Measurement report: Balloon-borne in-situ profiling of Saharan dust over Cyprus with the UCASS optical particle counter

Abstract

Abstract. This paper presents measurements of mineral dust concentration in the diameter range from 0.4 to 14.0 μm with a novel balloon-borne optical particle counter, the Universal Cloud and Aerosol Sounding System (UCASS). The balloon launches were coordinated with ground-based active and passive remote-sensing observations and airborne in-situ measurements with a research aircraft during a Saharan dust outbreak over Cyprus from 20 to 23 April 2017. The aerosol optical depth at 500 nm reached values up to 0.5 during that event over Cyprus and particle number concentrations were as high as 50 cm−3 for the diameter range between 0.8 and 13.9 μm. Comparisons of the total particle number concentration and the particle size distribution from two cases of balloon-borne measurements with aircraft observations show reasonable agreement in magnitude and shape despite slight mismatches in time and space. While column-integrated size distributions from balloon-borne measurements and ground-based remote sensing show similar coarse-mode peak concentrations and diameters, they illustrate the ambiguity related to the missing vertical information in passive sun photometer observations. Extinction coefficient inferred from the balloon-borne measurements agrees with those derived from coinciding Raman lidar observations at height levels with particle number concentrations smaller than 10 cm−3 for the diameter range from 0.8 to 13.9 μm. An overestimation of the extinction coefficient of a factor of two was found for layers with particle number concentrations that exceed 25 cm−3. This is likely the result of a variation in the refractive index, the shape- and size-dependency of the extinction efficiency of dust particles along the UCASS measurements.

The Unmanned Systems Research Laboratory (USRL): A New Facility for UAV-Based Atmospheric Observations

“…Depending on the configuration mode and the laboratory calibration, UCASS can measure either aerosols in the diameter (optical) range between 0.4 and 17.0 µm or cloud droplets in the detection range from 1.0 to 40.0 µm. UCASS airborne particle size distributions and number concentrations were found to be in close resemblance with other reference OPCs on-board the DLR Falcon manned research aircraft [30]. The UCASS DAQ system is the same as the one of OPC-N2 described above.…”

“…High-altitude atmospheric measurements in the upper troposphere and lower stratosphere (up to 15 km) above the Eastern Mediterranean is of particular interest since African dust layers up to 8 km altitude can be observed over Cyprus [30]. The updraft of air pollution from Asia during the monsoon period, the long-range transport of this pollution and its subsidence over the Eastern Mediterranean [31] is another motivation to profile the atmospheric column above Cyprus at higher altitudes.…”

Balloon-borne aerosol–cloud interaction studies (BACIS): field campaigns to understand and quantify aerosol effects on clouds

“…Smith et al (2019) developed a novel, lowcost, and lightweight open-path configuration optical particle counter, UCASS (Universal Cloud Aerosol Sampling System), for a wide range of particle size measurements covering both aerosol and cloud. Kezoudi et al (2021) and Mamali et al (2018) used UCASS to report balloon-borne in situ measurements of dust aerosol and compared UCASS with ground-based and airborne instruments. However, BACIS campaigns are designed to understand and quantify aerosolcloud interactions.…”