Tropical cyclones can help drive heat and ozone pollution far from their path

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NORMAN, Okla. – Tropical cyclones are known for destructive winds and heavy rainfall, but their influence can extend far beyond the storm itself. New research from the University of Oklahoma shows how unusual atmospheric conditions linked to tropical cyclones can contribute to compound extreme heat and ground-level ozone pollution, even far from the storm, increasing risks to human health.

Xiao-Ming Hu, Ph.D., and Chenghao Wang, Ph.D., led the study, with colleagues at OU and Adriana Larrea Valdivia at Universidad Nacional de San Agustín de Arequipa in Peru. The team looked at compound heat and ozone episodes in Oklahoma City during periods influenced by Atlantic tropical cyclones.

“Tropical cyclones can influence weather and air quality far beyond the areas directly affected by the storm,” said Hu, senior research scientist in the Center for Analysis and Prediction of Storms. “Understanding these connections is essential for predicting compound heat and air-pollution hazards and protecting public health.”

The researchers examined three of the worst ozone episodes in Oklahoma City since 2014, focusing on June 2021, when the pollution arrived alongside extreme heat. Using satellite observations and high-resolution atmospheric chemistry modeling, they found that an unusual combination of regional weather patterns and pollutant emissions contributed to the compound event.

During the June 2021 episode, persistent northeasterly winds transported pollutants from the Tulsa metropolitan area toward Oklahoma City. At the same time, weak winds ahead of an approaching front reduced atmospheric ventilation over Oklahoma City, allowing pollutants to accumulate and enhancing conditions favorable for ozone formation.

The findings show how extreme heat and air pollution in one city can be influenced by emissions and atmospheric processes far beyond the local area. They also highlight how large-scale weather systems, including those associated with tropical cyclones, can reorganize regional atmospheric circulation and pollutant travel far from a storm’s direct path.

Recent events illustrate why these long-distance connections deserve greater attention. According to the researchers, Typhoon Dolphin, which made landfall in eastern China in August 2026, demonstrates tropical cyclones' far-reaching influence. Dolphin coincided with compound extreme heat and ozone pollution episodes across parts of the North China Plain, including Shenyang, illustrating how tropical cyclones affect air quality.

Heat and polluted air each threaten health. When they arrive together, the threat grows. Compound episodes, when extreme heat and high levels of pollution occur at the same time, are an increasing danger to public health, especially for people in cities, according to earlier OU research. According to the National Weather Service, in 2025, Extreme heat was the deadliest weather hazard in the country, causing more deaths that year than any other weather-related hazard.

“This study is part of our broader effort to understand compound heat and ozone pollution across U.S. cities,” said Wang, an assistant professor in the School of Meteorology and Department of Geography and Environmental Sustainability. “An important question is how much of a city’s air pollution comes from local emissions versus emissions transported from other regions. Understanding these local and non-local contributions, and how they interact with extreme weather, can help us better assess and predict compound heat and air-pollution risks.”

The OU team plans to investigate these interactions across more tropical-cyclone events and geographic regions to improve predictions of compound extreme heat and air-pollution events worldwide.