Emissions from the tropics more damaging than thought

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Copyright: Elena Chernyshova / Panos

Speed read

  • Ozone forming emissions like nitrogen oxide have strong photochemical reaction
  • South-East Asia has contributed the most to global ozone increase
  • Study does not absolve rich countries due to absolute high, historical emissions

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[BANGALORE] A new study says the amount of pollutants emitted has less impact than where it was generated on the creation of “bad ozone” or the ozone that is created at the troposphere level and is toxic.
Emissions closer to the equator go on to do the most damage and would create global ozone even if there were a decrease in global emission of greenhouse gases which create ground-level ozone, says a study by researchers from the University of North Carolina.

“One ton of emissions (nitrogen oxides) from South-East Asia is roughly eight times the global ozone emissions from North America.”

Jason West, University of North Carolina


“International efforts should prioritise actions in regions closest to the equator to reduce global ozone” emphasises Jason West, lead author and associate professor at the Department of Environmental Sciences & Engineering University of North Carolina.
The future global ozone burden will be determined mainly by emissions from low latitudes, says his paper titled “Tropospheric Ozone Change from 1980 to 2010 Dominated by Equatorward Redistribution of Emissions” published in  the journal Nature Geoscience in November 2016.
The study looks at increase in tropospheric ozone in this period when emissions of CO (carbon monoxide), NOx (nitrogen oxide) and NMVOCs (non-methane volatile organic compounds), all contributing to ozone creation, decreased in the United States, Europe and China while shooting up in South Asia and South-East Asia.  
The study found that emissions changes from South-East Asia contributed the most in the 1980–2010 global ozone increase, followed by East Asia and South Asia.  South-East Asia emerges as most critical although its emission increased by only 22 per cent.
It is known that ozone formation occurs when NOx, CO and VOCs react in the presence of sunlight and warmer temperatures resulting to more ozone formed in tropical regions.
“One ton of emissions (nitrogen oxides) from South-East Asia is roughly eight times the global ozone emissions from North America. For South Asia, one ton roughly causes three times as much,” says West.
“What is new here is that we demonstrate the importance of emissions near the equator in a way that hadn't been shown before,” West tells SciDev.Net.
Anumita Roychowdhury, head of research at Delhi-based advocacy group Centre for Science and Environment, says that the study highlights the role of spatial atmospheric conditions in tropics and subtropical climate around the equator which is more conducive for formation of tropospheric ozone and “shows that there is equatorward shift of these emissions”.

However, she emphasises that the study does not negate the past and present CO2 emissions by developed countries.
“This should not confuse the differentiated responsibility for mitigation of long-lived climate pollutant like CO2 by the rich and poorer countries. The argument of locational disadvantage for ozone cannot be used to demand that the poorer countries around the equator would need to take on the larger burden of mitigation responsibility,” says Roychowdhury.
“The developed world will still have to take on the larger burden of mitigation of CO2 due to their absolute high emissions as well as historical emissions.”
This piece was produced by SciDev.Net’s South-East Asia & Pacific desk.