Volatile and particulate organic compounds in the ambient air of a eucalyptus forest in Portugal during the FIELDVOC'94 campaign

Abstract

During the FIELDVOC campaign in a eucalyptus forest in Portugal the distributions of monoterpenes compounds and particulate carbon were measured in the ambient air above the forest. Monoterpenes compounds in the eucalyptus forest atmosphere consisted mainly of β-pinene, α-pinene, 1,8-cineol, limonene and trans-ocimene.

For several monoterpenes, such as β-pinene and α-pinene, atmospheric levels were higher at night than during the day. This was partially attributed to a decrease in atmospheric turbulence and transport of emissions from nearby pine forests during the night by the low intensity of easterly winds. β-Pinene, which is emitted by pine trees but not in any noticeable amount by eucalyptus, was used as a tracer.

Particulate carbon was measured as organic carbon and black carbon (BC). The measurement of particulate carbon levels was also done during the FIELDVOC'94 campaign at a coastal site, where clean air masses arriving from the Atlantic were sampled. The concentrations of atmospheric particulate carbon were higher in the forest than along the coast. Based upon a mass balance, it was possible to estimate an upper limit to the inclusion of biogenic volatile organic emissions into the organic aerosol component when air masses were transported from the coast inland during sea breezes. A value of as much as 40% of the particulate organic carbon (POC) can be attributed to emissions from vegetation of compounds such as monoterpenes which, after oxidation to less volatile products, are transferred to the particulate phase.