The study analyzed how tropospheric ozone levels in different layers of the atmosphere changed in China from 2005 to 2020. They found that ozone in the lower part increased each year, while ozone in the middle part decreased. These changes were influenced by factors like nitrogen oxides reduction, volatile organic compounds increase, vegetation growth, higher temperatures, and boundary layer height. The findings suggest that human activities and environmental changes have a significant impact on ozone levels in China over the past 15 years.