
Urban areas have more smog due to all of these factors
More traffic → more NO_2
Hotter temps due to low albedo of blacktop
More VOCs due to gas stations & factories
More electricity demand; more NO_x emissions from nearby power plants
Impacts & Reduction of Smog
Env. | Reduces sunlight; limiting photosynthesis; O_3 damages plant stomata and irritates animal resp. tracts
Humans | Resp. 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 ag. yields due to less sunlight reaching crops & damage to plant stomata
Vehicles | Decreasing the number of vehicles on the road decreases NO_2 emissions; Fewer vehicles = less gas = fewer VOCs
Energy | Increased electricity production from renewable sources that don’t emit NOx (solar, wind, hydro); Nat. gas power plants release far less NOx than coal
Reduction - Carpooling, public transport, biking, walking, working from home.
7.3 Thermal Inversion
Learning Objective: STB-2.C: Describe thermal inversion and its relationship with pollution.
Essential Knowledge:
STB-2.C.1: During a thermal inversion, the normal temperature gradient in the atmosphere is altered as the air temperature at the Earth's surface is cooler than the air at higher altitudes.
STB-2.C.2: Thermal inversion traps pollution close to the ground, especially smog and particulates.
Urban Heat Island Effect
Urban areas tend to have higher surface & air temperature than surrounding suburban and rural areas due to:
Lower albedo; concrete & 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 & 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 & distributes them higher into the atmosphere
During a thermal inversion, a cooler air mass becomes trapped near earth’s surface (Inverting normal gradient)
Due to a warm front moving in over it
Or due to hot urban surfaces cooling 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 cary pollutants up & away
Effects of Thermal Inversion
Air pollutants (smog, PM, ozone, SO2, NOx) trapped closer to earth
Respiratory irritation: asthma flare ups leading to hospitalization, worsened COPD, emphysema
Decreased tourism revenue
Decreased photosynthetic rate
7.4 Atmospheric CO_2 & PM
Learning Objective: STB-2.D: Describe natural sources of CO_2 and particulates.
Essential Knowledge:
STB-2.D.1: CO_2 appears naturally in the atmosphere from sources such as respiration, decomposition, and volcanic eruptions.
STB-2.D.2: There are a variety of natural sources of particulate matter.
Natural Sources of Air Pollutants
Lightning Strikes Convert N2 in atm. to NOx
Forest Fires
Combustion of biomass also releases CO2 & H2O vapor (greenhouse gasses).
SO2, PM, CO, NOx
Volcanoes
Plants emit VOCs
Ex: terpenes & ethylene from pine, fir, spruce trees
This forms natural photochemical smog in Smoky Mountains
Natural Sources of CO_2 & PM
Respiration
All living things (plants included) release CO_2 through respiration
Decomposition
Aerobic Decomposition: Decomposition of organic matter by bacteria & decomposers in the presence of oxygen → releases CO_2
Anaerobic Decomposition: Decomposition of organic matter by bacteria & decomposers in low or oxygen-free conditions → releases CH_4 (methane)
Leads to haze (scattering of sunlight & reduced visibility)
PM10 vs. PM2.5
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 & cause inflammation
PM2.5 ( <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
Learning Objective: STB-2.E: Identify indoor air pollutants.
Essential Knowledge:
STB-2.E.1: Carbon monoxide is an indoor air pollutant that is classified as an asphyxiant.
STB-2.E.2: Indoor air pollutants that are classified as particulates include asbestos, dust, and smoke.
STB-2.E.3: Indoor air pollutants can come from natural sources, human-made sources, and combustion.
STB-2.E.4: Common natural source indoor air pollutants include radon, mold, and dust.
STB-2.E.5: Common human-made indoor air pollutants include insulation, Volatile Organic Compounds
(VOCs) from furniture, paneling and carpets; formaldehyde from building materials, furniture,
upholstery, and carpeting; and lead from paints.
STB-2.E.6: Common combustion air pollutants include carbon monoxide, nitrogen oxides, sulfur dioxide, particulates, and tobacco smoke.
STB-2.E.7: Radon-222 is a naturally occurring radioactive gas that is produced by the decay of uranium found in some rocks and soils.
Essential Knowledge:
STB-2.F.1: Radon gas can infiltrate homes as it moves up through the soil and enters homes via the basement or cracks in the walls or foundation. It is also dissolved in groundwater that enters homes through a well.
STB-2.F.2: Exposure to radon gas can lead to radon-induced lung cancer, which is the second leading cause of lung cancer in America.
Developing vs. Developed Countries
Developing nations use more subsistence fuels such as wood, manure, charcoal (biomass)
These biomass fuels release CO, PM, NO_x, VOCs ( can also cause deforestation)
Often combusted indoors with poor ventilation, leading to high concentrations
Est. 3 billion people globally cook with subsistence fuels, resulting in est. 3.5 - 4.3 million deaths annually
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 & Asbestos
Particulates (PM) are a common indoor air pollutant
Ex: Smoke (from indoor biomass combustion or cigarettes), dust, and asbestos
Asbestos is a long, silicate particle previously used in insulation (since been linked to lung cancer & asbestosis)
Phased out of use, but still remains in older buildings
Not dangerous until insulation is disturbed and asbestos particles enter air & then resp. tract
Should be removed by trained professionals with proper respiratory equipment, ventilation in the area it’s being removed from, plastic to seal off area from rest of the building
CO (Carbon Monoxide)
CO is produced by incomplete combustion of basically any fuel
Not all the fuel is combusted due to low O_2 or temp.
CO is an asphyxiant: causes suffocation due to CO binding to hemoglobin in blood, displacing O_2
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
Can be detected by carbon monoxide detectors (similar to smoke detectors)
Developing nations: CO emitted from indoor biomass combustion for heating/cooking
VOCs (Volatile Organic Compounds)
Chemicals used in 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, seal panels
Formaldehyde is a common adhesive in particle board and carpet glues (new carpet smell)
Cleaners: Common household cleaners and deodorizers such as febreeze
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 & then disperses up from basement/foundation through home
Can also seep into groundwater sources & enter body through drinking water
2nd leading cause of lung cancer after smoking
EPA recommends testing homes with airborne Radon monitor
Sealing cracks in foundation can prevent it from entering and increasing ventilation in the home can disperse it if it’s detected
Dust & 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 (under sinks/showers, behind panels in walls and ceiling)
Black mold is a class of mold that releases spores into air
Especially harmful to resp. system
Can be removed by physically cleaning mold out and fixing the water leak or ventilation issue that lead to mold forming
Lead
Found in paint in old homes (EPA banned lead paint in 78’)
Paint chips off walls/windows and is eaten by small children (due to curiosity & sweet taste) or inhaled as dust
Lead water pipes can also release lead into drinking water sources (as in Flint) but it’s less common than lead paint
Damages central nervous system of children due to smaller size and still developing brain
Can be removed from home by stripping lead paint and replacing with non-lead based paint
Lead water pipes can be replaced by cities with copper pipes
7.6 - Reduction of Air Pollutants
Learning Objective: STB-2.G: Explain how air pollutants can be reduced at the source.
Essential Knowledge:
STB-2.G.1: Methods to reduce air pollutants include regulatory practices, conservation practices, and alternative fuels.
STB-2.G.2: 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.
STB-2.G.3: 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 H_2O).
STB-2.G.4: Wet and dry scrubbers are air pollution control devices that remove particulates and/or gases from industrial exhaust streams.
STB-2.G.5: Methods to reduce air pollution from coal-burning power plants include scrubbers and electrostatic precipitators.
Reducing Emissions = reducing air pollutants
Drive less, walk/bike/bus more
Conserve electricity (smart appliances)
Eat more plants, less meat
Renewable, non-pollution emitting energy (solar, wind, hydro)
Laws/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 fuel
Requires vehicle manufacturers to work to make more efficient vehicles
More efficient vehicles burn less gasoline and release less NOx, PM, CO, and CO2
Pollution Credits
Similar to ITQs for fish
Companies that reduce emissions well below EPA-set levels earn pollution credits
They can sell these to companies that release more than acceptable levels
Reducing Vehicle Air Pollutants
Vapor Recovery Nozzle
Capture hydrocarbon VOCs released from gasoline fumes during refueling
Separate tube inside nozzle captures vapors & returns them to underground storage tank beneath the gas station
Reduces VOCs, which contribute to smog & irritate resp. tracts
Also reduces benzene (carcinogen) released from gasoline vapors
Catalytic Converter (CC)
Required on all vehicles after 1975
Contains metals (platinum & palladium) that bind to NO_x and CO
CC converts NOx, CO, and other hydrocarbons into CO2, N2, O2, and H_2O
Reducing SOx & NOx
Crushed Limestone (SO_2)
Used to reduce SO_2 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_x)
Fluidizing jets of air pumped into combustion “bed”
Jets of air bring more O2 into rxn, making combustion more efficient and bringing SO2 into more contact with calcium carbonate in limestone
Also allows coal to be combusted at lower temp, which emits less NO_x
Wet & Dry Scrubbers
Dry Scrubbers (NOx, SOx, VOCs)
Large column/tube/pipe filled with chemicals that absorb or neutralize oxides (NOx, SOx, VOCs) from exhaust streams (emissions)
Calcium oxide is a common dry scrubber additive which reacts with SO_2 to form calcium sulfite
Wet Scrubbers (NOx, SOx, VOCs + PM)
May involve chemical agents that absorb or neutralize NOx, SOx, 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 @ top by mist eliminator
Sludge collection system traps polluted water for disposal
Reducing PM
Electrostatic Precipitator
Power plant/factory emissions passed through device with a neg. charged electrode, giving particles a neg. Charge
Neg. charged particles stick to pos. 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
PM collected & taken to landfill
7.7 Acid Rain
Learning Objective:
STB-2.H: Describe acid deposition.
Essential Knowledge:
STB-2.H.1: Acid rain and deposition is due to nitrogen oxides and sulfur oxides from anthropogenic and natural sources in the atmosphere.
STB-2.H.2: Nitric oxides that cause acid deposition come from motor vehicles and coal-burning power plants. Sulfur dioxides that cause acid deposition come from coal-burning power plants.
Learning Objective:
STB-2.I: Describe the effects of acid deposition on the environment.
Essential Knowledge:
STB-2.I.1: Acid deposition mainly affects communities that are downwind from coal-burning power plants.
STB-2.I.2: Acid rain and deposition can lead to the acidification of soils and bodies of water and corrosion of human-made structures.
STB-2.I.3: Regional differences in soils and bedrock affect the impact that acid deposition has on the region-such as limestone bedrock's ability to neutralize the effect of acid rain on lakes and ponds.
Major Sources
Sources of NOx & SO2
SO_2 - Coal fired power plants, metal factories, vehicles that burn diesel fuel
NO_x - vehicle emissions, diesel generators coal power plants
NOx and SO2 are the primary pollutants that cause most acid precipitation
Since passage of Clean Air Act, acid deposition has decreased significantly
Acid Formation
NOx 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^+ conc.) deceases soil and water pH; can limit tree growth in forests down wind from major SO2 & NOx sources
Env. Effects of Acid Rain
Soil/Water Acidification
H^+ ions displace or leech other pos. charged nutrients (Ca^{2+}, K^+) from soil
H^+ ions also make toxic metals like aluminum and mercury more soluble in soil and water
This can slow growth or kill plants and animals living in the soil or water
Acidity = higher H^+ ion concentration, lower pH
Env. Effects of Acid Rain
pH Tolerance
Aquatic species have diff. pH tolerances
As pH decreases (more acidic) outside optimal range for a species, pop. declines
When pH leaves range of tolerance, they cannot survive at all, due to:
Aluminum toxicity
Disrupted blood osmolarity (Na^+/Cl^- balance disrupted at low pH)
Indicator species can be surveyed and used to determine conditions of an ecosystem (soil, water, etc.)
Ex: high whitemoss/filamentous algae pop. indicates pH < 6.0
High crustacean pop. indicates pH > 6.0
Mitigating Acid Rain
Limestone
Calcium carbonate (CaCO3) reacts with H^+ ions, forming HCO3 and giving off Ca^{2+}
This “neutralizes” acidic water/soil, moving it closer to a pH of 7
Limestone (calcium carbonate) is a natural base that can neutralize acidic soil/water
Regions with limestone bedrock have some natural buffering of acid rain
Humans can also add crushed limestone to soils/waters to neutralize
Limiting SO2& NOx
Decreasing these primary pollutants that drive acid rain can reduce it
Renewable energy sources, decreasing coal comb.
Fluidized bed combustion & lower burning temp. for existing coal power plants
Dry or wet scrubbers
Acid rain can corrode human structures, especially those made from limestone
7.8 Noise Pollution
Learning Objective: STB-2.J: Describe human activities that result in noise pollution and its effects.
Essential Knowledge:
STB-2.J.1: Noise pollution is sound at levels high enough to cause physiological stress and hearing loss.
STB-2.J.2: Sources of noise pollution in urban areas include transportation, construction, and domestic and industrial activity.
STB-2.J.3: Some effects of noise pollution on animals in ecological systems include stress, the masking of sounds used to communicate or hunt, damaged hearing, and causing changes to migratory routes.
Urban Noise Pollution
Construction: jack hammers, trucks, concrete pouring
Transportation: cars, busses, trains
Industrial activity: manufacturing plants
Domestic activity: neighbor’s music, lawn mowing, home projects
Any noise at great enough volume to cause physiological stress (difficulty communicating, headaches, confusion) or hearing loss
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
Could drive pollinator species decline
Hearing: can prevent predators from hearing prey and vice versa; can prevent mates from locating each other (both of these 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 & gas surveying ships