Many countries are attempting to reduce energy consumption and CO2 emissions while increasing the productivity and efficiency of their industries. An undesirable-output-oriented data envelopment analysis (DEA) model with slacks-based measure (SBM) was used to evaluate the changes in the environmental efficiency of the transportation sector in 30 Chinese provinces (municipalities and autonomous regions) between 2003 and 2012. The potential for decreasing CO2 emissions and energy saving was also assessed. Transportation was found to be inefficient in most of the provinces and the average environmental efficiency was low (0.45). The overall average efficiency reached a maximum in 2005 and continually decreased until a minimum was reached in 2009; since then, it has increased. In general, transportation is more efficient in eastern than in central or western China. A sensitivity analysis was also carried out on the input and output indicators. Based on these findings, some policies are proposed to improve the environmental efficiency of the transportation sector in China.
Vehicular emissions have become one of the important sources of air pollution, and their effective control is essential to protect the environment. The Chengdu-Chongqing Urban Agglomeration (CCUA), a less developed area located in the southwest of China with higher vehicle population and special topographic features, was selected as the research area. The aims of this study were to establish multi-year vehicular emission inventories for ten important air pollutants in this area and to analyze emission control policy scenarios based on the inventories. The results showed that the ten vehicular pollutant emissions had differences during the past decade, and CO2 and NH3 increased markedly between 1999 and 2015. Chengdu and Chongqing were the dominant contributors of vehicular emissions in the CCUA. Eight scenarios based on these inventories were designed and the alternative energy replacement scenario was studied from the life-cycle perspective. Compared with the business as usual scenario, elimination of substandard vehicles scenario is the most effective policy to control NOx, PM2.5, PM10, and CH4 emissions; the radical alternative energy replacement scenario could decrease the vehicular NMVOC, CO2, N2O, and NH3 emissions; the elimination of motorcycles scenario could decrease the vehicular CO emissions; and the raising fuel standards scenario could reduce vehicular SO2 emissions significantly (by 94.81%). The radical integrated scenario (combining all of the reduction control measures mentioned above) would achieve the maximum emission reduction of vehicular pollutants CO, NMVOC, NOx, PM2.5, PM10, CO2, N2O, and NH3 compared with any scenario alone.
Xi’an is a key city for air-pollution prevention and control in China, and its near-ground ozone (O3) pollution has become a key issue whose resolution is urgent. The spatial and temporal variations in ozone pollution and their relationship with meteorological factors, transport pathways, and potential source distribution in Xi’an City were investigated in this study using the backward trajectory clustering analysis, potential source contribution function (PSCF), and concentration weight trajectory (CWT) methods coupled with the hourly ozone-mass concentration observations and meteorological data from 2014 to 2020. The results indicate that Xi’an City has suffered from increasingly severe ozone pollution in recent years. Overall, the annual average mass concentration of O3_8h_max presented an upward trend, exhibiting a 34.94% increase from 2014 to 2020. A seasonal variation peak occurred in summer, and the monthly variations featured an inverted “V” shape. Furthermore, the diurnal variation was significantly affected by the near-surface atmospheric photochemical process, showing a discernible single-peak and single-valley distribution with a peak between 15:00 and 17:00. The O3 concentration demonstrated a significant linear positive correlation with surface temperature and sunshine duration. When the relative humidity was 30~50%, the temperature was above 30 °C, and the wind speed was ≤4 m/s, high-concentration O3 pollution was liable to occur. The transmission mainly relied on short-distance airflow during periods of heavy O3-polluted weather. In this context, in addition to local O3 generation, high O3 concentrations were also affected by the large NOx and VOC emissions from heavy industries in neighboring cities in Shaanxi Province, southwest Shanxi Province, and northern Henan Province. Therefore, joint prevention and control measures on the O3 pollution in Xi’an City must be adopted throughout the Fenwei Plain area with the aim of strictly controlling the emissions from regional pollution sources.
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