Autofluorescence of atmospheric bioaerosols – fluorescent biomolecules and potential interferences

C Pöhlker,J A Huffman,U Pöschl

doi:10.5194/amt-5-37-2012

Abstract

Abstract. Primary biological aerosol particles (PBAP) are an important subset of air particulate matter with a substantial contribution to the organic aerosol fraction and potentially strong effects on public health and climate. Recent progress has been made in PBAP quantification by utilizing real-time bioaerosol detectors based on the principle that specific organic molecules of biological origin such as proteins, coenzymes, cell wall compounds and pigments exhibit intrinsic fluorescence. The properties of many fluorophores have been well documented, but it is unclear which are most relevant for detection of atmospheric PBAP. The present study provides a systematic synthesis of literature data on potentially relevant biological fluorophores. We analyze and discuss their relative importance for the detection of fluorescent biological aerosol particles (FBAP) by online instrumentation for atmospheric measurements such as the ultraviolet aerodynamic particle sizer (UV-APS) or the wide issue bioaerosol sensor (WIBS). In addition, we provide new laboratory measurement data for selected compounds using bench-top fluorescence spectroscopy. Relevant biological materials were chosen for comparison with existing literature data and to fill in gaps of understanding. The excitation-emission matrices (EEM) exhibit pronounced peaks at excitation wavelengths of ~280 nm and ~360 nm, confirming the suitability of light sources used for online detection of FBAP. They also show, however, that valuable information is missed by instruments that do not record full emission spectra at multiple wavelengths of excitation, and co-occurrence of multiple fluorophores within a detected sample will likely confound detailed molecular analysis. Selected non-biological materials were also analyzed to assess their possible influence on FBAP detection and generally exhibit only low levels of background-corrected fluorescent emission. This study strengthens the hypothesis that ambient supermicron particle fluorescence in wavelength ranges used for most FBAP instruments is likely to be dominated by biological material and that such instrumentation is able to discriminate between FBAP and non-biological material in many situations. More detailed follow-up studies on single particle fluorescence are still required to reduce these uncertainties further, however.

Highlights

1.1 Primary biological aerosol particlesPrimary biological aerosol particles (PBAP), referred to as bioaerosols, are a diverse collection of small pieces of material emitted directly from the biosphere into the atmosphere (Despres et al, 2012)
Microscopic investigations have shown that PBAP can account for up to ∼30 % of fine (1 μm) particulate matter (PM) in rural and rain forest air, and estimates of PBAP emissions range from ∼60 Tg a−1 of fine PM to ∼1000 Tg a−1 in all size ranges (Penner, 1994; Jaenicke, 2005; Elbert et al, 2007)
In this study we provide a synthesis of literature data as well as original laboratory measurements, designed to give a broad overview of intrinsic fluorophores most likely to be important within ambient aerosols

Summary

Introduction

Primary biological aerosol particles (PBAP), referred to as bioaerosols, are a diverse collection of small pieces of material emitted directly from the biosphere into the atmosphere (Despres et al, 2012). They are globally ubiquitous, in some cases can dominate suspended particle concentrations, and comprise a diverse selection of particle types, including: whole organisms (e.g. bacteria, algae), reproductive entities (e.g. pollen, spores from fungi, bacteria, ferns, mosses), biopolymers (e.g. DNA, chitin, cellulose and other polysaccharides), plant debris, insect parts, and decaying biomass Fungal spores in particular account for a large proportion of PBAP with typical mass concentrations of ∼1 μg m−3 in continental boundary layer air and estimated global emissions in the order of ∼50 Tg a−1 (Elbert et al, 2007)

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