New research found that increasing pollution over the past two decades resulted in higher ozone levels. While this may seem obvious, no previous study about ozone used data collected directly by commercial aircraft.

In the study published in the journal Science Advances, researchers gathered measurements from aircraft on international flights. They discovered increasing ozone levels in the lowest part of Earth’s atmosphere in the Northern Hemisphere over the last two decades.

This occurs even as tighter emission controls have lowered ground-level ozone in certain areas of North America and Europe. Despite better regulations, the ozone levels in Earth’s atmosphere continue to rise. Called tropospheric ozone, it occurs between Earth’s surface and 12 to 15 kilometers above Earth. The greenhouse gas can lead to lung damage in humans and kill plants at high levels.

What climate experts have to say

“That’s a big deal because it means that as we try to limit our pollution locally, it might not work as well as we thought,” said Audrey Gaudel, the study’s lead author and a Cooperative Institute for Research in Environmental Sciences (CIRES) scientist at NOAA. She said that she and her colleagues found the largest increases in ozone in the tropics. Gaudel went on to say that ozone exported from the tropics may cause increases in other areas of the Northern Hemisphere. She and other researchers from CIRES at the University of Colorado Boulder contributed to the study.

Gaudel and her co-authors, CIRES scientists in NOAA and international colleagues, discovered the greatest ozone increases in areas where it had been lowest previously. Malaysia/Indonesia, Southeast Asia, and India, for example, had the highest levels. However, between 1994-2004, those regions had low ozone levels. Between 2011 and 2016, those areas saw dramatic increases.

Gaudel said that prior studies couldn’t draw definite conclusions on the data due to a few long-term monitoring locations. Also, new satellites record data globally, so the results on ozone trends vary widely. Taking this into account, the researchers decided to use aircraft data from Europe’s In-Service Aircraft for the Global Observing System (IAGOS) program.

 “Since 1994, IAGOS has measured ozone worldwide using the same instrument on every plane, giving us consistent measurements over time and space from Earth’s surface to the upper troposphere,” Gaudel said. Between 1994 and 2016, commercial aircraft took 34,600 different ozone measurements or four profiles each day. Using these measurements, Gaudel and her team analyzed changes in tropospheric ozone from the mid-1990s to 2016. They calculated these changes in ozone above 11 regions in the Northern Hemisphere.

A scientists explains these trends

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They discovered an upward trend in ozone in all 11 regions, including four in the mid-latitudes and two in the subtropics. Also, they found an increase in two areas of the tropics and three equatorial regions. On average, the median values had risen by 5% per decade.

In the lower troposphere, which sits closer to Earth, ozone levels have decreased above some mid-latitude regions in Europe and the U.S. Here. Tighter ozone emission controls have led to reductions in pollution. However, these decreases have been offset by increases in the upper troposphere. This resulted in an increase in ozone overall from the surface to 12 km into the atmosphere.

What caused these changes in ozone levels?

The team analyzed emissions of one of the main drivers of ozone increases – nitrogen oxides – to understand what caused these changes. They input this data for the global chemistry transport model MERRA-2 GMI, which accurately reproduces the IAGOS measurements. This model showed that increased emissions in the tropics likely caused the subsequent increase in the Northern Hemisphere.

After taking this data into account, the team wants to focus on the tropics’ ozone levels for future studies. They believe Africa may soon become a global hotspot for air pollution precursors, and the IAGOS data will show recent  trends there. The team will also compare tropical measurements from IAGOS with measurements from the NASA Atmospheric Tomography (ATom) field campaign. This measures small levels of gases and aerosol particles in more isolated, less polluted regions, including tropics.

Finally, the team will eventually analyze measurements from TROPOMI, an instrument on a European Space Agency satellite that gathers data on atmospheric composition.

“We want to understand the variability of ozone and its precursors and the impact of polluted regions on remote regions,” Gaudel said. “So we’re using the best tools we have, including IAGOS, ATom data, and TROPOMI data, to get profiles and columns of ozone and its precursors from different kinds of human activities and natural sources.”

What does this data mean?

With all of this data, they will better understand how pollution affects these levels, especially in areas near the tropics. According to the Climate & Clean Air Coalition, tropospheric ozone air pollution causes around 1 million premature deaths worldwide. It also leads to millions of chronic diseases, especially in the elderly and small children. Furthermore, it results in further warming of the atmosphere, worsening climate change.

In the stratosphere, ozone helps shield life on Earth from the Sun’s potent ultraviolet rays. However, in lower troposphere levels, a build-up leads to human and ecosystem damage. It also contributes greatly to smog, found mostly in large urban cities such as Los Angeles and New Delhi.

Experts say that limiting ozone in lower atmosphere levels boils down to reducing methane and cutting fossil fuels. Also, reducing pollution from agriculture will greatly aid in reducing tropospheric ozone. Ozone causes global crop production losses totaling 79-121 million tonnes, equaling $11-18 billion annually.

Final thoughts on ozone increase due to pollution

Experts have found a direct link between increasing ozone levels and pollution worldwide. Malaysia, Indonesia, Southeast Asia, and India show particularly high levels of ozone in recent years. While emission controls have been enforced in North America and European areas, this only reduces ground-level ozone. In higher levels of the atmosphere, that amount increases, leading to health problems and crop failure.

Climate experts and researchers say that reducing methane and fossil fuel production can lower ozone levels. Greener technologies can lead to better health for humans and the planet, giving us a better quality of life.