Beijing's ozone trends (2013–2023) show a lengthening Ozone Season despite strict emission controls. While low-percentile ozone levels rose, mean and high-percentile values remained stable. Key shifts include a later daily exposure window, flattened diurnal cycles (lower peaks, higher troughs), and reduced ozone production/loss rates. These findings establish a baseline for urban pollution evolution and provide critical insights for future policy formulation and public health protection.

Aerosol-cloud interactions and ice formation processes are key to modelling mixed-phase clouds in cold-air outbreaks. However, no studies have investigated the joint effects of these processes. Here, we used perturbed parameter ensembles and model emulators to show that these processes have strongly interacting effects on the properties of cold air outbreak clouds. Single sensitivity tests may therefore provide incomplete information about cloud-controlling factors.