A1260020748NTFCL

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Marine Algae, Aerosols Clouds, and Climate
Change Colin ODowd University of
Helsinki National University of
Ireland, Galway
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What are Aerosols?
An aerosol particle is a suspended liquid or
solid mass the air.
Aerosols range in size from 1 nm to hundreds of
microns
Concentrations clean 300 cm-3, Polluted 50,000
cm-3

• Aerosols are produced via three mechanisms
• Phase transitions (nucleation/condensation)
• (2) Mechanical disruptions of a surface
• (3) Combustion processes.

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Phase transitions (nucleation) produces particles
of the order of 1 nm and grow by further
condensation to sizes approaching microns.
This is typically thermodynamically limited and
very few vapours in the atmosphere are present
in sufficient concentrations to nucleate new
particles.
The number concentration of atmospheric aerosols
is dominated or controlled by this formation
pathway. Typical vapours condensing are
sulphuric acid and water, organics.
Mechanically produced aerosols are typically
micron sized and larger. These particles dominate
aerosols mass and surface area. Sea-spray, desert
dust.
Combustion particles are typically 10s nms to
microns. In urban areas, these particles
dominate number and mass. Soot carbon, fly-ash.
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Why are aerosols important?
Precipitation Development
In-Direct Radiative Forcing
Cloud Chemistry
Direct Radiative Forcing
Cloud formation
Remote Sensing
Ozone Loss
Aerosols
Haze layers
Aqueous Chemistry
Health Effects
Surface Chemistry
Condensation sinks
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Where do we stand in our understanding of
aerosol-cloud-climate effects?
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Marine Aerosols
Marine aerosols and clouds are one of the most
important aerosols species in terms of climate
change for the following reasons

1. 75 of the Earths surface is covered by oceans

• The ocean surface is darker than land surfaces
• (I.e. more energy is absorbed)

1. The ocean has a large thermal capacity

• Marine clouds are more sensitive to change
  compared to continental
• clouds (that are near saturation)

Small changes in the source rate of marine
aerosols can have significant changes in climate.
An increase in aerosols that leads to a 20
increase in cloud droplets concentration can give
rise to a radiative forcing of 1-2 W m2.
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Predicting Climate Change due to Aerosols Effects
Challenges
Anthropogenic influences cannot be fully
quantified before the natural sources of aerosol
are.
The relationship between new particle formation
(1 nm) and radiatively-active sizes (gt100 nm) is
highly non-linear.
The actual gaseous species leading to new
particle formation (homogeneous nucleation) are
not determined, and consequently, neither are the
formation processes.
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New Particle Formation and Nucleation
Nucleation is the formation of a stable cluster
which continues to grow via vapour condensation.
The critical cluster size depends on condensable
vapour thermodynamics and concentration.
In the H2SO4 - H2O - NH3 system, a
thermodynamically stable cluster (TSC) is of the
order of 1 nm and contains of the order of 10
acid molecules.
If the cluster does not reach a critical size, it
will evaporate.
If the cluster does not grow rapidly, it will be
scavenged by coagulation to the larger particles.
(Diffusion ? 1/D2)
We define new particle formation as when a
critical embryo/TSC grows to 3 nm or larger.
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Schematic of New Particle Formation (Nucleation)
Sulphuric Acid Water Vapour
Stable Embryo
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Condensation Growth
1-3 nm
3 nm to 1000 nm
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Coagulation Loss
Coagulation is when two particles diffuse through
the air and collide.
When they collide, the smaller one is consumed by
the larger one.
Diffusivity decreases strongly with size (1/d2)
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Vapour Concentrations and Source Rates
Aerosol Formation Growth
Vapour Source Rate 5 x 10-7 cm-3 s-1
Aerosols Condensation Nuclei
Cloud Droplets
1-3 nm
lt 100 nm
lt 10 ?m
Condensation
Condensation
Activation
Coagulation
Coagulation
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Most Likely Nucleating Systems
Upper Troposphere H2SO4 - H2O
Lower Troposphere H2SO4 - H2O-NH3 Organics

To date, no direct experimental evidence
available to determine which system dominates in
different regions.
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Can We Characterise New Particles?
No!
Stable clusters cannot be physically measured -
current day limits in particle detection extend
down only to 3 nm.
The chemistry of new particles cannot be
determined either Very difficult to separate
sufficient new particle mass from the existing
aerosol to perform chemical analysis.
If we can chemically characterise particles of a
few nm, this can tell us something about new
particle formation. To date, there are little or
no chemical measurements for sizes less than 10
nm (represents the current limit).
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Specially designed EU project to understand the
processes involved in producing new particles in
the marine atmosphere.
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Mace Head Research Station
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Particle Production Trends
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Coastal Production Event
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Hygroscopic Growth Factor (GF)
GF D(RH90) / D(RH40)
GF 1.4 Soluble like ammonium sulphate GF 1.0
non-soluble
PARFORCE Growth Factors GF 1.05 during events,
increasing to 1.3 when event coincides with
periods of high sulphuric acid production. Particl
e production is driven by non-soluble species and
helped by sulphuric acid when present (not
dependent on sulphuric acid)
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TEM EDAX Analysis of 6-8 nm Particles
Aerosol Peaks
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Emissions from Coastal Biota
CH2I2 and IO, a by-product of CH2I2 photolysis
are observed to have tidal cycles
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Main PARFORCE Results
Production is not correlated with Sulphuric Acid,
although this cannot rule out its involvement in
TSC production.
Particle production from TSC requires vapour
concentrations gt 7 x 109 molecules cm-3 and
source rates of gt 5 x 107 molecules cm-3 s-1.
Sub-10 nm particle composition is non-soluble and
therefore cannot be ammonium sulphate aerosol.
Iodine is identified in 6 nm particles for the
first time. Sulphur is sometimes present.
Only halogenated VOCs were identified in coastal
biota emissions. Suggests particle production is
driven by a condensable iodine vapour.
Special Issue JGR Atmospheres, 2002. Preprints at
http//macehead.nuigalway.ie/parforce
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UV
O3
Wind
CH2I2
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Laboratory Studies into Particle Production from
CH2I2
CH2I2 photolysed in the presence of ozone.
Studies undertaken at Dortmund (Thorsten
Hoffmann) Caltech (John Seinfeld).

• CH2I2 (ppt) 15, 50, 500, 5000, 50000
• RH lt 2, 65
• Light Intensity Full, ¼, 0
• O3 (ppb) 100, 0

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Chamber Particle Production
Nucleation
Condensation
Coagulation
Wall loss
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Aerosol Mass Spectrometer Composition
Possible thermal decompositions in AMS vaporizer
( 600 C) I4O9 ( 120C) ? I2 O2
I2O5 HIO3 ( 200C) ? I2O5 H2O I2O4 ( 200C)
? I2O5 I2 I2O5 ( 400C) ? I2 O2
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Reaction Scheme
CH2I2
Photolysis Reaction
Aerosol Uptake
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Experimental Conclusions
Condensable Iodine Vapour nucleation occurs at
coastal concentrations of CH2I2
Nucleation of H2SO4-H2O-NH3 is not required!
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What About Open Ocean Aerosol Production?
Current Theory DMS ? SO2/SO3 ? H2SO4 ? TSC ?
Aerosol ? CCN Charlson et al., Nature 1987
State-of-the-art marine aerosol formation
modelling has shown that DMS cannot produce new
particles in the marine boundary layer, although
nucleation can occur. Pirjola, L., C. D.
O'Dowd, I. M. Brooks, and M. Kulmala, Can new
particle formation occur in the clean marine
boundary layer?, 105, 26,531-26,546, Jr. Geophys.
Res., 2000
Can the open ocean biogenic iodine source rate
explain open ocean particle production?
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Modelling the Production of particles from
Condensable Iodine Vapours
Global marine source of 1012 g yr-1
Globally-averaged marine mixed-layer source
rate of iodine atoms is estimated at 1.4 x 103
atoms cm-3 s-1. Compares favourably to the
recent estimate of 1 x 104 atoms cm-3 required
to explain the observed concentration of IO and
OIO (up to 1.6 x 108 cm-3 ) over the open
ocean McFiggans et al., 2000 Allen et al, 2000.

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Crossing the Coagulation Sink Barrier
Q (103 mol. cm-3 s-1) Growth Rate Particle Size
CoagSink 0 0.2 nm hour-1 1 2 x 10-3 s-1 25
1.1 hour-1 3 2 x 10-4 s-1 6 4 x 10-5
s-1
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A New Climate Feedback System?
Studies into the emissions of iodo-carbons from
marine biota have shown that emissions can
increase by up to 5 times resulting from changes
in environmental conditions associated with
global change. Laturnus, F., B. Giese, C.
Wiencke and F. Adams, Fres. Low molecular-weight
organoiodine and organobromine compouds released
by polar macroalgae the influence of abiotic
factors. J. Anal., Chem., 368, 297-302, 2000.
Increasing the source rate of CIVs 5-fold will
result in an increase in marine aerosol and CCN
concentrations by the order of 20-60 .
Increasing the cloud droplet concentration by
20 results in the increase in albedo of 1.7,
leading to an enhanced radiative forcing of -1 W
m-2.
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Conclusions
Nucleation and Particle production do not mean
the same thing.
H2SO4 concentrations can explain nucleation of
TSCs, but cannot explain the production of
particles
Particle production in coastal zones is driven by
condensable iodine vapours.
Particle production over oceans is driven by
condensable iodine vapours.
Changes in environmental conditions influencing
marine algae will lead to changes in iodine
emissions, aerosol production, and consequently,
climate change
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Coastal Production Event
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Growth of the Coastal Aerosol Plume
Aerosol Scattering CCN concentrations increase
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Direct Scattering of Radiation
Schmid et al. 2000
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Indirect Aerosol Radiative Forcing (Cloud effects)
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Marine particle formation by biogenic iodine
emissions Colin D. ODowd, Jose L. Jimenez
Roya Bahreini, Richard C. Flagan, John H.
Seinfeld, Kaarle Hämeri Liisa Pirjola, Markku
Kulmala, S. Gerard Jennings Thorsten
Hoffmann. Department of Physics, National
University of Ireland, Galway, Ireland.
Department of Physical Sciences, University of
Helsinki, Helsinki, Finland Departments of
Environmental Science and Engineering and
Chemical Engineering, California Institute of
Technology, Pasadena, USA. Finnish Institute for
Occupational Health, Helsinki, Finland Helsinki
Polytechnic Technology, Helsinki,
Finland Institute of Spectrochemistry and
Applied Spectroscopy, Dortmund,
Germany Hopefully accepted in Nature this week!
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Tidal regions near Mace Head
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Main Collaborators
Markku Kulmala, Liisa Pirjola, Karrle Hameri -
University of Helsinki Thorsten Hoffmann -
ISAS, Dortmund John Seinfeld, Jose Jimenez -
Caltech
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Predicted Aerosol Composition
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Predicted Gas Phase Concentrations
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Looking to the Atlantic
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Radiative Forcing Effects
Sulphate -0.26 W m2 to -0.82 W m2
Dust 0.09 W m2 to -0.46 W m2
Fossil fuel Soot carbon 0.16 W m2 to 0.42
W m2.
Biomass burning -0.14 W m2 to -0.74 W m2 .
Nitrates and organics not well defined
Clouds -0.3 W m2 to -1.8 W m2 .
Haywood Boucher, Reviews of Geophyiscs