Abstract
Abstract. The Spectral Aerosol Extinction Monitoring System (SǼMS) is presented that allows us to continuously measure the spectral extinction coefficient of atmospheric aerosol particles along an approximately 2.7 km long optical path at 30–50 m height above ground in Leipzig (51.3° N, 12.4° E), Germany. The fully automated instrument measures the ambient aerosol extinction coefficients from 300 to 1000 nm. The main goal of SǼMS observations are long-term studies of the relationship between particle extinction and relative humidity from below 40% to almost 100%. The setup is presented and observations (a case study and statistical results for 2009) are discussed in terms of time series of 550 nm particle optical depth, Ångström exponent, and particle size distribution retrieved from the spectrally resolved extinction. The SǼMS measurements are compared with simultaneously performed EARLINET (European Aerosol Research Lidar Network) lidar, AERONET (Aerosol Robotic Network) sun photometer, and in situ aerosol observations of particle size distribution and related extinction coefficients on the roof of our institute. Consistency between the different measurements is found, which corroborates the quality of the SǼMS observations. Statistical results of a period of 1 yr (2009) show mode extinction values of 0.09 km−1 (SǼMS), 0.075 km−1 (AERONET), and 0.03 km−1 (in situ). Ångström exponents for this period are 0.19 (390–880 nm, SǼMS) and 1.55 (440–870 nm, AERONET).
Highlights
The SÆMS measurements are compared with simultaneously performed EARLINET (European Aerosol Research Lidar Network) lidar, AERONET (Aerosol Robotic Network) sun photometer, and in situ aerosol observations of particle size distribution and related extinction coefficients on the roof of our institute
The interaction of atmospheric aerosol particles with water vapor and the related changes in the particle optical properties has been an important aspect of atmospheric research for decades (Hänel, 1976, 1984; Fitzgerald et al, 1982; Carrico et al, 1998, 2000; McInnes et al, 1998; Gasso et al, 2000; Bundke et al, 2002; Fierz-Schmidhauser et al, 2010; Zieger et al, 2011, 2013)
The basic measurement principle of SÆMS is adapted from LP-DOAS (Platt and Perner, 1983; Platt, 1994)
Summary
The interaction of atmospheric aerosol particles with water vapor and the related changes in the particle optical properties has been an important aspect of atmospheric research for decades (Hänel, 1976, 1984; Fitzgerald et al, 1982; Carrico et al, 1998, 2000; McInnes et al, 1998; Gasso et al, 2000; Bundke et al, 2002; Fierz-Schmidhauser et al, 2010; Zieger et al, 2011, 2013). As a function of particle chemical composition, particle age, and state of aerosol mixture, aerosols can show a very different hygroscopic behavior (i.e., water uptake with increasing relative humidity), and can have a rather complex impact on the optical properties of the atmosphere. There is a clear need for more field observations of aerosol optical properties as a function of relative humidity from low (< 40 %) to very high values (> 95 %) in order to better describe aerosols in climate models, to better separate aerosols and clouds in satellite remote sensing products, and for a better understanding of aerosol–cloud interaction (Koren et al, 2007, 2009). Emissions from local sources may affect the results The aim of this first paper on SÆMS is to present the measurement setup and the measurement procedure.
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