Unit 7 – Atmospheric Pollution

Carbon Monoxide (CO)

• Source: Incomplete combustion of fossil fuels (vehicles, power plants, residential heating)
• Health Impact: Binds hemoglobin with 200x affinity of O₂; reduces oxygen delivery; impairs cognition, coordination
• Ambient Concentration: ~0.1-0.5 ppm typical; vehicles inside tunnels can exceed 10-50 ppm (dangerous)
• Fate: Oxidized to CO₂ in atmosphere (lifetime ~30-60 days); long enough to mix globally
• Current Trend: Declining due to vehicle emission controls; not major issue in developed nations anymore

Nitrogen Oxides (NOx) - NO and NO₂

• Source: High-temperature combustion (vehicles, power plants, industrial processes)
• Formation: N₂ + O₂ → 2NO at high temps; NO oxidizes to NO₂ in atmosphere
• NO: Colorless, toxic; oxidized to NO₂ (half-life ~1-2 hours)
• NO₂: Brown, toxic gas; precursor to ground-level ozone; contributes to acid rain
• Health Impact: Irritates airways; exacerbates asthma; impairs lung function; at high concentrations (~1 ppm) causes pulmonary edema
• Standards: EPA 1-hour standard 100 ppb; 8-hour standard 70 ppb (2015 revision)

Sulfur Dioxide (SO₂)

• Source: Coal burning (power plants, industrial), petroleum refining, smelting
• Formation: S + O₂ → SO₂ during combustion (sulfur content in fossil fuels)
• Characteristics: Colorless, pungent gas; denser than air (settles near ground)
• Health Impact: Irritates airways; triggers asthma attacks; cardiovascular effects; sensitive populations (asthmatics, elderly, children) at risk
• Secondary Formation: Oxidized to SO₃ → forms sulfuric acid (H₂SO₄) - major acid rain component
• Standards: EPA 1-hour standard 75 ppb; 8-hour standard 30 ppb

Particulate Matter (PM)

• Definition: Mixture of liquid droplets and solid particles suspended in air
• Size Categories: PM₁₀ (coarse, 10 μm) deposited in upper respiratory tract; PM₂.₅ (fine, 2.5 μm) reaches deep lungs/bloodstream; PM₀.₁ (ultrafine) crosses into brain
• Sources: Combustion (vehicles, power plants), dust (desert, construction, roads), fires (wildfires, biomass burning), industrial processes, secondary formation (from NOx, SO₂, VOCs)
• Health Impact: Respiratory disease, cardiovascular disease, cancer, premature death; ~7 million deaths/year attributable to PM
• Standards: EPA PM₂.₅ annual 12 μg/m³; 24-hour 35 μg/m³ (WHO stricter: annual 5 μg/m³, daily 15 μg/m³)
• Persistence: PM₂.₅ can remain suspended weeks; travels intercontinentally (Saharan dust reaches Americas)

Ozone (O₃) - Ground-Level

• Important Distinction: Ground-level ozone (pollutant, harmful) ≠ stratospheric ozone (protective UV shield)
• Formation: NO₂ + sunlight → NO + O; O + O₂ → O₃; requires NOx and VOCs (both from fossil fuel use)
• Peak Time: Afternoon (maximum solar radiation); problem worst summer afternoons
• Health Impact: Strong oxidizing agent; damages lung tissue; reduces lung function; triggers asthma; cardiovascular effects; even low exposures (~0.07 ppm, 8-hour) harmful
• Agricultural Impact: Damages crops; reduces yields 5-15% in ozone-polluted regions
• Standards: EPA 8-hour standard 70 ppb; most exceedances in summer afternoons

1. Radiation Inversion (Most Common)

• Mechanism: Clear, calm nights; ground radiates heat to space; ground cools rapidly; air near ground cooled by contact; air aloft stays warm
• Timing: Forms at night; typically dissipates by mid-morning as sun heats ground
• Strongest: Clear skies (no clouds trap heat), calm conditions (no wind mixes), long winter nights (longer radiation period)
• Valley Traps: Mountain valleys most affected (cold air drains downhill, concentrates); basin cities (LA, Mexico City, Denver) prone
• Example: "Cold pockets" in valleys where frost occurs; air stagnates overnight; pollution concentrations peak early morning
• Pollution Signature: High pollution early morning; improves afternoon as inversion breaks

2. Subsidence Inversion (Synoptic)

• Mechanism: High-pressure system descends; air layer descends gradually; air compresses, heats (adiabatic warming); creates inversion aloft; traps lower air
• Duration: Lasts days/weeks (as long as high-pressure system persists); much more persistent than radiation inversion
• Seasonal Pattern: Summer in subtropical highs (LA summer smog); persists during high-pressure systems
• Strength: Can be extremely stable; inversion height 500-2,000 m aloft; very shallow mixing layer below
• Worse Than Radiation: Multi-day pollution accumulation possible; air quality doesn't improve until weather pattern breaks
• Example: Los Angeles summer smog; typical July high-pressure system creates inversion; pollution accumulates all week

3. Frontal Inversion

• Mechanism: Warm front passes; warm air mass displaces cool air; temperature discontinuity at front acts as inversion
• Duration: Temporary; until front passes (hours to 1-2 days)
• Occurrence: Associated with weather systems; can occur any season when fronts active
• Severity: Moderate; temporary but can cause brief severe pollution events

How Inversion Worsens Pollution

• Vertical Mixing Suppressed: Pollutants can't escape upward; confined to shallow layer near ground
• Concentration Buildup: Same emissions, smaller volume = higher concentrations; pollution levels rise 5-10x in hours
• Stagnation: Wind often weak during inversions (high pressure); pollutants stay in place, accumulate
• Duration Matters: Multi-day inversions cause extreme pollution; Donora PA 1948 industrial smog (28 deaths, ~6,000 ill) from multi-day inversion with SO₂
• Secondary Formation: NO₂, SO₂, VOCs trapped; chemical reactions concentrated; secondary pollutants (O₃, H₂SO₄) form rapidly in small volume
• Visible Haze: Brown/grey layer visible; limited visibility; psychological impact heightens concern (justified)

Health Consequences

• Acute Effects: Eye irritation, respiratory symptoms, asthma attacks within hours during severe episodes
• Vulnerable Groups: Children (lungs developing), elderly (cardiopulmonary disease), asthmatics, outdoor workers
• Recommendations: Air quality alerts issued when inversion predicted; public advised to reduce outdoor exposure; sensitive groups shelter indoors
• Historical Events: Great Smog of London 1952 (radiation inversion, SO₂ from coal, 12,000 deaths); Donora PA 1948 (industrial sulfur smog, 28 deaths); Mexico City 1989 (subsidence inversion, extreme NO₂/O₃)
• Prevention: Emission controls reduce pollution during inversion; ventilation encourages air exchange breaking inversion; public transportation reduces vehicles during episodes

Size Classification and Lung Deposition

• PM₁₀ (Coarse, <10 μm): Settles quickly (hours-days); deposits in upper respiratory tract (nose, mouth, throat); <5% reaches lungs
• PM₂.₅ (Fine, <2.5 μm): Remains suspended weeks; penetrates deep into lungs (alveoli); can enter bloodstream; most dangerous category for health
• PM₁ (Ultrafine, <1 μm): Crosses lung-blood barrier; enters systemic circulation; reaches organs (heart, brain); emerging concern
• Comparison: Human hair ~70 μm; PM₂.₅ 30x smaller; invisible to naked eye; can't be filtered by nose
• Deposition Pattern: Upper respiratory: PM>10 μm; tracheobronchial: 5-10 μm; alveolar: <5 μm (most harmful)
• Health Implication: PM₁₀ mostly filtered; PM₂.₅ causes systemic damage; ultrafine most dangerous per particle

PM Sources and Composition

• Primary PM (emitted directly): Soot (combustion), dust (road, construction, deserts), sea salt aerosols, pollen
• Secondary PM (formed in atmosphere): Sulfate (from SO₂), nitrate (from NOx), organic aerosols (from VOCs); accounts 30-70% of PM₂.₅ depending on location
• Combustion Sources: Vehicles (NO + SO₂ → secondary particles), power plants, residential heating, industrial processes, biomass burning
• Natural Sources: Sea salt spray, dust storms (Saharan dust), wildfires, volcanic ash; intercontinental transport (Sahara dust reaches Americas)
• Seasonal Variation: Winter higher in some regions (heating); summer higher in others (secondary formation + wildfires)
• Urban vs. Rural: Urban PM higher ~50% due to local sources; rural areas affected by regional transport
• Composition Impact: Sulfate/nitrate aerosols acidic; black carbon (soot) absorbs solar radiation; organic aerosols affect clouds

Health Impacts of PM

• Respiratory Disease: Bronchitis, pneumonia, asthma exacerbation; increased emergency room visits on high-PM days
• Cardiovascular Disease: PM penetrates lungs; triggers inflammation; alters heart rhythm; increases heart attack/stroke risk; largest PM-related burden of disease
• Cancer: Long-term PM₂.₅ exposure increases lung cancer risk; WHO classified outdoor PM pollution Group 1 carcinogen (2013)
• Neuroinflammation: Ultrafine particles reach brain via olfactory nerve or bloodstream; linked to dementia, Alzheimer's in recent research
• Mortality: ~7 million premature deaths annually attributed to ambient air pollution (mostly PM); exceeds deaths from smoking, malaria, tuberculosis combined
• Children Impacts: Developing lungs more vulnerable; reduced lung function growth; increased childhood asthma; cognitive impairment
• Dose-Response: No safe level identified; even low exposures have health effects; WHO guidelines based on lowest observable adverse effect level
• Vulnerable Populations: Elderly, children, people with cardiopulmonary disease, outdoor workers, low-income communities disproportionately affected

Air Quality Standards and Geographic Context

• EPA Standards (USA): PM₂.₅ annual 12 μg/m³; 24-hour 35 μg/m³; PM₁₀ annual 150 μg/m³; 24-hour 150 μg/m³ (haven't changed much since 1997)
• WHO Guidelines (2021, stricter): PM₂.₅ annual 5 μg/m³; 24-hour 15 μg/m³; PM₁₀ annual 15 μg/m³; 24-hour 45 μg/m³ (based on health evidence)
• Actual Levels (Problem Areas): Delhi ~150 μg/m³ (30x WHO); Beijing ~80 μg/m³; Cairo ~100+ μg/m³; many developing cities exceed standards 2-5x
• USA Improvement: PM₂.₅ declined ~40% since 2000 despite population/economy growth; Clean Air Act driving progress
• Regional Exceedances: Some USA areas (Los Angeles, Salt Lake City) still exceed standards during summer; require emission reduction plans
• Wildfire Impact: Western USA summers filled with smoke; PM spikes; PM often exceeds standards during fire season
• Saharan Dust: African dust transport affects Caribbean, southern USA; PM₂.₅ increases observable; transboundary pollution difficult to control

💡 Exam Tip: CO₂ rising ~2 ppm/year from fossil fuels; ~420 ppm currently. PM₂.₅ most dangerous (penetrates deep lungs, enters bloodstream). 7 million deaths/year from air pollution mostly PM-related. PM₂.₅ includes primary + secondary (sulfate, nitrate from SO₂/NOx). Know size differences: PM₁₀ settles days, PM₂.₅ settles weeks, can transport intercontinentally. WHO standards stricter than EPA; most cities globally exceed WHO guidelines!

Radon (Rn-222)

• Source: Radioactive gas from soil and bedrock (uranium decay chain); naturally occurring, not from human activity
• Entry: Seeps into buildings through foundation cracks, basement floors, sump pumps, poorly sealed pipes; higher in basements (ground-level contact)
• Geographic Distribution: Varies by geology; granitic regions (mountain states, New England, parts of Europe) have highest levels; some areas 5-10x higher than others
• Concentration Indoors: Typical ~1-2 pCi/L (picocuries per liter); EPA action level 4 pCi/L; some homes >100 pCi/L (extreme)
• Health Impact: Alpha particle emitter; inhaled radon decays to polonium in lungs; alpha particles damage lung DNA; second-leading cause of lung cancer after smoking; ~21,000 deaths/year USA
• Cancer Risk: 4 pCi/L lifetime risk ~100 deaths per million exposed (significant); smoking increases risk multiplicatively
• Remediation: Radon testing inexpensive (~$100-300); mitigation systems (sub-slab depressurization) ~1,000-2,500; very effective (~99% reduction)
• Prevention: Seal foundation cracks; improve ventilation; radon-resistant construction in high-risk areas

Secondhand Smoke (Environmental Tobacco Smoke - ETS)

• Composition: Mixture of mainstream smoke (exhaled by smoker) and sidestream smoke (from cigarette tip); 4,000+ chemicals including 200+ toxic, 70+ carcinogenic
• Global Exposure: ~1 billion people exposed; third-hand smoke (residue on surfaces) also harmful
• Health Effects: Lung cancer, heart disease, stroke in nonsmokers; respiratory disease in children; asthma exacerbation; even low exposure harmful
• Children Impacts: Secondhand smoke exposure increases asthma onset; ear infections; respiratory infections; SIDS (sudden infant death syndrome) risk increases
• Dose-Response: No safe level; even brief exposure increases cardiovascular stress; chronic exposure increases cancer risk
• Workplace Exposure: Hospitality workers (bars, restaurants) historically most exposed; smoking bans eliminate exposure
• Global Deaths: ~1.2 million annual deaths from secondhand smoke (60% children); preventable with smoking bans
• Prevention: Smoking bans (most effective), ventilation, designated smoking areas (less effective); complete elimination only full protection

Formaldehyde (HCHO)

• Sources: Off-gasses from particle board, plywood, MDF (medium-density fiberboard), furniture adhesives, insulation, carpets, paints, textiles
• Indoor Levels: Typical 0.03-0.06 ppm; can exceed 0.1 ppm in new furniture/buildings; higher with poor ventilation
• Emission Pattern: Highest when new (off-gassing); decreases over weeks/months as binder cures; temperature/humidity increase emission rate
• Health Effects: Eye, nose, throat irritation; respiratory symptoms; asthma exacerbation; headaches; fatigue; classified probable carcinogen (limited evidence)
• Standard: EPA has no indoor standard; WHO suggests <0.03 ppm; some studies suggest <0.05 ppm; no safe level definitively established
• Prevention: Low-VOC furniture, plywood alternatives (bamboo), ventilation, off-gassing new furniture before bringing indoors, air purifiers
• Product Standards: California formaldehyde standards stricter; CARB compliance reduces levels; green certification programs (GreenGuard)

Volatile Organic Compounds (VOCs)

• Sources: Paints, varnishes, solvents, cleaning products, air fresheners, perfumes, office equipment (printers, copiers), pesticides
• Indoor Levels: Typical 0.5-5 ppm; during/after painting can spike to 20-100 ppm
• Common VOCs: Benzene (carcinogen), toluene, xylene, formaldehyde, acrolein (irritant); hundreds detected in homes
• Health Effects: Eye, nose, throat irritation; headaches; dizziness; neurological effects at high concentrations; some carcinogenic; reactions with ozone form secondary pollutants indoors
• Emission Pattern: Highest immediately after application (painting, cleaning); decreases days-weeks
• Prevention: Use low-VOC products (certified), ventilate during/after use, avoid aerosol sprays, limit air freshener use, allow curing time in separate space
• Indoor Reactions: VOCs + ozone (from printers) form secondary organic aerosols (SOA); contributes indoor PM₂.₅; creates "ozone damage" odor

Mold and Moisture

• Causes: High humidity (>50-60%); water damage; poor ventilation; inadequate drainage; condensation on cold surfaces
• Health Effects: Mold spore inhalation triggers allergic reactions; asthma exacerbation; respiratory infections; immunocompromised at risk of invasive infections
• Mycotoxins: Some molds (black mold - Stachybotrys) produce toxins; health effects controversial but precautions warranted
• Indoor Locations: Bathrooms (humid), basements (moisture), kitchens (moisture), window sills (condensation)
• Prevention: Moisture control (fix leaks, dehumidifiers), ventilation (exhaust fans), air circulation, regular cleaning, remove wet materials promptly
• Remediation: Clean mold with bleach/detergent; source moisture must be eliminated or regrowth occurs; professional remediation for large areas

Biomass Burning Indoors (Major Global Issue)

• Global Impact: 3+ billion people cook/heat with biomass (wood, dung, crop waste) on open fires; major indoor air pollution source
• Exposure: Mostly women, children spend 8+ hours near smoke; exposure equivalent to smoking 1-2 packs cigarettes daily
• Pollutants Released: Extreme PM₂.₅ levels (100-1,000 μg/m³ indoors vs. 10-50 outdoor ambient); CO, formaldehyde, PAHs, other toxins
• Health Burden: ~3 million annual deaths; respiratory infections (children), COPD (women), lung cancer, heart disease
• Burden of Disease: 5-6% of global disability-adjusted life years (DALYs); worse than malaria in many regions
• Solutions: Improved cookstoves (high-efficiency, low-emission); liquefied petroleum gas (LPG) alternatives; solar cookers; biogas digesters; policy support for clean fuels
• Progress: ~900 million improved cookstoves deployed; WHO goal: universal access to clean cooking by 2030 (on track for only 70%)

Catalytic Converters

• Introduction: 1970s USA; converts harmful pollutants to less harmful; required on all USA vehicles since 1975
• Technology: Catalytic converter substrate coated with platinum, palladium, rhodium; chemical reactions catalyzed
• Reactions: CO + O₂ → CO₂; NOx + hydrocarbons → N₂ + CO₂; oxidizes carbon monoxide, reduces nitrogen oxides
• Efficiency: Reduces CO, NOx, VOCs by 90-95%; must reach operating temperature (~600°C) to function
• Effectiveness: CO emissions down ~95% since 1970s despite more vehicles; NOx more difficult to control
• Three-Way Catalyst: Controls CO, NOx, and hydrocarbons simultaneously
• Limitation: Doesn't address PM or CO₂; cold-start problem (ineffective before warm); high cost catalytic materials

Fuel Efficiency and Engine Standards

• CAFE Standards (USA): Corporate Average Fuel Economy; regulated since 1975; currently ~35 mpg (2023); improves over time
• EU Standards: 95 g CO₂/km by 2021; stricter than USA; drives technological innovation
• Benefit: More efficient = less fuel burned = fewer emissions per mile
• Technology Improvements: Lighter materials, aerodynamic design, turbocharging, direct injection, hybrid systems
• Modern Engines: 2024 vehicles 2-3x more efficient than 1980s models per mile
• Limitation: Efficiency standards don't address CO₂ directly; only reduce fuel consumption; rebound effect (more driving)

Electric Vehicles (EVs)

• Zero Tailpipe Emissions: No CO, NOx, VOCs from vehicle; eliminates local air pollution source
• Lifecycle Emissions: Depend on grid electricity source; if coal-heavy grid, significant emissions in generation; renewable grid makes EVs zero-carbon
• Growth: ~2% of global vehicle sales currently; projected 50%+ by 2050 in developed nations
• Cost/Barriers: Expensive batteries; cost parity with gas vehicles ~2025; charging infrastructure needs expansion
• Range: Modern EVs 200-400 miles per charge; sufficient for most driving; long trips still challenging
• Air Quality Impact: Urban air quality dramatically improves if EVs replace gas vehicles (zero local emissions); major health benefit

SO₂ Control - Scrubbers

• Technology: Flue gas desulfurization (FGD); spray lime slurry into exhaust; SO₂ reacts with lime → calcium sulfite/sulfate; removed by electrostatic precipitator/bag filter
• Efficiency: Removes ~95% SO₂; very effective
• Cost: High capital cost (~$100 million for coal plant); ongoing operational cost; byproduct (gypsum) can be sold as wallboard material
• Implementation: Mandated by Clean Air Act; most coal plants retrofitted with scrubbers
• Success: USA SO₂ emissions down ~95% since 1970s despite more electricity generation
• Limitation: Doesn't address CO₂ or PM; only removes SO₂

NOx Control - Selective Catalytic Reduction (SCR)

• Technology: Inject ammonia or urea into exhaust; catalysts convert NOx to harmless N₂ + H₂O
• Efficiency: Removes ~95% NOx; very effective
• Cost: Similar to scrubbers; operational cost for ammonia/urea + catalyst replacement
• Deployment: Increasingly required globally; coal, gas, diesel plants adopting SCR
• Vehicle Application: Diesel vehicles use SCR for NOx reduction; ammonia tank refilled with fuel
• Limitation: Catalyst poisoning by sulfur (requires low-sulfur fuel); additional operating cost

PM Control

• Electrostatic Precipitators (ESP): Charge particles; attract to collecting plates; ~99% efficient for large particles; less effective for fine PM
• Baghouses: Fabric filter bags collect particles; ~99.9% efficient; work for all particle sizes
• Diesel Particulate Filter (DPF): Vehicles; ceramic filter traps particles; periodically regenerated (high-temperature burn-off)
• Cost/Effectiveness: Very effective technology; all modern coal plants have particulate controls
• Secondary PM Formation: Doesn't address SO₂/NOx forming secondary sulfate/nitrate particles; requires upstream SO₂/NOx controls

Lead Phase-Out

• Background: Lead added to gasoline 1920s-2000s; improves octane; but highly toxic neurotoxicant
• Health Impact: Lead exposure reduces IQ, causes behavioral problems, increases cardiovascular disease; no safe level
• Phase-Out Timeline: USA 1970s-1990s; Europe, Japan similar; developing nations slower; worldwide phase-out by ~2025
• Success: Blood lead levels dropped 90%+ in developed nations; prevented millions of IQ points lost; estimated benefits ~$200 billion annually (USA)
• Lesson: Demonstrates regulatory action can quickly eliminate dangerous pollutant; phased transition manageable

Renewable Energy Transition

• Direct Impact: Replacing coal/gas with renewables eliminates emissions from power sector (~40% of air pollution)
• Health Benefit: Each coal plant closure prevents ~100-300 premature deaths/year (pollution-related)
• Progress: USA coal generation down 50% since 2005; renewable generation tripled; air quality improving
• China Challenge: Still building coal plants; but also leading renewable capacity; air quality rapidly improving
• Technology Maturity: Solar/wind cost-competitive; further deployment depends on policy, not technology

Clean Air Act (USA, 1970; Amended 1990)

• National Ambient Air Quality Standards (NAAQS): EPA sets enforceable limits for pollutants (CO, NOx, SO₂, PM, O₃, Pb, etc.)
• State Implementation Plans (SIPs): States must develop plans to attain standards
• Tailpipe Standards: Light-duty vehicles must meet emission limits (catalytic converters required)
• Power Plant Standards: Coal plants must install pollution controls (scrubbers, SCR)
• Cap-and-Trade (Acid Rain Program): SO₂ allowances distributed; utilities can trade; creates market incentive for reduction
• Success Metrics: 70% emissions reduction despite 3x GDP growth; 230,000 lives saved annually (benefits $30 trillion); most cost-effective environmental policy ever
• Global Model: EU, Canada, other countries adopted similar frameworks based on CAA success

Success Story: London Smog Elimination

• The Problem: 1952 Great Smog; radiation inversion traps SO₂ from coal heating/power; 12,000 excess deaths
• Response: Clean Air Act 1956; banned coal burning in urban areas; transition to gas/electric heating; power plant relocation
• Result: Smog eliminated by 1960s; air quality dramatically improved; SO₂ >95% reduction
• Legacy: Modern London has London-grade smog; air quality now among best in world; proves rapid transition possible
• Lesson: Strong regulation + political will = rapid improvement; similar improvements occurring globally (Los Angeles, Asian cities)
• Cost: Relatively small; heating fuel transition manageable; prevented millions of health impacts

Transboundary Pollution

• Transport Range: SO₂ lifetime ~10 days; travels 1,000-2,000 km; NOx lifetime ~1 day but forms acid long-range
• Regional Examples: Chinese coal pollution affects Korea, Japan; US Midwest pollution affects Northeast; European pollution affects Scandinavia
• Precipitation Pattern: Emissions in one region; acid rain falls downwind in different region/country
• Political Challenge: Receiving country can't control upwind sources; international cooperation necessary
• Treaties: US-Canada agreement (1991) reduced acid rain; EU protocols; Chinese-Korean discussions (ongoing conflict)
• Worst-Affected: Scandinavia (Norway, Sweden, Finland) very affected by coal burning in Germany, UK, Eastern Europe; lakes fishless

Geographic Hotspots

• Coal Belt Regions: Eastern China (pH 4.5-5.0 rain common), Appalachia USA (coal mining + power plants), Eastern Europe (coal dependence)
• Worst Acidity: Adirondack Mountains USA (pH <4), some Scandinavian lakes (pH <4.5), Chinese coal areas (pH 3.5-4.5)
• Sensitivity Varies: Granite bedrock can't buffer acid (low alkalinity); limestone regions more resistant (alkaline, neutralizes acid)
• Vulnerability Map: Eastern USA most vulnerable (sensitive geology + pollution); Western mountains similarly sensitive; developing coal regions will worsen

Aquatic Ecosystems

• Fish Mortality: pH <6.0 stressful; pH <5.0 lethal to most fish; eggs fail to hatch; acidified lakes become biologically dead
• Specific Impacts: Salmon, trout populations collapse; smallmouth bass eliminated; only acid-tolerant species survive
• Food Web Disruption: Zooplankton, aquatic insects decline; algae imbalance; phytoplankton changes; energy flow disrupted
• Example: 10,000-14,000 lakes in USA became fishless due to acid rain; 1000s in Scandinavia similarly affected
• Aluminum Mobilization: Low pH dissolves aluminum from rocks/soil; toxic to fish; interferes with respiration; kills gills
• Recovery Timeline: Very slow even with emission reduction; buffering capacity depleted; soil sulfur pool takes decades to normalize
• Liming Solution: Limestone added to lakes temporarily raises pH; must repeat every 2-3 years; expensive, temporary fix

Soil and Forest Impacts

• Soil Acidification: Acid rain lowers soil pH; nutrient loss (calcium, magnesium, potassium leached); reduced nutrient availability for plants
• Forest Decline: Documented in Europe (Black Forest Germany, forests in Czech Republic); trees weakened; susceptible to insect/disease damage
• Symptoms: Needle yellowing, crown thinning, dieback from top; reduced growth; productivity decline
• Aluminum Toxicity: Leached aluminum poisons root tips; reduces water uptake; "slender root syndrome"
• Global Concern: Boreal forests (Canada, Russia, Scandinavia) at risk; sensitive to acid deposition
• Recovery Slow: Soil buffering capacity takes decades to recover after emission reduction

Material Corrosion

• Stone Dissolution: Acid rain dissolves limestone (CaCO₃) and marble (same mineral); historic structures corroded
• Building Damage: Cathedrals, monuments, statues degraded; carved details smoothed; ancient structures at risk
• Paint/Metal Corrosion: Acid accelerates rusting; paint degradation; bridges, vehicles affected
• Economic Cost: Billions annually to repair/replace corroded infrastructure; cultural heritage lost
• Example: Parthenon (Athens), Cologne Cathedral, Washington Monument all damaged by acid rain
• Acceleration: pH 4.0 rain accelerates corrosion ~10x vs. clean rain; severe acid rain causes visible damage within years

Solutions and Progress

• SO₂ Reduction: Scrubbers, fuel switching (less sulfur coal), renewable energy; most effective
• NOx Reduction: SCR, vehicle emission standards, renewable electricity
• Success Story: US acid rain <60% reduction since 1990; Scandinavian improvements with EU cooperation; Chinese air quality improving (SO₂ down 70% since 2005)
• Ongoing Issues: India, rapidly-developing coal-dependent regions; acid rain worsening in parts of Asia despite controls elsewhere
• Recovery Rate: Emissions must drop; then soil/lakes slowly recover; Scandinavia lakes recovering 20+ years after emission reductions

Major Noise Sources

• Traffic (80-85 dB): Most common; continuous; affects ~1 billion people; most annoying of all sources in urban surveys
• Aircraft (75-140 dB): Takeoff/landing very loud; worst near airports; affects ~100 million people;night flights particularly disruptive
• Construction (80-90 dB): Temporary but intense; often early morning (disturbs sleep); affects neighborhoods during projects
• Industrial (80-100 dB): Factory noise; affects workers primarily; occupational exposure regulation exists
• Music Venues (100-110 dB): Concerts, nightclubs; young people exposed; hearing damage risk high
• Recreational (75-120 dB): Motorcycles, snowmobiles, personal watercraft; usually short-duration
• Household (60-100 dB): Appliances, TV, music systems; cumulative exposure
• Urban Ambient: 70-80 dB typical in cities; rural 40-50 dB; difference ~30 dB (1,000x intensity)

Global Impact

• Exposed Population: ~1 billion people affected by harmful noise; 700 million in developed countries
• Burden of Disease: 1.6 million DALYs lost annually (disability-adjusted life years); significant but underappreciated
• Burden Greater Than: Traffic injuries, alcohol abuse for some populations; comparable to second-hand smoke impact
• Health Costs: €40 billion annually in Europe from noise-related health impacts
• Inequity: Low-income communities near highways, airports; disproportionate exposure to noise + air pollution

Hearing Loss

• Mechanisms: Sound waves cause hair cells in cochlea to vibrate; excessive vibration damages/kills hair cells; permanent once lost (no regeneration in humans)
• Noise-Induced Hearing Loss (NIHL): Exposure to >85 dB for 8 hours causes damage; >90 dB more rapid damage; >120 dB immediate damage
• Cumulative Effect: Damage accumulates over time; no recovery period; continued exposure worsens loss
• Young People at Risk: Attending concerts/clubs (100-110 dB); using earbuds at high volume; 1+ billion teenagers at risk of NIHL
• Occupational NIHL: Construction workers, factory workers, military combat zone soldiers all experience NIHL
• Prevention: Hearing protection (earplugs, earmuffs); 85+ dB occupational limit with protection required
• Irreversible: Hearing aid technology helps but doesn't restore; prevention critical

Sleep Disruption

• Night Sleep Impact: Noise >50-55 dB at night disrupts sleep; frequent awakenings; reduced sleep quality
• WHO Recommendation: <55 dB day, <45 dB night for undisturbed sleep; many urban areas exceed
• Effects: Sleep deprivation → cognitive impairment, mood changes, increased risk of accidents, health problems
• Urban Problem: Traffic, aircraft noise at night; adaptation possible but never complete (even sleepers startle awake)
• Children Vulnerable: Sleep loss during development affects cognitive development, school performance
• Long-term Effects: Chronic sleep disruption increases cardiovascular disease risk

Cardiovascular and Cognitive Effects

• Stress Response: Noise triggers fight-or-flight response; cortisol/adrenaline increase; blood pressure rises even during sleep
• Hypertension: Chronic noise exposure increases blood pressure; persistent elevation increases heart attack/stroke risk
• Annoyance/Stress: Noise induces psychological stress; affects quality of life; depression/anxiety correlated with noise exposure
• Learning Impairment: Children exposed to traffic/aircraft noise show lower reading comprehension, smaller vocabulary
• Cognitive Development: Chronic noise exposure during critical periods affects brain development
• Concentration: Noise reduces ability to concentrate; workplace/school productivity declines
• Long-term Health: WHO estimates noise exposure associated with 1.6 million DALYs annually; cardiovascular disease largest fraction

Vulnerable Populations

• Children: Developing ears/brain; sleep disruption affects development; school performance impaired
• Elderly: Already have age-related hearing loss; noise further impairs; cardiovascular effects significant
• Workers: Occupational exposure; construction, factory workers highest risk
• Musicians: Hearing loss from occupational music exposure; 50% of musicians have noise-induced hearing loss
• Low-Income Communities: Cannot afford quieter neighborhoods; disproportionate exposure
• People with Existing Conditions: Cardiovascular disease patients; hypertension exacerbated by noise

Individual Protection

• Hearing Protection: Earplugs, earmuffs reduce noise 15-30 dB; critical for occupational/recreational high-noise exposure
• Volume Limits: Earbuds/headphones maximum 60% volume, <1 hour daily prevents hearing damage
• Quiet Spaces: Seek low-noise environments (parks, libraries) for recovery/concentration
• Sleep Protection: Earplugs, white noise machines, quiet bedroom promote sleep quality

Urban/Infrastructure Solutions

• Sound Barriers: Walls, berms along highways reduce traffic noise; partial effectiveness; expensive
• Building Insulation: Double-pane windows, acoustic insulation reduce indoor noise; effective for fixed sources
• Quieter Vehicles: Electric vehicles quieter than combustion engines; reducing traffic noise benefit
• Reduced Speed Limits: Lower speeds reduce noise (noise increases with speed cubed); 80 km/h quieter than 100 km/h
• Urban Green Space: Trees absorb sound; parks provide quiet refuges
• Airport Management: Flight path changes, curfews, noise fees incentivize quieter aircraft/operations

Policy and Regulation

• Occupational Standards: USA OSHA: 85 dB 8-hour limit with hearing protection; 90 dB requires protection
• Environmental Standards: EU noise directive; noise mapping requirements; action plans for hotspots
• Vehicle Noise Limits: Regulations limit exhaust noise from motorcycles, cars; enforcement variable
• Land Use Planning: Zoning keeps airports/highways away from residential areas; mixed-use planning reduces commute distances
• Education: Hearing conservation programs; volume limit campaigns for youth; awareness of sleep/health impacts
• Challenge: Noise regulation often lower priority than air pollution; underappreciated public health issue