Wintertime optical properties of atmospheric particles and weather

Atmospheric particles from the boundary layer were collected on Nuclepore filters at the summit of a mountain near Frankfurt am Main (Germany). The optical properties (absorption, scattering and extinction coefficients, the asymmetry parameter of the phase function of scattered light and the complex refractive index) and the soot content of the particles were determined using a photometric method and a subsequent mathematical inversion. The dependence of the optical properties and the soot content on meteorological parameters measured at the sampling site and on large and mesoscale motions of the atmosphere was investigated. The major findings are: (I) The observed optical properties of the particles are correlated with the air temperature measured at the sampling site. (2) The optical properties change during the passage of a cold front. (3) The optical properties depend on the existence of a stable stratified layer in the lower troposphere. (4) The optical properties depend on the local weather situation and on the history of the air masses arriving at the sampling site.