10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Aerosol Optical Property Measurements of European Background Aerosol under Clean and Polluted Conditions
SEBASTIAN DÜSING, Birgit Wehner, Albert Ansmann, Holger Baars, Ralf Käthner, Nan Ma, Thomas Müller, Patric Seifert, Holger Siebert, Gerald Spindler, Alfred Wiedensohler, Nicolas Bukowiecki, Joel Corbin, Martin Gysel, Leibniz-Institute for Tropospheric Research
Abstract Number: 1180 Working Group: Aerosol Physics
Abstract Observations of the vertical distribution of aerosol are quite important since they allow to describe the radiative transport in the atmosphere. For this, remote sensing and airborne in-situ measurements are potential approaches to study the vertical aerosol distribution. But, both approaches underlie limitations and assumptions. Inter-comparison studies are therefore needed to a) compare the results of these approaches and b) to improve remote sensing algorithms and provide recommendations for vertical in situ measurements. Two campaigns were conducted and the results of these unique data-set for European background aerosol will be presented in this contribution.
Both campaigns took place in the vicinity of the rural ACTRIS (Aerosol, Clouds, and Trace gases Research InfraStructure Network) super-site at Melpitz (51.5° N, 12.9° E and 90 m above sea level).
In the first campaign (June 2015) 11 flights were conducted with a helicopter-borne payload up to a height of 2.3 km. This payload determined a) the ambient RH, T and b) the aerosol particle number size distribution (PNSD) within a particle diameter-range from 8 nm to 2.8 µm. Each flight contained horizontal flight legs of at least 10 min to determine statistically significant mean PNSD measurements. Three different instruments recorded the aerosol optical properties: particle light absorption (σabs) was determined by a small sized Aethalometer (AE51) at 880 nm wavelength whereas the Single Channel Tri-Colour Absorption Photometer (STAP) measured σabs at 450, 525, and 624 nm, while scattering (σsca) and extinction coefficient (σext) were recorded with the Cavity Attenuation Phase Shift monitor (CAPSssa) at 630 nm wavelength.
In the second campaign (February/ March 2017) a box deployed on a tethered balloon included instruments determining σabs during 5 launches (AE51, STAP). The PNSD has also been detected within an optical particle diameter-range of 300 nm to 10 µm. All in situ measurements were conducted under dry conditions below 40% RH.
In both campaigns, the in situ measurements were complemented by a continuously running ground-based 3+2 multiwavelength polarization Raman lidar system PollyXT measuring profiles of the aerosol particle light backscatter coefficient (σbsc). Also we derived profiles of σext. Furthermore, an almucantar sun-photometer was measuring the aerosol optical thickness at different wavelengths.
These measurements were completed by measurements of the chemical aerosol composition as well as by measurements of the aerosol optical properties on ground. On the basis of the chemical composition measurements we derived the complex refractive index and the hygroscopicity of the aerosol particles.
Assuming that the chemical composition on ground is applicable for higher atmospheric altitudes, we first converted the in situ measured PNSD to its ambient state PNSD which has been used furthermore to calculate ambient state aerosol optical properties with a Mie theory based model.
Our measurements show that ground-based measurements are representative for the well-mixed planetary boundary layer. Furthermore, the in situ dry state modelled σsca and σext showed good agreements with the airborne in situ measured equivalents. But especially the comparisons with filter-based absorption (σabs) instruments (STAP, AE51) and our Mie-calculations showed deviations which requires further research. Comparing the ambient state optical properties (model and in situ) with the measurements of the lidar, we detected cases were the model is in agreement (within measurement uncertainties) with the lidar observations. But we also observed also cases were the model calculated significantly lower σext and values than observed by the lidar.
Not all flights/lunches are investigated yet, but conclusions and findings of the observations will be presented in this conference contribution.