ABSTRACT - TOPIC #6

Unresolved and Unexplained Mass

Topic Leader: Hans Puxbaum
Contributor: Andras Gelencser

Recent investigations have revealed that a major unidentified part of organic aerosol mass consists of macromolecular substances (“atmospheric polymers”). It appears that various sources, primary as well as secondary, natural as well as anthropogenic, contribute to the occurrence of organic polymers in the atmosphere. None of these polymers are accessible by standard analytical techniques for organic aerosol speciation. Thus, new analytical techniques have to be introduced for assessing the role of the polymeric substances as part of the organic aerosol. The purpose of this session is to review the results of laboratory investigations and field measurements with regard to organic polymers in the atmosphere and their contribution to the organic material in the atmospheric aerosol. The major groups identified until now and to be discussed in this section in detail are “viable bio-particles”, “bio-polymers” and “humic-like substances“ (HULIS). Viable particles in inhalable sizes are bacteria, algae, fungal spores, and other fine particles; e.g., those emitted from pollen. Bio-polymers are polymeric materials derived from debris from plants or animals, and can be identified in specific forms of occurrence such as cellulose, lignin, and proteins. HULIS are less-defined macromolecular compounds, present predominantly in the water soluble fraction with molecular weights in the range of 300 – 1000 Da.

No simple analytical techniques are available to assess specifically the polymeric part of the organic aerosol. However, thermal techniques are able to allow a first order estimate of the polymeric vs. monomeric part of the aerosol. Specific techniques are used to move towards a mass closure and, finally, new analytical techniques have to be developed.

An overview by topic leader Hans Puxbaum (Vienna University of Technology) will provide a framework for discussion by raising the following general key questions:

1. How can organic speciation help define the reconciliation of organic mass measured by thermal techniques?
2. To what extent can we move towards organic aerosol mass closure with the inclusion of estimated concentrations of atmospheric polymers?
3. Will measurements of organic macromolecules in bulk be a good next step?
4. Do secondary atmospheric polymers represent a major sink for individual volatile or semi-volatile species?

The second presentation by Andras Gelencser (University of Veszprem) will explain the various potential pathways of formation of atmospheric HULIS and their role in the mass closure of organic aerosol. Andras Gelencser and his group have not only developed analytical techniques for low level determination of HULIS in the aerosol, but have also studied one potential pathway of their formation mechanism. He will show the ubiquitous occurrence of HULIS in continental aerosols, even in the free troposphere. And discuss the possibility of a standardized analytical technique.

The presentations will be followed by an open discussion aimed at clarifying the importance of bio-aerosols and HULIS in the reconciliation of organic mass in aerosols, as well as recommendations for further studies on possible sources and their contributions to observed atmospheric levels.