"This was not the right weather for our study, so we decided to fly a survey flight northwards to find out what was happening," explained study lead author Jacqueline Hamilton of the University of York, England.
"It was then that we came across the chemical equator," she said.
As their aircraft, which was rigged with chemical detectors, traveled north, its sensors detected a tremendous difference in pollutant levels.
Not everything nasty is blocked, however.
"Eventually chemicals can cross this barrier if they remain intact in the air on a timescale of longer than around one year," cautioned lead author Hamilton.
While carbon monoxide and many aerosols will be kept out, chemicals that linger longer in the atmosphere, such as the greenhouse gas carbon dioxide, will not.
"This finding means that, [when the chemical equator was observed], pollution was not going into the upper atmosphere where it could alter the chemistry of both clouds and the ozone layer," May said.
This phenomenon could make mapping pollutants easier for researchers, but there are still many unknowns.
"[These are the] really early days—we still need to know a lot more about how atmospheric chemistry and weather interact before we can know what the implications of this discovery really are," May said.
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