What is PM2.5?

PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometers or smaller, a critical component of air pollution. Here's a detailed breakdown:

​What is PM2.5?

• ​Definition: PM2.5 stands for ​Particulate Matter 2.5, denoting airborne particles ≤2.5 micrometers in diameter (about 1/30th the width of a human hair).
• ​Composition: A mix of solids and liquids, including sulfates, nitrates, black carbon, organic compounds, metals, and dust. These can be ​primary (directly emitted) or ​secondary (formed via atmospheric reactions of gases like SO₂ and NOₓ).

​Sources

• ​Human-made: Vehicle exhaust, power plants, industrial emissions, agricultural burning, and residential heating.
• ​Natural: Wildfires, dust storms, volcanic eruptions, and sea spray.
• ​Indoor: Cooking, smoking, and burning candles or incense.

​Health Impacts

• ​Penetration: PM2.5 bypasses the body’s defenses, entering deep into the lungs and bloodstream.
• ​Short-term: Eye/nose/throat irritation, coughing, shortness of breath, and exacerbated asthma.
• ​Long-term: Increased risk of chronic respiratory diseases (e.g., bronchitis), cardiovascular issues (heart attacks, strokes), lung cancer, and premature death.
• ​Vulnerable Groups: Children, elderly, and individuals with pre-existing heart or lung conditions.

​Environmental Effects

• Reduces visibility (haze).
• Alters ecosystem balance by depositing harmful substances.
• Contributes to climate change by affecting cloud formation and absorbing/scattering sunlight.

​Measurement & Regulation

• ​Units: Concentration measured in micrograms per cubic meter (µg/m³).
• ​Standards:
  • WHO guideline: ≤5 µg/m³ annual mean.
  • U.S. EPA: ≤9 µg/m³ annual mean, 35 µg/m³ 24-hour average.
• ​Air Quality Index (AQI): PM2.5 levels are a key factor in AQI calculations, with higher values indicating greater health risks.

​Mitigation

• ​Personal: Use N95 masks, air purifiers (HEPA filters), and avoid outdoor activities on high-pollution days.
• ​Policy: Emission controls (scrubbers, catalytic converters), promoting renewables, and urban planning (green spaces, public transit).
• ​Global: Cross-border cooperation to address transboundary pollution.

​Why It Matters

PM2.5 is a leading environmental health risk, linked to millions of deaths annually. Monitoring and reducing exposure is vital for public health and environmental sustainability.