Multidecadal ozone trends in China and implications for human health and crop yields: a hybrid approach combining a chemical transport model and machine learning

Abstract

Abstract. Surface ozone (O3) is well known for posing significant threats to both human health and crop production worldwide. However, a multidecadal assessment of the impacts of O3 on public health and crop yields in China is lacking due to insufficient long-term continuous O3 observations. In this study, we used a machine learning (ML) algorithm to correct the biases of O3 concentrations simulated by a chemical transport model from 1981–2019 by integrating multi-source datasets. The ML-enabled bias correction offers improved performance in reproducing observed O3 concentrations and thus further improves our estimates of the impacts of O3 on human health and crop yields. The warm-season trends of increasing O3 in Beijing–Tianjin–Hebei and its surroundings (BTHs) as well as in the Yangtze River Delta (YRD), Sichuan Basin (SCB), and Pearl River Delta (PRD) regions are 0.32, 0.63, 0.84, and 0.81 µg m−3 yr−1 from 1981 to 2019, respectively. In more recent years, O3 concentrations experienced more fluctuations in the four major regions. Our results show that only BTHs have a perceptible increasing trend of 0.81 µg m−3 yr−1 during 2013–2019. Using accumulated O3 over a threshold of 40 ppb (AOT40-China) exposure–yield response relationships, the estimated relative yield losses (RYLs) for wheat, rice, soybean, and maize are 17.6 %, 13.8 %, 11.3 %, and 7.3 % in 1981, increasing to 24.2 %, 17.5 %, 16.3 %, and 9.8 % in 2019, with an increasing rate of +0.03 % yr−1, +0.04 % yr−1, +0.27 % yr−1, and +0.13 % yr−1, respectively. The estimated annual all-cause premature deaths induced by O3 increased from ∼55 900 in 1981 to ∼162 000 in 2019 with an increasing trend of ∼2980 deaths per year. The annual premature deaths related to respiratory and cardiovascular disease are ∼34 200 and ∼40 300 in 1998 and ∼26 500 and ∼79 000 in 2019, having a rate of change of −546 and +1770 deaths per year during 1998–2019, respectively. Our study, for the first time, used ML to provide a robust dataset of O3 concentrations over the past 4 decades in China, enabling a long-term evaluation of O3-induced crop losses and health impacts. These findings are expected to fill the gap of the long-term O3 trend and impact assessment in China.