Ambient measurements of biological aerosol particles near Killarney, Ireland: a comparison between real-time fluorescence and microscopy techniques

D J O'Connor,J R Sodeau,C Pöhlker,J A Huffman,D A Healy,U Pöschl

doi:10.5194/acp-14-8055-2014

Abstract

Abstract. Primary biological aerosol particles (PBAPs) can contribute significantly to the coarse particle burden in many environments. PBAPs can thus influence climate and precipitation systems as cloud nuclei and can spread disease to humans, animals, and plants. Measurement data and techniques for PBAPs in natural environments at high time- and size resolution are, however, sparse, and so large uncertainties remain in the role that biological particles play in the Earth system. In this study two commercial real-time fluorescence particle sensors and a Sporewatch single-stage particle impactor were operated continuously from 2 August to 2 September 2010 at a rural sampling location in Killarney National Park in southwestern Ireland. A cascade impactor was operated periodically to collect size-resolved particles during exemplary periods. Here we report the first ambient comparison of a waveband integrated bioaerosol sensor (WIBS-4) with a ultraviolet aerodynamic particle sizer (UV-APS) and also compare these real-time fluorescence techniques with results of fluorescence and optical microscopy of impacted samples. Both real-time instruments showed qualitatively similar behavior, with increased fluorescent bioparticle concentrations at night, when relative humidity was highest and temperature was lowest. The fluorescent particle number from the FL3 channel of the WIBS-4 and from the UV-APS were strongly correlated and dominated by a 3 μm mode in the particle size distribution. The WIBS FL2 channel exhibited particle modes at approx. 1 and 3 μm, and each was correlated with the concentration of fungal spores commonly observed in air samples collected at the site (ascospores, basidiospores, Ganoderma spp.). The WIBS FL1 channel exhibited variable multimodal distributions turning into a broad featureless single mode after averaging, and exhibited poor correlation with fungal spore concentrations, which may be due to the detection of bacterial and non-biological fluorescent particles. Cladosporium spp., which are among the most abundant fungal spores in many terrestrial environments, were not correlated with any of the real-time fluorescence channels, suggesting that the real-time fluorescence instruments are relatively insensitive to PBAP classes with dark, highly absorptive cell walls. Fluorescence microscopy images of cascade impactor plates showed large numbers of coarse-mode particles consistent with the morphology and weak fluorescence expected of sea salt. Some of these particles were attached to biological cells, suggesting that a marine source influenced the PBAPs observed at the site and that the ocean may be an important contributor to PBAP loadings in coastal environments.

Highlights

The in situ monitoring of primary biological aerosol particles (PBAPs) with high time resolution represents an important technological development made capable, in part, by long-standing, military-led research into the detection of Published by Copernicus Publications on behalf of the European Geosciences Union.D
Several classes of bioaerosols have been shown to act as cloud and ice nuclei in laboratory settings (e.g., Maki et al, 1974; Diehl et al, 2001; Morris et al, 2004, 2013; Möhler et al, 2007; Pummer et al, 2012; Haga et al, 2013), and ambient measurements have shown PBAPs to be ubiquitously associated with rain and snowfall as well as present in clouds (Christner et al, 2008; Pöschl et al, 2010; DeLeonRodriguez et al, 2013; Huffman et al, 2013; Prenni et al, 2013)
It has been suggested that PBAPs may impact precipitation and the hydrological cycle, and may affect the weather and climate of a region (Sands et al, 1982; Morris et al, 2008, 2014)

Summary

Introduction

The in situ monitoring of primary biological aerosol particles (PBAPs) with high time resolution represents an important technological development made capable, in part, by long-standing, military-led research into the detection of Published by Copernicus Publications on behalf of the European Geosciences Union. Several classes of bioaerosols have been shown to act as cloud and ice nuclei in laboratory settings (e.g., Maki et al, 1974; Diehl et al, 2001; Morris et al, 2004, 2013; Möhler et al, 2007; Pummer et al, 2012; Haga et al, 2013), and ambient measurements have shown PBAPs to be ubiquitously associated with rain and snowfall as well as present in clouds (Christner et al, 2008; Pöschl et al, 2010; DeLeonRodriguez et al, 2013; Huffman et al, 2013; Prenni et al, 2013). A review of biological aerosol properties and detection methods is beyond the scope of this text, but comprehensive PBAP overviews are available (e.g., Madelin, 1994; Ho, 2002; Fröhlich-Nowoisky et al, 2009; Womack et al, 2010; Caruana, 2011; Xu et al, 2011; Després et al, 2012; Fröhlich-Nowoisky et al, 2012)

Methods

Results

Conclusion