Ozone, a gas with a dual nature, presents both benefits and risks depending on its altitude. While it acts as a protective shield against harmful ultraviolet radiation in the stratosphere, ozone closer to the Earth’s surface is a dangerous pollutant, negatively impacting human health and contributing to global warming. Recent trends show ozone levels continuing to rise in the upper troposphere, the atmospheric layer where most aircraft fly, despite efforts to curb ground-level emissions.
A new study published in Environmental Science and Technology by a team of MIT scientists provides compelling evidence linking this increase to human activities. “We confirm that there’s a clear and increasing trend in upper tropospheric ozone in the northern midlatitudes due to human beings rather than climate noise,” states Xinyuan Yu, lead author, and graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).
The complexity of ozone’s behavior makes pinpointing its drivers a significant challenge. Unlike pollutants emitted directly, ozone forms through reactions between precursor chemicals like nitrogen oxides and volatile organic compounds (VOCs) in the presence of sunlight. These precursors originate from various human activities, including vehicle emissions, industrial processes, and power generation.
Disentangling the influence of human activities from natural climate variability on ozone levels, particularly in the upper troposphere, has proven particularly difficult. “Near the surface, ozone has been observed to decrease in some regions, and its variations are more closely linked to human emissions,” Yu explains. “In the upper troposphere, the ozone trends are less well-monitored but seem to decouple with those near the surface, and ozone is more easily influenced by climate variability.”
To isolate the human impact, the researchers employed a novel approach using climate model simulations. They generated multiple scenarios, each with identical human-caused ozone precursor emissions but varying initial climate conditions. This allowed them to identify a distinct signal consistent across all scenarios, a “fingerprint” indicative of human-induced ozone.
Comparing this fingerprint to 17 years of satellite data (2005-2021) from NASA’s Aura satellite, the team found a match, confirming their model’s predictions. The signal was particularly strong over Asia, a region experiencing rapid industrial growth and frequent weather patterns that lift pollutants, including ozone and its precursors, into the upper troposphere.
This study marks a critical step towards understanding and mitigating human impact on ozone levels in the upper troposphere. “Being able to separate human-caused impacts from natural climate variations can help to inform strategies to address climate change and air pollution,” says Arlene Fiore, co-author and Professor in Earth, Atmospheric and Planetary Sciences at MIT. The team’s future research will focus on identifying the specific human activities most responsible for this increase, paving the way for targeted interventions to combat ozone’s contribution to global warming.
Responses (0 )