Evaluation of coupling relationship between urbanization and air quality based on improved coupling coordination degree model in Shandong Province, China

Accurately elucidating the coupling coordination relationship (CCR) between urbanization and air quality is an important prerequisite for improving their coordinated development and realizing new urbanization. In previous studies, a traditional coupling coordination degree model (CCDM) was used whose contribution coefficients of urbanization and air quality are assumed equal, which is inconsistent with the facts and could easily mislead decision makers, resulting in mistaken choices and policies. In addition, because the traditional CCDM is a static model, it cannot reflect the dynamic CCR between the two during the study period. This paper introduced an improved CCDM and a dynamic decoupling model to explore and elucidate the CCR between urbanization and air quality during 2013–2019. Our results revealed the following: (1) The static CCR between urbanization and air quality in Shandong Province shifted from moderate to good coordination during the study period. The dynamic CCR between urbanization and air quality includes weak decoupling, expansive negative decoupling and expansive connection, of which expansive negative decoupling is the main type. (2) The contribution coefficients α and β of the CCDM affects not only the magnitude but also the type of coupling coordination degree. Compared with the traditional model, the improved model can reflect the CCR between urbanization and air quality more objectively and accurately, and thus provide more reliable and useful information for effective decision-making. (3) Using both the improved model and Tapio’s decoupling model, the CCR between urbanization and air quality and its changing trends can be accurately and comprehensively grasped from static as well as dynamic perspectives, providing a timely scientific basis for decision makers to formulate reasonable proactive and reactive measures