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Stratospheric Processes And their Role in Climate
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| Home | Initiatives | Organisation | Publications | Meetings | Acronyms and Abbreviations | Useful Links |
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Stratospheric Processes And their Role in Climate
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| Home | Initiatives | Organisation | Publications | Meetings | Acronyms and Abbreviations | Useful Links |
1. IGAC is concerned with processes which control the trace gas and particulate composition of the troposphere.
2. The main components are studies of:
a) biogenic emissions from land and ocean and impact of human
emissions
b) photochemistry leading to oxidation processes, particularly
with free radicals
c) aerosol physics and chemistry
d) transport processes in the troposphere
The output from many field and laboratory studies is fed into 3D chemical transport models of tropospheric chemistry.
3. A recent model intercomparison exercise carried out with support from the European IGAC Project Office (EIPO) revealed substantial differences between the models, which can only be resolved with a much larger data base on tropospheric composition requiring many more in situ experiments and hopefully new observations from satellites which will be launched in the next few years.
4. Some current issues are:
a) production of natural and anthropogenic sulphate and organic
aerosols over the ocean
b) global transport of emissions from biomass burning and urban/regional
pollution, particularly ozone-spread of pollution
5. Tropospheric chemistry is very efficient. It has controlled atmospheric composition over geological time.
When it is ineffective, it causes key problems, e.g.
a) CO2: long lifetime due to no photolysis plus no oxidation reactions
b) CFCs: not removed by tropospheric chemistry, contrast with HCs, which are and lead to ozone production in the troposphere.
6. One of the prime consequences of tropospheric chemistry is the large in situ production and loss of ozone.
Stratospheric/Tropospheric exchange produces ~ 400 MT in troposphere
Gaseous deposition ~ 1000 MT/yr
Tropospheric chemistry produces ~ 4000 MT/yr
Tropospheric chemistry destroys ~ 3500 MT/yr
Distribution is poorly known because of sparseness of sonde sites, particularly in the tropics.
A new effort to use satellites is being mounted by NASA and ESA including:
a) An attempt to use a geostationary satellite for tropospheric ozone.
b) A major new programme entitled GTOP (Global Tropospheric Ozone Programme) with the purpose of stimulating measurements of ozone in the troposphere.
7. Where is IGAC going?
a) Links with SPARC including a new group with Ravi in charge
to consider common issues related to atmospheric chemistry.
b) IGAC is currently producing a book concerned with findings
over the last decade in a process of integration and synthesis
The following 5 Chapters will be produced in the year 2000
. Introduction
. Biosphere/Atmosphere Interactions
. Photochemistry/Oxidising Capacity
. Aerosols
. Synthesis