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Study aerosol properties (size and composition) in the infrared spectral region
The aim of the project is to study the properties (radiative effects, composition) of aerosols using FTIR emission spectroscopy. To determine seasonal changes in aerosol properties the measurements will be carried out year round on a weekly schedule.
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.
Situated in the Arctic Ocean the planetary boundary layer over Ny Ålesund is dominated by marine aerosols. Hight and time variation of boundary layer aerosols are examined with the tropospheric lidar system in Ny Ålesund. To determine the aerosol and its optical properties more exactly information from more wavelenghts are necessary as the sun-photometer at the Koldewey Station can provide. First combined evaluation of photometer and LIDAR data during the ASTAR-campaign in spring 2000 demonstrated feasibility and advantages of this method for the free troposphere. Furthermore this method is to be applied on boundary layer aerosol to research also its optical properties.
The subject is to determine the horizontal distribution of aerosol and trace gases by airborne measurements with the Gulfstream III (transarctic flight), ground based measurements in Ny Ålesund (Koldewey Station, Rabben) and satellite measurements with SAGE II / SAGE III. Objective is to get vertical and horizontal aerosol profiles, to research the trace gase variations in the Arctic and to compare remote sensing und in situ measurements.
In situ measurements of the tropospheric and tropopause and if possible lower stratospheric water vapour content will be carried out with different balloon sondes. Start of up to three balloons with Snow White Sensor-Package prepared by a team from the University of Nagoya and University of Kyoto. Possibly water vapour sondes from NOAA (S. Oltmans) will be started within the scope of an EU-project. This may happen earliest in autumn.
Total deposition sampling is performed at Ny-Ålesund to study atmospheric fluxes of heavy metals to the Arctic. In addition wet only deposition sampling is carried out with an automatic precipitation sampler. The samples are analysed at the home laboratory for tracer elements for seaspray components, earthcrust weathered material and anthropogenic elements by atomic absorption spectrometry and inductively coupled plasma-mass spectrometry (ICP-MS). One aim of our study is to distinguish element distribution between the dissolved and particulate phase. In addition to the element analyses the concentration of anions is determined by ionchromatography. In 1996 an automatically operating aerosol sampler was installed, which is combined with the automatic precipitation sampler to study element washout from aerosol particles via rain and snow.
In recent years, much attention has been directed towards understandig the effects of aerosols on a variety of processes in the earth atmosphere. Aerosols play an integral role in limiting visibility, they serve as nuclei for the formation of fog and cloud droplets, they affect the earth radiative budget, and thus climate, both directly and indirectly, and they inhibit the propagation of electromagnetic radiation. The Arctic aerosols, especially Arctic Haze and tropospheric ice crystals possible have important climatic and ecological and global change implications. Since 1991 Sun photometer observations of the polar atmopheric aerosol have been performed at the Koldewey Station in Ny-Aalesund, Spitzbergen. In order to complete the coverage and quality of measurements during the polar night a high sensitive Star photometer is installed since January 1996. Both measurements, the daylight Sun photometer measurements and night Star photometer measurements will be continued.
Stratospheric aerosols like Polar Stratospheric Clouds (PSCs) or volcanic aerosols are investigated by different types of balloon borne sensors in co-operation with the University of Nagoya, Japan, and the University of Wisconsin, Laramie, Wisconsin. The sensors flown are dedicated optilca particle counters (OPC) or backscatter sondes (BKS), respectively.
A tropospheric lidar system with a Nd:YAG-Laser was installed at the Koldewey-Station in 1998. It operates at a laser wavelengths of 355, 532, and 1064 nm with detection at 532 nm polarised and depolarised, and at Raman wavelengths like 607nm (nitrogen). It records profiles of aerosol content, aerosol depolarisation and aerosol extinction. During polar night the profils reach from the ground up to the tropopause level, while during polar day background light reduces the altitude range. The main goal of the investigations is to determine the climate impact of arctic aerosol. Analysis of the climate impact will be performed by a high resolution regional model run at the Alfred Wegener Institute (HIRHAM). The lidar system is capable to obtain water vapour profiles in the troposphere. Water vapour profiles are crucial for the understanding of the formation of aerosols. The water vapour profiles are also used for the validation of profiles measured by the CHAMP satellite from 2001 onwards.
The stratospheric multi wavelength LIDAR instrument, which is part of the NDSC contribution of the Koldewey-Station, consists of two lasers, a XeCl-Excimer laser for UV-wavelengths and a Nd:YAG-laser for near IR- and visible wavelengths, two telescopes (of 60 cm and 150 cm diameter) and a detection system with eight channels. Ozone profiles are obtained by the DIAL method using the wavelengths at 308 and 353 nm. Aerosol data is recorded at three wavelengths (353 nm, 532 nm, 1064 nm) with depolarization measurements at 532 nm. In addition the vibrational N2-Raman scattered light at 608 nm is recorded. As lidar measurements require clear skies and a low background light level, the observations are concentrated on the winter months from November through March. The most prominent feature is the regular observation of Polar Stratospheric Clouds (PSCs). PSCs are known to be a necessary prerequisite for the strong polar ozone loss, which is observed in the Arctic (and above Spitsbergen). The PSC data set accumulated during the last years allows the characterization of the various types of PSCs and how they form and develop. The 353 and 532 nm channels are also used for temperature retrievals in the altitude range above the aerosol layer up to 50 km.