1. Generation of Sea-Salt Aerosols Magdalena Anguelova Bridging the Gap October 30 - 31, 1999

2. What are Aerosols?  Aerosols are minute stable particles, solid or liquid, suspended in the atmosphere. Clean (rural) air Polluted (urban) air

3. Tiny Particles  Seen as...  Why red?

4. Aerosol Types  The aerosols are:  Natural:  Man-made: Soil dust; Sea salt; Volcanic dust; Organic particles. Industrial sulfates; Burning biomass; Soot; Organic particles.  The most numerous are:

5. Climate Effects of the Aerosols  Aerosols can influence climate:  Directly:  Indirectly: - by reflecting incoming sunlight back to space. - by modifying the properties and lifetime of the clouds.

6. Cloud Properties  More aerosols = more cloud droplets.  Clouds reflect more sunlight.  Net result: cooling.

7. Cloud Lifetime  More aerosols inhibit the growth of cloud droplets.  Droplet condensation and rain are delayed.  Net result: prolonged cloud lifetime.

8. Aerosols in Climate Models  Inclusion of aerosol effects in climate models improves the predictions.  Assess the effect of man- made aerosols.  The effect of background aerosols.  Cooling effect.

9. Aerosol Cooling  Man-made sulfates.  Natural sulfates. Phytoplankton Pollution

10. Relative Abundance  Sulfate aerosols dominate in polluted air.  Sea-salt aerosols dominate in clean air.

11. Sea-Salt Aerosols  Major constituent of a remote marine atmosphere.

12. Sea-Salt Aerosols and Climate  The major contributor to sunlight reflection.  Facilitate the formation of cloud drops.  Medium for chemical reactions in the atmosphere.

13. Oceanic Whitecaps  The major source for sea-salt drops.  1.3 GT (=1.3  10 9 kg) sea salt annually.

14. Wave Breaking  As waves break,  air mixes into the water,  and forms clouds of bubbles.

15. Sea Spray Formation  The large bubbles rise to the surface,  and while floating on the water, burst.

16. Film Drops  Upon bursting, bubble caps shatter into thousands of small droplets. Film drops form.

17. Jet Drops  The bubble cavity collapses. Jet drops form.

18. Spume Drops  Under very high winds drops are torn from the wave crests and blown directly into the air. Spume drops form.

19. Sea Spray  In the air, this sea spray: sea-salt aerosols.  evaporates,  shrinks,  and forms  So, whitecaps fill the air with film, jet, and spume drops.

20. Sea Spray Sizes  Film drops: 0.5 to 5  m  Jet drops: 3 to 50  m  Spume drops: 20 to > 500  m r,  m 5001001010.1  Depend on the generation mechanism:

21. Sizes Relevant to Aerosol Cooling  Long residence time.  Gravitational settling. Heat exchangeAerosol cooling r,  m 5001001010.1

22. Modeling Sea Spray dF/dr = dF 0 /dr + dF 1 /dr r,  m 5001001010.1  Indirect;  Direct. (Monahan et al., 1986)

23. Explicit Expressions d F 0 /d r = 1.373 U 10 3.41 r -3 (1 + 0.057r 1.05 ) 10 1.19e -B2-B2 B = (0.38 - log r) / 0.65 d F 1 /d r = 0 r  10  m d F 1 /d r = 8.60  10 -6 e 2.08U r -2 10  m  r  75  m d F 1 /d r = 4.83  10 -2 e 2.08U r -4 75  m  r  100  m 10 d F /d r = f (U 10, r)

24. Wind Dependence Fitzgerald, 1991

25. Size Dependence Radius,  m Number of aerosols, cm -3 O’Dowd et al., 1997 Surface area,  m 2 cm -3

26. In Climate Models d F/d r = d F 0 /d r + d F 1 /d r ImprovementsBest available

27. My Research d F 0 /d r = f (U 10, r) W (U 10,  T, T w, S, f, d, C) W (U 10 )

28. Questions