The intrinsic fluorescence spectra of selected pollen and fungal spores

Primary Biological Aerosol Particles (PBAP) are ubiquitous in the atmosphere and recently the measurement of their fluorescence properties, in real-time, have been used to discriminate biological (particularly pollen and fungal spores) from non-biological particles in ambient environments. In the laboratory study reported here, the fluorescence spectra of several types of PBAP have been measured at 370 nm excitation. By this means, instructive spectroscopic signatures have been obtained for the various botanical families and orders studied here. All the spore emission spectra were shown to closely resemble each other: they display peaks at 415 nm and broad continua between 450 and 500 nm. In comparison the pollen gave discriminating spectra. For example, the Betulaceae exhibit three distinctive and virtually identical features at 420 nm, 465 nm and 560 nm. The conifers (Pinus sylvestris, Picea abies and Taxus baccata) pollen also display these features although with differing relative intensity ratios compared to the Betulaceae. Importantly, the grasses not only show the common pollen spectral features but also a sharp band at 675–680 nm: this observation demonstrates the presence of chlorophyll-a. The latter fluorescence signal could, in principle, be used in the real-time atmospheric identification of grass pollen, which are known carriers of aeroallergens. A PCA analysis was also conducted on the obtained spectra and demonstrated that grass pollen were separable from the other samples under investigation.