In August of 2015, China’s National People’s Congress ratified the fourth revision of the Air Pollution Control and Prevention Law (Daqi Wuran Fangzhi Fa). The passage of the law marks the latest milestone in a longstanding struggle to control air pollution in China. As with many other major legal reforms, the effects of this law will likely hinge less on the national government than municipal government’s approach to regulation. The main aim of this paper is to distill some of the key factors underlying different approaches to municipal air pollution regulation in China. Although both located in the Yangtze River Delta, faced with similarly severe air pollution, and under a common set of regulations and policies enacted by the central government, Shanghai and Nanjing took different routes in air pollution prevention and control. The Shanghai municipal government took what may be characterized as a pragmatic approach to air pollution prevention and control. Starting from 2000, the government has issued a set of five incrementally more advanced “Action Plans for Environmental Protection” (2000-2002, 2003-2005, 2006-2008, 2009-2011, and 2012-2014). The sixth Action Plan for Environmental Protection is currently under deliberation. Projects have been planned and carried out under those action plans for achieving better environmental results. Not until 2014 did the Shanghai municipal government codify the Shanghai Ordinance on Air Pollution Prevention and Control. In contrast, the Nanjing municipal government enacted its first Nanjing Ordinance on Air Pollution Prevention and Control in 2004 that was later amended in 2011. In 2010, it then introduced the Nanjing Blue Sky Action Plan (2010-2015). While care should be taken in extrapolating from these differences, it appears that Shanghai moved earlier with more stringent targets and more frequent revisions than Nanjing. A survey of air pollution and ambient air quality data from the past years also suggests that Shanghai has enjoyed more regulatory success than Nanjing. While the paper’s primary objective is to tease out the factors contributed to pragmatic and formalistic choices made by the Shanghai and Nanjing municipal governments, findings from this research may contribute to the literature on policy learning and government accountability more broadly.