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Volume 18, issue 2
Atmos. Chem. Phys., 18, 1263-1290, 2018
https://doi.org/10.5194/acp-18-1263-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue: HD(CP)2 Observational Prototype Experiment (AMT/ACP...

Atmos. Chem. Phys., 18, 1263-1290, 2018
https://doi.org/10.5194/acp-18-1263-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 31 Jan 2018

Research article | 31 Jan 2018

Helicopter-borne observations of the continental background aerosol in combination with remote sensing and ground-based measurements

Sebastian Düsing1, Birgit Wehner1, Patric Seifert1, Albert Ansmann1, Holger Baars1, Florian Ditas1,2, Silvia Henning1, Nan Ma1, Laurent Poulain1, Holger Siebert1, Alfred Wiedensohler1, and Andreas Macke1 Sebastian Düsing et al.
  • 1Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 2Multiphase Chemistry Department, Max Planck Institute for Chemistry, P.O. Box 3060, 55020, Mainz, Germany

Abstract. This paper examines the representativeness of ground-based in situ measurements for the planetary boundary layer (PBL) and conducts a closure study between airborne in situ and ground-based lidar measurements up to an altitude of 2300m. The related measurements were carried out in a field campaign within the framework of the High-Definition Clouds and Precipitation for Advancing Climate Prediction (HD(CP)2) Observational Prototype Experiment (HOPE) in September 2013 in a rural background area of central Europe.

The helicopter-borne probe ACTOS (Airborne Cloud and Turbulence Observation System) provided measurements of the aerosol particle number size distribution (PNSD), the aerosol particle number concentration (PNC), the number concentration of cloud condensation nuclei (CCN-NC), and meteorological atmospheric parameters (e.g., temperature and relative humidity). These measurements were supported by the ground-based 3+2 wavelength polarization lidar system PollyXT, which provided profiles of the particle backscatter coefficient (σbsc) for three wavelengths (355, 532, and 1064nm). Particle extinction coefficient (σext) profiles were obtained by using a fixed backscatter-to-extinction ratio (also lidar ratio, LR). A new approach was used to determine profiles of CCN-NC for continental aerosol. The results of this new approach were consistent with the airborne in situ measurements within the uncertainties.

In terms of representativeness, the PNSD measurements on the ground showed a good agreement with the measurements provided with ACTOS for lower altitudes. The ground-based measurements of PNC and CCN-NC are representative of the PBL when the PBL is well mixed. Locally isolated new particle formation events on the ground or at the top of the PBL led to vertical variability in the cases presented here and ground-based measurements are not entirely representative of the PBL.

Based on Mie theory (Mie, 1908), optical aerosol properties under ambient conditions for different altitudes were determined using the airborne in situ measurements and were compared with the lidar measurements. The investigation of the optical properties shows that on average the airborne-based particle light backscatter coefficient is 50.1% smaller for 1064nm, 27.4% smaller for 532nm, and 29.5% smaller for 355nm than the measurements of the lidar system. These results are quite promising, since in situ measurement-based Mie calculations of the particle light backscattering are scarce and the modeling is quite challenging. In contrast, for the particle light extinction coefficient we found a good agreement. The airborne-based particle light extinction coefficient was just 8.2% larger for 532nm and 3% smaller for 355nm, for an assumed LR of 55sr. The particle light extinction coefficient for 1064nm was derived with a LR of 30sr. For this wavelength, the airborne-based particle light extinction coefficient is 5.2% smaller than the lidar measurements. For the first time, the lidar ratio of 30sr for 1064nm was determined on the basis of in situ measurements and the LR of 55sr for 355 and 532nm wavelength was reproduced for European continental aerosol on the basis of this comparison. Lidar observations and the in situ based aerosol optical properties agree within the uncertainties. However, our observations indicate that a determination of the PNSD for a large size range is important for a reliable modeling of aerosol particle backscattering.

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