Air quality and synergistic health effects of ozone and nitrogen oxides in response to China's integrated air quality control policies during 2015–2019

O pollution had been worsening in mainland China in the past decade, posing significant human health challenges. The NO control would trigger increasing O concentrations in response to a series of released China emission reduction policies. This study used sensitivity analysis methodology to explore the effectiveness of integrated sectoral emission control policies that have been expanded throughout China. Air quality and synergistic health effects of O and NO were investigated to obtain an in-depth understanding of the O control, especially under a VOC-limited regime. The findings demonstrated that although the NO-titration effect triggered an increase in O, the combined health effects of two pollutants tended to improve in most regions of China under a VOC-limited regime. The region-based annual average NO concentrations exhibited a larger reduction in Hong Kong (HK) than in the Pearl River Delta Economic Zone (PRD EZ). The short-term measures led to substantial health benefits for Shenzhen and HK. The sectoral emission controls demonstrated a considerable health improvement for the major PRD EZ cities. Joint national control efforts confined the domain-wide health risks below the safety line in China. National cooperative efforts in China could avoid more than 1.5–2% of the emergency hospital admissions for cardiovascular and respiratory diseases attributed to NO and O exposure. The observed O increases due to the NO-titration effect for calculating the integral health effects of emission control on concentration reduction called for simultaneously strengthened controls on both NO and VOC in areas subject to a VOC-limited regime.