Scattering enhancement factor, f(RH), is used to measure the effect of ambient relative humidity (RH) on scattering coefficient of aerosols. In this study, we use ground instruments, namely, a visibility meter, an integrating nephelometer, an aethalometer, a lidar, and a weather monitor to measure f(RH) and to obtain a model of the annual variation of f(RH) in Chiba city, Japan. In the first approach, chemical analysis data are exploited for calculating f(RH). Second, we use visibility and aethalometer data to model monthly trends of f(RH) at 550 nm. Summer months show higher f(RH) values while autumn, spring and winter months show relatively lower f(RH) values. This can be attributed to the general pattern of regional climatology as well as the loading of different particle types into the lower troposphere. In the third approach, f(RH) values at 532 nm are obtained from lidar and aethalometer measurements. Campaign measurements during November show low and constant f(RH) values while measurements during May show higher and increasing f(RH) values. The occurrence of dust events during March 2015, in one of the measurement campaigns, showed decreasing f(RH) values against RH.