Biological micro-particles in rain water

This work constitutes the first report on the morphology and chemical identification of biological micro‐particles in rain water at two sites (Shizuoka and Tsukuba) from Japan. Micro‐particles in rain water were deposited directly onto electron microscopic grids using ultracentrifugation. Particles with diameters more than 0.2 µm were examined using an electron microscope equipped with an energy‐dispersive X‐ray analyzer. Biological particles in rain water were found to be bacteria and leaf debris, and most of those particles were associated with minerals. Peaks of phosphorus and potasium in the X‐ray spectra, which are characterized as chemical components of bacteria or leaves, were observed in all the biological particles. These particles in rain water were present in number percentages of 23 to 34% of the total insoluble particles, with concentrations of 1.6×104 to 2.4×104 cm−3 of rain water. This finding suggests that these biological particles are captured effectively in cloud water and/or precipitation, and that they may play a role in cloud condensation and/or ice nucleation.