Health impacts under different ozone mitigation pathways in Beijing-Tianjin-Hebei and its surroundings.

To evaluate the effects of the various ozone (O) control approaches on environmental health and health inequalities, 121 reduction scenarios for nitrogen oxides (NO) and volatile organic compounds (VOCs) were developed, and their environmental health impacts were calculated. With the target of achieving the 90th percentile of the daily maximum 8 h mean O concentration (MDA8-90th) of 160 μg/m in Beijing-Tianjin-Hebei and its surroundings ("2 + 26" cities), three typical scenarios namely, High-NO reduction ratio (HN, NO/VOCs = 6:1), High-VOCs reduction ratio (HV, NO/VOCs = 3:7), and Balanced reduction ratio (Balanced, NO/VOCs = 1:1) were investigated. The results show that O formation is currently NO-limited at the regional scale, while some developed cities are VOC-limited, indicating that NO mitigation should be the core for achieving the targeted concentration (160 μg/m) at the regional scale, whereas cities such as Beijing in the short term should focus on VOCs mitigation. The population-weighted O concentrations in the HN, Balanced, and HV scenarios were 159.19, 159.19, and 158.44 μg/m, respectively. In addition, the O-related premature mortality was 41,320 in "2 + 26" cities; control measures under HN, Balanced, and HV could potentially decrease O-related premature deaths by 59.94 %, 60.25 %, and 71.48 %, respectively. The HV scenario has been found to be more advantageous in lowering the O-related environmental health impacts than the HN and Balanced scenarios. It was further found that premature deaths avoided by the HN scenario were mainly concentrated in economically unadvanced regions, whereas those prevented by the HV scenario were mainly concentrated in developed cities. This may lead to geographical inequities in environmental health. As ozone pollution in large cities with high population density is primarily VOC-limited, decrease in VOCs should be focused on in the short term to avoid more O-related premature deaths, whereas NO control may be more important in decreasing ozone concentrations and ozone-related mortality in the future.