Responses of fine particulate matter and ozone to local emission reductions in the Sichuan Basin, southwestern China

The Sichuan Basin (SCB) in southwestern China is largely affected by air pollution. Understanding the responses of air pollutant concentrations to emission changes is critical for designing and evaluating effective control strategies. Thus, this study used the Community Multi-scale Air Quality (CMAQ) model to simulate PM₂.₅ (i.e., particulate matter with an aerodynamic diameter ≤ 2.5 μm) in winter (January 2015) and ozone (O₃) in summer (July 2015) under nine emission reduction scenarios. For each scenario, the anthropogenic emissions of each air pollutant in each SCB grid cell were reduced by the same percentage, ranging from 10% to 90%. We found that approximately 30–70% emission reductions are required to reduce the January mean PM₂.₅ concentrations in all the SCB urban centers to a value that is less than the Chinese standard for daily mean PM₂.₅ (24-h PM₂.₅: 75 μg m⁻³). However, the January mean PM₂.₅ concentrations under 90% emission reduction still exceeded the World Health Organization (WHO) guideline (25 μg m⁻³) in 16 SCB urban centers. Moreover, reducing both SCB and non-SCB emissions were critical for achieving the PM₂.₅ level recommended by WHO. An 80% emission reduction was required to prevent the occurrence of 8-h O₃ (i.e., daily maximum 8-h mean O₃) non-attainment days in all SCB urban centers. Under 90% emission reduction, July mean 8-h O₃ concentrations still exceeded the WHO guideline of 47 ppb in approximately 35% of the SCB areas. In conclusion, this study suggests that (1) compared with the governmental emission reduction targets for 2015–2020 (2–27%), more significant emission reductions are required to meet the Chinese and WHO pollution standards; and (2) both SCB and non-SCB emissions must significantly reduce to achieve the desired pollution targets.