PNNL

Abstract

Ice nucleating particles (INPs) are a rare subset of atmospheric aerosol that can initiate primary ice formation and thus trigger cloud glaciation. There is a significant gap between our ability to measure INPs and to predict their concentrations and variability in large-scale models of weather and climate. Accurate simulation of INPs requires accurate simulation of their major particle sources, as well as representative parameterizations of their IN efficiency. Thus there is a need for measurements of INP concentrations, delineated by particle type, to validate and improve model prediction of INP concentrations. Here we present a novel method for speciating INP concentrations into the relative contributions from dust, sea spray aerosol (SSA), and bioaerosol using single particle mass spectrometry and fluorescence measurements. In a field campaign at Bodega Bay (coastal California), we find that bioaerosols were the primary source of INPs between -12 and -20 °C, while dust was a relatively minor source and SSA did not contribute significantly. We show that recent INP parameterizations for dust and SSA are able to accurately predict ambient INP concentrations for these particle types. Finally, we use the speciated INP concentrations to evaluate the simulation of INPs at Bodega Bay, using a Lagrangian approach to connect the locally-observed aerosol with regionally-widespread emissions parameterizations. We find that we are able to skillfully simulate dust and SSA INPs, but not bioaerosol INPs. This points to a need for additional research to identify the major factors controlling the emissions and INP efficiency of bioaerosol INPs in order to develop improved parameterizations and enable their improved representation in models.