Tracing biological, human, and inorganic sources of coarse aerosols via single-particle fluorescence and optical morphology

Abstract. Coarse-mode aerosol particles influence the environment, climate, and human health in diverse ways depending on their type. While mineral dust and sea spray aerosol (SSA) dominate this size range, rarer biological particles can have outsized impacts, for example by initiating ice formation at relatively warm temperatures. Hence, accurate, type-specific characterization of coarse-mode aerosol is essential for understanding their roles in climate and the environment. Using laboratory measurements of single-particle ultraviolet light-induced fluorescence (UV-LIF) spectroscopy and morphology, we provide a new reference dataset for coarse-mode aerosols from common sources, including pollen, dust, bacteria, and microplastics. Comparisons with previously published datasets reveal consistent source-dependent fluorescence features, but also highlights similarities between biological and non-biological particles that can bias classifications based on fluorescence alone. We present an improved machine learning-based classification algorithm that integrates fluorescence and morphology using laboratory data for training, and evaluate its performance using observations made at Zeppelin Observatory, Svalbard. We apply domain adaptation using field data to improve the identification of combustion-sourced particles, and to better distinguish dust from SSA. The new algorithm reproduces the previously published annual bioaerosol cycle, yields higher concentrations than a fluorescence-only approach, and maintains comparable correlations with biological and combustion tracers. This open-source algorithm provides a basis for quantifying bioaerosols across diverse environments, can revise bioaerosol estimates in previously analyzed observations, and can be refined as additional characterization data become available.