Free Unit Notes

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I. Introduction to Air Pollution (Topic 7.1)

  A. Pollutant types and exposure

1. Air pollution occurs when gases or particles reach levels that harm people, other organisms, or materials.

2. A primary pollutant enters the air directly. Examples include carbon monoxide from engines and ash from fires.

3. A secondary pollutant forms through reactions in the atmosphere. Examples include ground-level ozone, sulfuric acid, and nitric acid.

4. A precursor helps form another pollutant. Some particulate matter is emitted directly; some forms through atmospheric reactions.

5. Harm depends on pollutant concentration, exposure time, and sensitivity. Children, older adults, and people with heart or lung disease are especially vulnerable.

  B. Major pollutants and their sources

1. Carbon monoxide (CO) forms during incomplete combustion. It binds to hemoglobin and reduces the blood’s ability to carry oxygen.

2. Nitrogen oxides (NOₓ) form during high-temperature combustion in vehicles and power plants. They help form ozone, photochemical smog, and nitric acid; NO₂ also irritates lungs.

3. Sulfur dioxide (SO₂) comes from burning sulfur-containing coal and oil, including diesel fuel, and from metal smelting. It irritates airways and helps form sulfuric acid and fine particles.
   a. SO₂ emissions depend on fuel sulfur content. Low-sulfur diesel releases less SO₂ than high-sulfur diesel.

4. Particulate matter (PM) includes airborne solids and liquid droplets, such as soot, dust, smoke, and ash. It harms health and reduces visibility.

5. Volatile organic compounds (VOCs) readily enter air as gases. Sources include gasoline, solvents, paints, furniture, and plants; some VOCs are toxic, and many help form smog.

6. Lead from metal processing and some fuels damages the nervous system, especially in children. Coal combustion can also release mercury and other toxic metals.

  C. Combustion and air-quality measurements

1. Complete combustion converts a fuel’s carbon mainly into CO₂. Incomplete combustion produces more CO and often soot and unburned hydrocarbons.

2. CO₂ is a greenhouse gas. Its warming effect differs from the oxygen-transport problem caused by CO.

3. Gas concentrations are often reported in ppm or ppb. On the same measurement basis, 1 ppm = 1,000 ppb; particles are often measured in µg/m³.

4. The Air Quality Index (AQI) translates pollutant measurements into categories of health concern. It is an index, not a concentration unit.

II. Photochemical Smog (Topic 7.2)

  A. Formation and daily patterns

1. Photochemical smog forms when sunlight drives reactions involving NOₓ and VOCs. Major products include ground-level ozone and peroxyacyl nitrates (PANs).

2. Sunlight splits NO₂, releasing an oxygen atom. That atom combines with O₂ to form ozone (O₃).
   a. Key steps are NO₂ + sunlight → NO + O and O + O₂ → O₃. Another air molecule carries away excess energy during ozone formation.

3. VOC reactions help convert NO back into NO₂ without consuming ozone. This allows ozone to accumulate.

4. Vehicle emissions often increase during morning traffic. Ozone commonly peaks later, in the afternoon, after sunlight-driven reactions have occurred.

5. Warm, sunny weather favors smog. Ozone is often higher in summer, but weather and emissions can change the pattern.

  B. Conditions, effects, and prevention

1. Urban traffic supplies many smog precursors. Trees also release natural VOCs that can react with human-produced NOₓ.

2. Weak winds, mountains, and thermal inversions limit pollutant dispersal. Wind can carry ozone and its precursors downwind.

3. Ground-level ozone irritates airways, worsens asthma, and reduces lung function. Smog can also irritate eyes; ozone and PANs damage plants and reduce growth.

4. Reduce NOₓ and VOCs through cleaner vehicles, less driving, public transportation, low-VOC products, and fuel-vapor recovery.
   a. Ozone responses depend on local chemistry, so reducing only one precursor does not always produce a simple, proportional decrease.

5. Stratospheric ozone absorbs harmful ultraviolet radiation. Ground-level ozone harms lungs and plants; the two have different effects because of their locations.

III. Thermal Inversion (Topic 7.3)

  A. Normal mixing and inversion conditions

1. In the lower atmosphere, temperature usually decreases with height. Surface heating can make near-ground air rise and mix, spreading pollutants through a larger air volume.

2. A thermal inversion occurs when warmer air lies above cooler surface air. The denser surface air does not rise easily through the warm layer.

3. Reduced vertical mixing traps smoke, smog, and other pollutants near the ground. Continued emissions increase concentrations where people breathe.

  B. Formation and dispersal

1. Clear, calm nights allow the ground and nearby air to cool rapidly. Cold air can also flow downhill and collect in valleys.

2. Sinking air under high pressure can create a warm layer above the surface. Mountains and weak winds can worsen pollutant buildup.

3. An inversion traps existing pollution; it does not create emissions. Surface warming, stronger winds, or a changing weather system may break it.

IV. Atmospheric CO₂ and Particulates (Topic 7.4)

  A. Natural carbon dioxide sources

1. Cellular respiration releases CO₂ as organisms break down food for energy. Decomposition in oxygen-rich conditions also releases CO₂.

2. Volcanoes release CO₂ from Earth’s interior. Wildfires release carbon stored in vegetation, and oceans can release dissolved CO₂.

3. Photosynthesis and ocean uptake remove atmospheric CO₂. Its atmospheric level depends on the balance between releases and removals.

  B. Particle sources and effects

1. Natural PM sources include windblown dust, volcanic ash, sea spray, pollen, spores, and wildfire smoke. Natural particles can still harm health.

2. Human sources include fuel combustion, construction, agriculture, and road dust. Atmospheric reactions also create secondary particles.

3. PM₁₀ includes particles with aerodynamic diameters of 10 µm or less. PM₂.₅ includes fine particles of 2.5 µm or less and is a subset of PM₁₀.

4. Fine particles reach deep into the lungs and contribute to respiratory and cardiovascular disease. Some particle components can enter the bloodstream.

5. Particles scatter or absorb light and reduce visibility. Soot absorbs sunlight; many lighter particles reflect it, so particle climate effects vary.

V. Indoor Air Pollutants (Topic 7.5)

  A. Combustion pollutants

1. Faulty heaters, engines, and poorly vented stoves can release CO. CO is an asphyxiant, meaning it prevents the body from getting or using enough oxygen.

2. Maintain and vent appliances, keep engines outdoors, and use CO alarms. CO has no color or smell, so people cannot reliably detect it themselves.

3. Tobacco smoke and burning wood, dung, crop residues, or coal release particles and harmful gases. Fuel and burning conditions affect releases of CO, NOₓ, and SO₂.

4. Smoke exposure increases risks of heart and lung disease and some cancers. Cleaner cooking fuels, effective exhaust ventilation, and smoke-free indoor spaces reduce exposure.

  B. Building materials and biological sources

1. Asbestos fibers can enter air when older insulation or other materials are disturbed. Inhalation can cause lung scarring, lung cancer, and mesothelioma.
   a. Trained professionals should assess and manage suspect materials; disturbing them can increase exposure.

2. Furniture, paneling, carpets, paints, and adhesives can release VOCs, including formaldehyde. These can irritate eyes and airways; some cause cancer.

3. Deteriorating or disturbed older lead paint produces dust that can be inhaled or swallowed. Lead-safe repair and qualified abatement reduce exposure.

4. Mold spores, dust, and dust-mite allergens can trigger allergies and asthma. Fixing leaks, controlling humidity, and cleaning dust reduce exposure.

  C. Radon

1. Radon-222 is a naturally occurring radioactive gas formed in the uranium decay chain in rocks and soils. Radium is its immediate parent.

2. Radon enters through foundation cracks and other openings. Dissolved radon can also escape into indoor air when well water is used.

3. Radon decay products can damage lung cells. Radon exposure is the second leading cause of lung cancer in the United States, after smoking.

4. Radon has no color or smell, so testing is necessary. A pipe and fan can draw soil gas from below a foundation and vent it outdoors above the roof.

5. Sealing openings can help, but sealing alone may be insufficient. Test again after mitigation to check whether levels fell.

  D. Indoor buildup and control

1. Tightly sealed buildings conserve energy but can trap pollutants without planned ventilation. Reduce sources and provide appropriate fresh-air exchange.

2. Particle filters trap dust and smoke particles but do not reliably remove CO or radon gas. Match the control to the pollutant.

3. Sick building syndrome describes symptoms associated with time spent in a building when no single specific illness or cause has been identified.

VI. Reduction of Air Pollutants (Topic 7.6)

  A. Prevention and regulation

1. Energy conservation, efficient buildings, carpooling, public transportation, and less idling reduce fuel use and emissions.

2. Wind and solar electricity avoid combustion emissions during generation. Low-sulfur fuels reduce SO₂; natural gas usually produces less SO₂ and PM than coal but still emits CO₂ and NOₓ.

3. The Clean Air Act provides the U.S. framework for regulating air pollution. EPA standards address six criteria pollutants: CO, lead, NO₂, ozone, PM, and SO₂.

4. Restrictions on lead in gasoline greatly reduced airborne lead. Emission limits require monitoring and enforcement to achieve reductions.

  B. Vehicle controls

1. A vapor recovery nozzle captures gasoline vapors during refueling, reducing VOC emissions. It does not treat engine exhaust.

2. A three-way catalytic converter uses catalysts to convert CO and hydrocarbons mainly into CO₂ and water, and NOₓ mainly into nitrogen gas.
   a. Example reactions are 2CO + O₂ → 2CO₂ and 2NO + 2CO → N₂ + 2CO₂.

3. A catalyst speeds reactions without being consumed overall. Catalytic converters reduce toxic emissions but do not capture CO₂ or eliminate fuel-related warming.

  C. Industrial controls

1. A wet scrubber brings exhaust into contact with liquid droplets. An alkaline slurry can absorb and neutralize SO₂; wet scrubbers can also capture particles.

2. A dry scrubber adds dry or nearly dry alkaline material that reacts with acidic gases such as SO₂. The resulting solids are collected.

3. An electrostatic precipitator charges particles and attracts them to collecting plates. It removes PM, rather than CO₂ or most pollutant gases.

4. A baghouse filter traps particles in fabric filters. Most gases pass through, and filters need maintenance.

5. Controls have tradeoffs. Scrubbers use materials and may use water; captured pollutants become liquid or solid wastes that need management.

6. A taller smokestack disperses pollutants farther away but does not remove them.

  D. Evaluating a pollution control

1. Percent reduction = [(initial value − final value) ÷ initial value] × 100. A decrease from 500 to 100 kg of SO₂ per day is an 80% reduction.

2. Compare the same pollutant with the same measurement method before and after treatment. Keep operating conditions comparable and repeat measurements.

3. For outdoor comparisons, account for wind, weather, traffic, and time of day. A concentration difference alone does not establish its cause.

VII. Acid Rain (Topic 7.7)

  A. Formation and transport

1. Acid deposition transfers acidic substances from the atmosphere to Earth’s surface. Wet deposition arrives in rain, snow, or fog; dry deposition occurs without precipitation.

2. SO₂ and NOₓ react with oxygen, water, and other atmospheric chemicals to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃).

3. Coal-burning power plants release SO₂ and NOₓ; vehicles release NOₓ. Sulfur-containing oil and metal smelting also release SO₂.

4. Natural sources include volcanic sulfur gases and lightning-produced NOₓ. Wind carries pollutants across borders, exposing communities downwind of sources.

  B. Acidity and environmental damage

1. pH measures acidity. A one-unit pH decrease means ten times the hydrogen-ion concentration; pH 4 water has ten times as much H⁺ as pH 5 water.

2. Rain is naturally mildly acidic because dissolved CO₂ forms carbonic acid. About pH 5.6 is a common clean-rain benchmark; natural rain varies.

3. Acid deposition lowers soil and water pH. Leaching removes soil nutrients such as calcium and magnesium, weakening plants.

4. Acidic conditions release aluminum from soil minerals. Aluminum can damage roots and fish gills; low water pH can reduce aquatic survival and reproduction.

5. Acids wear away limestone and marble buildings and monuments and can accelerate metal corrosion.

  C. Buffering and solutions

1. Buffering capacity is the ability to resist pH change. Calcium carbonate in limestone neutralizes acids, protecting some soils, lakes, and ponds.

2. Thin soils and poorly buffering bedrock, such as granite, increase vulnerability. Buffering materials can eventually be depleted.

3. Reduce SO₂ and NOₓ through cleaner energy, low-sulfur fuels, scrubbers, and vehicle controls.

4. Cap-and-trade sets an overall emission limit and allows regulated sources to trade allowances within that limit.

5. Adding limestone can temporarily raise lake pH but does not stop incoming pollution. Emission reductions address the source.

VIII. Noise Pollution (Topic 7.8)

  A. Sources and effects

1. Noise pollution is unwanted sound that disrupts life or reaches harmful levels. Sources include traffic, aircraft, trains, construction, machinery, and loud entertainment.

2. Loud sound can permanently damage hearing. Noise also disrupts sleep and concentration and causes physiological stress that can contribute to cardiovascular problems.

3. Wildlife can experience hearing damage and stress. Masking occurs when noise covers sounds used to communicate, find mates, hunt, or navigate.

4. Animals may change their calls, leave habitat, or alter migration routes. Boats and sonar can disrupt marine animals that depend on sound.

  B. Sound levels and reduction

1. Sound levels are measured in decibels (dB) on a logarithmic scale. A 10 dB increase means ten times the intensity; a 20 dB increase means 100 times the intensity.

2. Intensity ratio = 10^(ΔL/10), where ΔL is the difference in decibels. An increase from 60 to 80 dB gives 10^(20/10) = 100 times the intensity.

3. Intensity differs from perceived loudness. A 10 dB increase is often heard as roughly twice as loud; health effects also depend on exposure duration.

4. Quieter equipment, maintenance, mufflers, traffic management, and limits on noisy activities reduce sound at its source.

5. Barriers, insulation, and greater distance reduce exposure along the sound’s path. Hearing protection reduces personal exposure but does not protect nearby ecosystems.

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