APES Unit 7 Atmospheric Pollution

Clean Air Act (1970)

Identified 6 criteria pollutants

• EPA is required to set acceptable limits for, monitor, and enforce

• SO₂, NOx, CO, PM, O₃, Pb

SO₂ Sulfur dioxide

Comes from: Coal combustion (electricity)

Major concerns: Respiratory irritant, smog, acid precipitation

NOx Nitrogen oxides

Comes from: All FF combustion (gas especially)

Major concerns: O₃, photochemical smog, acid precipitation

• NO nitric oxide and NO₂ nitrogen dioxide

CO Carbon monoxide

Comes from: Incomplete combustion

Major concerns: O₃, lethal to humans

PM Particulate matter

Comes from: FF/Biomass combustion

Major concerns: Respiratory irritant, smog

O₃ Ozone (tropospheric ozone)

Comes from: Photochemical oxidation of NO₂

Major concerns: Respiratory irritant, smog, plant damage

Pb Lead

Comes from: Metal plants, waste incineration

Major concerns: Neurotoxicant

Why is CO₂ not one of the 6 pollutants in the Clean Air Act?

Does not directly lower air quality from a human health standpoint

• not toxic to organisms to breath

• not damaging to lungs/eyes

• doesn’t lead to smog, decreased visibility

• is a GHG → leads to earth warming and human health consequences (basis for SC ruling in 07’)

Why we care about coal

Released more air pollutants than other FFs; around 35% of global electricity

• releases CO, CO₂, SO₂, NOx toxic metals and PM

Impacts of SO₂ (sulfur dioxide)

• Respiratory irritant, worsens asthma and bronchitis

• Sulfur aerosols (Sulfate SO₄)

• Sulfurous (grey) smog

• H₂SO₄ - sulfuric acid → acid precipitation

N₂+O₂

2NO

2NO+O₂

2NO₂

Sunlight+NO₂

NO

Primary air pollutants

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

• including: NOx, CO, CO₂, VOCs, SO₂, PM, hydrocarbons

Secondary air pollutants

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

• occur more during the day (since sunlight often drives formation)

• include: tropospheric O₃ (ozone), H₂SO₄ (sulfuric acid), SO₄^2- (sulfate), HNO₃ (nitric acid), NO₃^- (nitrate)

Volatile Organic Compounds (VOCs)

Carbon-based compounds that volatize (evaporate) easily

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

Photochemical smog precursors

• NO₂

  • broken by sunlight into NO+O (free O+O₂→O₃)

• VOCs (hydrocarbons)

  • that bind with NO and form photochemical oxidants

• O₃

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

  • respiratory irritant in troposphere

  • damaging to plant stoma, limiting growth

Photochemical smog conditions

• Sunlight

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

• Warmth

  • hotter atmospheric temperature speeds O₃ formation, evaporation of VOCs and thus smog formation

Process of normal tropospheric ozone formation

Sunlight interacts with NOx and VOCs (emitted from sources like cars, factories, and power plants), causing a series of chemical reactions that ultimately produce ozone molecules

• most active on hot, sunny days

Process of formation of photochemical smog

Sunlight breaks down NO₂ from vehicle emissions, releasing oxygen atom which then combines with atmospheric oxygen to create O₃; this O₃ builds up in the atmosphere under conditions like stagnant air, creating hazy brown smog

Factors that increase smog

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

• More sunlight (summer, afternoon) = more O₃

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

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

Why do urban areas have more smog?

• More traffic → more NO₂

• Hotter temps due to low albedo of blacktop

• More VOCs due to gas stations and factories

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

Impacts of smog

• Reduces sunlight, limiting photosynthesis

• O₃ damages plant stomata and irritates animal respiratory tracts

• Respiratory irritant; worsens asthma, bronchitis, COPD; irritates eyes

• Increased cost of healthcare

• Lost productivity due to sick workers

• Agricultural yields decreased due to less sunlight

How can we reduce the formation of smog?

• Decrease the number of vehicles, which decreases NO₂ emissions

  • fewer vehicles = less gas = fewer VOCs

• Change energy sources

  • increased electricity production from renewable sources that don’t emit NO₂ (solar, wind, hydro)

  • natural gas power plants release far less NOx than coal

Why do urban areas have higher surface and air temperature?

• 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 into the atmosphere

  • cools off rural and suburban areas which have more vegetation

Normal atmospheric temperature pattern

Warm air rises and air convection carries pollutants away from earth’s surface and distributes them higher into the atmosphere

• warmest air (closest) → cooler air → cold air (furthest)

Thermal inversion

Cooler air mass becomes trapped near earth’s surface (inverting normal gradient)

• due to a warm front moving in over it OR hot urban surfaces cooling overnight while IR radiation absorbed during the day is still being released

• cooler air (closest) → warmer air → cold air (furthest)

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

Lightning strikes

Converts N₂ in atmosphere to NOx

Forest fires emit…

CO, PM, NOx

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

Volcanoes emit…

SO₂, PM, CO, NOx

Natural causes of PM

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

Aerobic decomposition emits…

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

Anaerobic decomposition emits…

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

Particulate matter (PM)

Solid or liquid particles suspended in air (also referred to as “particulates”)

PM₁₀

PM <10 micrometers/microns

• 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

PM <2.5 micrometers

• particles from combustion (especially vehicles)

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

• associated with chronic bronchitis and increased risk of lung cancer

Sources of air pollution in developing countries

Subsistence fuels (e.g. wood, manure, charcoal (biomass))

• biomass fuels release CO, PM, NOx, VOCs

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

Sources of air pollution in developed countries

Commercial fuels (e.g. coal, oil, natural gas) supplied by utilities

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

• chemicals in products: adhesives in furniture, cleaning supplies, insulation, lead paint

Asbestos

Long, silicate particle previously used in insulation

• linked to lung cancer and asbestosis

• phased out of use, but still remains in older buildings

• not dangerous until insulation is disturbed, and asbestos particles enter air and then respiratory tract

• should be removed by trained professionals with proper respiratory equipment, ventilation in the area it’s being removed from, and plastic to deal off area from the rest of the building

How is CO produced?

Incomplete combustion of any fuel

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

• lethal in high concentrations

Where does radon gas come from?

Decay of uranium naturally found in rocks and underground

• especially granite

• gets in the house from cracks in the foundation and the disperses up from basement/foundation through home and groundwater sources

Why is radon gas dangerous?

2nd leading cause of lung cancer

• use radon monitor, seal cracks in foundation, and increase ventilation in home if detected

Dust

Settles in homes naturally, is disturbed by movement, entering air and then respiratory tract

Mold

Develops in creas that are dark, damp, and aren’t well ventilated (e.g. under sinks/showers, behind panels in wall and ceiling)

Black mold

Class of mold that releases spores into the air

• especially harmful to respiratory system

• can be removed by physically cleaning mold out and fixing the water leak or ventilation issue that led to mold forming

Lead concerns

Damages CNS of children due to smaller size and still developing brain

Where is lead found?

Paint, water pipes, and leaded gasoline

Clean Air Act (1970)

Allows EPA to set acceptable levels for criteria air pollutants

• monitor emission levels from power plants and other fcilities

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

CAFE (Corporate Average Fuel Economy) vehicle standards (1978)

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 emissions less

Pollution credits

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

• they can sell these credits to companies that release more than acceptable amounts

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 gas station

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

• reduces benzene (carcinogen) released from gasoline vapors

Catalytic converter (1975)

Contains metals that bind to NOx and CO

• required on all vehicles after 1975

Crushed limestone

Used to reduce SO₂ from coal power plants

1. mix coal and limestone before burning

2. calcium carbonate in limestone combines with SO₂ to produce calcium sulfate, reducing the SO₂ being emitted

Fluidized bed combustion (NOx)

Fluidizing jets of air (O₂) pumped into combustion “bed“ which makes combustion more efficient and bringing in SO₂ into more contact with calcium carbonate in limestone

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 sulfate

Wet scrubbers (NOx, SOx, VOCs, PM)

May involve chemical agents that absorb or neutralize NOx, SOx, VOC, but also include mist nozzles that trap PM in water droplets as well

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

• sludge collection system traps polluted water for disposal

Electrostatic Precipitator (PM)

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

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 collects and taken to landfill

Major sources of acid rain

• SO₂

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

• NOx

  • vehicle emissions, diesel generators, coal power plants

How to limit acid rain

Reduce NOx and SO₂ emissions

• higher CAFE standards

• more public transportation

• renewable energy sources

• more efficient electricity use

Why is acid deposition worse on the east?

Winds blow pollution from large industrial areas from the Midwest to the East

Formation of acid rain

1. NOx and SO₂ react with O₂ and H₂O in the atmosphere, forming nitric and sulfuric acid

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

3. Acidic rainwater (higher H⁺ concentration) decreases soil and water pH; can limit tree growth in forests downwind from major SO₂ and NOx sources

Environmental effects of acid rain

Soil/Water acidification

• H⁺ ions leach other positively charged nutrients from soil

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

  • slows growth or kills plants and animals living in the soil or water

Limestone/Calcium carbonate and acid rain

Natural base that can neutralize acidic soil/water

• reacts with H⁺ ions, forming HCO₃ and giving off Ca²⁺, which “neutralizes” acidic water/soil

Noise pollution

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

• construction, transportation, industrial activity, domestic activity

Where does aquatic noise pollution come from?

Ship engines, military sonar, and seismic air blasts from oil and gas surveying ships

Whales and noise pollution

Whales are especially prone to having migration routes disrupted as their vocal communication is disrupted from noise pollution

Seismic surveying

Ships send huge air blasts down into the water, searching for oil by recording how the echo is returned from the ocean floor