7.4

• Natural sources of air pollutants:

  • Lightning converts N2 n atmosphere to NOx
  • Forest fires CO, PM, NOx; combustion of biomass also releases CO2 and H2O vapor (greenhouse gases)
  • Plants (especially conifers) emit VOCs; forms natural photochemical smog (Smoky mountains)
  • volcanoes emit SO2, PM, CO, NOx
• PM-10 vs PM-2.5;

  • Particulate matter: solid/liquid particles suspended in air
  • PM-10 (<10 micrometers)
  • particles/droplets like dust, pollen, ash, or mold
  • too small to be filtered out by nose hairs and trachea cilia; can irritate respiratory tract and cause inflammation
  • PM-2.5 (<2.5 micrometers)
  • particles from combustion
  • more likely to travel deep into lungs due to smaller size
  • associated with chronic bronchitis and increased risk of lung cancer