The contribution of bacteria and fungal spores to the organic carbon content of cloud water, precipitation and aerosols

To estimate the contribution of bacterial and fungal carbon to the carbon content of atmospheric samples, the number concentrations of bacteria and fungal spores in cloud water, snow, rain and aerosol samples collected at a continental background site in the Austrian Alps were determined. Based on these number concentrations, bacterial and fungal carbon was calculated and related to the total carbon (TC) and organic carbon (OC) contents of the samples. In cloud water samples, an average of 4.5 × 103 spores ml-1 was found, which corresponds to 1.5% of OC. The average bacterial abundance was 2.0 × 104 cells ml-1 corresponding to 0.01% of OC. In snow samples, the average concentrations of bacteria and fungi were 3.1 × 103 cells ml-1 corresponding to 0.015% of TC and 6.2 × 102 spores ml-1 corresponding to 1.8% of TC, respectively. In aerosol samples, average concentration of bacteria amounted to 1.2 × 104 cells m-3, which corresponds to 0.03% of OC, while fungal concentrations averaged to 7.3 × 102 spores m-3 or 0.9% of OC. As fungal spores occur predominantly in the size range > 2.1 œm aerodynamic equivalent diameter (a.e.d.), their contribution to the coarse size fraction (2.1-10 œm) was investigated and amounted up to 9.9% of OC. Œ 2002 Elsevier Science B.V. All rights reserved.