Increase in air pollution in the regions near the equator has led to the formation of more total ozone worldwide, compared to the amount of pollution being emitted, researchers have found.
“Emissions are growing in places where there is a much greater effect on the formation of ozone,” said lead researcher Jason West, Associate Professor at University of North Carolina.
The reason is that ozone, a greenhouse gas and toxic air pollutant, is not emitted but forms when ultraviolet light hits nitrogen oxides (basically combustion exhaust from cars and other sources).
When these pollutants interact with more intense sunlight and higher temperatures, the interplay speeds up the chemical reactions that form ozone.
Higher temperatures near the equator also increase the vertical motion of air, transporting ozone-forming chemicals higher in the troposphere, where they can live longer and form more ozone, the researchers said.
“A tonne of emissions in a region close to the equator, where there is a lot of sunlight and intense heat, produces more ozone than a tonne of emissions in a region farther from it,” West explained
The study showed that China’s emissions increased more than India’s and Southeast Asia’s from 1980 to 2010. But, Southeast Asia and India, despite their lower growth in emissions during this period, appear to have contributed more to the total global ozone increase due to their proximity to the equator.
“Our findings suggest that ‘where the world emits’ is more important than ‘how much it emits’,” West added.
The study provides a much-needed path forward on where in the world to strategically reduce emissions of pollutants that form ozone, which when present in the lower atmosphere, or troposphere, is one of the primary causes of air pollution-related respiratory problems and heart disease.
However, Owen Cooper from the University of Colorado-Boulder, in the US said: “Even if there is a net reduction in global emissions, ozone levels may not decrease if emissions continue to shift toward the equator.”
“But, continuing aircraft and satellite observations of ozone across the tropics can monitor the situation and model forecasts can guide decision-making for controlling global ozone pollution,” Cooper noted.
The study appears in the online issue of the journal Nature Geoscience.