Aerosol climatology in an Alpine valley



[1] Aerosol optical depth (AOD) is measured with a Precision Filter Radiometer in Innsbruck, Austria, from 2007 to 2011. The 5-year time series is analyzed with respect to the Ångström parameterα and quadratic coefficient γ. Information on the aerosol size distribution is obtained by adopting a graphical framework showing the particle fine mode fraction as well as the effective fine mode radius. The aerosol conditions in Innsbruck reveal a typical midlatitudinal pattern for continental urban sites with low pollution. Small particles originating from traffic pollution as well as natural sources dominate leading to an overall mean α of 1.53 +/− 0.28 and γ of −0.54 +/− 0.25. Low AOD at 500 nm is observed in winter with multiannual monthly means as low as 0.08 and higher AOD in spring and summer with multiannual monthly means up to 0.18. The maximum daily mean AOD at 500 nm always remains below 0.5. Special events such as Saharan dust events or presence of volcanic ash are detected and discussed.