High temperatures worsen ground-level Ozone production, creating a dangerous combination of extreme heat and poor air quality. This poses a significant risk to vulnerable populations such as children, seniors, and individuals with respiratory illnesses.

China, like the rest of the world, is experiencing rising temperatures and more frequent heatwaves. However, due to its rapid development and energy-intensive practices, China is also facing an increase in the production of ozone precursors, volatile organic compounds (VOCs), and oxides of nitrogen (NO_x). This poses a major health threat, particularly in densely populated urban areas like Beijing.

A collaborative team of researchers from the Harvard-China Project at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Hong Kong Baptist University has now identified large-scale climate patterns that can predict the occurrence of heatwaves and ozone days in China months in advance. These predictions, similar to those for hurricanes and wildfires, can help the government prepare and implement strategies to reduce the severity of these occurrences.

The study, published in the Proceedings of the National Academy of Sciences, provides valuable insights for agencies such as China’s Ministry of Ecology and Environment to prepare for high heat and Ozone Levels.

Lead author Fan Wang emphasizes the importance of this research, stating, “Our research could have important implications in the future that would allow agencies such as the Ministry of Ecology and Environment in China to prepare for high summer heat and ozone in springtime.”

The research team, led by Professor Michael McElroy and Professor Meng Gao, analyzed past meteorological data and daily ozone levels to identify patterns that indicate the likelihood of extreme heat and ozone levels. As daily observations of ground-level ozone concentrations are limited, the team used a sophisticated machine learning model to reconstruct ozone levels dating back to 2005. They found that sea surface warming in the western Pacific Ocean, the western Indian Ocean, and the Ross Sea off the coast of Antarctica preceded summers with high heat and ozone in northeast China.

These warming ocean regions lead to reduced precipitation, cloud cover, and circulation in the North China Plain, which is home to approximately 300 million people. The team’s model successfully correlated these anomalies with increased heatwaves and ozone levels about 80% of the time.

By utilizing these predictions, government agencies can issue early warnings for human health and agriculture and take proactive measures to reduce ozone and its precursors in the atmosphere before extreme heatwaves occur.

Professor McElroy expresses excitement about the findings, stating, “The ability to forecast unusually hot summers and high levels of summertime ozone in China based on temperature patterns observed months earlier in remote ocean regions is truly remarkable.”

The co-authors of the study include Yihui Ding, Zhiwei Wu, Yangyang Xu, Xiao Lu, Zifa Wang, and Gregory R. Carmichael.