Identification and monitoring of Saharan dust: An inventory representative for south Germany since 1997

An inventory of Sahara dust (SD) events at the Hohenpeiβenberg Global Atmosphere Watch station (Germany) is presented for the period 1997-2013. Based on daily in-situ measurements, high Ca2+-ion concentrations and large particle volume concentrations at diameters dp ≈ 0.5-7 μm are inferred as indicators for days influenced by SD. The resulting SD catalogue agrees with SD time series from Schneefernerhaus, Augsburg and Jungfraujoch stations. On average, SD occurs in 5-15 SD events (SDE) per year covering about 10-60 days/yr in the mixing layer. SDE exhibit a clear seasonality with spring and early autumn maxima, and typically last for 1-3 days. SDE are equally frequent but more significant at Alpine levels due to lower background. Wet deposition of Ca2+ at the surface is little correlated (R2 = 0.14) with particle Ca2+ on a daily basis and yields an average annual Ca2+ immission of 0.22 ± 0.04 g/m2 yr, about 40% of which is due to SD. The majority of outstanding weekly Fe and Al depositions are associated with SDE. SD contributes about 0.5 ± 0.1 μg/m3 to the total particle mass with a decreasing trend from 6% to 4% (−0.1%/yr) in the 1997-2013 period. Except from one, all threshold exceedances according to European legislation (daily PM10 > 50 μg/m3) at Hohenpeiβenberg are due to SD. Implications are discussed with respect to SD-related circulation patterns, SD-induced temperature anomalies in weather forecast models and the capability of aerosol models to capture SDE.