Lecture 7

• Aerosols: tiny particles suspended in the atmosphere
• Main Aerosols:

  • sea salt
  • volcanic dust
  • desert dust
  • smoke from forest fires
  • human-made - burning of coal and oil
• How are aerosols measured: use satellites equipped with radiometers to measure the amount of light that aerosols scatter ad absorb in the atmosphere
• Aerosol's optical depth of...

  • <0.05 - clear sky with relatively few aerosols and maximum visibility
  • 1 - hazy conditions
  • > 2 or 3 - very high concentrations
• Why should Aerosols be monitored? - Human activities since pre-industrial era have doubled the global concentration of most aerosols

  • adverse affects on human health at regional and national scale
  • influence on climate change
  • effects on hydrological cycle
• Control variable: Aerosol Optical Depth (AOD)

  Planetary Boundary: Not yet quantified
• Transport of aerosols in the atmosphere: most remain suspended for short periods (4 days-1 week) but can travel vast differences
• Effects of Aerosols on human health:

  • cardiopulmonary disease
  • tracheal, bronchial and lung cancer
  • acute respiratory infection in urban areas
• Effects of Aerosols on human health:

  • convert to about 800,000 premature deaths - mostly in developing Asian countries
  • mortality due to exposure to indoor smoke from solid fuels - about double of urban air pollution (around 1.6million)
• Toxic dust - The Aral Sea:

  • dried lake beds are abundant sources of dust - filled with lights, fine-grained sediment that winds can lift easily
  • one of the most harmful sources of dust worldwide
• Toxic dust - The Aral Sea: Build-up of fertilisers, pesticides, heavy metals and other chemical pollutants in Aral Sea lakebed - dust that can travel thousands of kms

  • impacts soil and vegetation
  • impacts physiological and mental health
• Aerosols: Impact on climate

  • create a cooling effect because they reflect sunlight back to space before it reaches the atmosphere
  • lead to less heat being trapped by GHGs because less light reaches surface to be absorbed
  • change weather patterns
  • reduce rainfall
• Aerosols indirect effects on climate- hydrological cycle:

  • aerosols provide condensation nuclei for cloud formation - cam impact reflection of radiation and precipitation patterns
• Aerosols direct effects on climate:

  • aerosols and their clouds reflect about 1/4th of sun's radiation back to space
  • some aerosols absorb radiation
  • black carbon aerosols absorb sunlight - warms the layer of atmosphere carrying the black carbon but shades and cools the surface below
• Aerosols: Atmospheric brown clouds

  • winter dry season in S.Asia - burning fossil fuels and biomass create huge brown cloud of pollution - black carbon, SO2 and NO2
  • decrease in surface radiation; less evaporation at surface; weakened monsoon rains
  • mask up to 50% of surface warming due to GHGs
• Volcanic aerosols: large eruptions may lift sulfate aerosols into atmosphere - usually cools climate for following 1-2 years

  • Indonesia, 1816 - cooling felt globally till New England
  • Philippines, 1991 - global surface cooling of 0.5degrees
• Can aerosols slow climate change:

  • potential to cool atmosphere - reflect solar radiation
  • BUT ... health impacts, alter rainfall patterns and shift monsoons with potentially devastating consequences for crops, unfair to those who would suffer the most (poorer people), damage to ozone, unsure it can be maintained due to countries having to collaborate 'forever' even those who are in the midst of war