MAINZ, Germany, Oct. 24 (UPI) -- Findings from an international team of scientists revealed Thursday that the storied wine-dark Mediterranean Sea -- the crossroads of the ancient world -- is now a crossroads for air pollution.
Pollution from Europe, Asia and North America meet miles above the Mediterranean with larger effects on global climate than suspected previously, such as suppressing rainfall in the Middle East and northern Africa.
"This is a very important problem with political dimensions," lead researcher Jos Lelieveld, an atmospheric chemist at Max Planck Institute for Chemistry, told United Press International. "The air pollution is causing difficulties where water availability is already a problem. This is rather unexpected, but it is quite clear this is the case."
Lelieveld said international cooperation will be needed to reduce this pollution. "By helping each other with technology developments, hopefully we can contribute to a cleaner world," he said, but cautioning, "it will take a large effort."
As reported in the Oct. 25 issue of the journal Science, investigators from eight countries conducted their research on Crete at a monitoring station equipped to measure solar radiation and dozens of gases and types of dust. In addition, two aircraft performed more than 20 research flights to sample Mediterranean air during six weeks in the summer of 2001.
The collected data, coupled with computer simulations, revealed levels of key air pollutants usually are 2-to-10-times higher in the Mediterranean than regions with relatively clean air. Most of the pollution originated in either Western and Eastern Europe, Lelieveld said. It was concentrated in an area up to 2.5 miles high and came from industrial activity, traffic and forest fires, as well as agricultural and domestic burning.
The soot reduces the amount of sunlight reaching the ocean by about 10 percent. "So what happens is by preventing solar radiation from reaching the surface, you are reducing evaporation," Lelieveld said. As a consequence, less moisture reaches northern Africa and the Middle East.
Because the Mediterranean is mostly cloudless during the summer, sunlight levels are high, chemically transforming the pollutants into smog, and thereby conveying toxic products from fires into the lungs. The researchers found EU air quality standards for ozone are exceeded throughout the summer across most of the Mediterranean. High ozone levels harm human health and damage ecosystems and agricultural crops.
At higher altitudes, in the lower stratosphere, pollution was observed originating in North America and Asia. It had been lifted by thunderstorms in the Indian monsoon or carried by the westerly winds typical outside the tropics.
The effects of this pollution are unclear, Lelieveld said. Although the chlorine gases it contains "could lead to destruction of ozone, for an effect much like the hole in the ozone layer," he said other pollutants wafted up could generate ozone smoke.
"The net effect of these processes are not known," he added. "We are putting air pollution in a part of the atmosphere where we did not expect much pollution. Now we have to worry about what it will do and what we can do about it."
Atmospheric chemist Joseph Prospero, of the University of Miami, called the findings substantial.
"The implications from the standpoint of climate are larger than what I think many of us expected," he said. Although this study "provides only a relatively short snapshot," Prospero said, it calls for longer-term, larger-range experiments. "It would be interesting to see how far these pollutants are carried into North Africa."
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(Reported by Charles Choi, UPI Science News, in New York)
