In recent years, the Chinese government has proposed a policy to replace coal use with natural gas and electricity in the northern region to reduce the air pollution caused by the large consumption of coal. In order to assess the air pollution reduction effect of the coal substitution policy in Liaoning Province, this paper proposes a data grouping grey model with a fractional order accumulation (FDGGM (1,1)). The empirical analysis results show that the new grey model can predict the monthly coal consumption more accurately than the traditional DGGM (1,1) model. The MAPEs of the training set in the FDGGM(1,1) and DGGM(1,1) models are 4.58% and 5.48%, and the MAPEs of the test set are 23.89% and 33.78%, respectively. And the policy achieves a great success based on the FDGGM(1,1) model. During the policy implementation period (from January 2015 to December 2018), the coal consumption in Liaoning Province decreased by 27.2501 million tons, while the emissions of CO2, SO2 and NOx fell by 0.714, 0.2316 and 0.2017 million tons, respectively. The results also provide a necessary support to the further implementation of the coal substitution policy.
Keywords: Air pollution; Coal substitution policy; FDGGM(1,1); Fractional order accumulation; Grey model; Policy assessment.