On atmospheric neutral and ion clusters observed in Hyytia¨la¨ spring 2011.

Atmospheric new particle formation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub-2 nm size range. We have recently shown that at a lower-troposphere site (Hyytia¨la¨, Southern Finland) with abundant biogenic emissions and moderate anthropogenic influence, based on comprehensive observations of atmospheric clusters in the size range of 1-2 nm mobility diameter, there are significant differences between neutral and charged cluster properties. The differences are with respect to cluster size and chemical composition, and whether the observations were made in background conditions or during periods of active aerosol formation. According to our results, sub-2 nm clusters were always present and cluster concentrations were dominated by neutral ones in all sizes and almost all the time, indicating that cluster formation and their subsequent growth i.e. atmospheric aerosol formation were dominated by neutral pathways. [ABSTRACT FROM AUTHOR]