Human-made fires pollute air with ozone half a world away

Desdemona Despair

By Cody Sullivan
27 January 2016

(Eos) – Ozone, a common air pollutant and greenhouse gas, harms lungs and plants and has contributed almost as much as methane to global warming since the start of the Industrial Revolution. Now researchers are reporting new evidence that local-scale slash and burn farming techniques, cooking fires, and wildfires can distribute large quantities of ozone across huge distances within the vast tropical belt that girds Earth. Ozone originating within this belt has the potential to harm health and the environment on the other side of the planet and to help drive climate warming that affects the entire world.

A recent study in Nature Communications [pdf] found that ozone produced mostly by human-caused fires in Africa and Southeast Asia traveled throughout the lower atmosphere all the way to the western Pacific. According to the researchers, the study’s findings suggest that legislation and other efforts to limit ozone’s effects by targeting industry, vehicles, and other fossil-fuel-burning sources of the gas—mainly outside the tropics— may do little to address these important challenges.

“What’s unique with our study is that we’re in the tropical western Pacific, almost as remote as you can get in the Northern Hemisphere, and we’re still seeing large effects from fires in Africa,” said lead author Daniel Anderson, a graduate student in atmospheric and ocean sciences at the University of Maryland in College Park.

Whenever fires burn once-living organic material, such as wood or fossil fuels, they emit ozone into the atmosphere. Globally, fires contribute up to 10% of the ozone in the lower atmosphere, Anderson said. In the tropics, fire’s effect is magnified, he added, because weather patterns make it difficult for smoke created in the tropics to escape its roughly 15°N and 15°S latitude bounds. […]

The new study makes it harder to argue against biomass burning as the source of the ozone pollution, said Matthew Alvarado, a senior scientist at Atmospheric and Environmental Research Inc., headquartered in Lexington, Mass., who was not involved in the work. He cited the “weight of evidence” the new research has brought to bear on the question.

Anderson noted that people in sub-Saharan Africa and Southeast Asia rely on slash and burn farming and igniting cooking fires as essential parts of daily life. Prohibiting those practices would be like “telling Americans you aren’t allowed to drive cars,” so suitable alternatives are needed to address this ozone problem. [more]

Human-Made Fires Pollute Air with Ozone Half a World Away

ABSTRACT: Air parcels with mixing ratios of high O₃ and low H₂O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300–700 hPa). Here, using data collected during aircraft sampling of the TWP in winter 2014, we find strong, positive correlations of O₃ with multiple biomass burning tracers in these HOLW structures. Ozone levels in these structures are about a factor of three larger than background. Models, satellite data, and aircraft observations are used to show fires in tropical Africa and Southeast Asia are the dominant source of high O₃ and that low H₂O results from large-scale descent within the tropical troposphere. Previous explanations that attribute HOLW structures to transport from the stratosphere or mid-latitude troposphere are inconsistent with our observations. This study suggest a larger role for biomass burning in the radiative forcing of climate in the remote TWP than is commonly appreciated.

A pervasive role for biomass burning in tropical high ozone/low water structures