Autumnal Observations of Biological Aerosol, Ice Nuclei, and Amino Acids in Upstate New York

Primary biological aerosol are an understudied component of the atmosphere that can impact both human health and climate. The human health effects arise from their activity as allergens or pathogens, while the climate effects are largely due to their ability to nucleate ice at relatively warm temperatures and associated impacts on clouds. Emission sources and seasonality of these particles are poorly constrained and few long-term measurements exist. In addition, only a few studies have reported observations of biological aerosol in conjunction with an assessment of their ability to act as ice nuclei (IN). Here we report loadings of fluorescent aerosol, which we use as a proxy for biological aerosol, measured on a single particle basis by an Instascope (DetectionTek, Longmont, CO) in a rural, forested environment in upstate New York. At the same site, we also report IN and amino acid abundances in size-segregated aerosol samples collected using a Micro-Orifice Uniform Deposition Impactor. IN are measured using a simple cold-plate drop-freeze assay. Amino acids are measured offline using fluorescent derivatization and separation via HPLC. We analyze variability in the abundance of warm-temperature IN over days to weeks during the transition from fall to winter as well as the relationships between observed IN, fluorescent particle loads and amino acid abundances. We also evaluate all three measurements as a function of particle size. We use back trajectory analysis to assess the dominant source contributions observed at our measurement site. These observations will help constrain sources and seasonality of biological aerosol and IN in a northern forest.