In the context pf PM2.5, what does 2.5 mean: 

The correct answer is Particulate matter of size 2.5 μm and less.

Key Points

• PM2.5 stands for particulate matter with a diameter of 2.5 micrometers or smaller.
• These fine particles are capable of penetrating deep into the respiratory tract and reaching the lungs.
• PM2.5 is often generated from combustion processes, including motor vehicles, power plants, and wildfires.
• High levels of PM2.5 are associated with adverse health effects, including respiratory and cardiovascular diseases.
• Due to their small size, PM2.5 particles remain suspended in the air for longer periods, increasing the likelihood of inhalation.

Additional Information

• Air Quality Index (AQI):
  • An index used to communicate how polluted the air currently is or how polluted it is forecast to become.
  • PM2.5 is one of the pollutants measured to determine the AQI.
• Sources of PM2.5:
  • Natural sources: Wildfires, volcanic eruptions, and dust storms.
  • Anthropogenic sources: Vehicle emissions, industrial processes, and fossil fuel combustion.
• Health Impacts:
  • Short-term exposure: Irritation of the eyes, nose, and throat; coughing; shortness of breath.
  • Long-term exposure: Aggravation of asthma, development of bronchitis, and increased risk of heart disease.
• Preventive Measures:
  • Wearing masks designed to filter out PM2.5 particles.
  • Using air purifiers indoors to reduce exposure.
  • Reducing outdoor activities when PM2.5 levels are high.