The grant provides for the laboratory analysis of airborne fine particles collected in different regions of the world at locations representative of characteristic vegetational communities. Complementing earlier work by the same investigator in which hydrocarbon types were the prime object of the laboratory analyses, the current project will emphasize the analysis of the oxygen-bearing species in the same samples stored up to ten years following earlier field- sampling operations. An important element of the research is the identification of "chemical signatures" in terms of the composition of plant waxes naturally released from the vegetation of plant communities characterizing areas of regional extent around the world. Some samples are included to represent both anthropogenic and natural combustion sources. The research will further define the organic chemistry of airborne particulate matter in the troposphere, and it will provide data on the chemistry of particulates from known regional origins for use in tracing atmospheric transport pathways.