Roadmap of coordinated control of PM2.5 and ozone in Yangtze River Delta

As dynamic growth engine of the economy of China, the Yangtze River Delta (YRD) region is one of the most densely populated regions around the globe with advanced industrial cluster and developed transportation network, which has brought the problem of high intensity of air pollutant emissions including nitrogen oxides (NOx), volatile organic compounds (VOCs), etc. Although PM2.5 air quality tremendously improved in recent years, ozone concentration showed an increasing trend, resulting in air pollution characterized by simultaneous high concentrations of PM2.5 and ozone. According to the 2020 Chinese Ecological and Environment Quality Bulletin issued by the Ministry of Ecology and Environment of China, 46% and 32% of the YRD cities are still above the Chinese air quality standards for PM2.5 and ozone respectively. Thus, coordinated control of PM2.5 and ozone has become the focus of improving air quality within the region. Facing the challenges of both climate change and air pollution, as a leading demonstration area in China, how can the YRD region first achieve the goal of simultaneous mitigating PM2.5 and ozone in the context of coping with climate change? In this study, based on a socio-economic development forecast framework coupled with the high-resolution air pollution emission inventory for the YRD region and the WRF-CMAQ air quality model, we simulated the improvement of regional air quality under different policy scenarios. The results show that the green low-carbon scenario (CP) has higher emission reduction potential than the business-as-usual (BAU) scenario and the more progressive scenario of end-of-pipe (EP) control policy, making it an important path in building a beautiful and green Yangtze River Delta in the long term. Under the CP scenario, compared to 2017, it is estimated that SO2, NOx, non-methane volatile organic compounds (NMVOCs), and primary PM2.5 emissions will decrease by 55.1%, 26.5%, 25.2%, and 27% in 2025; and 66%, 56.4%, 36.1% and 39.4% in 2035. The annual average PM2.5 concentration and the 90th percentile of daily maximum 8-h average ozone concentration (O-3-8 h 90th) in YRD will reach 26 and 129 mu g m(-3), respectively by 2035, with 50% of 41 municipal cities in the region will even meet the standards in WHO IT-2. We show that to continuously improve the regional air quality, nationwide collaborations in the implementation of the strengthened abatement measures are needed in the medium and long-term attempts to simultaneously mitigate PM2.5 and ozone pollution. In the short- and medium-term, the end-of-pipe control scenario driven by the goal of "beautiful and green Yangtze River Delta" will play an important role in air pollution control. Starting from 2030, low-carbon policies driven by carbon neutral goals are expected to contribute significantly to the further reductions of both PM2.5 and ozone. To summarize, continuous and vigorous abatement in NOx and NMVOCs is the key to mitigate PM2.5 and ozone pollution, and to achieve the current national air quality standard for both PM2.5 and ozone, the NOx and NMVOCs emissions are expected to be reduced at least by 56% and 40% respectively, compared to 2017. The existing end-of-pipe control policy, in combination with other measures, including industrial restructuring, especially for NMVOCs-emission related industries (i.e. , industrial coating, petrochemical, chemical, rubber and plastics, pharmaceuticals), transportation restructuring, as well as the promotion of clean energy vehicles, non-road vehicles and ships are thus important means to the pollution control in the medium and long-term development in YRD region.