Bits of pollen, leaf fragments and even dandruff from people and animals make up a significant portion of dusty stuff in the atmosphere but have been ignored by climate modelers, German researchers said Thursday.
WASHINGTON Bits of pollen, leaf fragments and even dandruff from people and animals make up a significant portion of dusty stuff in the atmosphere but have been ignored by climate modelers, German researchers said Thursday.
Their painstaking, 15-year measurements turned up a collection of human and animal skin particles, fur, fragments of plants, pollen, spores, bacteria, algae, fungi, and viruses.
They are the right size and shape to act as nuclei for ice crystals, which in turn form clouds and rain, and thus could potentially affect weather and climate, they report in Friday's issue of the journal Science.
Overall this dust could make up 25 percent of so-called aerosols -- particles in the atmosphere that affect pollution, cloud formation and which can both reflect and absorb radiation from the sun, said atmospheric scientist Ruprecht Jaenicke of the University of Mainz.
"We collected particles, all particles from the air," Jaenicke said in a telephone interview. They collected samples from the university campus, from Russia's remote Lake Baikal, from Amazon ground stations, Antarctica, the Swiss Alps and Greenland ice cores.
"We looked into rain. We took measurements from airplanes," Jaenicke said.
They then used various microscopes to identify dead biological material by using stains that react to protein and also by visually identifying the tiny pieces.
"We counted all particles and determined their size," Jaenicke said.
They found as much as 80 percent of the particulate matter collected was biological in origin -- ranging from 15 percent over the Swiss Alps to 80 percent from the Amazon and Lake Baikal in the autumn.
On average, 20 to 25 percent of the aerosol material they collected was biological.
Air of Mystery
This is significant because atmospheric and climate scientists admit that as much as 40 percent of all aerosols are unidentified, and climate models do not fully take into account the effects of aerosols, Jaenicke said.
Other known sources of aerosols include sulfur pollution, dust and industrial emissions, smoke from fires and volcanic aerosols.
While he is not claiming that dandruff affects global warming, Jaenicke said he also ran tests that showed his particles could easily affect cloud formation.
"To form clouds you need water and particles," he said. "Each particle is a nucleus. To form rain you need certain ice nuclei which transform a droplet into an ice crystal." These then collide and form rain droplets.
Jaenicke's team was unable to say how much of this biological dust is pollen and how much is actually dandruff.
"This material is comparatively low in density," he said, adding it is small enough to travel very far.
"It is easily lifted up." For instance, it is lighter than desert sands that are carried across oceans.
"They are distributed easily around the world," he said.
Jaenicke urged other climate scientists to study the components of aerosols so they can make more accurate models for predicting weather and climate change.