Enhancement of ozone formation by increased vehicles emission and reduced coal combustion emission in Taiyuan, a traditional industrial city in northern China

Coal combustion and industrial processes were often the main sources of atmospheric pollutants in traditional industrial cities in northern China. Studies on sensitivity analysis and source apportionment of ozone formation, which are the basis of ozone pollution controlling, are limited in those cities. The systematic observations of ambient Volatile Organic Compounds (VOCs) were performed to better investigate the major anthropogenic sources of summertime O₃ during different O₃ episodes in Taiyuan, a traditional industrial city in northern China. Average mixing ratio of VOCs was 21.80 ppbv during the summer sampling period, and the highest value was measured at the traffic-intensive area. Source apportionment carried by positive matrix factorization model (PMF) showed that VOCs from vehicular emissions exceeded those from coal combustion, and their contributions to the total ambient VOCs were 28.12% and 25.95%, respectively. VOCs limited regime of summertime O₃ formation was revealed by using a photochemistry model. Alkenes group was the most crucial contributor to O₃ formation. Vehicular emissions made the largest anthropogenic contribution (25.35%) to total O₃ formation, while industrial processes with the contribution of 29.81% to O₃ was also unacceptable in high O₃ episodes. Multi-sources joint prevention and control, especially the joint of vehicular emissions and industrial processes emissions, may effectively reduce the summertime O₃ pollution in Taiyuan. Given the vigorous implementation of the coal reform policies and future economic and energy restructuring, effects of vehicular emissions on VOCs and summertime O₃ should become more remarkable, indicating that the implementation of more stringent control strategies of vehicular emissions may be the key to alleviate O₃ pollution in traditional industrial cities in the future.