Amazon has low levels of anthropogenic emissions ..

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The Impact of Secondary Organic Aerosol
Derivatives of Isoprene on Cloud Formation and
Albedo

• Akua Asa-Awuku
• EAS6410 Term Paper Presentation

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Summary

• Motivation
• Biogenic Emissions
• Sources of Isoprene
• Sources of SOA from Isoprene
• The impact of SOAs on Cloud Formation
• Cloud Formation and Albedo
• Hydrological Implications

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The Importance of Biogenic Emissions

• Amazon has low levels of anthropogenic emissions
• Isoprene emissions in US larger than
  anthropogenic particulate matter
• Eight Different Vegetation Types are major
  sources of Isoprene

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Major Sources of NMHC
Tg C yr-1
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What is Isoprene

• Olefinic
• Highly reactive Double Bonds
• Volatile Organic Compound (VOC)
• Non-Methane Hydrogen Carbon (NHMC)

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Products of Isoprene Photooxidation
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Derivatives of Photoxidation

• Assumed to be extremely volatile (e.g
  formaldehyde)
• Assumed Most likely not to be SOAs
• Two newly identified species hypothesized to be
  SOAs from photooxidation of isoprene
• Formation of SOA via acidic catalysts

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Data Collection

• Data Samples collected from LBA-CLAIRE campaign
  July 25 -27 Claeys, 2004
• Assumptions
• Very low Anthropogenic emissions
• Tropics site of high photoxidation
• Samples Subjected to GS-MS

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SOA from Isoprene

• Gas Chromatography results that show presence of
  a product of isoprene photo-oxidation
• Similar 5 carbon skeleton as that of isoprene

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SOA from Isoprene

• Proposed formation of the 2-methyltetrols from
  isoprene by reaction with OHO2 followed by
  self-and cross-reactions with radicals
• Intermediate 1,2, diols have been previously
  reported under low NOx conditions Ruppert, 2000

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Significance of (1) and (2)

• SOAs have low yield from Isoprene photooxidation
• However, large emissions of Isoprene, suggest
  significant annual formation of SOAs
• Estimated 2 Tg per year of (1) and (2) in Amazon
  Basin
• IPCC estimates 8 to 40 Tg of biogenic SOA
  annually
• Low Vapor Pressure and High Hygroscopicity

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SOAs via Sulfuric Acid Catalysts

• Urban and Rural Areas contain sufficient amounts
  of background acidic catalysts
• Also significant emissions of Isoprene in these
  regions
• Limbeck explained that proposed pathway
  contribute to the explanation of HULIS substances
  on continental Europe

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• Reaction Yield increases with catalyst
• Influence of ozone as competing oxidant
• Effect of Relative air Humidity

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Short Recap

• SOAs from Isoprene Exist
• Photooxidative products have low vapor pressures
• Humic-like substances generated from acidic
  catalysts
• All SOAs from Isoprene can be considered to be
  highly hydroscopic

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Cloud Formation

• Kohler Equation
• Kelvin Effects
• Strong functions of Surface Tension
• Humic-like aerosols decrease s

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Decreasing Surface Tension
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Kohler Curves
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Consequences of Surfactants

• Great Cloud Droplet Number
• 30 decrease in s yields a 20 increase in
  droplet number
• Smaller cloud droplet Radii
• Average 6 decrease in droplet size
• Significant Change in Cloud Properties (hence
  Albedo)

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Droplet Number and Albedo
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Albedo and Cloud Optical Thickness
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Susceptiblity

• defined as the sensitivity of cloud albedo in
  comparison to cloud droplet number concentration
• ten percent increase in droplet number
  concentration, leads to an increase of 0.75 in
  albedo

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Albedo and Cloud Optical Thickness
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Hydrological Cycle
Cloud Albedo
Cloud Formation
SOA Formation
Isoprene Emissions
Precipitation/ Water Stress
Surface Temperature
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Conclusions

• SOAs from Isoprene do exist
• Humic-like SOAs decrease surface tensions of
  pure water by 30 increase the droplet number
  concentration by 20
• 20 increase in droplet number, correlates to a
  change in top of atmospheric cloud albedo of
  nearly 1
• a global mean forcing of almost -1 Wm-2 due to
  SOAs from Isoprene

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