7.1 - Introduction to Air Pollution (Pollutants)

Air Pollution Basics

• Clean Air Act (1970) identified 6 criteria air pollutants that the EPA is required to set acceptable limits for, monitor, and enforce

• Sulfur Dioxide (SO2)

  • Coal combustion (electricity)

  • Resp. irr. | smog | acid precip.

• Nitrogen Oxides (NO and NO2)

  • All FF combustion (gas esp.)

  • O3 | photochem smog | acid precip.

• Carbon Monoxide (CO)

  • Incomplete combustion

  • O3 | lethal to humans

• Particulate Matter (PM)

  • FF/biomass combustion

  • Resp. irr | smog

• Tropospheric Ozone (O3)

  • Photochemical oxidation of NO2

  • Resp. irr | smog | plant damage

• Lead (Pb)

  • Metal plants, waste incineration

  • Neurotoxicant

Air Pollutants

• CO2 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’)

• 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 env. and human health consequences (basis for SC ruling in 07’)

Coal Combustion

• Releases more air pollutants than other FFs; ~35% of global electricity

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

• Impacts of SO2

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

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

  • Forms sulfurous (grey) smog

  • Combines with water & O2 in atmosphere to form sulfuric acid → acid precip.

Nitrogen Oxides (NOx)

• 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 O2

  • sunlight converts NO2 back into NO

• Env. & Human Health Impacts

  • Resp. irritant

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

  • Combines with water & O2 in atm. 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 NOx, 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, SO2, PM, 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) & sulfate (SO42-)

  • Nitric acid (HNO3) & 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 & form photochemical oxidants

      • Carbon-based compounds that volatilize (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

      • Resp. irr. in troposphere (@earth’s surface)

      • Damaging to plant stomata, limiting growth

• Conditions

  • Sunlight

    • Drives O3 formation by breaking down NO2 → NO + O; then free O atom binds with O2

  • Warmth

    • Hotter atm. temp. speeds O3 formation, evaporation of VOCs & 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

• Normal O3 Formation

• VOCs bond with NO to form photochemical oxidants

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

• O3 combines with photochem. oxidants (NO + VOCS) to form photochemical smog

Factors that Increase Smog Formation

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

• More sunlight (summer, afternoon) = more O3

• Higher VOCs emissions (gas stations, laundromats, petrochem. & plastic factories)

• Warmer temperature, speedes evap. of VOCs and rxn that lead to O3

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

  • More traffic → more NO2

  • Hotter temps due to low albedo of blacktop

  • More VOCs due to gas stations & factories

  • More electricity demand; more NOx emissions from nearby power plants

Impacts and Reduction of Smog

• Impacts

  • Environmental

    • Reduces sunlight; limiting photosynthesis

    • O3 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

• Reduction

  • Vehicles

    • 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

  • 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

7.3 - Thermal Inversion

Urban Head 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 carry 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

7.7 - Acid Rain

Sources of NOx and SO2

• NOx 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

  • NOx - vehicle emissions, diesel generators coal power plants

• Limiting Acid Rain

  • Reducing NOx & SO2 emissions

    reduces acid deposition

    • Higher CAFE Standards

    • More public transit

    • Renewable energy sources

    • More efficient electricity use

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

Acid Rain 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

• Acidity = higher H+ ion concentration, lower pH

• Soil/Water Acidification

  • H+ ions displace or leech other pos. charged nutrients (Ca2+, 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

• Aquatic species have different pH tolerances

• pH tolerance

  • 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) 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 SO2 and 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

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

    • 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

  • 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

7.4 - Atmospheric CO2 and PM

Natural Sources of Air Pollutants

• Lightning Strikes

  • Convert N2 in atmosphere to NOx

• Forest Fires

  • CO, PM, NOx

  • Combustion of biomass also releases CO2 and H2O vapor (greenhouse gasses)

• Plants (esp. conifers)

  • Plants emit VOCs

    • Ex. terpenes and ethylene from pine, fir, spruce trees; forms natural photochemical smog in Smoky Mountains

• Volcanoes

  • SO2, PM, CO, NOx

Natural Sources of CO2 and PM

• Respiration

  • All living things (plants included) release CO2 through respiration

• Aerobic Decomposition

  • Decomposition of organic matter by bacteria & decomposers in the presence of oxygen → releases CO2

• Anaerobic Decomposition

  • Decomposition of organic matter by bacteria & decomposers in low or oxygen-free conditions → releases CH4 (methane)

• Natural PM Sources

  • Sea salt, pollen, ash from forest fires & volcanoes

    dust (windborne soil)

  • Leads to haze (scattering of sunlight & reduced visibility)

PM10 versus 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

7.4 - Indoor Air Pollutants

Developing vs. Developed Countries

• Developing

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

    • These biomass fuels release CO, PM, NOx, 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

  • 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 a common indoor air pollutant

  • Ex: Smoke (from indoor biomass combustion or cigarettes), dust, and asbestos

• Asbestos: 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 O2 or temp.

  • 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

    • 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 deodorizer 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 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 (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

Reducing Emissions

• 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

• 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

• 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

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 NOx and CO

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

Reducing SOx and NOx

• Crushing 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 (NOx)

• 

  • 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 NOx

Wet and 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 SO2 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