Identifying convergence in nitrogen oxides emissions from motor vehicles in China: A spatial panel data approach

Motor vehicles have become an important source of nitrogen oxides (NOx) emissions in China. It is critical to identify the development trend of NOx emissions from motor vehicles (NOV). This study revealed the spatial distribution changes of NOV during 2006–2015. Moreover, we emphasized the verification of the convergence in cross-province NOV per capita (NOVPC) and NOV per vehicle (NOVPV), and we applied a kernel density estimation approach and a dynamic spatial convergence model to examine σ and β convergence, respectively. The results showed that the total NOV and NOV proportion both presented significantly increasing trends. In addition, provincial NOV, NOVPC, and NOVPV were found to be positively spatially autocorrelated. The kernel density estimates showed that NOVPC diverged from 2009 to 2012 and converged after 2012, while NOVPV showed a convergence trend during the entire sample period. The spatial β convergence model results confirmed both absolute and conditional β convergence in provincial NOVPC and NOVPV. Furthermore, the speed of absolute convergence was lower than that of conditional convergence. Lastly, increases in vehicles per capita and traffic pressure were responsible for the growth in NOVPC and NOVPV, although the growth of NOVPC was also attributed to rapid urbanization, while technological progress could play a decisive role in reducing NOVPV.