Generation of Sea-Salt Aerosols

Magdalena Anguelova

Bridging the GapOctober 30 - 31 , 1999

What are Aerosols?& Aerosols are minute stable particles, solid

or liquid, suspended in the atmosphere.

Clean (rural) air

Polluted (urban) air

Tiny Particles

& Seen as...

Why red?

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:

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.

Cloud Properties

More aerosols = more cloud droplets.

Clouds reflect more sunlight.

Net result: cooling.

Cloud Lifetime

More aerosols inhibit the growth of cloud droplets.

Droplet condensation and rain are delayed.

Net result: prolonged cloud lifetime.

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.

Aerosol Cooling

Man-made sulfates. Natural sulfates.

Phytoplankton

Pollution

Relative Abundance

Sulfate aerosols dominate in polluted air.

Sea-salt aerosols dominate in clean air.

Sea-Salt Aerosols

& Major constituent of a remote marine atmosphere.

Sea-Salt Aerosols and Climate

The major contributor to sunlight reflection.

Facilitate the formation of cloud drops.

Medium for chemical reactions in the atmosphere.

Oceanic Whitecaps

The major source for sea-salt drops.

1.3 GT (=1.3109 kg) sea salt annually.

Wave Breaking As waves

break,

air mixes into the water,

and forms clouds of bubbles.

Sea Spray Formation The large bubbles rise to

the surface,

and while floating on the water, burst.

Film Drops

Upon bursting, bubble caps shatter into thousands of small droplets.

Film drops form.

Jet Drops The bubble cavity

collapses.

Jet drops form.

Spume Drops Under very high winds drops are

torn from the wave crests and blown directly into the air.

Spume drops form.

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.

Sea Spray Sizes

Film drops: 0.5 to 5 m Jet drops: 3 to 50 m Spume drops: 20 to > 500

mr, m5001001010.1

& Depend on the generation mechanism:

Sizes Relevant to Aerosol Cooling

& Long residence time.

Gravitational settling.

Heat exchangeAerosol cooling

r, m5001001010.1

Modeling Sea Spray

dF/dr = dF0 /dr + dF1 /dr

r, m5001001010.1

Indirect; Direct.

(Monahan et al., 1986)

Explicit Expressions

d F0 /d r = 1.373 U103.41 r -3(1 + 0.057r1.05) 101.19e -B2

B = (0.38 - log r) / 0.65

d F1 /d r = 0 r 10 md F1 /d r = 8.6010-6 e 2.08U r -2 10 m r 75 md F1 /d r = 4.83 10-2 e 2.08U r -4 75 m r 100 m

10

10

d F /d r = f (U10 , r)

Wind Dependence

Fitzgerald, 1991

Size Dependence

Radius, m

Num

ber o

f aer

osol

s , c

m-3

O’Dowd et al., 1997

Surf

ace

area

, m

2 cm

-3

In Climate Models

d F/d r = d F0 /d r + d F1 /d r

Improvements Best available

My Research

d F0 /d r = f (U10 , r)

W (U10 , T, Tw , S, f , d , C)

W (U10)

Questions