WASHINGTON (Reuters Mar 13, 2009 ) - Visibility on clear days has declined in much of the world since the 1970s thanks to a rise in airborne pollutants, scientists said on Thursday.

They described a “global dimming” in particular over south and east Asia, South America, Australia and Africa, while visibility remained relatively stable over North America and improved over Europe, the researchers said.

Aerosols, tiny particles or liquid droplets belched into the air by the burning of fossil fuels and other sources, are responsible for the dimming, the researchers said.

“Aerosols are going up over a lot of the world, especially Asia,” Robert Dickinson of the University of Texas, one of the researchers, said in a telephone interview.

Dickinson and two University of Maryland researchers tracked measurements of visibility — the distance someone can see on clear days — taken from 1973 to 2007 at 3,250 meteorological stations worldwide.

The data will help researchers understand long-term changes in air pollution and how these are associated with climate change, said Kaicun Wang of the University of Maryland.

ZED COMMENT: The hydrogen fuelled ZED engine does not contribute to “global dimming” as the fuel is made from water and returns to being water by the engine. When the environmental benefit is extrapolated from hundreds of millions of vehicles worldwide using a ZED engine, the atmosphere is expected to improve considerably.