Abstract
Abstract. We measured the size distribution of atmospheric neutral and charged clusters and particles down to mobility diameter around 1.5 nm by applying pulse-height CPC technique at SMEAR II station in Hyytiälä, southern Finland during spring 2007 and May 2008. The concentration of molecular clusters smaller than 3 nm seems to be highly variable in boreal forest environment, the concentration varied typically between 500–50 000 cm−3. By comparing to concentrations measured with ion spectrometers, we conclude that ion clusters and neutral clusters produced by ion-ion recombination are usually not sufficient to explain all of the observed clusters; the median fraction of recombination products from all neutral clusters was 4.9%. Before and during most new particle formation events the cluster formation rate rose only slightly, or remained close to stable. Nocturnal formation of clusters was also frequently observed.
Highlights
Aerosol particles affect the climate both directly by scattering and absorbing solar radiation and indirectly via cloud processes
By comparing to concentrations measured with ion spectrometers, we conclude that ion clusters and neutral clusters produced by ion-ion recombination are usually not sufficient to explain all of the observed clusters; the median fraction of recombination products from all neutral clusters was 4.9%
The existence of stable neutral atmospheric clusters and their role in new particle formation is the key question in understanding atmospheric nucleation process
Summary
Aerosol particles affect the climate both directly by scattering and absorbing solar radiation and indirectly via cloud processes. Detailed knowledge of nucleation process is needed to include secondary aerosol particles to climate models. The existence of stable neutral atmospheric clusters and their role in new particle formation is the key question in understanding atmospheric nucleation process. New particle formation has been observed on numerous locations around the world (Kulmala et al, 2004a), but the exact mechanisms how particles are formed from precursor vapors are still under debate. The prevailing nucleation mechanism, at least in boreal forest environment, is suggested to be activation of neutral atmospheric clusters approximately 1–2 nm in diameter (Kulmala et al, 2000, 2006, and 2007a). Ion-ion recombination is known to produce neutral clusters (Turco et al, 1998)
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