Abstract
Abstract. The behaviour of primary biological aerosols (PBAs) at an elevated, un-polluted North American forest site was studied using an ultra violet-light induced fluorescence (UV-LIF) measurement technique in conjunction with hierarchical agglomerative cluster analysis (HA-CA). Contemporaneous UV-LIF measurements were made with two wide-band integrated bioaerosol spectrometers, WIBS-3 and WIBS-4, which sampled close to the forest floor and via a continuous vertical profiling system, respectively. Additionally, meteorological parameters were recorded at various heights throughout the forest and used to estimate PBAP (Primary Biological Aerosol Particle) fluxes. HA-CA using data from the two, physically separated WIBS instruments independently yielded very similar cluster solutions. All fluorescent clusters displayed a diurnal minimum at midday at the forest floor with maximum concentration occurring at night. Additionally, the number concentration of each fluorescent cluster was enhanced, to different degrees, during wet periods. A cluster that displayed the greatest enhancement and highest concentration during sustained wet periods appears consistent with behaviour reported for fungal spores. A cluster that appears to be behaviourally consistent with bacteria dominated during dry periods. Fluorescent particle concentrations were found to be greater within the forest canopy than at the forest floor, indicating that the canopy was the main source of these particles rather than the minimal surface vegetation, which appeared to contribute little to overall PBA concentrations at this site. Fluorescent particle concentration was positively correlated with relative humidity (RH), and parameterisations of the aerosol response during dry and wet periods are reported. The aforementioned fungal spore-like cluster displayed a strong positive response to increasing RH. The bacteria-like cluster responded more strongly to direct rain-fall events than other PBA types. Peak concentrations of this cluster are shown to be linearly correlated to the log of peak rainfall rates. Parallel studies by Huffman et al. (2013) and Prenni et al. (2013) showed that the fluorescent particle concentrations correlated linearly with ice nuclei (IN) concentrations at this site during rain events. We discuss this result in conjunction with our cluster analysis to appraise the candidate IN.
Highlights
Primary biological aerosols (PBAs) are a diverse and complex classification of aerosols usually defined as those aerosols that are directly introduced to the atmosphere in the condensed phase and are composed of both viable and non-viable classes of potentially regenerative biological material (Després et al, 2012)
Cluster B3 has been shown to exhibit a strong diurnal response, with maximum concentrations occurring at night when relative humidity (RH) is enhanced (Fig. 4)
This cluster was found to respond strongly to increases in RH, with the cluster accounting for 60 % of the observed fluorescent material at high RH under wet conditions (Fig. 12). This behaviour is consistent with that of emission of fungal spores as described earlier (Hirst, 1953; Pringle et al, 2005; Elbert et al, 2007; Jones and Harrison, 2004), as such we suggest that cluster B3 is representative of fungal spores
Summary
Primary biological aerosols (PBAs) are a diverse and complex classification of aerosols usually defined as those aerosols that are directly introduced to the atmosphere in the condensed phase and are composed of both viable and non-viable classes of potentially regenerative biological material (Després et al, 2012). Responses to such criticisms usually focus on the heterogeneity in PBA sources that are difficult to capture using traditional bioaerosol sampling methods and the impact of different meteorological factors in different bio-geographical environments Whilst this is an ongoing area of debate and realtime discrimination and quantification remains a significant technical problem, investigations continue to elucidate possible feedback pathways to inform model sensitivity studies for regional and global models that include PBA emissions (Després et al, 2012; Forster et al, 2007; Heald and Spracklen, 2009; Hummel et al, 2014; Matthias-Maser and Jaenicke, 1995; Jacobson and Streets, 2009). Reported recently for the same study (Huffman et al, 2013; Prenni et al, 2013; Tobo et al, 2013)
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