"Chemical Equator" Divides Earth's Hemispheres

Matt Kaplan
for National Geographic News
October 2, 2008

A worldwide weather "barrier" that can block air pollution from traveling southward, has been discovered, a new study says.

Called a "chemical equator," the 31-mile-(50-kilometer) wide boundary separates the Northern Hemisphere's dirty air from that of the less polluted Southern Hemisphere.

Carbon monoxide, a toxic gas generated by forest fires and internal combustion engines, increased from 40 parts per billion south of the boundary to 160 parts per billion north of it, scientists found.

Aerosol particles, produced by the burning of fossil fuels, also shot up dramatically.

The finding is reported in the Journal of Geophysical Research - Atmospheres.

(Related: "Chinese Air Pollution Deadliest in World, Report Says" [July 9, 2007].)

Serendipitous Discovery

The chemical equator has long been thought to exist. But scientists expected to find it within the Intertropical Convergence Zone, a band of thunderstorms and clouds circling the globe near Earth's actual Equator.

Instead, the line was found in clear skies 621 miles (1,000 kilometers) north of the zone, showing that the chemical and meteorological divide between the hemispheres is not the same.

"One would expect to see some chemical isolation, but not to this degree and closer to the zone," said Peter May, an atmospheric scientist at the Centre for Australian Weather and Climate Research in Melbourne, Australia. He assisted with the logistics behind the research but was not involved in the study itself.

The group of climatologists who found the chemical equator didn't set out with that goal.

The team were studying how storms transported chemicals in Darwin, on the northern coast of Australia, when the weather suddenly became clear and windy.

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