The source, size and chemical composition of the winter arctic tropospheric aerosol layer observed by lidar at Eureka, Canada

During the winter seasons from 1993-94 to 1998-99 at Eureka (80.0 degreesN, 86.0 degreesW) in the Canadian high arctic, we have observed tropospheric aerosol layers by using a Mie-scattering-polarization lidar system and we have investigated lidar parameters (Mie backscattering coefficients, aerosol depolarization ratios, and Angstrom exponents) of the layers. We calculated isentropic back trajectories in order to investigate the source regions of these layers. We also estimated the size of the particles in the layers by calculating modeled lidar parameters and comparing them with the observed lidar parameters. Daily sampling of aerosol particles was carried out in the late winter of 1998-99. Isentropic back trajectories of the aerosol layer observed over Eureka at different altitudes suggested that the source regions of the aerosol were Eurasia, the northern Pacific and Atlantic Oceans, the Arctic Ocean, and regions near the coast of the Arctic Ocean. The lidar parameters calculated by using the Mie theory and the modeled particle size distribution suggested that, although the Mie backscattering coefficient was determined largely by the number concentration of the accumulation mode particles of diameter 0.2 mum to 0.3 mum, the aerosol depolarization ratio and,Angstrom exponent of the aerosol layers were influenced strongly by the number concentration and the geometric mean diameter of the coarse particles. The trajectories, characteristics, and chemical compositions of aerosols suggest that the arctic layers observed by lidar were composed of sulfate aerosol or sea salt.