Articles | Volume 16, issue 7
Atmos. Chem. Phys., 16, 4539–4554, 2016

Special issue: The Pan European Gas-Aerosols Climate Interaction Study...

Atmos. Chem. Phys., 16, 4539–4554, 2016

Research article 13 Apr 2016

Research article | 13 Apr 2016

Studying the vertical aerosol extinction coefficient by comparing in situ airborne data and elastic backscatter lidar

Bernadette Rosati1, Erik Herrmann1, Silvia Bucci2, Federico Fierli2, Francesco Cairo2, Martin Gysel1, Ralf Tillmann3, Johannes Größ4, Gian Paolo Gobbi2, Luca Di Liberto2, Guido Di Donfrancesco5, Alfred Wiedensohler4, Ernest Weingartner1,a, Annele Virtanen6, Thomas F. Mentel3, and Urs Baltensperger1 Bernadette Rosati et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
  • 2Institute of Atmospheric Sciences and Climate (ISAC-CNR), National Research Council, 00133 Rome, Italy
  • 3Institute for Energy and Climate Research (IEK-8), Forschungszentrum Jülich, 52428 Jülich, Germany
  • 4Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany
  • 5Italian National Agency for New Technologies, Energy and Environment (ENEA), 00044 Frascati, Italy
  • 6Department of Applied Physics, University of Eastern Finland, 70211 Kuopio, Finland
  • anow at: Institute for Aerosol and Sensor Technology, University of Applied Science Northwestern Switzerland, 5210 Windisch, Switzerland

Abstract. Vertical profiles of aerosol particle optical properties were explored in a case study near the San Pietro Capofiume (SPC) ground station during the PEGASOS Po Valley campaign in the summer of 2012. A Zeppelin NT airship was employed to investigate the effect of the dynamics of the planetary boundary layer at altitudes between ∼  50 and 800 m above ground. Determined properties included the aerosol particle size distribution, the hygroscopic growth factor, the effective index of refraction and the light absorption coefficient. The first three parameters were used to retrieve the light scattering coefficient. Simultaneously, direct measurements of both the scattering and absorption coefficient were carried out at the SPC ground station. Additionally, a single wavelength polarization diversity elastic lidar system provided estimates of aerosol extinction coefficients using the Klett method to accomplish the inversion of the signal, for a vertically resolved comparison between in situ and remote-sensing results. Note, however, that the comparison was for the most part done in the altitude range where the overlap function is incomplete and accordingly uncertainties are larger. First, the airborne results at low altitudes were validated with the ground measurements. Agreement within approximately ±25 and ±20 % was found for the dry scattering and absorption coefficient, respectively. The single scattering albedo, ranged between 0.83 and 0.95, indicating the importance of the absorbing particles in the Po Valley region. A clear layering of the atmosphere was observed during the beginning of the flight (until ∼  10:00 LT – local time) before the mixing layer (ML) was fully developed. Highest extinction coefficients were found at low altitudes, in the new ML, while values in the residual layer, which could be probed at the beginning of the flight at elevated altitudes, were lower. At the end of the flight (after ∼  12:00 LT) the ML was fully developed, resulting in constant extinction coefficients at all altitudes measured on the Zeppelin NT. Lidar estimates captured these dynamic features well and good agreement was found for the extinction coefficients compared to the in situ results, using fixed lidar ratios (LR) between 30 and 70 sr for the altitudes probed with the Zeppelin. These LR are consistent with values for continental aerosol particles that can be expected in this region.

Short summary
We present vertical profiles of aerosol optical properties, which were explored within the planetary boundary layer in a case study in 2012 in the Po Valley region. A comparison of in situ measurements recorded aboard a Zeppelin NT and ground-based remote-sensing data was performed yielding good agreement. Additionally, the role of ambient relative humidity for the aerosol particles' optical properties was investigated.
Final-revised paper