Characteristic Enhancements of Ice Nucleation by Biological Aerosols

Both continental and marine sources supply vast concentrations of primary biological aerosol particles (PBAPs), some of which are capable of catalyzing heterogeneous ice nucleation events at warm temperatures. Continentally, pollen represents as a substantial fraction of annual PBAP emissions (47-84 Tg). Whole pollen grains are released from plants and rupture during pollen season, releasing pollen grain fragments referred to as subpollen particles (SPPs). Whole pollen grains and SPPs can act as ice nucleating particles (INP) influencing cloud formation and precipitation. Accurate characterization of meteorological conditions required to trigger pollen emissions is needed to quantify the contribution and timing of pollen to the BPAP population. In the marine environment, aerosol contains a significant amount of organic matter derived from phytoplankton productivity. Through laboratory and field experiments, we demonstrate that high growth rates in biologically productive waters result in increased production of effective INP. Further, we have evaluated the ice nucleation activity of individual amino acids, proteins, and nucleic acids that are involved in rapid phytoplankton growth. Surprisingly, amino acids, DNA, and certain enzymes are effective INP nucleating ice between -19.2 degrees C and -7.8 degrees C, well above the freezing temperatures of most non-biological INP.