Southwest Ohio has been known for PM2.5 issues due to emissions from multiple local sources, such as industry and multimodal traffic, as well as regional impacts from sulfates, nitrates, and ammonia. To better understand the speciation characteristics of PM2.5 in this area, data from five monitoring sites, Taft, Hook Field, St. Bernard, Lower Price Hill, and Chase, were studied for the time period of 2003 to 2013. The total concentration of PM2.5 has decreased significantly since the last decade, from 13.41 µg m–3 in 2003 to 10.55 µg m–3 in 2013. The overall PM2.5 concentration also exhibited seasonal variations, with four out of five of the highest concentrations occurring in summer and the fifth one occurring in winter. Due to various air pollution control measures (such as the Cross-State Air Pollution Rule, and Mercury and Air Toxics Standards), both the total concentrations and the speciation of PM2.5 have changed over time. The most dominant components of PM2.5 include sulfates, organic matter (OM), and nitrates, which contributed 33.4%, 31.7%, and 17.7%, respectively (Taft data from 2009 to 2013). Elemental carbon (EC) and crustal materials, on the other hand, accounted for much smaller portions—2.84% and 3.61%, respectively. The highest concentrations of sulfate occurred in summer, while those for nitrates occurred in winter. EC and OM followed the same seasonal trends, peaking in fall and summer and dropping to their lowest levels in winter. Crustal materials exhibited the lowest concentrations in winter. A comparison of Cincinnati (the Taft site) with other major cities nearby reveals that the highest concentration of PM2.5 and the largest fraction of sulfates is found in Cincinnati. Efforts to control these emissions are still necessary.