Organic aerosols are one of the big unknowns in atmospheric science. Sources, chemical composition and properties are very poorly known. The report from the meeting of this Task Team workshop held at the Hyytiälä (Finland) field station on 10-12 May 2004 has been turned into a paper in the journal Atmospheric Chemistry and Physics Discussions.
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Important general issues that organic aerosols are important for are identified as:
- direct radiative aerosol effect ;
- aerosol-cloud interactions and cloud radiative properties;
- clouds and the hydrological cycle;
- transport of pollutants (human health, environmental stress).
Scientific questions connected with organic aerosols within the above general issues are:
- emissions of organic aerosols: (natural vs. anthropogenic, primary aerosols vs. secondary aerosols, emission of aerosol-genic gaseous precursors);
- new particle formation (mechanisms, temporal and spatial occurrence, global importance);
- secondary organic aerosol (SOA) vs. primary organic aerosols (quantifying the ratio in different conditions);
- thermodynamic properties of organic aerosols (hygroscopicity, water activity, surface tension etc.);
- state of mixing within particles (properties of organic aerosols depend heavily on the state of mixing);
- aging processes of organic aerosol (aging changes chemical composition, state of mixing and thermodynamic properties; aging may occur through gas-solid reactions or aqueous phase reactions);
- modeling of organic aerosol processes at different scales.
In order to increase the level of knowledge on organic aerosols and the processes they are involved in, essential tools should be improved and agreed within the scientific community:
- sampling techniques (positive and negative artifacts);
- chemical characterization (organic carbon/black carbon separation through thermal evolution is still not standardized, chemical analysis is performed by different groups not only with different techniques, but also with different conceptual approaches, single particle analysis of organic compounds is still in its infancy);
- physical characterization (new improved techniques are needed for number/mass size distribution, measurement of thermodynamic properties needs to be improved);
- hierarchy of models dealing with aerosol processes (process models, box models, CTMs at different scales) need to be developed with the smaller scale ones able to feed parameterizations into the higher scale ones.
A joint ILEAPS/IGAC/SOLAS workshop should be organized to agree on a research agenda on the issue. The details are the following:
- three-day workshop to be held in spring 2004 (in September 2003 a small European meeting will take place, the outcome of this meeting should be a starting point for the IGBP workshop);
- venue to be agreed (possible linkable meetings are: AGU, 17-21 May 2004, Montreal, Canada; EGU, 26-30 April 2004, Nice, France);
- meeting should be by invitation only to gather a limited number of experts and be effective;
Sandro Fuzzi (IGAC), Andi Andreae (ILEAPS), Barry Hubert (SOLAS) will be the co-conveners of the workshop. The expected outcome of the workshop will be:
- an internationally agreed ‘IGBP’ research agenda on organic aerosol research;
- the possibility to initiate a few joint research tasks within IGAC, SOLAS, ILEAPS on organic aerosol-related issues.