Introduction to Air Pollution

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🌎 UNIT 7 — Atmospheric Pollution: Comprehensive Notes

7.1 Air Pollution Basics

🌫 What is Air Pollution?

  • Contamination of indoor or outdoor air by harmful chemical, physical, or biological agents.

  • “Air pollution refers to the contamination of the indoor or outdoor environment…”

📊 Air Quality Index (AQI)

  • Converts pollutant concentrations into a health‑based index.

  • Categories: | AQI | Category | 0–50 | Good | Normal outdoor activity | | 51–100 | Moderate | Sensitive groups limit strenuous activity | | 101–150 | Unhealthy for Sensitive Groups | Limit prolonged outdoor activity | | 151–200 | Unhealthy | Sensitive groups avoid outdoor exposure | | 201–300 | Very Unhealthy | Everyone avoid outdoor activity | | 301–500 | Hazardous | Avoid all outdoor exertion |

🏛 Clean Air Act (CAA) & NAAQS

  • EPA sets acceptable pollutant concentrations through National Ambient Air Quality Standards.

  • CAA regulates all major sources of atmospheric emissions.

🧪 Six Criteria Air Pollutants

“Clean Air Act (CAA) identified 6 criteria air pollutants…”

Pollutant

Source

Effects

SO₂

Coal combustion, diesel

Respiratory irritant, smog, acid rain

NOx (NO & NO₂)

All fossil fuel combustion

Ozone formation, smog, acid rain

CO

Incomplete combustion

Lethal, reduces oxygen delivery

PM

Fossil fuel/biomass combustion

Respiratory irritation, smog

O₃ (tropospheric)

Secondary pollutant from NO₂ + sunlight

Respiratory irritant, plant damage

Pb

Metal smelting, old gasoline

Neurotoxin

🌍 Air Pollutants vs. Greenhouse Gases

  • CO₂ is not a criteria pollutant.

  • Does not irritate lungs or cause smog.

  • Is a greenhouse gas → climate change.

7.1 Combustion Pollutants

🏭 Coal Combustion

“Releases more air pollutants than other FFs (by far)”

Releases:

  • CO, CO₂

  • SO₂

  • NOx

  • Toxic metals (Hg, As, Pb)

  • PM (often carrying metals)

SO₂ impacts:

  • Respiratory irritation

  • Sulfate aerosols → reduced visibility

  • Acid precipitation

🔥 Nitrogen Oxides (NOx)

  • Formed when N₂ reacts with O₂ during combustion.

  • Sunlight converts NO₂ → NO + O → O₃.

Effects:

  • Respiratory irritation

  • Ozone formation → photochemical smog

  • Acid rain (nitric acid)

🧴 Volatile Organic Compounds (VOCs)

Sources:

  • Plants (terpenes)

  • Paints, cleaners, pesticides, gasoline

  • Evaporation & combustion

Effects:

  • Eye, throat, lung irritation

  • Some are carcinogenic

  • Combine with NO to form photochemical oxidants

🧠 Lead (Pb)

  • Former gasoline additive (TEL).

  • Phased out by EPA (1974–1996).

  • Damages catalytic converters.

  • Neurotoxin.

Primary vs. Secondary Pollutants

Primary

Secondary

Emitted directly

Formed in atmosphere

CO, CO₂, NOx, SO₂, VOCs, PM

O₃, H₂SO₄, HNO₃, sulfates, nitrates

Sources: vehicles, factories, fires

Require sunlight, water, O₂

7.2 Photochemical Smog

🌆 What Causes Smog?

“Photochemical smog is formed when nitrogen oxides and volatile organic hydrocarbons react with heat and sunlight…”

Ingredients:

  • NOx

  • VOCs

  • Sunlight

  • Warm temperatures

⏰ Daily Pattern

  • Morning: NO₂ spikes from traffic.

  • Afternoon: Sunlight breaks NO₂ → O → O₃.

  • Ozone peaks in afternoon.

🌡 Conditions That Increase Smog

  • More sunlight

  • Higher temperatures

  • More VOC emissions

  • More vehicle traffic

  • Urban heat island effect

😷 Impacts

  • Respiratory irritation

  • Eye irritation

  • Reduced photosynthesis

  • Lower crop yields

  • Economic losses (healthcare, productivity)

🚗 Reducing Smog

  • Reduce NOx & VOCs:

    • Fewer vehicles

    • Public transit

    • Renewable energy

    • Natural gas instead of coal

7.3 Thermal Inversion

🌡 Normal Conditions

Warm air at surface rises → carries pollutants upward.

🧊 Thermal Inversion

“Cold air at the surface is trapped beneath the warmer mass above…”

  • Warm air overlays cold air → traps pollutants near ground.

  • Common in valleys & cities like Los Angeles.

🚫 Effects

  • Smog, PM, SO₂, NOx trapped near surface.

  • Increased asthma, COPD, hospitalizations.

  • Reduced tourism.

  • Reduced photosynthesis.

7.4 Natural Sources of CO₂ & PM

🌬 Natural CO₂ Sources

  • Respiration

  • Decomposition

  • Volcanic eruptions

🌫 Natural PM Sources

  • Dust

  • Pollen

  • Ash from fires

  • Volcanic ash

🔥 Forest Fires

Release:

  • CO₂

  • PM

  • NOx

⚡ Lightning

  • Converts N₂ → NO

🌲 Plants

  • Emit VOCs (terpenes) → natural smog (e.g., Smoky Mountains)

🧪 PM10 vs PM2.5

“PM2.5… more likely to travel deep into the lungs…”

Type

Size

Source

Health Impact

PM10

<10 µm

Dust, pollen, mold

Irritates respiratory tract

PM2.5

<2.5 µm

Combustion

Enters lungs → cancer risk

7.5 Indoor Air Pollutants

🏠 Natural Indoor Pollutants

  • Radon

  • Mold

  • Dust

🧪 Human‑Made Pollutants

  • VOCs from furniture, carpets, cleaners

  • Formaldehyde

  • Lead paint

🔥 Combustion Pollutants

  • CO

  • NOx

  • SO₂

  • PM

  • Tobacco smoke

☢ Radon

“Radon-222 is a naturally occurring radioactive gas…”

  • Enters through foundation cracks.

  • Second leading cause of lung cancer.

🧱 Asbestos

  • Former insulation material.

  • Causes mesothelioma, lung cancer.

  • Dangerous when disturbed.

🧽 Mold

  • Grows in damp, dark areas.

  • Black mold releases harmful spores.

🚗 Carbon Monoxide

  • Asphyxiant: binds hemoglobin.

  • Odorless, colorless → requires detectors.

Developing vs. Developed Nations

🌍 Developing Nations

  • Use biomass fuels (wood, manure, charcoal).

  • Indoor combustion → high PM, CO, NOx, VOCs.

  • ~3.2 million annual deaths from indoor air pollution.

🌎 Developed Nations

  • Use commercial fuels (coal, oil, natural gas).

  • Indoor pollutants mainly from chemicals in products.

7.6 Reducing Air Pollutants

🏛 Regulatory Methods

  • Clean Air Act

  • CAFE vehicle standards

  • Pollution credits

🚗 Vehicle Controls

Vapor Recovery Nozzle

  • Captures gasoline VOC fumes.

Catalytic Converter

“Converts pollutants (CO, NOx, hydrocarbons) into less harmful molecules…”

Produces:

  • CO₂

  • N₂

  • O₂

  • H₂O

🏭 Industrial Controls

Wet & Dry Scrubbers

  • Remove SO₂, NOx, VOCs, PM.

Electrostatic Precipitators

  • Charge PM → stick to plates.

Baghouse Filters

  • Fabric filters trap PM.

Crushed Limestone

  • Reacts with SO₂ → CaSO₄ (solid).

Fluidized Bed Combustion

  • Lower combustion temp → less NOx.

7.7 Acid Rain

🌧 Causes

  • SO₂ from coal plants

  • NOx from vehicles & power plants

  • Form sulfuric & nitric acid in atmosphere

🌱 Environmental Effects

  • Soil acidification

  • Leaching of nutrients (Ca²⁺, K⁺)

  • Lower water pH → kills aquatic species

  • Corrodes buildings (especially limestone)

🪨 Limestone Buffering

  • Neutralizes H⁺ ions.

  • Regions with limestone bedrock are less affected.

7.8 Noise Pollution

🔊 Sources

  • Transportation

  • Construction

  • Industrial activity

  • Domestic tools (lawnmowers, power tools)

🧠 Human Effects

  • Physiological stress

  • Headaches

  • Hearing loss

🐳 Wildlife Effects

  • Disrupted communication

  • Masked mating/predator sounds

  • Stress

  • Altered migration routes

  • Marine animals harmed by sonar & seismic airguns

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