\"Few studies have reported contributions of bioaerosol to atmospheric aerosol mass, especially for tropical regions,\" John CY Chan of China\'s Sun Yat-sen University told \"environmentalresearchweb\" To our knowledge, our results are the first published estimates of fungal spore contributions in a tropical region, indicating the significance of bioaerosol species as atmospheric aerosol constituents. As shown in a few recent studies, bioaerosols can have important effects on regional and global climate as they influence cloud physical processes.\"

Chan and colleagues used a molecular tracer method; they measured the atmospheric concentrations of the polyols (sugar alcohols) arabitol and mannitol, which are commonly found in fungal spores. This relatively new technique has been proposed as a replacement for the more common methods of cultivation and microscopic examination.

\"The cultivation method is limited by the culturability of microorganisms, that is, only a small fraction of all fungal spores can be cultivated,\" explained Chan. \"Microscopic techniques are laborious and time-consuming, and the results are usually operator-dependent.\" The molecular tracer technique, in contrast, avoids these limitations and gives more reproducible results.

The team measured polyol concentrations using high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). They took samples of ambient air from the tropical rainforest of Jiangfengling Mountain, Hainan Island, which lies off the South China coast.

\"Our measurements of the fungal tracers arabitol and mannitol in South China revealed rather high concentrations of the two polyols in ambient air, specifically in PM10 [particles with diameters less than or equal to 10 microns],\" said Chan. \"Relative contributions of fungal spores to ambient PM10 mass and organic carbon in PM10 were as high as 18.2% and 26.1%, respectively, based on our estimates using the measured tracer concentrations.\"

The two tracers tended to occur together, particularly for aerosols with diameters from 2.5 to 10 microns. What\'s more, the levels of arabitol and mannitol were generally higher when conditions were more humid and temperatures were warmer; this indicates that fungal spores are emitted more readily in wet conditions.

Chan worked with colleagues from Sun Yat-Sen University, Bureau of Forestry, and Hong Kong Polytechnic University, China, and National Tsing Hua University and Academia Sinica, Taiwan.

Now the researchers would like to establish conversion factors between arabitol/mannitol concentrations, fungal mass, organic carbon content and spore-number concentrations in specific regions, such as different ecological systems. \"By using these conversion factors, we can more accurately yet easily assess the abundance of the fungal biomass, and derive the contribution of fungal spores to ambient aerosol mass directly from arabitol/mannitol concentrations at specific locations,\" said Chan.

The researchers reported their work in Environmental research letter (ERL).