It's already been known that there is a mobile cloudy belt known as the Intertropical Convergence Zone that span the globe roughly at the level of the equator. This separates the more polluted air of the northern hemisphere from the cleaner air of the southern hemisphere.

However, a team of scientists has found evidence of a second barrier between polluted and cleaner air. The team led by Jacqueline Hamilton of the University of York, U.K., found a 50 km wide "line" north of Australia.

Carbon monoxide levels were four times higher to the north of the line than they were to the south. The study was carried out in January and February 2006, during the Australian-Indonesian monsoon, and the effect may be seasonal, according to Hamilton.

The research will be published in a future issue of the Journal of Geophysical Research — Atmospheres, a publication of the American Geophysical Union.

Hamilton said:

"The shallow waters of the Western Pacific, known as the Tropical Warm Pool, have some of highest sea surface temperatures in the world, which result in the region's weather being dominated by storm systems.

The position of the chemical equator was to the south of this stormy region. Powerful storms may act as pumps, lifting highly polluted air from the surface to high in the atmosphere where pollutants will remain longer and may have a global influence."