Biomarkers as indicators of fungal biomass in the atmosphere of São Paulo, Brazil

Abstract

The biogenic aerosol contribution to atmospheric particulate matter (PM) mass concentration is usually neglected due to the difficulty in identifying its components, although it can be significant. In the Metropolitan Area of São Paulo (MASP)-Brazil, several studies have been performed to identify sources for PM, revealing vehicular emissions and soil re-suspension as the main identified sources. The organic fraction has been related primarily to biomass burning (BB) and fuel combustion, although there is significant presence of green areas in the city which render biogenic emissions as an additional source of organic carbon (OC). The objectives of this work are to (i) characterise the composition of the PM₁₀ (ii) estimate the relative mass contribution of fungal spores to PM concentrations with sizes smaller than 10μm (PM₁₀) in MASP and (iii) assess the main sources of PM₁₀. To achieve these objectives, we measured markers of biogenic sources and BB, during the fall-winter transition, which along with other constituents, such as ions, organic/elemental carbon, elemental composition and fungal spore concentrations, help assess the PM₁₀ sources. We used receptor models to identify distinct source-related PM₁₀ fractions and conversion factors to convert biomarker concentrations to fungal mass. Our results show the mean contributions of fungal aerosol to PM₁₀ and OC mass were 2% and 8%, respectively, indicating the importance of fungal spores to the aerosol burden in the urban atmosphere. Using specific rotation factor analysis, we identified the following factors contributing to PM: soil re-suspension, biogenic aerosol, secondary inorganic aerosol, vehicular emissions and BB/isoprene-related secondary organic aerosol (I-SOA). BB/I-SOA was the main source representing 28% of the PM₁₀ mass, while biogenic aerosol explained a significant (11%) fraction of the PM₁₀ mass as well. Our findings suggest that primary biogenic aerosol is an important fraction of PM₁₀ mass, yet not considered in most studies.

Keywords: Atmospheric particulate matter; Bioaerosol; Biomass burning markers; Fungal biomarkers; Primary biogenic aerosols; Receptor modelling.