A decade of China’s air quality monitoring data suggests health impacts are no longer declining

China's national air quality monitoring network has revealed a rapid improvement in air quality during the 2010s, during which fine particulate matter (PM_2.5) and other priority pollutant levels fell, except for ozone, which concurrently increased. However, recent changes in China's economic outlook mean that the future trajectory of China's air quality is highly uncertain. Here we analyse the last 10 years of air quality monitoring data to assess whether China's air quality has continued to improve in recent years. We find that the period of steep negative trends in PM_2.5 observed during 2014-2019 (-2.47 µg m^-3 year^-1) has ended, slowing to -0.18 µg m^-3 year^-1 during 2021-2024. Meanwhile, ozone levels continued to increase during 2021-2024, with a trend of 2.06 µg m^-3 year^-1. We demonstrate that population PM_2.5 exposure in China can be accurately constrained using only surface monitoring station data, and we use this to estimate future health impacts under three observationally-based future PM_2.5 scenarios. We show that the current government PM_2.5 reduction target is insufficient to sustain the decrease in PM_2.5-attributed mortality that was achieved during 2014-2019, and a ∼2 times more ambitious target is needed to offset the effects of China's ageing population.