'Chemical equator' keeps pollution in the north
Once released, pollution doesn't disperse evenly around the world - meteorological conditions seem to be instilled with a natural sense of fair play and keep the emissions of the industrialised north out of the relatively clear-skied south.
But research by chemists at the University of York shows for the first time that the chemical and meteorological boundaries are not necessarily the same.
The scientists found huge differences in air quality on either side of the chemical equator, which was 50 km wide and well to the north of the ITCZ.
Their study revealed that carbon monoxide, a tracer of combustion, was four times higher in the north.
The difference in pollutant levels was increased by extensive forest fires to the north of the boundary and very clean air south of the chemical equator being pulled north from the Southern Indian Ocean by a land based cyclone in northern Australia.
The discoveries will be useful for mapping and predicting pollution levels.
"Powerful storms [in the tropics] 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," said Dr Jacqueline Hamilton, of the Department of Chemistry at York.
"To improve global simulations of pollutant transport, it is vital to know when the chemical and meteorological boundary are in different locations."