Measurements and comparison of primary biological aerosol above and below a tropical forest canopy using a dual channel fluorescence spectrometer

Abstract

Original article can be found at: http://www.atmos-chem-phys.net/10/issue10.html Copyright - the authors. Authors grant any third party the right to use the article freely as long as its original authors and citation details are identified. The article and any associated published material is distributed under the Creative Commons Attribution 3.0 License.Aerosol particle size distributions were measured below and above a tropical rainforest canopy in Borneo, Malaysia, in June/July 2008 using the WIBS-3: a single particle dual channel fluorescence spectrometer. Material in the size range 0.8???20 ??m was characterized according to optical equivalent diameter (DP), morphology and fluorescence at 310???400 nm and 400???600 nm following excitation at 280 nm and 370 nm respectively. Particles fluorescent after both excitations are likely to be fluorescent primary biological aerosol particles (FBAP). Measured FBAP number concentration (NFBAP) at both sites exhibited clear diurnal cycles. The largest variability was observed in the understorey, where NFBAP reached a minimum of 50???100 L???1 in late morning. In mid afternoon it exhibited strong transient fluctuations as large as 4000 L???1 that were followed by sustained concentrations of 1000???2500 L???1 that reduced steadily between midnight and sunrise. Above the canopy FBAP number ranged from 50???100 L???1 during the daytime to 200???400 L???1 at night but did not exhibit the transient enhancements seen in the understorey. The strong FBAP fluctuations were attributed to the release of fungal spores below the canopy and appeared to be linked to elevated relative humidity. The mean FBAP number fraction in the size range 0.8 ??m<DP<20 ??m was 55% in the understorey and 28% above canopy. A size mode at 2 ??m<DP<4 ??m appears at both sites and is primarily FBAP, which dominated the coarse (DP???2.5 ??m) number concentration at both sites, accounting for 75% in the understorey and 57% above the canopy. In contrast, the concentration of non-fluorescent particles (NNON) at both sites was typically 200???500 L???1, the majority of which occupied a size mode at 0.8<DP<1.5 ??m. Enhanced understorey NNON was observed daily in mid-afternoon and also at midday on three occasions: the former coincided with the FBAP enhancements and measured approximately 10% of their magnitude; the latter occurred independently of the NFBAP diurnal cycle and comprised particles smaller than 2 ??m. Particle diameter of 3???5 ??m is consistent with smaller fungal spores, though absolute identification of biological species is not possible with the UV-LIF technique. Based on the measured FBAP and non-fluorescent particle abundances and their observed recovery times following rain showers, FBAP originated beneath the canopy while the non-fluorescent material was transported from further away. It is concluded that these separate sources contributed the majority of the aerosol measured by the WIBS-3 at both sites

Identification of single microbial particles using electro-dynamic balance assisted laser-induced breakdown and fluorescence spectroscopy

“…Previously it has been reported that real-time LIF analysis enables classification of bioaerosols from other aerosols in atmosphere (Gabey et al 2010;Huffman et al 2010;Pan 2015). Our results show that combined LIF and LIBS analysis is promising tool for online classification of atmospheric bioaerosols.…”

“…Fluorescence-based online bioaerosol instruments, such as BioScout, WIBS, and UV-APS, have been used in various environments, but it is really challenging to classify different types of bioaerosols with these instruments (Gabey et al 2010;Huffman et al 2010;Saari et al 2014). It should be noted that fluorescence analysis alone may include uncertainties due to fluorescent non-biological artifacts in ambient air leading to false counts of bioaerosols (P€ ohlker et al 2012;Saari et al 2013).…”

Fluorescence calibration method for single-particle aerosol fluorescence instruments

“…We validated the procedure using a commercially available WIBS (model 4A), first described by Kaye et al (2005) and later in significant detail by Gabey et al (2010) and Perring et al (2015). We will briefly describe its operating principles and the instrument settings used in this study.…”

“…The use of these fluorescence magnitudes, however, varies widely in the published literature. Several recent studies have employed a binary yes-no classification of fluorescence above a threshold (e.g., Gabey et al, 2010;Perring et al, 2015), essentially ignoring the fluorescence magnitude beyond the threshold. Fluorescence magnitudes have been used as input variables in automated particle-clustering analyses (Robinson et al, 2013;Crawford et al, 2015) and to manually sort sampled particles into groupings (Wright et al, 2014).…”

Continuous bioaerosol monitoring in a tropical environment using a UV fluorescence particle spectrometer

“…The fully analysed bioaerosol dataset with species identification is discussed in a separate publication (Gabey et al, 2010).…”