Closure study on optical and microphysical properties of a mixed urban and Arctic haze air mass observed with Raman lidar and Sun photometer

[1] We present a comprehensive optical and microphysical characterization of an intense haze event observed over Leipzig (51.3°N, 12.4°E), Germany, in April 2002. This event was characterized by unusually high optical depths. The haze consisted of a mixture of urban and Arctic haze aerosols which were advected from the Arctic regions across eastern Europe and Scandinavia. For the first time a closure study on such an event could be carried out on the basis of combined observations with Raman lidar and Sun photometer. This study also served as a performance test of the inversion algorithms that are used for retrieving microphysical particle properties from the optical data sets. A comparison of parameters derived in this study to respective quantities determined in the Arctic regions showed that Arctic-haze-like material dominated the optical and microphysical particle properties, although a significant amount of this haze must have consisted of urban aerosols. The urban aerosols from eastern Europe had properties rather similar to those characteristic for the well-aged particles of Arctic haze. The major part of the haze was confined to heights below 3 km. Optical depth was 0.4-0.5 at 532 nm on 8 April 2002. The particle backscatter-to-extinction (lidar) ratio varied between 35 and 75 sr at 355 and 532 nm. The Angstrom exponent of particle extinction in the wavelength range from 355 to 532 nm was 1.8-2.8. The inversion of the lidar optical data resulted in particle effective radii around 0.19 ± 0.04 μm, volume concentrations of 16-33 μm 3 cm -3 , surface area concentrations of 270-510 μm 2 cm -3 , and a single-scattering albedo around 0.97 ± 0.06 at 532 nm. Particle size distributions showed a rather pronounced monomodal structure in the accumulation mode, which is characteristic for well-aged particles. The particle properties derived from the two instruments agreed well for intensive parameters, i.e., Angstrom exponents, lidar ratio, effective radius, and single-scattering albedo. Extensive parameters, i.e., total particle surface area and particle volume concentration, showed similar values.

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