Air Pollution Calculators

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Air pollution is the presence of substances in the atmosphere that cause harm to human health, ecosystems, or the climate. Major air pollutants include particulate matter (PM2.5, PM10), ground-level ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), carbon monoxide (CO), and volatile organic compounds (VOCs). These pollutants originate from combustion (vehicles, power plants, industry), agricultural activities (NH₃, NOₓ), and natural sources (wildfires, dust). The Air Quality Index (AQI, scale 0–500) communicates daily pollution levels and associated health risks to the public.

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Major Air Pollutants

  • PM2.5: Fine particles < 2.5 μm; from combustion, wildfires, secondary formation; penetrate deep into lungs and bloodstream; most harmful; WHO annual guideline: 5 μg/m³
  • PM10: Coarser particles 2.5–10 μm; dust, pollen; less deeply inhaled
  • Ground-level ozone (O₃): Formed from NOₓ + VOCs + sunlight (photochemical smog); respiratory irritant; worst in summer afternoons
  • NO₂: From vehicles and industry; respiratory irritant; reacts to form O₃ and PM2.5
  • SO₂: From coal combustion and metal smelting; causes acid rain; respiratory irritant
  • CO: Incomplete combustion; binds hemoglobin → reduces O₂ transport

Health Effects

PM2.5: cardiovascular disease, lung cancer, premature death. Ozone: asthma exacerbation, reduced lung function. NO₂: respiratory inflammation. CO: headache, confusion, death at high concentrations.

Control Strategies

  • Vehicle emissions: catalytic converters; EVs; Euro/US emission standards
  • Power plants: scrubbers (SO₂ removal); selective catalytic reduction (NOₓ)
  • Regulatory: Clean Air Act (US); NAAQS standards

Glossary

PM2.5
Fine particulate matter < 2.5 μm diameter; most health-significant air pollutant; penetrates deep into lungs; causes cardiovascular and respiratory disease; WHO annual guideline: 5 μg/m³.
Ground-Level Ozone (O₃)
Secondary pollutant formed from NOₓ + VOCs + sunlight; respiratory irritant; peaks on hot sunny afternoons; measured as 8-hour average concentration; AQI > 100 is unhealthy for sensitive groups.
AQI (Air Quality Index)
0–500 scale communicating air pollution and health risk; 0–50 = Good; 51–100 = Moderate; 101–150 = Unhealthy for sensitive groups; > 200 = Very Unhealthy; based on PM2.5, O₃, NO₂, SO₂, CO.

Frequently Asked Questions

Major regulated air pollutants (NAAQS criteria pollutants in the US): PM2.5 (fine particles < 2.5 μm): from combustion (vehicles, wood burning, industry), wildfires, and secondary formation from SO₂ and NOₓ. Most health-significant pollutant. PM10 (inhalable particles 2.5–10 μm): road dust, construction, agriculture. Ground-level ozone (O₃): not directly emitted; forms when NOₓ + VOCs react in sunlight (photochemical smog); worst on hot sunny days. NO₂: from vehicle exhaust, power plants; indicator of combustion pollution. SO₂: coal combustion, metal smelting; forms sulfate aerosols (PM2.5) and acid rain. CO: incomplete combustion; elevated near heavy traffic, garages, wood stoves. Lead (Pb): leaded aviation fuel, industrial sources; still a NAAQS pollutant.

PM2.5 (fine particulate matter, diameter < 2.5 μm) is the air pollutant with the strongest and broadest health evidence: Penetration: PM2.5 is small enough to penetrate deep into the alveoli (gas exchange regions) of the lungs; the smallest particles (< 0.1 μm, ultrafine) can enter the bloodstream. Mechanisms: inflammation; oxidative stress; systemic vascular effects. Health effects: Respiratory: asthma exacerbation; COPD worsening; reduced lung function. Cardiovascular: myocardial infarction; stroke; cardiac arrhythmias; heart failure. Long-term: lung cancer (IARC Group 1 carcinogen); premature death. Mortality: WHO attributes ~7 million premature deaths/year globally to air pollution — PM2.5 is responsible for most. Each 10 μg/m³ increase in long-term PM2.5 is associated with ~6% increase in cardiovascular mortality.

Photochemical smog is a type of air pollution formed by the reaction of sunlight with NOₓ and VOCs in the atmosphere. Formation sequence: Vehicles and industry emit NO + VOCs. NO + O₃ → NO₂ + O₂ (initially depletes O₃). NO₂ + sunlight (UV) → NO + O. O + O₂ + M → O₃ (ozone production). VOCs also react with OH radicals to form additional RO₂ radicals → more NO₂ → more O₃. Conditions for photochemical smog: high temperature, intense sunlight, stagnant air, and high NOₓ + VOC emissions. Famous examples: Los Angeles (1950s–70s); Mexico City; Beijing; Athens. Health effects: O₃ is a strong respiratory irritant; causes chest pain, coughing, reduced lung function, asthma attacks. Also damages crops and materials.

Vehicle emissions controls: Three-way catalytic converter: oxidizes CO → CO₂; hydrocarbons → CO₂ + H₂O; reduces NOₓ → N₂ + O₂. 90%+ reduction in CO, HC, and NOₓ from gasoline vehicles. Diesel particulate filters (DPF): trap PM from diesel exhaust. SCR (selective catalytic reduction): injects urea to convert NOₓ → N₂ + H₂O in diesel engines. Electric vehicles: zero tailpipe emissions; shifting pollution to power generation (cleaner if renewable). Stationary source controls: Flue gas desulfurization (wet scrubber): removes 90%+ of SO₂ from coal power plants. SCR for NOₓ removal from power plants. HEPA and electrostatic precipitators: capture particles from industrial exhaust. Regulatory: US Clean Air Act; EU Air Quality Directives; WHO Air Quality Guidelines (stricter than US NAAQS for PM2.5).