Pathways toward PM2.5 air quality attainment and its CO2 mitigation co-benefits in China's northern cities by 2030

Rapid economic development and urbanization have left millions of people in urban areas vulnerable to the adverse effects of air pollution. Reducing serious PM2.5 pollution remains a major policy challenge for Chinese cities, such as the "2 + 26" Cities in the most polluted region of China, despite adopting various air pollution-control measures since 2017. In this study, we use a Greenhouse Gas and Air Pollution Interactions and Synergies model for the "2 + 26" Cities to explore feasible pathways for achieving the PM2.5 air quality annual standard (35 & mu;g/m3) until 2030 by developing four future scenarios based on a 2017 emission inventory. The results show that by continuing the control policies from before 2020, including the Air Pollution Prevention and Control Action Plan from 2013 and the Three-Year Action Plan for Wining the Blue Sky Defense Battle from 2018, and implementing the policies likely to be proposed after 2020, the "2 + 26" Cities will not succeed in achieving the standard by 2030; furthermore, the amount of the population living below 35 & mu;g/m3 will not exceed 12%. Nevertheless, by combining the best available technologies, the regional average PM2.5 concentration in the "2 + 26" Cities is 34 & mu;g/ m3 by 2030, attaining the target; moreover, more than half of the population will experience air quality that conforms to the standard. Under this scenario, emissions of primary PM2.5, SO2, NOx, NH3 and NMVOCs are estimated to decrease by 75%, 69%, 76%, 32% and 52%, respectively, in 2017-2030. The emission reductions under alternative scenarios vary widely across cities, indicating the need for differentiated control strategies among cities. Considering the predominant contributions to emissions and the lack of effective control measures, fuel conversion, off-road, agricultural and solvent use sectors should be paid more attention to enable further emission reductions in future. In addition, CO2 emission reduction co-benefits of implemented clean air action measures have been identified; however, the negative reduction effects of these measures should be given more attention (e.g., increased carbon emissions in the power sector from electrification of end-users).