Spatio-temporal variation of the coupling relationship between urbanization and air quality: A case study of Shandong Province

Over the past 30 years, China's urbanization has strongly supported the rapid growth and sustained transformation of economy; it has also led to a continuous increase in atmospheric environmental stress. A deep understanding of the coupling relationship between urbanization and air quality is essential for evaluating the quality of urbanization and long term sustainability. We first constructed a set of indexes to evaluate the extent of urbanization, and then used the global principal component analysis, harmony degree model, as well as the coupling coordination degree model and Geographic Information System (GIS) to explore the coupling relationship between urbanization and air quality in Shandong Province from 2014 to 2017. The results show that: (1) in 2014, cities with a high coupling coordination degree (D > 0.7) between urbanization and air quality index (AQI) as well as pollutants were mainly distributed in coastal regions of Shandong Province. The coupling relationships between urbanization and AQI and PM2.5 in part of central Shandong were basically uncoordinated (0.3 < D <= 0.5), and that between urbanization and PM10, SO2 and NO2 were severely uncoordinated (D <= 0.3). Cities in the northwest and southwestof the province were seriously uncoordinated; (2) by 2017, the coupling relationship had improved by varying degrees, with 94.12% of all cities becoming coordinated cities in terms of urban development and air quality status. A highly coordinated development was observed in Eastern Shandong, while all cities in central Shandong had also reached a higher level of coordination (0.5 < D <= 1) in terms of both AQI and air pollutants; only Heze in the southwest part of the province remain at uncoordinated status (0.3 < D <= 0.5); (3) The number of cities with urbanization gets ahead decreased from 7 in 2014 to 5 in 2017, indicating that the effect of atmospheric environmental governance had emerged gradually. We concluded by suggesting that those highly coordinated cities should play more leading roles to the surrounding areas in the blue peninsula economic zone; basically coordinated-urbanization gets ahead cities could focus on the joint prevention of pollution with large regions in the process of economic transformation; and those that are basically coordinated (or uncoordinated)-urbanization lags behind need to strength the environmental protection policies and actively integrate into the economic circle of the provincial capital city group and into the western economic rising belt in order to achieve more rapid urban development. (C) 2020 Elsevier Ltd. All rights reserved.