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

- Biogenic aerosol contribution to PM mass concentrations is usually neglected.
- Biogenic sources accounted for 11% of PM10 burden in MASP.
- Fungal aerosol contributions to PM10 and OC mass were 2% and 8%, respectively.
- Carbohydrates, ions, elements, WSOC and OC/EC were measured.
- Biomass burning/isoprene-related SOA contributed ~ 1/4 of PM10.

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 10 μm (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.

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