What was done
Aerosol electrical-mobility size-distribution measurements were made before and during the initial stage of an atmospheric nucleation event over a boreal forest in Finland on 2 May 2000.  Simultaneously, organic vapor growth rate measurements were made of particles that nucleated into organic cloud-droplets in the flow-tube cloud chamber of a modified condensation-particle counter.

What was learned
The authors demonstrated, for what they call "the first time," that newly-formed aerosol particles over forested areas "are composed primarily of organic species, such as cis-pinonic acid and pinic acid, produced by oxidation of terpenes in organic vapours released from the canopy."

What it means
The authors note that "aerosol particles produced over forested areas may affect climate by acting as nuclei for cloud condensation," but they say there remain numerous uncertainties involving complex feedback processes "that must be determined if we are to predict future changes in global climate."  This being the case, we wonder how anyone can presume to decide what should or should not be done about anthropogenic CO2 emissions; for if we can't predict future changes in global climate without the knowledge just specified, how do we know if we even need to be worried about the matter?