Subpollen Particles as Atmospheric Cloud Condensation Nuclei

Bioparticles constitute a significant fraction of atmospheric aerosol. Their size range varies from nanometers (macromolecules) to hundreds of micrometers (plant pollen and vegetation residues). Like other atmospheric aerosol particles, the degree of involvement of bioaerosols in atmospheric processes largely depends on their hygroscopic and condensation properties. This paper studies the ability of subpollen particles of pine, birch, and rape to serve as cloud condensation nuclei. Secondary particles are obtained by the aqueous extraction of biological material from pollen grains and the subsequent solidification of atomized liquid droplets. The parameters of cloud activation are determined in the size range of 20-270 nm and water-vapor supersaturations of 0.1-1.1%. Measurement data were used to determine the hygroscopicity parameter that characterizes the effect of the chemical composition of subparticles on their condensation properties. The hygroscopic parameter varies in the range from 0.12 to 0.13. In general, the results of measurements have shown that the condensation activity of subpollen particles is comparable with the condensation activity of secondary organic aerosols and depends weakly on the type of primary pollen.