Abstract. Knowledge of the particle lidar ratio (Sλ) and the particle linear depolarisation ratio (δλ) for different aerosol types allows for aerosol typing and aerosol-type separation in lidar measurements. Reference values generally originate from dedicated lidar observations but might also be obtained from the inversion of AErosol RObotic NETwork (AERONET) sun/sky radiometer measurements. This study investigates the consistency of spectral Sλ and δλ provided in the recently released AERONET version 3 inversion product for observations of undiluted mineral dust in the vicinity of the following major deserts: Gobi, Sahara, Arabian, Great Basin, and Great Victoria. Pure dust conditions are identified by an Ångström exponent <0.4 and a fine-mode fraction <0.1. The values of spectral Sλ are found to vary for the different source regions but generally show an increase with decreasing wavelength. The feature correlates to AERONET, retrieving an increase in the imaginary part of the refractive index with decreasing wavelength. The smallest values of Sλ=35–45 sr are found for mineral dust from the Great Basin desert, while the highest values of 50–70 sr have been inferred from AERONET observations of Saharan dust. Values of Sλ at 675, 870, and 1020 nm seem to be in reasonable agreement with available lidar observations, while those at 440 nm are up to 10 sr higher than the lidar reference. The spectrum of δλ shows a maximum of 0.26–0.31 at 1020 nm and decreasing values as wavelength decreases. AERONET-derived δλ values at 870 and 1020 nm are in line with the lidar reference, while values of 0.19–0.24 at 440 nm are smaller than the independent lidar observations by a difference of 0.03 to 0.08. This general behaviour is consistent with earlier studies based on AERONET version 2 products.

Abstract. A low-cost miniaturized particle counter has been developed by The University of Hertfordshire (UH) for the measurement of aerosol and droplet concentrations and size distributions. The Universal Cloud and Aerosol Sounding System (UCASS) is an optical particle counter (OPC), which uses wide-angle elastic light scattering for the high-precision sizing of fluid-borne particulates. The UCASS has up to 16 configurable size bins, capable of sizing particles in the range 0.4–40 µm in diameter. Unlike traditional particle counters, the UCASS is an open-geometry system that relies on an external air flow. Therefore, the instrument is suited for use as part of a dropsonde, balloon-borne sounding system, as part of an unmanned aerial vehicle (UAV), or on any measurement platform with a known air flow. Data can be logged autonomously using an on-board SD card, or the device can be interfaced with commercially available meteorological sondes to transmit data in real time. The device has been deployed on various research platforms to take measurements of both droplets and dry aerosol particles. Comparative results with co-located instrumentation in both laboratory and field settings show good agreement for the sizing and counting ability of the UCASS.

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Knowledge of the particle lidar ratio (S&lt;sub&gt;&amp;#955;&lt;/sub&gt;) and the particle linear depolarisation ratio (&amp;#948;&lt;sub&gt;&amp;#955;&lt;/sub&gt;) for different aerosol types allows for aerosol typing and aerosol-type separation in lidar measurements. Reference values generally originate from dedicated lidar observations but might also be obtained from the inversion of AERONET sun/sky radiometer measurements. This study investigates the consistency of spectral S&lt;sub&gt;&amp;#955;&lt;/sub&gt; and &amp;#948;&lt;sub&gt;&amp;#955;&lt;/sub&gt; provided in the recently released AERONET version 3 inversion product for observations of undiluted mineral dust in the vicinity of major deserts: Gobi, Sahara, Arabian, Great Basin and Great Victoria deserts. Pure dust conditions are identified by an &amp;#197;ngst&amp;#246;m exponent &lt;&amp;#8201;0.4 and a fine-mode fraction &lt;&amp;#8201;0.1. &lt;br&gt;&lt;br&gt; The values of spectral S&lt;sub&gt;&amp;#955;&lt;/sub&gt; are found to vary for the different source regions but generally show an increase with decreasing wavelength. The feature correlates to AERONET retrieving an increase in the imaginary part of the refractive index with decreasing wavelength. The smallest values of S&lt;sub&gt;&amp;#955;&lt;/sub&gt;&amp;#8201;=&amp;#8201;35&amp;#8211;45&amp;#8201;sr are found for mineral dust from the Great Basin desert while the highest values of 50&amp;#8211;70&amp;#8201;sr have been inferred from AERONET observations of Saharan dust. Values of S&lt;sub&gt;&amp;#955;&lt;/sub&gt; at 675, 870, and 1020&amp;#8201;nm seem to be in reasonable agreement with available lidar observations while those at 440&amp;#8201;nm are up to 10&amp;#8201;sr higher than the lidar reference. The spectrum of &amp;#948;&lt;sub&gt;&amp;#955;&lt;/sub&gt; shows a maximum of 0.26&amp;#8211;0.31 at 1020&amp;#8201;nm and decreasing values as wavelength decreases. AERONET-derived &amp;#948;&lt;sub&gt;&amp;#955;&lt;/sub&gt; at 870 and 1020&amp;#8201;nm are close to the lidar reference while values of 0.19&amp;#8211;0.24 at 440&amp;#8201;nm are smaller than the independent lidar observations. This general behaviour is consistent with earlier studies based on AERONET version 2 products.&lt;/p&gt;

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) of the Cyprus Institute is a new mobile exploratory platform of the EU Research Infrastructure Aerosol, Clouds and Trace Gases Research InfraStructure (ACTRIS). USRL offers exclusive Unmanned Aerial Vehicle (UAV)-sensor solutions that can be deployed anywhere in Europe and beyond, e.g., during intensive field campaigns through a transnational access scheme in compliance with the drone regulation set by the European Union Aviation Safety Agency (EASA) for the research, innovation, and training. UAV sensor systems play a growing role in the portfolio of Earth observation systems. They can provide cost-effective, spatial in-situ atmospheric observations which are complementary to stationary observation networks. They also have strong potential for calibrating and validating remote-sensing sensors and retrieval algorithms, mapping close-to-the-ground emission point sources and dispersion plumes, and evaluating the performance of atmospheric models. They can provide unique information relevant to the short- and long-range transport of gas and aerosol pollutants, radiative forcing, cloud properties, emission factors and a variety of atmospheric parameters. Since its establishment in 2015, USRL is participating in major international research projects dedicated to (1) the better understanding of aerosol-cloud interactions, (2) the profiling of aerosol optical properties in different atmospheric environments, (3) the vertical distribution of air pollutants in and above the planetary boundary layer, (4) the validation of Aeolus satellite dust products by utilizing novel UAV-balloon-sensor systems, and (5) the chemical characterization of ship and stack emissions. A comprehensive overview of the new UAV-sensor systems developed by USRL and their field deployments is presented here. This paper aims to illustrate the strong scientific potential of UAV-borne measurements in the atmospheric sciences and the need for their integration in Earth observation networks.