Estimating Spatiotemporal Variation in Ambient Ozone Exposure during 2013-2017 Using a Data-Fusion Model

Since 2013, clean-air actions in China have reduced ambient concentrations of PM2.5. However, recent studies suggest that ground surface O-3 concentrations increased over the same period. To understand the shift in air pollutants and to comprehensively evaluate their impacts on health, a spatiotemporal model for O-3 is required for exposure assessment. This study presents a data-fusion algorithm for O-3 estimation that combines in situ observations, satellite remote sensing measurements, and model results from the community multiscale air quality model. Performance of the algorithm for O-3 estimation was evaluated by five-fold cross-validation. The estimates are highly correlated with the in situ observations of the maximum daily 8 h averaged O-3 (R-2 = 0.70). The mean modeling error (measured using the root- mean-squared error) is 26 mu g/m(3), which accounts for 29% of the mean level. We also found that satellite O-3 played a key role to improve model performance, particularly during warm months. The estimates were further used to illustrate spatiotemporal variation in O-3 during 2013-2017 for the whole country. In contrast to the reduced trend of PM2.5, we found that the population-weighted O-3 mean increased from 86 mu g/m(3) in 2013 to 95 mu g/m(3) in 2017, with a rate of 2.07 (95% CI: 1.65, 2.48) mu g/m(3) per year at the national level. This increased trend in O-3 suggests that it is becoming an important contributor to the burden of diseases attributable to air pollutants in China. The developed method and the results generated from this study can be used to support future health-related studies in China.