When it comes to air pollution, scientists say where we emit matters more than how much
When it comes to air pollution, a new study has found countries close to the equator do more damage than their northern neighbours, even when those in the tropics produce fewer emissions.
The study, published today in the journal Nature Geoscience, looks specifically at global levels of ozone — a greenhouse gas and toxic air pollutant — which have increased worldwide over the last three decades.
“We wanted to ask the question how much of that change that’s happened over the last three decades is due to the change in location of emissions versus the increase in total emissions globally,” Jason West, who led the research at the University of North Carolina-Chapel Hill, told CBC News. “So we separated out those two factors and we found that change in location was by far the most important.”
That means where we pollute matters more than how much we pollute, at least when it comes to ozone-producing chemicals from car exhaust fumes, power plants, biomass burning and more.
So while China’s emissions have increased more than India’s and Southeast Asia’s from 1980 to 2010, the last two have contributed more to the total global ozone increase, the researchers say.
These findings are significant as more ozone-forming emissions come from rapidly industrializing nations in South and Southeast Asia — places like India and Indonesia.
Historically, most emissions have come from North America and Europe, says West.
“But that’s changed a lot over the past few decades as we have controlled our emissions and other parts of the world have industrialized,” West said. “So that shifted emissions toward the equator.”
More sun, more ozone
The sunny climate in these nations exacerbates the problem.
That’s because people don’t actually emit ozone into the atmosphere. Rather, we emit a whole slew of other pollutants called nitrogen oxides, which form ozone when they come into contact with ultraviolet light.
In the stratosphere, part of the upper atmosphere, ozone protects us against the sun’s ultraviolet rays. But when ozone forms in the lower atmosphere, or troposphere, it becomes very dangerous to human health, causing respiratory problems and heart disease.
The intense, heat-producing sunlight near the equator speeds up the chemical reactions that form ozone. The higher temperatures also push the air up faster, transporting more pollutants higher into the troposphere, where they stick around longer and produce more ozone.
None of this is groundbreaking — scientists have long known that emissions from tropical locations have a greater impact on ozone production — but the scale of it took the researchers by surprise.
“We thought that the change in location would be important, but we didn’t expect really that it would be the most important,” West said. “When we first saw the results we thought it was surprising, and so of course we checked and double checked and found that that was the case.”
Nobody’s off the hook
Those findings, he said, should have a serious impact on policymaking going forward, especially as it pertains to international agreements to combat air pollution.
“The world is changing and emissions are continuing to grow and they’re continuing to shift toward the equator,” West said.
But nobody’s off the hook. Global ozone levels affect everybody, West said, and when it comes to our health, local air quality matters most.
“So we have every incentive to reduce our own emissions.”