基于空间计量模型的中国城市化发展与城市空气质量关系

采用中国289个地级及以上城市2016年的空气质量指数（AQI）和夜间灯光数据，运用空间滞后模型，从空间溢出效应视角出发探究了城市化发展与空气质量之间的定量关系。从空间滞后模型的估计结果来看，城市空气污染存在显著的空间溢出效应，周边地区空气质量的下降会导致本地空气污染情况加重。在城市发展过程中，城市经济发展水平的提高，引致的城市建设用地的扩张使得空气质量不断恶化；政府管制力的加强对空气污染的治理起到了促进作用，而居民环保意识和城市技术创新水平的提高有利于空气质量的改善。此外，PM2.5质量浓度的上升导致空气质量恶化。公路货运量在统计上与空气质量的关系不显著。从研究结果来看，协调城市发展与空气质量的关系以及加强空气污染防治的联防联控机制，是未来空气污染治理工作的重点。

Impact of Urbanization on Urban Air Quality Based on Spatial Econometric Models

China has been experiencing rapid urbanization and has also suffered from a serious air pollution problem. Hence, the main aim of this research was to investigate how urbanization affects air pollution in China based on a unique cross-sectional dataset of 289 cities in China for the year 2016. Specifically, we used the Air Quality Index (AQI), an accurate, well-recognized, and comprehensive indicator, to describe urban air pollution and employed nighttime light data to denote urbanization levels. Then, we considered spatial spillover effects and applied spatial lag models to test the impact of urbanization on air pollution. The findings of the study are as follows. From the results of spatial autocorrelation tests for the air pollution of the 289 cities by means of four spatial weights matrices, we observed that the air pollution of the cities exhibited strong spatial clustering. Additionally, according to the results of the spatial lag models, we found that the spatial autoregressive coefficient was statistically significant and positive, indicating that spatial spillover effects were present. In other words, local air quality is affected by the air pollution of neighboring cities. In addition, the variable of urbanization was also found to be significant and positive, implying that urbanization has a positive impact on air pollution. A possible interpretation is that the increase in the level of the urban economy at the early stage of rapid urban sprawl increases built-up areas and subsequently degrades the air quality of the city. The variable of regulation was found to be significant and positive. This was the case because close relationships between governments and enterprises hinder air pollution prevention and control because of lower and laxer environmental regulations to increase the competitive advantages of local firms and contribute to the local economy. However, the environmental awareness variable was found to have a negative impact on the AQI. It is projected that air pollution will be reduced greatly as income levels and environmental awareness continue to increase. Regarding the variable of PM2.5, the primary air pollutant, an increase in PM2.5 concentrations drives up the AQI because the estimated coefficient is significantly positive. Lastly, we observed that the variable of highway freight traffic was highly insignificant. One possible reason for this result is that we lack a satisfactory indicator for this variable. From the above analysis, policy implications based on the findings of the research may be threefold. One is that the trade-off between urbanization development and air quality cannot be overstated because the severe problem of urban air pollution poses a huge threat to the sustainability of China’s cities. The second is that making joint efforts and implementing efficient regional policies by local governments to prevent and control urban air pollution should be the first priority in an attempt to realize long-term and sustainable urban development. The last one is that innovation capacities should be increased and encouraged by local governments through a series of policies, e.g., tax relief, because improvements in the technological levels of cities will promote efficiency of cities and reduce air pollutant emissions, which may help to improve air quality and the environment.