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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. Summary. Motivation Biogenic Emissions Sources of Isoprene Sources of SOA from Isoprene The impact of SOA’s on Cloud Formation
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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
Summary • Motivation • Biogenic Emissions • Sources of Isoprene • Sources of SOA from Isoprene • The impact of SOA’s on Cloud Formation • Cloud Formation and Albedo • Hydrological Implications
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
Major Sources of NMHC Tg C yr-1
What is Isoprene • Olefinic • Highly reactive Double Bonds • Volatile Organic Compound (VOC) • Non-Methane Hydrogen Carbon (NHMC)
Derivatives of Photoxidation • Assumed to be extremely volatile (e.g formaldehyde) • Assumed Most likely not to be SOA’s • Two newly identified species hypothesized to be SOA’s from photooxidation of isoprene • Formation of SOA via acidic catalysts
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
SOA from Isoprene • Gas Chromatography results that show presence of a product of isoprene photo-oxidation • Similar 5 carbon skeleton as that of isoprene
SOA from Isoprene • Proposed formation of the 2-methyltetrols from isoprene by reaction with OH’O2 followed by self-and cross-reactions with radicals • Intermediate 1,2, diols have been previously reported under low NOx conditions [Ruppert, 2000]
Significance of (1) and (2) • SOA’s have low yield from Isoprene photooxidation • However, large emissions of Isoprene, suggest significant annual formation of SOA’s • 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
SOA’s 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
Reaction Yield increases with catalyst • Influence of ozone as competing oxidant • Effect of Relative air Humidity
Short Recap • SOA’s from Isoprene Exist • Photooxidative products have low vapor pressures • Humic-like substances generated from acidic catalysts • All SOA’s from Isoprene can be considered to be highly hydroscopic
Cloud Formation • Kohler Equation • Kelvin Effects • Strong functions of Surface Tension • Humic-like aerosols decrease σ
Consequences of Surfactants • Great Cloud Droplet Number • 30% decrease in σ yields a 20% increase in droplet number • Smaller cloud droplet Radii • Average 6% decrease in droplet size • Significant Change in Cloud Properties (hence Albedo)
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
Hydrological Cycle Cloud Albedo Cloud Formation SOA Formation Isoprene Emissions Precipitation/ Water Stress Surface Temperature
Conclusions • SOA’s from Isoprene do exist • Humic-like SOA’s 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 SOA’s from Isoprene
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