An Analysis of Cointegration Relationship between Public Transportation and Air Quality of Healthy Cities

We constructed a cointegration analysis model of public transit and healthy urban air quality was constructed to quantify the impact of public transportation on urban air quality. The annual average concentration of sulfur dioxide was selected as the air quality index, and the share index of public transit by all modes was selected as the public transit index. Unit root tests were performed on the raw data of indexes by DF-GLS test and KPSS test, which were all shown as non-stationary sequences. After the first difference processing, the data were presented as stationary sequences. The result shows that a long-term equilibrium relationship exists between the two indexes. A Granger causality test showed that the share index of public transit by all modes is the Granger cause of the annual average value of sulfur dioxide concentration, while the latter is not the Granger reason of the former.