This paper investigates the influence of internationally-transported pollution on China, with a specific highlight on the formation of secondary PM2.5 in the form of nitrate. While sources from within China have traditionally been of most interest for domestic air quality policy, these have diminished over recent years, so sources from outside China may become more significant. The topic of transboundary exchange of air pollution has long been studied in other parts of the world, in particular among CLRTAP signatory countries in North America and Europe, but East Asian transboundary pollution represents a different challenge, in part owing to differences in geography and emissions, but also compared to Europe in particular, the transportation scales are much larger. This work not only quantifies the impacts of long distance pollution on Chinese air quality, but also highlights the complex chemical interactions between the local and transboundary pollutants. Papers such as this will likely influence the debate regarding international controls of air pollutants.