The evaluation of the sources and effects of atmospheric particulate matter (PM), as well as the analysis of possible mitigation measures and of their outcomes, requires the knowledge of the chemical composition of PM. To this aim, during the last two decades many results have been obtained in terms of complete characterisation of the inorganic fraction (macro- micro- and trace components), while the much higher complexity of the organic fraction has limited the range of the analysed species to organic matter as a whole or to some groups of components, generally of interest for their toxicity (e.g. polycyclic aromatic hydrocarbons) or for their ability to trace PM sources (e.g. n-alkanes, levoglucosan). Given the huge number of organic species in PM, the determination of each individual concentration is a very ambitious, if not impossible, task. At the state of art, no more than 20% of the organic mass can be speciated. Among others, the unidentified fraction includes the bioaerosol (primary biological aerosol particles, PBAPs), that is the biomass deriving from fungi, bacteria, plant pollen, spore material and from non-viable vegetal and animal debris (Despres et al 2012). These PM fraction contains complex molecules that are generally not suitable for standard chemical analysis. Up to now, most of the study addressing the identification of bioaerosol have been carried out by cultivating viable bacteria and fungi on appropriate media or by determining specific biomarkers (e.g. ergosterol for fungi and fungal spores). Both approaches have limitations, as the culture-based technique apply to viable microorganisms only (Fierer et al 2008), and the use of biomarkers requires the knowledge of appropriate marker-into-biomass conversion factors (Bauer et al 2008). More recent approaches include complex and time-expensive molecular biological methods (An et al 2006). We describe here the development of a new method for the semi-quantitative determination of the overall contribution of all types of bioaerosol to atmospheric PM. The method consists in the sampling of atmospheric particles on polycarbonate filters, staining of the sample with appropriate fluorochromes (propidium iodide - PI) and analysis by microscopy of the bioaerosol, that appears red (Figure 1). The labelled elements are then counted, and their images elaborated by a software that allows an estimation of their volume and mass. The new method has been applied to a series of 24-h atmospheric PM10 samples collected during 1 year in the vicinity of Rome, Italy. These determinations give a first overview of bioaerosol concentration and of its seasonal variations. Side-by-side samples were also collected to determine the mass concentration of PM10, by the beta-attenuation method, and its organic matter content, by thermo-optical analysis. The concentration of atmospheric bioaerosol was in the range 0.2 - 5 ug/m3, with maximum values during the summer period. The biomass contribution to PM10 and to organic matter was in the range 0.5 - 20% and 1 - 30%, respectively. A variant of the method has been developed to be applied to size-segregated samples, collected by a multi-stage impactor (ten stages between 0.18 and 18 um). Field results showed that the size distribution of bioaerosol is single-mode, with maximum in the range 3.2 - 5.6 um and about 90% of the mass in the size range above 2.5 um. This method offers the first possibility to evaluate the global contribution of all types of bioaerosol to atmospheric PM. This contribution has shown to be remarkable for the coarse fraction of atmospheric particles, where it may reach values as high as 40%.
A new method for determining bioaerosol mass concentration in atmospheric PM
Perrino C;Marcovecchio F
2015
Abstract
The evaluation of the sources and effects of atmospheric particulate matter (PM), as well as the analysis of possible mitigation measures and of their outcomes, requires the knowledge of the chemical composition of PM. To this aim, during the last two decades many results have been obtained in terms of complete characterisation of the inorganic fraction (macro- micro- and trace components), while the much higher complexity of the organic fraction has limited the range of the analysed species to organic matter as a whole or to some groups of components, generally of interest for their toxicity (e.g. polycyclic aromatic hydrocarbons) or for their ability to trace PM sources (e.g. n-alkanes, levoglucosan). Given the huge number of organic species in PM, the determination of each individual concentration is a very ambitious, if not impossible, task. At the state of art, no more than 20% of the organic mass can be speciated. Among others, the unidentified fraction includes the bioaerosol (primary biological aerosol particles, PBAPs), that is the biomass deriving from fungi, bacteria, plant pollen, spore material and from non-viable vegetal and animal debris (Despres et al 2012). These PM fraction contains complex molecules that are generally not suitable for standard chemical analysis. Up to now, most of the study addressing the identification of bioaerosol have been carried out by cultivating viable bacteria and fungi on appropriate media or by determining specific biomarkers (e.g. ergosterol for fungi and fungal spores). Both approaches have limitations, as the culture-based technique apply to viable microorganisms only (Fierer et al 2008), and the use of biomarkers requires the knowledge of appropriate marker-into-biomass conversion factors (Bauer et al 2008). More recent approaches include complex and time-expensive molecular biological methods (An et al 2006). We describe here the development of a new method for the semi-quantitative determination of the overall contribution of all types of bioaerosol to atmospheric PM. The method consists in the sampling of atmospheric particles on polycarbonate filters, staining of the sample with appropriate fluorochromes (propidium iodide - PI) and analysis by microscopy of the bioaerosol, that appears red (Figure 1). The labelled elements are then counted, and their images elaborated by a software that allows an estimation of their volume and mass. The new method has been applied to a series of 24-h atmospheric PM10 samples collected during 1 year in the vicinity of Rome, Italy. These determinations give a first overview of bioaerosol concentration and of its seasonal variations. Side-by-side samples were also collected to determine the mass concentration of PM10, by the beta-attenuation method, and its organic matter content, by thermo-optical analysis. The concentration of atmospheric bioaerosol was in the range 0.2 - 5 ug/m3, with maximum values during the summer period. The biomass contribution to PM10 and to organic matter was in the range 0.5 - 20% and 1 - 30%, respectively. A variant of the method has been developed to be applied to size-segregated samples, collected by a multi-stage impactor (ten stages between 0.18 and 18 um). Field results showed that the size distribution of bioaerosol is single-mode, with maximum in the range 3.2 - 5.6 um and about 90% of the mass in the size range above 2.5 um. This method offers the first possibility to evaluate the global contribution of all types of bioaerosol to atmospheric PM. This contribution has shown to be remarkable for the coarse fraction of atmospheric particles, where it may reach values as high as 40%.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
