Aerosols, tiny particles in the air, are widely studied because they are an important factor in regulating climate, variously absorbing heat to warm the air and reflecting sunlight to cool it. They are also important in forming rain and snow.

But the amount of cellular material -- bacteria, plant fragments, spores, fungi and so forth -- had been thought to be only a small proportion compared with mineral dusts, clay and sea salt.

Now, Ruprecht Jaenicke of the Institute for Atmospheric Physics at Mainz University in Germany has studied air samples and discovered that biological materials can range up to 25 percent of aerosols in some areas, and as high as 40 percent in others.

His findings are reported in Friday's issue of the journal Science.

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http://edition.cnn.com/2005/TECH/science/03/31/dandruff.pollution.ap/index.html