Source Fluxes of Remote Oceanic Aerosol:
Ultrafine Sea-Salt, Sulfate and CCN
Antony Clarke, J. Zhou, University of Hawaii, School of Ocean, Earth Science and Technology
Jeff Pierce, Peter Adams, Carnegie Mellon University,Center for Atmospheric Particle Studies (CAPS)
???
0.1
1
Film Drops:
6 The bubble thin
liquid cap bursts and
shatters into many small
droplets.
1
3
10
100
Jet Drops:
6Produced by the
collapse of a
spherical cavity
after bursting.
r (μm)
500
Spume Drops:
6Wind speed > 8-10
m/s tear wave crests
and inject large spume
drops
2
4
1
Overview
Natural Sea-salt largest aerosol mass flux globally.
Sea-salt particles down to 10nm from breaking waves.
Size resolved number flux for 100% bubble coverage is scaled to
open ocean flux vs. wind speed.
Relative contribution of SSA to CCN flux into MBL (Dp>80nm)
compared with entrainment of sulfate from Free Troposphere.
Global influence on CCN using CTM model (Pierce and Adams,
2006)
2
UH Tower –
Bellows
AFS
20m
10m
5m
10m
20m
4 Hour Period on Julian Day 119, 2000
5m
View from top of tower
3
Small particles vary with coarse scattering
O Waves break,
produce foam, and
dissipate over about a
distance of 20m and
enhance CN and light
scattering
O There is a linear
relationship between
CN (small particles) &
scattering (large
particles) (R=.93)
4
Particles Produced from Breaking Waves down
to 0.01um are stable at 350C – like Sea-Salt
Similar distributions
for heated (350C) and
unheated particles
from breaking waves
suggest sea-salt.
Cumulative
Optically active
Average refractory
distributions reveal
60% of number found
in sizes below 0.1 um,
previously
uncharacterized.
5
Flux into bottom of box = Flux out of side of box
S100 [ Aavg L + 0.5 wo] τ dl = Cs k (Vw ) h τ dl
S100 = Cs k (Vw ) h / [ Aavg L + 0.5 wo]
S100 has units of [#/cm2 s ]
number of aerosols produced per unit area of
100% bubble covered surface per second
Cs = Measured mean BW CNhot (background removed) at
5 m (30 cm-3 ± 5.3 cm-3)
k
= Multiplier for tower Cs compared to mean profile
(1.5 ± 0.3)
Vw = Mean surf zone wind speed (7.3 m/s ± 1.1 m/s)
h
= Height of plume layer for beach profile (4 m ± 0.6 m)
Aavg = Mean bubble fractional coverage area between waves
(0.4 ± 0.12)
L
= Distance wave travels to shore (35 m ± 3 m)
wo = Initial width of BW bubble front (2 m ± 0.5 m)
APPROACH
Assume bubbles from
ocean whitecaps have
similar distribution to
coastal waves.
Monohan 1986
Determine flux for
100% bubble coverage
from COASTAL
breaking waves and
scale to OPEN OCEAN
based upon whitecap
coverage for given
wind speed.
7
Source Function (# /cm2/s) comparison for 9 m/s
whitecaps using nominal Monohan whitecap coverage
This study - SEAS coastal ocean 2003
De Leeuw – coastal 2001
MN93 Martensen wave tank 2003
M86 - Monahan wave tank 1986
LS04 – Lewis and Schwartz Book, 2004
8
QUESTION?
With this new SS number fluxWhat is the importance of Sea-Salt
as a source of CCN for the Clean
Marine Boundary Layer compared
to “sulfate” entrained from the
Free Troposphere?
Activated CCN
Clarke, A.D., et al., Particle production in the remote marine atmsophere: Cloud outflow and subsidence during ACE-1, Jour. Geophys, Res., 103, 1998
9
Comparison of Nominal SS Surface flux and FT
Sulfate Flux for various Wind Speeds and
Entrainment Rates
Nominal CCN, Dp>80nm
WS=15m/s
10m/s
FT Entrainment at 0.8 cm/s; 0.4 cm/s; 0.2 cm/s
5m/s
10
COMPARE refractory
particles in two
regimes
(scatterometer data)
Christmas Island
Located in low wind
from E at (<4 m/s)
subsidence zone
with FT source of
volatile sulfates
Hawaii
Located in region of
moderate Trade
Winds (>7m/s) from
NE
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Estimated % contribution of Sea-Salt to total CCN flux
> 80nm for various wind speeds and entrainment rates
Wind Speed >
5 ms-1
10 ms-1
15 ms-1
(6 cm-2s-1)
(64 cm-2s-1)
(254 cm-2s-1)
FT Entrainment
0.2 cm s-1
20 %
73 %
91 %
11%
58 %
84 %
6%
41 %
73 %
(23 cm-2s-1)
0.4 cm s-1
(46 cm-2s-1)
0.8 cm s-1
(92 cm-2s-1)
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SSA Flux Conclusions
• Small particles down to ~10nm diameter are produced by BW.
• About 60% of total number flux are smaller than 100nm.
• Chemically confirmed to be SSA down to 90 nm .
• Over half of these SS sizes are introduced as effective CCN (Dp>80nm).
• SSA appears to be major contributor to global natural CN and CCN fluxes.
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Putting This SSA flux in GCM model
GISS II – prime
Models SSA concentrations and not just fluxes
Allows interaction with sulfur cycle (Adams and Seinfeld, 2002).
Global Evaluation of CCN Formation by
Direct Emission of Sea-Salt and Growth of
Ultrafine Sea-Salt
Jeff Pierce and Peter Adams
JGR-Atmospheres, 2006
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Motivation
Sea-salt source function uncertainty
Sea-salt impact on cloud condensation
nuclei
• All sea-salt
• Ultrafine sea-salt
Uncertainty in indirect effect
15
Wind driven emissions in model
underestimated
3.41
U Model
U
3.41
NCEP
=
EmisModel
Emis NCEP
Model underpredicts
sea-salt emissions by
about 30% compared
to NCEP reanalysis
16
Model Details
ƒ NASA Goddard Institute for Space Studies
GCM II-prime
–
–
–
4° latitude x 5° longitude
9 vertical layers between surface and 10 mb
One hour tracer time step
ƒ Two Moment Aerosol Sectional (TOMAS)
aerosol microphysics algorithm
– Explicitly calculates both aerosol number and
mass in each size section
– 30 size sections (~10 nm - ~10 μm)
– Sea-salt and sulfate aerosols only
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Models Runs
Run
Name
Sea-salt
Emissions
Include Ultrafine
Sea-salt
SULF
None
NA
CLRK
MART
MON
OD
Clarke, 2004
Martensson, 2003
Monahan, 1986
O'Dowd, 1997
yes
yes
no
no
CL100
MA100
Clarke, 2004
Martensson, 2003
no
no
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Model evaluation
Sea-salt Mass Distribution
Andreae et al. [1999]
MART
CLRK
19
Model evaluation
Marine Number Distribution
Ultrafine seasalt emissions
consistent with
observations
over S. Ocean
Observations from Heintzenberg et al. [2000]
20
Sea-salt impact on cloud condensation nuclei
All sea-salt CCN(0.2%) Concentrations (cm-3)
Sulfate only
Sea-salt and Sulfate
(CLRK)
21
Sea-salt impact on cloud condensation nuclei
All sea-salt CCN(0.2%) - Percent Change relative to sulfate
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Sea-salt impact on cloud condensation nuclei
CCN(0.2%) Percent Change from Ultrafine Sea-salt
ƒ Increases in CCN
greater than could be
explained without
microphysics
ƒ Condensation of sulfate
onto UF sea-salt
dominant growth
process
ƒ Similar uncertainties in
cloud forcing
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Uncertainty in Indirect Effect
Typical Marine Stratus Cloud
P
0.6
P
P
0.5
MART
Albedo
C
C
OD
0.4
ΔA = 0.075
C
ΔA = 0 .12
0.3
P
-3
Liquid water content = 0.3 g m
Cloud Height = 100 m
0.2
0
25
50
75
100
125
150
175
200
-3
Cloud Droplet Number Concentration [cm ]
C
C = clean marine region
P = polluted marine region
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Cloud Forcing Estimate for Southern
latitudes
(following Seinfeld and Pandis, 1998)
1) Clean unpolluted marine region and nominal
supersaturation of 0.2%
2) averaged over clear and cloudy sky
Varies by 4 W/m2 for different SSA emission scenarios
Increases by 1 W/m2 due to presence of ultrafine SSA in
model
[ this implies uptake of sulfate on SSA moves ultrafines
into CCN active sizes ]
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CONCLUSIONS
Model results with new SSA emission flux
ƒ Model shows best agreement with observed size distributions
for Clarke SSA emission flux
ƒ Three fold increase in CCN over Southern Ocean
ƒ 50% increase over parts of Atlantic
ƒ Range of forcing differences for SSA flux up to 4 W/m2 over S.
Ocean
ƒ Ultrafine SSA interact with sulfate to grow to CCN
ƒ Important to get “clean” CCN correct if forcing due to
perturbations is to be assessed.
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