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 UCASS-derived extinction coefficient of a factor of 2 compared to the lidar measurement was found for layers with particle number concentrations that exceed 25 cm−3, i.e. in the centre of the dust plume where particle concentrations were highest. This is likely the result of a variation in the refractive index and the shape and size dependency of the extinction efficiency of dust particles along the UCASS measurements. In the future, profile measurements of the particle number concentration and particle size distribution with the UCASS could provide a valuable addition to the measurement capabilities generally used in field experiments that are focussed on the observation of coarse aerosols and clouds.

Investigation of the Vertical Distribution Characteristics and Microphysical Properties of Summer Mineral Dust Masses over the Taklimakan Desert Using an Unmanned Aerial Vehicle

“…The PNC in the desert area was approximately 1/10th of that in the urban area, whereas R eff and Cv were larger than the values observed by urban UAV and mobile monitoring. In addition, R eff was similar to observations in desert and forest land; however, the PNC varied greatly [37,52,53].…”

“…Some relevant studies were reviewed for comparison with previous observations. As listed in Table 3, only a few studies have addressed these parameters based on UAV, and large differences exist between the values obtained from observations of different land types [34,37,52,53]. The particle size range of the instrument carried by Weinzierl during UAV observations in the Sahara Desert was similar to that in this study.…”

“…For example, [33] used aircraft and tethered balloons to investigate the vertical structure of the aerosol size distribution showing particles characterized by a large size within a dust plume during the Charmex campaign in 2013. However, aircraft require an airport to initiate frequent deployment of exhaust engines, which requires us to consider the limitations of the site [34][35][36][37][38]. Currently, the unique advantages attributed to unmanned aerial vehicles (UAVs), namely, having strong mobility and stability, and being exhaust-free, low-risk, and cost-effective, help detect lower tropospheric atmospheres and are considered one of the most suitable platforms for observing the vertical distribution of aerosols and measuring their physical and optical properties.…”

A review of coarse mineral dust in the Earth system

“…Renard et al (2018) frequently observed particles sized larger than 40 μm at concentrations above 10 -4 cm -3 at a distance from source regions. Other instruments, such as the Universal Cloud and Aerosol Sounding System (UCASS, Smith et al, 2019), a lightweight OPC which can be deployed on radiosondes, dropsondes or UAVs to measure size distributions between optical diameters between 0.4 to 17 μm have also been developed and show promising results (Kezoudi et al, 2021a(Kezoudi et al, , 2021b.…”