Characteristics of Aerosol Optical Properties During Haze and Fog Episodes at Shangdianzi in Northern China

The Northern China is one of the regions with the high incidence of fog and haze. With the rapid development of economy in the recent years, the anthropogenic pollutants, such as aerosol and its precursors have brought about serious visibility degradations in the regions. In the fall of 2004, several heavy fog and haze episodes with visibility less than 1 km are observed at Shangdianzi (SDZ) Atmospheric Background Station. During the fog and haze periods, aerosol scattering and absorption coefficients are measured simultaneously at the Station with Nephelometer (M9003, ECOTECH) and 7 band Aethalometer (AE31, Magee Scientific). The results of aerosol optical properties indicate that aerosols over the region are strongly influenced by weather conditions. Under the influence of fog and haze, aerosols at the Station show higher values of scattering and absorption coefficient and higher aerosol single scattering albedo (ω), while relatively lower aerosol scattering coefficient, absorption coefficient and ω are observed after the haze and fog episodes. For the 4 fog/haze episodes, the aerosol single scattering albedo decreases by about 0.1, with the value of 0.94-0.97 during the fog/haze influencing periods and the lower value of 0.84-0.86 during the cleaner periods after the fog/haze process. Through a detailed analysis of the time series of the surface aerosol optical properties for a heavy fog and haze case, combined with the column AOD and weather condition changes, the evolution of aerosol optical properties are discussed. It is found that the fog and haze event takes on significant regional effects, air masses from polluted directions leads to higher ω, higher scattering and absorption coefficients of aerosols. This result suggests that the haze and fog weather conditions favor the accumulation of aerosol pollutants, especially favor the production of the light scattering aerosols, which reflect that the formation of secondary aerosols and their contribution to the light extinctions might be more significant during the haze and fog influencing periods.