ABSTRACT
Aerosols serve as cloud condensation nuclei (CCN) and thus have a substantial effect on cloud properties and the initiation of precipitation. Large concentrations of human-made aerosols have been reported to both decrease and increase rainfall as a result of their radiative and CCN activities. At one extreme, pristine tropical clouds with low CCN concentrations rain out too quickly to mature into long-lived clouds. On the other hand, heavily polluted clouds evaporate much of their water before precipitation can occur, if they can form at all given the reduced surface heating resulting from the aerosol haze layer. We propose a conceptual model that explains this apparent dichotomy.
ABSTRACT
Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOF-MS) was applied in the identification of organic compounds in atmospheric aerosols from coniferous forest. The samples were collected at Hyytiälä, Finland, as part of the QUEST campaign, in Spring 2003. Manual and automated search procedures were compared in the identification. An automated procedure is preferable when a large number of data files need to be processed; but manual search was more accurate with the present samples, where the number of compounds was large and most of the compounds of interest were present at trace level. Altogether, about 50 compounds were identified on the basis of mass spectra and linear retention indices. The identified compounds included oxidised monoterpenes, acyclic alkanes, alkenes, ketones and aldehydes, as well as a few alcohols, acids, and aromatic compounds.
