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•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 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. 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: DMS 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) 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 speculation that greater nutrient availability in coastal zones should preferentially invigorate the microbial losses, so the fluxes are assumed to be small Nitrogen Species 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) 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 High emission rates of methyl halides have been observed in coastal terrestrial ecosystems 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 Macroalgae are known sources of volatile organo-bromine and organo-iodine compounds. 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. Possibly 70% of world’s bromoform produced by macroalgae (Carpenter and Liss 2000). Halogenated Compounds Organic-Iodide compounds (methylated iodines) have been associated with new particle production in tidal areas. Interaction with NOx will release HCl from aerosol and this has the potential to end up as radical-Cl. (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 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? 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 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 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? 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)?