One-year aerosol profiling with EUCAARI Raman lidar at Shangdianzi GAW station: Beijing plume and seasonal variations

The study examines seasonal and air-flow-dependent variations of the vertical distribution of aerosols at the Global Atmospheric Watch (GAW) station of Shangdianzi in the North China Plain 100 km northeast of Beijing. One-year Raman lidar observations of profiles of aerosol extinction and backscatter coefficients at 532 nm were performed from April 2009 to March 2010 in the framework of the European Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) project. In the nighttime statistics a two-layer structure with the main haze layer reaching to 1-1.5 km height asl and an elevated aerosol layer on top with a top height of 2.5-5 km height asl was generally observed. A case study of a Beijing haze plume is presented to document the drastic changes in the environmental conditions over the background monitoring station during the passage of a strong haze front. Aerosol optical depth (AOD) and extinction coefficients increased from 0.2 to 1.2 and from 200 Mm(-1) to 1000 Mm(-1), respectively, within less than two hours. The statistical analysis revealed layer mean extinction coefficients of the haze layer most frequently from 200-600 Mm(-1) and typically from 50-100 Mm(-1) in the elevated layer. The AOD ranged from about 0.3 for northerly air flows to, on average, 0.95 during southerly air flows. The lidar ratio shows a narrow distribution peaking at 60 sr in the haze layer caused by anthropogenic fine-mode aerosol and a broad distribution from 40-90 sr in the elevated layer caused by the complex mixture of aged desert dust, biomass burning smoke, and industrial pollution over eastern Asia.