[Scenario Analysis of PM_2.5 Concentration Targets and Milestones in China]

Reports of decreasing PM_2.5 concentrations in some developed countries and regions, as well as the trends of annual average concentrations of PM_2.5 in the 74 key cities of China from 2013 to 2016 were analyzed. The cities were categorized based on PM_2.5 concentration ranges and the regions where they are located. The average annual declining rates of PM_2.5 concentration were calculated for these categories. Based on previous PM_2.5 rates, we proposed different scenarios of decreasing PM_2.5 concentration in Chinese cities for the future decades. Future PM_2.5 concentration was calculated for each of the Chinese cities, and the milestones for 31 provinces and key areas were analyzed. The results showed that the annual average concentration of PM_2.5 in China could meet the national air quality standard by 2025 and drop below 30 μg·m^-3 in 2030 under both scenarios. The PM_2.5 concentration in Beijing-Tianjin-Hebei and surrounding areas could meet the standards in 2030, and the Yangtze River Delta area in 2025. It will be difficult for Beijing, Tianjin, Hebei, and Henan to meet the standard in 2030. Even in the scenario where measures were intensified in the key areas, the cities failed to meet the PM_2.5 concentration standards. In Beijing-Tianjin-Hebei and surrounding areas, the values were close to 40% of the target by 2030. To accelerate the reduction of PM_2.5 concentration, extreme efforts will be needed in the highly polluted areas.