When Heat Meets Pollution: How Rising Temperatures Intensify Ozone Risks in China and the U.S.

Snow Goose

15-09-2025

Kingfisher: “Sir, I encountered countless small and terrifying ghosts on another night. They swarmed and injected me with needles, each carrying a poisonous substance that caused itch, numbness, pain, and intense heat. I fainted in my dream, and when I woke up, they continued to inject me until my soul left my body, leaving only my skeletal remains.”

In “Ghosts”; Wild Wise Weird [1]

© Andrei Lazarev

Surface ozone (O₃) is not emitted directly but forms when sunlight drives reactions between nitrogen oxides (NOₓ) and volatile organic compounds (VOCs). While ozone high in the stratosphere protects life from harmful radiation, near the ground it is a pollutant that harms human health, agriculture, and ecosystems. As global warming accelerates, scientists are increasingly concerned about the “climate penalty” of heat: higher temperatures that worsen ozone pollution.

A new study by Bao and colleagues [2] compares long-term data from China and the United States to investigate how rising temperatures influence ozone formation. Analyzing monitoring records from 2015 to 2022 with statistical models, structural equation modeling, and photochemical simulations, the researchers uncovered key contrasts between the two countries.

The results show that ozone–temperature sensitivity is stronger in China, with a climate penalty factor of 2.9 μg/m³ per °C compared to 2.1 μg/m³ per °C in the U.S.. This heightened response is linked to China’s higher NO₂ and VOC emissions, which fuel ozone production under heat. In China, ozone levels rise sharply during heatwaves, particularly in the Jing–Jin–Ji region, the Yangtze River Delta, and the Sichuan Basin. By contrast, in the U.S., ozone increases plateau under prolonged heat events, reflecting both different meteorology and more mature emission controls [2].

The COVID-19 lockdowns offered a natural experiment. In China, reductions in traffic and industrial activity curbed ozone during high temperatures, showing that aggressive emission cuts can offset the climate penalty. In the U.S., however, ozone continued to rise during heat events despite lower emissions, underscoring the dominant role of meteorological drivers such as solar radiation and stagnant air masses.

These findings highlight the urgent need for region-specific strategies. China must prioritize coordinated reductions in NOₓ and VOCs, while the U.S. should integrate heat adaptation into air quality management [3-5].

Human activities alter emissions and climate, which in turn reshape atmospheric chemistry and health risks [6]. Recognizing these interdependencies strengthens the society’s Nature Quotient (NQ)—the capacity to understand and act on ecological feedbacks. Elevating NQ in policy, science, and society means seeing heatwaves not just as weather, but as signals of our intertwined future with the atmosphere. Every emission cut reduces not only warming but also the compounding risks of ozone pollution [7].

References

[1] Vuong QH. (2024). Wild Wise Weird. https://books.google.com/books?id=N10jEQAAQBAJ

[2] Bao J, et al. (2025). Comparative analysis of the impact of rising temperatures on ozone levels in China and the United States. npj Clean Air, 1, 23. https://www.nature.com/articles/s44407-025-00023-8

[3] Lu C, et al. (2021). An unusual high ozone event over the North and Northeast China during the record-breaking summer in 2018. Journal of Environmental Sciences, 104, 264-276. https://doi.org/10.1016/j.jes.2020.11.030

[4] Steiner AL, et al. (2010). Observed suppression of ozone formation at extremely high temperatures due to chemical and biophysical feedbacks. PNAS, 107, 19685-19690. http://pnas.org/doi/10.1073/pnas.1008336107

[5] Schnell JL, Prather MJ. (2017). Co-occurrence of extremes in surface ozone, particulate matter, and temperature over eastern North America. PNAS, 114, 2854-2859. https://www.pnas.org/doi/10.1073/pnas.1614453114

[6] Nguyen MH. (2024). How can satirical fables offer us a vision for sustainability? Visions for Sustainability, 23(11267), 323-328. https://doi.org/10.13135/2384-8677/11267

[7] Vuong QH, Nguyen MH. (2025). On Nature Quotient. Pacific Conservation Biology, 31, PC25028. https://doi.org/10.1071/PC25028