generation of sea-salt aerosols
DESCRIPTION
Bridging the Gap October 30 - 31 , 1999. Generation of Sea-Salt Aerosols. Magdalena Anguelova. Polluted (urban) air. Clean (rural) air. What are Aerosols?. Aerosols are minute stable particles, solid or liquid, suspended in the atmosphere. Tiny Particles. - PowerPoint PPT PresentationTRANSCRIPT
What are Aerosols?& Aerosols are minute stable particles, solid
or liquid, suspended in the atmosphere.
Clean (rural) air
Polluted (urban) air
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.
Relative Abundance
Sulfate aerosols dominate in polluted air.
Sea-salt aerosols dominate in clean air.
Sea-Salt Aerosols and Climate
The major contributor to sunlight reflection.
Facilitate the formation of cloud drops.
Medium for chemical reactions in the atmosphere.
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)
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