Elucidating Tropospheric Radical Chemistry and Atmospheric Oxidation Capacity: Insights from the EXACT Campaign in China

Atmospheric radicals are central to the oxidation capacity and self-cleansing ability of the troposphere, driving the formation of secondary air pollution and the removal of short-lived climate forcers such as methane (CH₄) and hydrofluorocarbons (HFCs). Understanding radical chemistry is thus critical for air quality improvement and climate change mitigation. While tropospheric radical chemistry has been extensively studied since the 1990s, significant gaps remain, particularly in the underestimation of hydroxyl (OH) and hydroperoxyl (HO₂) radicals under low- and high-NO concentration regimes, respectively. These gaps hinder the development of effective pollution control and climate mitigation strategies.

In this study, we introduce the Ensembled eXperiment of Atmospheric oxidation Capacity in the Troposphere (EXACT) campaign conducted in China. This comprehensive initiative employs state-of-the-art instrumentation to measure key radicals (OH, HO₂, RO₂, NO₃) and their precursors, covering diverse chemical and environmental conditions across urban, regional, and background settings in the North China Plain. Seasonal campaigns conducted in autumn, winter, spring, and summer aim to unravel the molecular-level sources and transformation mechanisms of atmospheric radicals. The research further seeks to elucidate the evolution patterns and driving mechanisms of atmospheric oxidation in critical regions of China.

This presentation will provide an overview of the EXACT campaign design and methodology, alongside preliminary results and discussions from the completed autumn and winter campaigns. These findings offer new insights into diurnal radical sources, transformation pathways, and the broader implications for atmospheric oxidation dynamics in China.