Mass concentrations of chemical compounds in both PM<sub>2.5</sub> (particle aerodynamic diameter, Dp < 2.5 μm) and PM<sub>2.5-10</sub> (2.5 < Dp < 10 μm), and acidity of aerosol particles were measured at an urban site in western Japan using a continuous dichotomous Aerosol Chemical Speciation Analyzer (ACSA-12) throughout 2014.