Abstract: From January to February, 2013, there were some foggy and hazy days accompanied by serious air pollution in northern China. A study on the pollution characteristics of aerosols and their optical properties was conducted during this period in the urban area of Tianjing. Continuous online parameters including aerosol mass concentrations, atmospheric visibility, aerosol scattering and absorption coefficients, and aerosol optical depth (AOD) were obtained to analyze their variations and correlations, combed with simultaneous meteorological conditions. The results show that the weather factors were abnormal during the observation period, with relative humidity higher by 11%, wind speed lower by 0.5m/s, and more precipitation than under normal condition. The numbers of foggy, misty, and hazy days were 8,1, and 29, respectively, accounting for 73% of the total observed days. The average ratio of PM_2.5 PM₁₀ was 0.65; the single scattering albedo (SSA) was 0.95; and the aerosol mass scattering efficiency (MSE) was 3.30m²/g on the hazy days. These values were higher than those on non-foggy-hazy days, indicating that the scattering effects of fine particles were the main contributor to the atmospheric extinction. Both aerosol scattering and absorption coefficients were higher on fog-haze days than on non-fog-haze days; this result indicats that the high RH value had a great influence on visibility, may be even exceeding the influence of aerosol particle concentration on heavy haze days. Indices of AOD_500nm and aerosol wavelength were higher on foggy-hazy days than in non-foggy-hazy conditions, also indicating the predominance of fine particles on foggy-hazy days, when there were higher aerosol capacities.