Pollen Emissions of Subpollen Particles and Ice Nucleating Particles

Pollen grains significantly contribute to the aerosol population, and levels are predicted to increase in the future. Under humid atmospheric conditions, pollen grains can rupture creating pollen grain fragments referred to as subpollen particles (SPPs) which are dispersed into the atmosphere with wind. In this laboratory study, SPP emission factors were determined for ryegrass, Lolium sp., and giant ragweed,Ambrosia trifida, in terms of the number of SPPs produced per pollen grain and the number of SPPs produced per m², which were compared to previously measured live oak,Quercus virginiana, emission factors. The SPP emission factors were 4.9 × 10¹³ ± 4.3 × 10¹³ SPPs per m² for ryegrass, 1.3 × 10¹⁵ ± 1.1 × 10¹⁵ SPPs per m² for giant ragweed, and 1.1 × 10¹⁵ ± 1.6 × 10¹⁵ SPPs per m² for live oak. SPPs and whole pollen grains from these species were evaluated for their ice nucleation efficiency in immersion and contact mode freezing. Measurements of the ice nucleation efficiency indicate that SPPs are weakly effective INPs in immersion mode, but that pollen grains represent a source of moderately efficient INPs in immersion and contact modes.