Monitoring of Saharan dust - influence on aerosol composition and snow chemistry
Marion Greilinger, ZAMG - Central Institute for Meteorology and Geodynamics, Vienna (AT)
Long-range transport of Saharan dust serves as a significant source of high particulate matter (PM) concentrations far away from the source region. High PM loads are relevant for climatic issues such as the radiation budget or cloud formation processes as well as for environmental issues such as acidity, ionic loads of precipitation and nutrient supply, but also for air quality issues and related topics such as human health. Extensive investigations of Saharan dust form the basis for further impact related studies. The Sonnblick observatory, located in the Nationalpark Hohe Tauern, runs an extensive Aerosol and Saharan dust monitoring to measure and sample aerosol loads, aerosol composition and deposition loads. Based on the approach of Coen et al. (2003), we regularly identify the occurrence of Saharan dust events (SDEs) on the basis of the optical properties of the aerosol (particularly scattering and absorbance). This, together with the observed aerosol mass, allows the computation of a "Saharan dust index” indicating a potential Saharan dust influence (Schauer et al., 2016). Within the project DUSTFALL the influence of SD on aerosol composition, in particular the chemical differences of the coarse (particles up to 10µm diameter, PM10) and fine (particles up to 1µm diameter, PM1) particles, is studied via the analysis of weekly aerosol filter samples of these two different fractions. During Saharan dust events, we assume that the two fractions differ significantly in mass, in the chemical composition and hence also in their optical properties. The differences in size and mass is of great interest when dealing with the questions of PM loadings and their influence on air quality issues such as exceedances of limit values of PM concentrations. Differences in size, number and mass together with the chemical composition plays an important role for the radiation budget or for cloud formation processes. Ecological issues are mostly related to differences in deposition and chemical composition. Concerning the investigation of ecological issues, we evaluate the influence of Saharan dust events on high alpine snow chemistry. Therefore we developed a method for a retrospective identification of Saharan dust layers in high alpine snow packs of the last three decades from 1987 until 2016 (compare Greilinger et al., 2016). This forms the basis for the investigation of the influence of Saharan dust events on the chemical composition of the snow pack, the influence of SDEs on the neutralization of acid compounds such as Sulfate and Nitrate and on the nutrient supply for snow colonizing bacteria and algae. Such a long-term snow chemistry data set is very unique and allows conclusions on the impact of Saharan Dust, not only on high alpine snow ecology, but also on additional ecological issues such as fertilization of surrounding ecosystems due to melt water run-off. We would like to present first results of the filter monitoring program of more than one year.