Abstract
Abstract. UV-LIF measurements were performed on ambient aerosol in Manchester, UK (urban city centre, winter) and Borneo, Malaysia (remote, tropical) using a Wide Issue Bioaerosol Spectrometer, version 3 (WIBS3). These sites are taken to represent environments with minor and significant primary biological aerosol (PBA) influences respectively, and the urban dataset describes the fluorescent background aerosol against which PBA must be identified by researchers using LIF. The ensemble aerosol at both sites was characterised over 2–3 weeks by measuring the fluorescence intensity and optical equivalent diameter (DP) of single particles sized 0.8 ≤ DP ≤ 20 μm. Filter samples were also collected for a subset of the Manchester campaign and analysed using energy dispersive X-Ray (EDX) spectroscopy and environmental scanning electron microscopy (ESEM), which revealed mostly non-PBA at D ≤ 1 μm. The WIBS3 features three fluorescence channels: the emission following a 280 nm excitation is recorded at 310–400 nm (channel F1) and 400–600 nm (F2), and fluorescence excited at 350 nm is detected at 400–600 nm (F3). In Manchester the primary size mode of fluorescent and non-fluorescent material was present at 0.8–1.2 μm, with a secondary fluorescent mode at 2–4 μm. In Borneo non-fluorescent material peaked at 0.8–1.2 μm and fluorescent at 3–4 μm. Agreement between fluorescent number concentrations in each channel differed at the two sites, with F1 and F3 reporting similar concentrations in Borneo but F3 outnumbering F1 by a factor of 2–3 across the size spectrum in Manchester. The fluorescence intensity in each channel generally rose with DP at both sites with the exception of F1 intensity in Manchester, which peaked at DP = 4 μm, causing a divergence between F1 and F3 intensity at larger DP. This divergence and the differing fluorescent particle concentrations demonstrate the additional discrimination provided by the F1 channel in Manchester. The relationships between fluorescence intensities in different pairs of channels were also investigated as a function of DP. Differences between these metrics were apparent at each site and provide some distinction between the two datasets. Finally, particle selection criteria based on the Borneo dataset were applied to identify a median concentration of 10 "Borneo-like" fluorescent particles per litre in Manchester.
Highlights
Primary biological aerosol (PBA) is the subset of the atmospheric aerosol that includes plant and insect debris, fungal and plant spores, pollen, cells, viruses and bacteria
Elevated number concentrations occur on several days, during which NF3 exceeds 1000 l−1 and NF2 and NF3 are strongly enhanced for 1.5 days from the 10–12 December
This work demonstrates that the ensemble aerosol at an urban and a tropical rainforest site can be partially distinguished based on the size distributions of particles fluorescent at 400– 600 nm after a 350 nm excitation, and this is consistent with previous studies
Summary
Primary biological aerosol (PBA) is the subset of the atmospheric aerosol that includes plant and insect debris, fungal and plant spores, pollen, cells, viruses and bacteria. PBA abundance in the atmosphere is poorly constrained and potential feedback on cloud-hydrological pathways is not yet fully included in climate models. Long-range PBA transport has implications for global biodiversity and disease transmission and there are potential effects on cloud microphysical processes because of the ability of PBA to act as “giant” cloud condensation nuclei (GCCN) and heterogeneous ice nuclei (IN) at temperatures as warm as −2 ◦C (Diehl et al, 2001, 2002). In rural areas the PBA is dominated by fungal spores whereas urban locations usually contain a more varied PBA population thought to contain a larger bacterial component (Matthias-Maser and Jaenicke, 1995) because of sources such as municipal waste treatment plants. Gabey et al.: The fluorescence properties of aerosol larger than 0.8 μm
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