Column aerosol optical properties and aerosol radiative forcing during a serious haze-fog month over North China Plain in 2013 based on ground-based sunphotometer measurements

摘要

In January 2013, North China Plain experienced several serious haze events.Cimel sunphotometer measurements at seven sites over rural, suburban andurban regions of North China Plain from 1 to 30 January 2013 wereused to further our understanding of spatial-temporal variation of aerosoloptical parameters and aerosol radiative forcing (ARF). It was found thatAerosol Optical Depth at 500 nm (AOD) during non-pollution periodsat all stations was lower than 0.30 and increased significantly to greaterthan 1.00 as pollution events developed. The Angstrom exponent (Alpha) waslarger than 0.80 for all stations most of the time. AOD averagesincreased from north to south during both polluted and non-polluted periodson the three urban sites in Beijing. The fine mode AOD during pollutionperiods is about a factor of 2.5 times larger than that during thenon-pollution period at urban sites but a factor of 5.0 at suburban andrural sites. The fine mode fraction of AOD was higher than80% for all sites during January 2013. The absorption AOD atrural sites was only about 0.01 during pollution periods, while~0.03–0.07 and 0.01–0.03 during pollution and non-pollutionperiods at other sites, respectively. Single scattering albedo variedbetween 0.87 and 0.95 during January 2013 over North China Plain. The sizedistribution showed an obvious tri-peak pattern during the most seriousperiod. The fine mode effective radius in the pollution period was about0.01–0.08 μm larger than during non-pollution periods, while thecoarse mode radius in pollution periods was about 0.06–0.38 μm lessthan that during non-pollution periods. The total, fine and coarse modeparticle volumes varied by about 0.06–0.34 μm, 0.03–0.23 μm, and 0.03–0.10 μm, respectively, throughout January2013. During the most intense period (1–16 January), ARF atthe surface exceeded −50 W m, −180 W m, and −200 W m at rural, suburban, and urban sites, respectively. The ARFreadings at the top of the atmosphere were approximately −30 W m inrural and −40–60 W m in urban areas. Positive ARF at the top of theatmosphere at the Huimin suburban site was found to be different from othersas a result of the high surface albedo due to snow cover.