The Three Faces of Ozone

Ozone, a gas with both natural and human sources, is known for its multiple "personalities." In the stratosphere ozone is benign, protecting Earth from incoming ultraviolet radiation. In the troposphere, it has two distinct harmful functions, depending on altitude. At ground level it's a pollutant that hurts living plants and animals, including humans. Higher in the troposphere, it's the third most important human-produced greenhouse gas, trapping outgoing thermal radiation and warming the atmosphere. 

TES data, in conjunction with data from other instruments on Aura, were used to disentangle these personalities, leading to a significantly better understanding of ozone and its impact on human health, climate and other parts of the Earth system.

Air currents in the mid- to upper troposphere carry ozone not only across continents but across oceans to other continents. A 2015 study using TES measurements found that the U.S. West Coast's tropospheric ozone levels were higher than expected, given decreased U.S. emissions, partly because of ozone that blew in across the Pacific Ocean from China. The rapid growth in Asian emissions of precursor gases -- gases that interact to create ozone, including carbon monoxide and nitrogen dioxide -- changed the global landscape of ozone.

"TES has borne witness to dramatic changes in which the gases that create ozone are produced. TES's remarkably stable measurements and ability to resolve the layers of the troposphere allowed us to separate natural changes from those driven by human activities," said JPL scientist Jessica Neu, a coauthor of the study. 

Regional changes in emissions of ozone precursor gases alter not only the amount of ozone in the troposphere, but its efficiency as a greenhouse gas. Scientists used TES measurements of ozone's greenhouse effect, combined with chemical weather models, to quantify how the global patterns of these emissions have altered climate. "In order to both improve air quality and mitigate climate change, we need to understand how human pollutant emissions affect climate at the scales in which policies are enacted [that is, at the scale of a city, state or country]. TES data paved the way for how satellites could play a central role," said Daven Henze, an associate professor in the department of mechanical engineering at the University of Colorado at Boulder.