Evaluating spatiotemporal variations and exposure risk of ground-level ozone concentrations across China from 2000 to 2020 using satellite-derived high-resolution data

Abstract. Understanding the spatiotemporal characteristics of long- and short-term exposure to ground ozone is crucial for improving environmental management and health studies. However, such studies have been constrained by the availability of high-resolution data. To address this, we characterized ground-level ozone variations and exposure risks across multiple spatial (pixel, county, region, and national) and temporal (daily, monthly, seasonal, and annual) scales using daily 1-km ozone data from 2000 to 2020, derived from satellite LST data via a machine-learning method. The model provided reliable estimates, validated through rigorous cross-validation and direct comparison with external ground-level measurements. Our long-term estimates revealed seasonal shifts in high-exposure ozone centers: spring in eastern China, summer in the North China Plain (NCP), and autumn in the Pearl River Delta (PRD). A non-monotonous trend was observed, with ozone levels rising from 2001–2007 at a rate of 0.47 μg/m³/year, declining after 2008 (-0.58 μg/m³/year), and increasing significantly from 2016–2020 (1.16 μg/m³/year), accompanied by regional and seasonal fluctuations. Notably, ozone levels increased by 0.63 μg/m³/year in summer in the NCP during the second phase, and by 6.38 μg/m³/year in autumn in the PRD during the third phase. Exposure levels over 100 μg/m³ have shifted from June to May, and levels exceeding 160 μg/m³ were primarily seen in the NCP, showing an expanding trend. Our day-to-day analysis highlights the influence of meteorological factors on extreme events. These findings emphasize the need for stronger mitigation efforts.