1. Atmospheric Chemistry Chemical effects on cloud activation with special emphasis on carbonaceous aerosol from biomass burning M. C. Facchini, S. Decesari, M. Mircea, F. Cavalli and S. Fuzzi Istituto di Scienze dell’Atmosfera e del Clima - C.N.R. Bologna, Italy

2. Atmospheric ChemistryAcknowledgements M. O. Andreae Max Planck Institute for Chemistry O. Majol-Bracero University of Puerto Rico R.J. Charlson University of Washington, Seattle, USA A. Nenes, J.A. Seinfeld California Institute of Technology, Pasadena, USA California Institute of Technology, Pasadena, USA M. Kulmala University of Helsinki, Helsinki, Finland

3. Atmospheric Chemistry

4. how does the chemistry of the cloud multiphase system influence formation and evolution of the cloud droplet population ?

5. Atmospheric Chemistry  Many years ago, Twomey suggested that the most important parameter influencing cloud droplet number (CDN) is aerosol number concentration, while aerosol chemical composition has a relatively minor effect  Recently, model and experimental results have induced to revisit this assumption and to re-examine the relative importance of the different factors influencing CDN distribution

6. Atmospheric Chemistry RH Dry particle wet aerosol Cloud droplet gas phase R R …an intuitive picture of aerosol - cloud interaction and chemistry Insoluble /absorbing material  Soluble fraction chemical composition

7. Atmospheric Chemistry Cloud formation  Atmospheric thermodynamic parameters (moisture availability, updraft velocity, temperature, etc.)  Aerosol properties: classically, the controlling chemical variables are CCN size distribution and water soluble mass

8. Atmospheric Chemistry Chemical factors controlling cloud formation  Not simply inorganic soluble salts influence cloud formation  Soluble or slightly soluble organics influence equilibrium water vapor pressure and decrease surface tension of the droplets  Soluble gases condensation (Charlson et al., Science 2001; Nenes et al., GRL, 2002) (Charlson et al., Science 2001; Nenes et al., GRL, 2002)

9. Atmospheric Chemistry Modified Köhler equation Kelvin term Raoult term

10. Atmospheric Chemistry Biomass burning aerosol chemical composition

11. Atmospheric Chemistry Fine fraction organic and inorganic speciation

12. Atmospheric Chemistry  Biomass carbonaceous aerosols can influence equilibrium supersaturation  “ adding” organic soluble or slightly soluble material (with different chemical structure with respect to wet season) ;  decreasing surface tension (HULIS)  changing mass and properties of insoluble fraction (WIOC)

13. Atmospheric Chemistry Surface tension decrease Po Valley Tenerife ACE II SMOCC-dry season

14. Atmospheric Chemistry Modelling of chemical effects  By using a cloud parcel model, we have shown that there are many conditions in the atmosphere in which chemical factors (soluble and slightly soluble organic and inorganic compounds, surface tension, dissolution of soluble gases) influence/control cloud microphysics to the same extent as cloud dynamics and/or aerosol number concentration (Nenes et al., GRL 2002)

15. Atmospheric Chemistry (Roberts et al., JGR 2003),  Recent results, using the same 1D cloud model, suggest that changes in cloud albedo are more influenced by chemical and physical properties in case of hight aerosol loading (as in dry season)  “The knowledge on CCN spectra alone is not sufficient to fully capture the climatic influence of biomass burning aerosol”

16. Atmospheric Chemistry Effect of size segregated chemical composition Dotted line: bulk composition Solid line: size-segr. compostion Mircea et al., oral A08432

17. Atmospheric Chemistry Water activity of multicomponent solutions data from Clegg et al., J. Aerosol Sci., 2001 modified Koher theory a w Clegg treatment as above + measured 

18. Atmospheric Chemistry Conclusions  The potential impact of “chemical factors” on cloud activation in the case of biomass burning aerosol can be high for several reasons:  Chemical composition: WSOC concentration; WIOC; INORGANIC/WSOC ratio   effect

19. Atmospheric Chemistry …still needed  Size segregated chemical composition  Speciation of molecular organic forms: wet vs. dry season  A w : the effect of mixture of organics with a few percent of inorganic salts can be described with traditional osmotic coefficient as used in KC ??