Transcript WG2_Forum

•CCN
•Ozone depletion
•Greenhouse gases
AEROSOLS
•Nitrogen inputs
•Hydrocarbons
•N,P,Si
•Trace metals
•Sea-salt
•Halogen cycling
TRACE
GASES
•Increased productivity
•Varied ecosystems
•Breaking waves
•DOM
•Anoxic zones
•Eutrophication
•Harmful algal blooms
#2. How do coastal zones impact
on atmospheric chemistry?
•N2O, CH4
•Halocarbons e.g.
CH3I, CHBr3
•Sulphur compounds
e.g. DMS, H2S, COS
A. Chuck
Some General Knowledge
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Coastal ecosystems are characterized by higher
primary productivity than open ocean systems.
Ocean-atmosphere interactions within coastal
zones reflect a transition from a relatively
contaminated continental land mass to a less
contaminated marine air mass
Coastal seas are dominant marine sources of some
trace gases globally e.g. nitrous oxide, carbonyl
sulphide, methane and important production sites
for almost all trace gases.
Hydrocarbons
The “Sea Surface Microlayer” (SSM) is often
aerosolized or may coat/be associated with
your regular sea-salt aerosol.
Some of the organic compounds in the aerosol
are bacteria or bacteria products.
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Functionalities include lipids, carbohydrates, but this
is very poorly characterized.
Macroalgae (seaweeds) have been shown to
produce a variety of halogenated compounds,
isoprene, and other NMHCs.
Sulfur Compounds
Coastal salt marshes have very high sulfur content in their
soils, which has two major effects in terms of trace gas
exchange:
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DMS
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Provide the substrate for the production of sulfur-containing trace
gases, such as H2S, COS, MeSH, and DMS
High sulfate levels inhibit methanogenesis, meaning that coastal
marshes produce very little methane relative to freshwater wetlands
Coastal phytoplankton species such as Phaeocystis are important
producers of DMS
DMS production rates in coastal waters are not particularly high
compared to open ocean areas.
DMS flux measurements in ocean regions, and the DMS-CCN-cloud
studies.
DMS oxidation produces SO2, which ultimately can produce particles.
H2S and other reduced-S and organo-S species may be
present in the gas-phase
Carbon Monoxide
CO is generated in the ocean by photochemical
degradation of CDOM (colored dissolved organic
matter)
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Main loss is microbial consumption.
Only about 15% of this cycling is vented to the
atmosphere, where it is believed to represent a mere
2% of the global atmospheric CO budget.
Very few measurements of CO exist in coastal
regions outside of some high latitude port cities
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speculation that greater nutrient availability in coastal
zones should preferentially invigorate the microbial
losses, so the fluxes are assumed to be small
Nitrogen Species
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Substantial evidence for organo-N being important (gasand aerosol-phases) in coastal regions, but these
compounds are very poorly characterized
Nitrates may play important roles in estuaries/coastal
regions as run-off from fertilizers. Nitrates in aerosol may
be important in perturbed coastal regions
Coastal upwelling regions are important sources of nitrous
oxide (N2O)
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Coastal regions have high rates of microbial N2O production as a
consequence of their high productivity
Upwelling provides an effective pathway for ventilating N2O, which is
produced primarily in subsurface waters, to the atmosphere
Anthropogenic nitrogen inputs to coastal areas can lead to large
enhancements in coastal N2O emissions
Halogenated Compounds
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High emission rates of methyl halides
have been observed in coastal terrestrial
ecosystems
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Particularly coastal salt marshes
Dependent on plant species and environmental
parameters
Emissions from tropical coastal regions from
vegetation
Coastal ecosystems are regions of high primary
productivity and high halide availability
Halogenated Compounds
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Macroalgae are known sources of volatile
organo-bromine and organo-iodine
compounds.
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Sources of a variety of iodinated compounds e.g.
CH2I2, methyl iodide.
Bromoform is the most abundant form of
biogenic reactive organic bromine and the
highest concentrations of bromoform are
invariably found in coastal waters.
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Possibly 70% of world’s bromoform produced by
macroalgae (Carpenter and Liss 2000).
Halogenated Compounds
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Organic-Iodide compounds (methylated iodines)
have been associated with new particle production
in tidal areas.
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Interaction with NOx will release HCl from aerosol
and this has the potential to end up as radical-Cl.
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(O’Dowd et al. 1999, 1998).
Br may also be released as a radical (not in as large of
quantities as Cl, of course).
Halogen cycling in coastal environments can be
substantial and important in terms of ozone and
other oxidant cycling
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Some observational evidence that Cl-radical chemistry in
polluted air over the coastal ocean can lead to net O3
production (Texas studies- Tanaka et al., 2003)
Ozone Depletion
Iodine
Chemistry in
the MBL
IO
O
hv
3
CH2I2
CH2IBr
CH3I,
I2
Inorganic
Iodine
I
eg OIO, HOI
IONO2, INO2,
HI, IX
New Particle
Production;
Climate Impact
Aerosol
hv
Transport
to
Continents
J. Plane
Tropospheric ozone depletion events (ODEs)
Bottenheim et al, 2002. Ozone contour plot at Alert (top) and surface ozone (bottom).
Satellite (Global Ozone Monitoring Experiment, GOME, on the ERS-2 satellite) observations
of tropospheric BrO “clouds” in the Arctic and Antarctic. Total BrO column densities in the
centre of the clouds exceed 1014 BrO molecules cm-3. The clouds are associated with total
loss of boundary layer ozone, occur only in springtime, and have a typical lifetime of one to a
few days. (Wagner et al., 2001) Copyright 2001 American Geophysical Union.
Polar coastal regions show some interesting chemistry
•Tropospheric ozone depletion events recorded at Arctic and Antarctic.
•Thought to be related to halogen chemistry, especially Br
•Mechanism? And initial source of Br?
•Role of frost flowers?
Photo courtesy of Scott Polar Research Institute
Methods for Constraining: More
Measurements?
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Need better and continuous observations for
several years at one (or multiple) location
locations.
Need to get estimates of surface area,
productivity, species abundance.
Better/more flux measurements?
Big Questions
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What are the physical and biological constraints
on trace gas exchange in the salt marsh?
What are the impacts of increased nutrients on
coastal ecosystem dynamics and the emission of
climatically active trace gases?
In addition to the gas emissions from the
microorganisms, what role is played by their
physical bodies/fragments?
Harmful algal blooms – trace gas production from
these species unknown
Kelp forests are large producers of methyl iodide,
but how much of it reaches the atmosphere?
Big Questions
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What is the effect of short-lived halogenated
compounds on atmospheric chemistry/aerosol
formation?
What is the size distribution of aerosol produced by
wave-breaking?
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important for CCN production and for atmospheric
chemistry.
What are the mechanisms producing the ultra-fine
particle bursts?
What is the organic composition of the aerosol
produced (and what they evolve into)?