The effects of Intensive Supervision Mechanism on air quality improvement in China

The Intensive Supervision Mechanism (hereafter referred to as ISM) is one of the most important institutional management innovations for air pollution control in China, but there is currently no consensus on the effects of the ISM on air quality improvement. In this study, a reliable quantitative model based on the Difference-in-Differences (DID) analysis was designed to evaluate the impacts of ISM on air quality (as indicated by good air quality days (hereafter referred to as GAD) and the concentrations of six major air pollutants (i.e. PM_2.5, PM₁₀, O₃_8H, NO₂, SO₂, and CO)), in China with focuses on the implementation cities of Henan Province. To optimize the model design, six meteorological factors, five socio-economic indicators, and VIIRS (Visible Infrared Imaging Radiometer Suite) data were also considered as alternative control variables for more comprehensive and effective results. In addition, the redundancy analysis (RDA) and Monte Carlo simulation were conducted to determine the optimal combination of those control variables which can best reflect the changes in explanatory variables. The main findings are as follows: (1) the statistical model applied in this study can well evaluate the impacts of ISM; (2) the implementation of ISM can significantly reduce the concentrations of SO_2, CO, and NO₂, but the improvements for PM_2.5, PM₁₀, GAD and O₃_8H were not significant. (3) the potential for air quality improvement due to ISM tends to be reduced over time, and thus the positive effects of ISM at its second stage were not increased significantly compared with those observed during its first stage. In general, those results not only demonstrate the effectiveness of ISM on air quality improvement, but also provide insights into how the ISM can be optimized to gain a sustained improvement of the ambient air quality in the future.Implications: As a policy measure implemented by the Chinese government, the Intensive Supervision Mechanism (ISM) has significantly contributed to the improvement of air quality since its execution. However, the potential for air quality improvement due to ISM tends to be reduced over time, and thus the positive effects of ISM at its second stage were not increased significantly compared with those observed during its first stage. In addition, the implementation of ISM requires a large amount of financial investment, and thus has limited sustainability. Considering the increased difficulty of this policy instrument, whether to insist on the ISM warrants further analyses on its cost and effectiveness. More importantly, more targeted measures of ISM should be applied to decrease the ozone concentration in the future.