A recent study from MIT highlights a concerning link between global warming and the increasing difficulty of controlling ground-level ozone, a dangerous air pollutant and key ingredient in smog.
The findings provide essential insights for scientists and policymakers aiming to formulate better strategies for enhancing air quality and safeguarding human health. Ground-level ozone is known to cause serious health issues, including asthma and heart disease, leading to thousands of premature deaths annually.
This research employs advanced modeling techniques, revealing that as our planet warms due to climate change, ground-level ozone becomes less responsive to reductions in nitrogen oxide emissions in regions like Eastern North America and Western Europe. Simply put, achieving improved air quality in these areas will require significantly larger cuts in nitrogen oxide emissions.
In contrast, the study indicates that in Northeast Asia, reducing emissions will yield more substantial benefits for lowering ground-level ozone levels in the future.
The team implemented a sophisticated modeling approach that merges a climate model, simulating meteorological factors such as temperature and wind patterns, with a chemical transport model that assesses the movement and composition of atmospheric chemicals.
By examining a range of potential future scenarios, the researchers’ ensemble approach captures inherent climatic variability, providing a more comprehensive understanding than many previous studies.
“As we plan for future air quality, it’s crucial to consider how climate change impacts pollution chemistry. We might need to implement more significant reductions in nitrogen oxide emissions to meet our air quality targets,” explains Emmie Le Roy, a graduate student with MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and the lead author of the study.
Co-authors of this research include Anthony Y.H. Wong, a postdoctoral fellow at the MIT Center for Sustainability Science and Strategy; Sebastian D. Eastham, a principal research scientist in the same center; Arlene Fiore, the Peter H. Stone and Paola Malanotte Stone Professor of EAPS; and senior author Noelle Selin, a professor in the Institute for Data, Systems, and Society (IDSS) and EAPS. This research article appears in Environmental Science and Technology.
Understanding Ground-Level Ozone
Ground-level ozone, distinct from the beneficial ozone layer that protects us from harmful UV radiation, is a dangerous respiratory irritant affecting the health of humans, animals, and plants alike.
Controlling ground-level ozone proves challenging due to its nature as a secondary pollutant formed through complex chemical reactions involving nitrogen oxides and volatile organic compounds, particularly in the presence of sunlight.
“Higher ozone levels are typically observed on warm, sunny days,” Le Roy notes.
Regulatory efforts aimed at limiting ground-level ozone often focus on reducing nitrogen oxide emissions from industrial activities. However, predicting the outcomes of such policies is complicated, as ozone interacts with nitrogen oxides and volatile organic compounds in unpredictable ways.
In certain chemical contexts, lowering nitrogen oxide emissions can ironically lead to increased ground-level ozone levels.
“While previous studies mainly emphasized the role of emissions in ozone formation, the meteorological influence is a crucial aspect of Emmie’s work,” says Selin.
To conduct their analysis, the researchers integrated a global atmospheric chemistry model with a climate model that predicts future meteorological conditions.
The climate model generated meteorological data for each year studied, simulating variables like temperature and wind speeds to account for a region’s natural climate variability.
This data was then fed into the atmospheric chemistry model to assess how emissions and meteorology alter the atmosphere’s chemical makeup.
The research focused on Eastern North America, Western Europe, and Northeast China—regions with historically high levels of ozone precursor chemicals and established monitoring systems.
They evaluated two future scenarios representing high and low warming over a 16-year period between 2080 and 2095, comparing these with a historical scenario from 2000 to 2015 to determine the impacts of a 10 percent reduction in nitrogen oxide emissions.
Addressing Climate Variability
“One of the most significant challenges is that climate naturally fluctuates from year to year. To isolate the effects of climate change, it’s vital to simulate a sufficient number of years to account for that variability,” Le Roy states.
Advancements in atmospheric chemistry modeling and parallel computing have enabled the researchers to simulate multiple years concurrently, resulting in 80 model years across five 16-year realizations for each scenario.
The findings indicate that Eastern North America and Western Europe are particularly sensitive to increases in nitrogen oxide emissions from the soil, driven by rising temperatures.
As the Earth warms and nitrogen oxide from soil gets released into the atmosphere, reducing emissions from human activities will have diminishing returns on ground-level ozone reduction.
“This underscores the importance of enhancing our models to better understand the biosphere’s role in air quality,” emphasizes Le Roy.
Conversely, as industrial emissions in Northeast Asia produce more ozone per unit of nitrogen oxide released, cutting these emissions may lead to more significant reductions in ground-level ozone amid future warming scenarios.
“But this doesn’t imply it’s a favorable situation since it results in overall higher ozone levels,” Le Roy cautions.
Utilizing detailed meteorological simulations instead of relying solely on annual weather averages has provided the researchers with a comprehensive view of potential human health implications.
“Average climate isn’t the only consideration. Just one high ozone day, even if it’s an anomaly, can impede our ability to meet air quality standards, negatively impacting human health,” Le Roy explains.
In the coming years, the researchers aim to continue examining the intersection of meteorology and air quality, expanding their modeling framework to incorporate other climate change factors that exhibit high variability, such as wildfires or biomass burning.
“We’ve demonstrated that it’s crucial for air quality scientists to take into account the full spectrum of climate variability, even if modeling poses challenges, as it fundamentally influences the outcomes,” says Selin.
This research is partially funded by the MIT Praecis Presidential Fellowship, the J.H. and E.V. Wade Fellowship, and the MIT Martin Family Society of Fellows for Sustainability.
Photo credit & article inspired by: Massachusetts Institute of Technology
