Remote sensing of the radiative properties of arctic aerosols at solar and thermal infrared wavelengths and retrieval of aerosol microphysical properties

The current scientific knowledge does not allow estimating accurately the surface radiative forcing caused by tropospheric aerosols and their influence on the evolution of the Earth climate. The radiative forcing depends on the optical properties of the aerosols at solar and thermal infrared wavelengths. These optical properties depend, in turn, on the chemical composition and size of the aerosols. Remote sensing with passive radiation sensors operating in the above-mentioned spectral ranges allows to measure the optical properties of the aerosols and to characterise their temporal variability. These data are needed for regional climate simulations of the Arctic, particularly for delineating the impact of the Arctic haze phenomenon. In this project, a synergetic effort will be made to obtain information about the radiative and microphysical properties of springtime arctic aerosols. Therefore, a polarisation-spectrometer for the solar spectral range, which is currently developed at the Free University of Berlin as a variant of the FUBISS spectrometer, will be operated from the surface in coincidence with the Fourier Transform InfraRed-spectrometer (FTIR) installed at Ny-Aalesund by the AWI. The former instrument measures the intensity and polarisation of the scattered solar radiation from the visible to the near-infrared. The latter measures the radiation emitted by the Atmosphere itself in the thermal infrared window region. Together, they thus provide a wealth of information about the aerosol optical properties at the interesting wavelengths (spectral optical depth, single-scattering albedo, and asymmetry factor of the phase function), which will allow inferring the aerosol microphysical properties. Complementary measurements of the aerosol microphysical properties will be provided by an aerosol volatility analyser, which is maintained by the University of Leeds and will also be brought to Ny-Aalesund. This instrument comprises a fast response scanning volatility system and an optical particle counter. From the thermal response of the aerosol number and the change in the size distribution conclusions can be inferred about the chemical composition and the state of mixing of aerosols as a function of size.