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

1. The Impact of Secondary Organic Aerosol Derivatives of Isoprene on Cloud Formation and Albedo Akua Asa-Awuku EAS6410 Term Paper Presentation

2. 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

3. 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

4. Major Sources of NMHC Tg C yr-1

5. What is Isoprene • Olefinic • Highly reactive Double Bonds • Volatile Organic Compound (VOC) • Non-Methane Hydrogen Carbon (NHMC)

6. Products of Isoprene Photooxidation

7. 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

8. 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

9. SOA from Isoprene • Gas Chromatography results that show presence of a product of isoprene photo-oxidation • Similar 5 carbon skeleton as that of isoprene

10. 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]

11. 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

12. 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

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

14. 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

15. Cloud Formation • Kohler Equation • Kelvin Effects • Strong functions of Surface Tension • Humic-like aerosols decrease σ

16. Decreasing Surface Tension

17. Kohler Curves

18. 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)

19. Droplet Number and Albedo

20. Albedo and Cloud Optical Thickness

21. 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

22. Albedo and Cloud Optical Thickness

23. Hydrological Cycle Cloud Albedo Cloud Formation SOA Formation Isoprene Emissions Precipitation/ Water Stress Surface Temperature

24. 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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