In this study, optical properties of aerosols were investigated from August 2012 to July 2013 in Nanjing, China. A three-wavelength photoacoustic soot spectrometer (PASS-3) was used to measure aerosol scattering and absorption coefficient (B_sca and B_abs) with the wavelength dependence (405, 532, and 781 nm). The readings of PASS-3 agreed with those of the conventional instruments. The seasonal and diurnal cycles of optical properties were analyzed using hourly averaged data. Both B_sca and B_abs increased in the order of summer (173.4 and 22.9 Mm⁻¹), spring (292.9 and 35.6 Mm⁻¹), fall (380.7 and 44.9 Mm⁻¹) and winter (507.3 and 66.7 Mm⁻¹). The highest aerosol loading occurred in winter. Compared to weak seasonal variation of single scattering albedo (ω₅₃₂), the highest Ångstrom scattering exponent (A_sca, 1.59 ± 0.31) and the lowest Ångstrom absorption exponent (A_abs, 1.11 ± 0.33) appeared in summer. The diurnal variation of B_sca, B_abs, A_sca, A_abs and ω₅₃₂ were multimodal and mainly affected by wind speed and relative humidity. The lower mass absorption efficiency (MAE) of elemental carbon (EC) (MAE ~7.2 m²/g) appeared in fall due to biomass burning, while the higher mass scattering efficiency (MSE~3.8 m²/g) in winter was due to aerosol aging. Air masses originating from inland China induced an increase in B_sca and B_abs according to backward trajectory cluster analysis. Organic matter, (NH₄)₂SO₄ and EC were the dominant species of light extinction under dry and ambient conditions. Secondary inorganic ions (NH₄⁺, NO₃⁻ and SO₄²⁻) were significantly correlated with B_sca and B_abs. Consistent results were obtained using three types of source analysis methods.