Figure. Interactions between air pollution and methane budget

Supported by the National Natural Science Foundation of China (42305101, 42375096, and 22188102), the research team led by Associate Professor Yuanhong Zhao from Ocean University of China and Associate Professor Bo Zheng from Tsinghua Shenzhen International Graduate School, in collaboration with international partners, has achieved progress in the field of global methane budget. The study, entitled " Air pollution modulates trends and variability of the global methane budget", was published online in Nature on May 28th, 2025. Paper link: https://www.nature.com/articles/s41586-025-09004-z.

Methane is the second-largest greenhouse gas, following  carbon dioxide (CO₂). The rapid increase in global methane concentrations has raised concerns about its sources, sinks, and the mechanisms regulating its atmospheric budget. The hydroxyl radical (OH^•) is the most important methane sink. However, a comprehensive quantification of how air pollutants influence OH^• and methane over decadal timescales remains incomplete. Traditional studies have typically relied on either observational data or atmospheric model simulations alone, making it difficult to fully capture the complex interactions among air pollutants, OH^• concentrations, and methane sinks.

To address this research gap, the research team developed an integrated framework that couples atmospheric observations with process-based modeling. This approach systematically analyzed how spatiotemporal variations in key OH^• precursors influenced global OH^• levels and the methane budget from 2005 to 2021. The results show that long-term increases in tropospheric ozone and water vapor, along with a decline in carbon monoxide (CO) concentrations, contributed to a 1.3–2.0 Tg yr^-2 increase in the global methane sink. This partially offset the accelerated methane growth driven by rising emissions. On interannual timescales, periods of unusually high methane growth were typically linked to abrupt OH^• level declines driven by fluctuations in air pollutants, especially during extreme events like mega wildfires and the COVID-19 pandemic.

This study reveals the complex regulatory mechanisms of air pollution in modulating the global methane budget and highlights the importance of accounting for synergistic effects between air quality and climate policies. The integrated observation–model framework introduced here offers a new tool for monitoring and assessing global OH^• variability and its implications for methane sinks. These important findings have both theoretical and practical implications for developing science-based strategies to control air pollution and mitigate climate change.