APES- Unit 7: Air Pollution

air pollutants

gases and particulate material added to the atmosphere

primary pollutants

pollutants that are directly harmful & can react to form other harmful substances

(ex. NO_x, SO_x, PM, CO)

secondary pollutants

pollutants that form when primary pollutants interact or react with components of the atmosphere

(ex. tropospheric ozone O₃ & sulfuric acid H₂SO₄)

residence time

time a pollutant stays in the atmosphere

• brief residence time exerts localized impacts over short time period (ex. smog, acid rain)

• long residence time exerts regional or global impacts (ex. climate change, ozone depletion)

what are the effects of pollution?

• reduced visual quality (reduced range, quality, & alteration in color or contrast)

• damage to vegetation (leaf tissues, needles, fruits, reduction of growth rates & germination, increased susceptibility to disease & pests)

• soil & water contamination (deposition of airborne chemicals & particles can toxify soils, alter pH, & reduce productivity)

• human health effects (irritation of eyes, nose, throat, & increased lung disease, asthma, emphysema, COPD, pneumonia, bronchitis)

clean air act (1970)

identified the EPA is required to set acceptable limits for 6 criteria pollutants → later CO₂, CH₄, GHGs,& 200+ were added

1) sulfur dioxide (SO_z)

formed from coal combustion → causes respiratory irritation, smog, & acid deposition

2) nitrogen oxides (NO_x)

formed from fossil fuel combustion → causes O₃ formation, smog, & acid deposition

3) carbon monoxide (CO)

formed from incomplete combustion of fossil fuels (engines & biomass) → causes smog, O₃ formation & human death (lethal b.c it binds to hemoglobin → suffocation)

4) particulate matter (PM_2:5 & PM₂₀)

formed from fossil fuel & biomass combustion → causes respiratory irritation, smog, & mercury deposition

5) tropospheric ozone (O₃)

formed from photochemical oxidation of NO_x → causes respiratory irritation & smog

6) lead (Pb)

pollutant from metal plating & waste incineration (previously from adding tetramethyl & tetraethyl to leaded gasoline) → is a neurotoxin

what are the leading sources of most major air pollutants?

extraction, refining, & combustion (coal & gas for electricity, gasoline & diesel in engines)

what pollutants are associated with fossil fuels?

CO, CO₂, CH₄,VOCs, PM_2:5, NO_x, N₂O, SO₂, O₃, PAN’s, HNO₃, H_2, SO₄

carbon dioxide (CO₂)

formed from combustion of fossil fuels, respiration, & decomposition of organic matter → causes global warming, extreme heat, severe storms, flooding, expanding ranges of tropical diseases, ocean acidification

how is particulate matter formed?

• fire (→ matter + gas)

• volcanoes (→ ash & gas)

• dust storms

asian brown ring

result of economic growth but little environmental regulation; a 2-mile thick haze of pollution in the dry season that reduces sunlight reaching Earth’s surface → premature death

smog

unhealthy mixture of air pollutants which typically form over urban areas

1) industrial smog 2) photochemical smog

industrial “sulfurous” smog

forms primarily as a result of unregulated coal burning from industry & electricity production (combustion of coal & crude oil) → produces carbon monoxide, sulfur dioxide, nitrogen dioxide, & particulate matter

formation of aerosolized particles in smog

sulfur + water → sulfuric acid → condenses into particulate matters → forms aerosolized particles that are main components of smog

photochemical smog

forms primarily as a result of automobile exhaust during hot, sunny weather & when sunlight drives a series of reactions involving primary pollutants

***traffic releasing NO₂ & VOCS + sunlight (intensity & duration summer afternoons in warm climates & urban areas) = conditions that increase smog

what are primary pollutants in photochemical smog?

NO₂, VOC’s, CO, PM

what are secondary pollutants in photochemical smog?

O_3, Nitric Acid (HNO₃), PAN’s

how is nitrogen dioxide (NO₂) formed?

forms from combustion of gasoline in cars (N₂+ O₂ → ₂NO 2NO+O₂→ 2NO₂)

formation of tropospheric O₃ in photochemical smog

1. exhaust from morning traffic releases NO₂ & VOC’s

2. day-time temperature rises → splits NO₂ to form NO & O

3. O atoms react with O₂ → O₃

4. afternoon commute begins & NO₂ & VOC levels increase as O₃ peaks

formation of nitric acid (HNO₃) with photochemical smog

nitrogen dioxide (NO₂) from exhaust also reacts with water vapor → forms additional NO & nitric acid (HNO₃)

3NO₂ + H₂O → 2HNO₃ + NO

nitrogen dioxide gas + water → nitric acid + hydrogen monoxide

formation of peroxyacyl nitrates (PAN’s) in photochemical smog

NO₂ + VOC’s → PAN’s → powerful eye & respiratory irritant, can cause damage to vegetation, very stable & persistent in atmosphere

thermal inversion layers

forms when cold air gets trapped beneath a layer of warm air → traps pollution close to the ground, especially particulate matter & smog → higher concentration of pollutants

coastal inversions

air over land heats faster than air over the ocean (land is warm & warms air faster) → cool ocean air blows onshore under layers of warm air → coastal mountains prevent cool, ocean air from spreading inland

mountain inversion

cold air sinks into valleys at night → when warm front approaches, it moves over top of mountains, capping cold air trapped in valleys

enviromental impacts of smog

• particulate matter reduces sunlight & limits photosynthesis

• O₃ enters stomata & interferes with photosynthesis + cellular respiration

• H₂SO₄ & HNO₃ result in acid deposition

human health impacts of smog

PAN’s & O₃ are eye & respiratory irritations that cause/worsen asthma, bronchitis, COPD & pneumonia

economic impacts of smog

• increased healthcare costs for acute & chronic respiratory conditions

• lost productivity due to missed work days

• decreased agricultural yields

methods to reduce smog

• reducing cars (especially older ones) → increasing public transit, carpools, biking, & more walkable cities

• requiring vapor recovery nozzles

• requiring emission control catalytic converters

indoor air pollution

air pollution within workplaces, schools and homes: in developed nations, greatest pollution comes from exposure to synthetic materials

• furniture: adhesives, paint, foam, flame retardants

• building materials: adhesives, paints, insulation, flooring

• cigarette smoke

particulates (PM₁₀ & PM_2:5)

common indoor pollutant, such as smoke from indoor biomass combustion or cigarettes, dust, & asbestos

asbestos

long, silicate particle previously used in insulation & linked to lung cancer (phased out with clean air act but remains in older buildings); not dangerous until insulation is disturbed & particles enter air then respiratory tract → removed by removing ventilation from area & using plastic to seal it off from the rest of the building

carbon monoxide (CO) as indoor pollution

• in developed nations, is released into homes by malfunctioning natural gas furnace ventilation or vehicle left running in the garage

• in developing nation, is released from indoor biomass combustion for heating/cooking

volatile organic compounds (VOC’s)

diverse group of chemicals used in variety of home products that easily vaporize & enter the air → causes eye, nose, & throat irritation, dizziness, nausea, lightheadedness, damage to the liver, kidney, central nervous system, suspected/known carcinogen

examples of indoor VOC’s

• furniture: foam, adhesives, upholstery treated with flame retardants or stain guards

• building materials: adhesives, wall paint, insulation, particle board/OS13/MDF/plywood, vinyl flooring

• cleaners: common household cleaners, deodorizes, moth repellents, aerosol sprays, dry cleaning chemicals, pesticides

• office supplies: printer & copper ink/toner, permanent markets, liquid white out, carbon paper

• plastics: just about everywhere

formaldehyde

common VOC released by adhesive in manufactured wood products & carpet glues → rashes, changes in lung function,systemic toxicity

radon gas (radon-222)

radioactive gas released by decay of uranium naturally found in rocks underground → enters homes through cracks in the foundation & spreads + can seep into groundwater sources → enter body

• sealing cracks in foundation can prevent it from entering + increasing ventilation can disperse it

dust & mold

natural indoor air pollutants that can worsen asthma, bronchitis, COPD, emphysema; settles in homes naturally → disturbed by movement & enters air then respiratory tract

• fungi, molds, & mildews develop in damp, dark, poorly-ventilated areas → removed physically & water leak/ventilation issue is fixed

lead (Pb) as indoor pollutant

paint chips off walls/windows & is eaten by small children or inhaled as dust + can be released into drinking water through lead water pipes → damages central nervous system of children

what are acids?

substances that release H+ into solutions

• in water, HNO₃ → H+ + NO₃-

• in water, H₂SO₄ → H+ + HSO₄-

**pH scale is logarithmic, so one decrease in one unit = 10x increase in H+

acid deposition

deposition of acid or acid-forming pollutants from the atmosphere onto earth’s surface; orginates from emissions of sulfur dioxide (SO₂) & nitrogen oxides (NO_x)

dry deposition

particulate matter containing acids forms compounds or gaseous compounds that bind to surfaces

acid precipitation

rain, snow, sleet, hail, fog with pH below 5.6

how ae sulfuric acid (H₃SO₄) & nitric acid (HNO₃) formed?

compounds react with water vapor, oxygen, & oxidants

• 3NO₂ +H₂O → 2HNO₃ + NO

• 2SO₂ + O₂ → SO₃ → SO₃ + H₂O → H₂SO₄

H₂0 + NO, SO₂ CO₂ = acid

water + nitrogen dioxide (produced by lighting), sulfur dioxide (produced by volcanoes), carbon dioxide (produced respiration & aerobic decomposition) = forms acids

sources of sulfur dioxide (SO₂)

combustion of coal in power plants to produce electricity, production of metals, diesel combustion

sources of NO_x

vehicle emissions, coal power plants, gas power plants

effects of acid rain

• directly harmful to human health

• soil & water acidification (directly with acid precipitation or when dry deposition interacts with water in aquatic ecosystems)

• damages buildings & monuments

• prevailing winds transport pollutants that cause acid deposition → damages throughout a region

• worse in spring after snow melts & releases acidified runoff

buffer

soils naturally contain calcium carbonate (CaCO₃) that helps solutions resist changes in pH by reacting with H+ to reduce H+ concentration

CaCO₃ ←> Ca² + CO₃²- ←> HCO₃-

**some soils contain more calcium carbonate but all can be overwhelmed

cation exchange capacity (CEC)

CEC of soil decreases when pH drops & H+ increases b.c H+ displaces cation nutrients (Ca²+, Mg²+, Na+, K+, NH₄+) from clay particles in the soil → leeching of nutrients into deeper soil horizons away from plant roots)

aluminum toxicity

increases when soil pH drops b.c decreasing pH & increasing H+ dissolves the common soil compound AI(OH)₃ → produces ion AI3+ which binds tightly to clay particles, displacing ration nutrients

effects of acid rain on aquatic ecosystems

there is some natural buffer but… → lowered pH causes aluminum toxicity, disruption of blood osmolarity (balance of Na+/CL-) & water balance → decreases outside of optimal range for aquatic species → physiological stress & changes in species composition

economic impacts of acid deposition

• reduces crop productivity (down cation exchange, up aluminum toxicity)

• reduces forest productivity: loss of provisioning (lumber services), loss of cultural services (tourism) economic value, loss of supporting services (biodiversity) that underlie functioning of ecosystems

• reduced productivity of freshwater & coastal ecosystems + their ecosystem services

• corrodes cars

• dissolves stone structure

cap & trade

introduced to clean air act in 1990 as emission trading program for SO₂ where pollution is capped at agreed upon level with hefty fines for exceeding & heavy polluters must buy additional allowances from competitors

scrubbers

large column/tube/pipe lined with lime (CaO) that absorbs or neutralized oxides (NO_x, SO_x VOCs) from exhaust streams (emissions) → mist droplets with pollutants & PM trapped in them fall to bottom of scrubber to get trapped at top by mist eliminator

electrostatic precipitators

power plant/factory emissions passed through device with a - charged electrode, giving particles a - charge → stick to + charged collection plates, trapping them → plates discharge occasionally so particles fall down into collection hopper for disposal in landfills