The fluorescence properties of aerosol larger than 0.8 μm in urban and tropical rainforest locations

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.

The contribution of fungal spores and bacteria to regional and global aerosol number and ice nucleation immersion freezing rates

“…New methods employing laser-induced fluorescence to identify and count biological particles (e.g. Gabey et al, 2010Gabey et al, , 2011Huffman et al, 2010) may offer new opportunities to evaluate model predictions. We note that existing PBAP emission schemes have not been designed to adequately represent seasonal and interannual variability.…”

Primary biological aerosol particles in the atmosphere: a review

“…An early generation UV-APS (Ho, 2002) was used for short periods to measure background FBAP concentrations at several military locations within Canada and Sweden (Ho and Spence, 1998;Ho et al, 2004), and a different LIF spectrometer design was utilised for detection of FBAP in ambient air in several US locations Pan et al, 2007;Pan et al, 2009). Recently, fluorescence measurements of biological aerosols have also been reported in more detail for tropical rainforest air (Prenni et al, 2009;Gabey et al, 2010;Po¨schl et al, 2010) as well as in two urban European locations (Huffman et al, 2010;Gabey et al, 2011).…”

Cluster analysis of WIBS single-particle bioaerosol data

“…Here we focus upon development of analysis techniques for the Wideband Integrated Bioaerosol Sensor (WIBS) range of auto-fluorescence detectors (Foot et al, 2008;Gabey et al, 2010Gabey et al, , 2011Kaye et al, 2005). We demonstrate the application of a cluster analysis technique to the WIBS single-particle data, allowing for robust statistical resolution of different PBAP subgroups.…”