Asbestos refers to silicate minerals belonging to the serpentine group (chrysotile) and the amphibole group (crocidolite, amosite, tremolite-asbestos, anthophyllite-asbestos and actinolite-asbestos). Such materials have strong effect on health, and real-time instrumentation is on demand to detect asbestos. The current real-time techniques use only some aspects of the optical properties of asbestos, since the scattering properties (brightness and linear polarization scattering functions) of the various natures of asbestos has not been yet fully determined. We present here the brightness and linear polarization scattering functions for 6 natures of asbestos in the 425-1650 nm spectral domain obtained with the PROGRA2 instrument. Although the samples exhibit different shapes, the linear polarization values remain low, bell-shaped as usual for irregular particles, and close to those of mineral particles previously studied with PROGRA2. On the opposite, asbestos brightness curves present strong differences for the different samples. The chrysotile is darker than the other samples in the 80 degrees-150 degrees angle range, probably due to its tubular shape that can act as a light trap for scattering angles greater than a few tens of degrees. Other asbestos particles can be distinguished from building materials such as glass wool or plaster through their brightness curves in some scattering angle ranges. These new laboratory measurements indicate that the optical scattered properties could be used in the future to tentatively detect asbestos particles in a medium generated from building materials. (C) 2020 Elsevier Ltd. All rights reserved.

Mineral dust from arid areas is a major component of global aerosol and has strong interactions with climate and biogeochemistry. As part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) to investigate atmospheric chemistry and its impacts in the Mediterranean region, an intensive field campaign was performed from mid-June to early August 2013 in the western basin including in situ balloon-borne aerosol measurements with the light optical aerosol counter (LOAC). LOAC is a counter/sizer that provides the aerosol concentrations in 19 size classes between 0.2 and 100 µm, and an indication of the nature of the particles based on dual-angle scattering measurements. A total of 27 LOAC flights were conducted mainly from Minorca Island (Balearic Islands, Spain) but also from Ile du Levant off Hyères city (SE France) under 17 light dilatable balloons (meteorological sounding balloons) and 10 boundary layer pressurised balloons (quasi-Lagrangian balloons). The purpose was to document the vertical extent of the plume and the time evolution of the concentrations at constant altitude (air density) by in situ observations. LOAC measurements are in agreement with ground-based measurements (lidar, photometer), aircraft measurements (counters), and satellite measurements (CALIOP) in the case of fair spatial and temporal coincidences. LOAC has often detected three modes in the dust particle volume size distributions fitted by lognormal laws at roughly 0.2, 4 and 30 µm in modal diameter. Thanks to the high sensitivity of LOAC, particles larger than 40 µm were observed, with concentrations up to about 10−4 cm−3. Such large particles were lifted several days before and their persistence after transport over long distances is in conflict with calculations of dust sedimentation. We did not observe any significant evolution of the size distribution during the transport from quasi-Lagrangian flights, even for the longest ones (∼ 1 day). Finally, the presence of charged particles is inferred from the LOAC measurements and we speculate that electrical forces might counteract gravitational settling of the coarse particles.

In the companion (Part I) paper, we have described and evaluated a new versatile optical particle counter/sizer named LOAC (Light Optical Aerosol Counter), based on scattering measurements at angles of 12 and 60°. That allows for some typology identification of particles (droplets, carbonaceous, salts, and mineral dust) in addition to size-segregated counting in a large diameter range from 0.2 µm up to possibly more than 100 µm depending on sampling conditions (Renard et al., 2016). Its capabilities overpass those of preceding optical particle counters (OPCs) allowing the characterization of all kind of aerosols from submicronic-sized absorbing carbonaceous particles in polluted air to very coarse particles (> 10–20 µm in diameter) in desert dust plumes or fog and clouds. LOAC's light and compact design allows measurements under all kinds of balloons, on-board unmanned aerial vehicles (UAVs) and at ground level. We illustrate here the first LOAC airborne results obtained from a UAV and a variety of scientific balloons. The UAV was deployed in a peri-urban environment near Bordeaux in France. Balloon operations include (i) tethered balloons deployed in urban environments in Vienna (Austria) and Paris (France), (ii) pressurized balloons drifting in the lower troposphere over the western Mediterranean (during the Chemistry-Aerosol Mediterranean Experiment – ChArMEx campaigns), (iii) meteorological sounding balloons launched in the western Mediterranean region (ChArMEx) and from Aire-sur-l'Adour in south-western France (VOLTAIRE-LOAC campaign). More focus is put on measurements performed in the Mediterranean during (ChArMEx) and especially during African dust transport events to illustrate the original capability of balloon-borne LOAC to monitor in situ coarse mineral dust particles. In particular, LOAC has detected unexpected large particles in desert sand plumes.

The study of aerosols in the troposphere and in the stratosphere is of major importance both for climate and air quality studies. Among the numerous instruments available, optical aerosol particles counters (OPCs) provide the size distribution in diameter range from about 100 nm to a few tens of µm. Most of them are very sensitive to the nature of aerosols, and this can result in significant biases in the retrieved size distribution. We describe here a new versatile optical particle/sizer counter named LOAC (Light Optical Aerosol Counter), which is light and compact enough to perform measurements not only at the surface but under all kinds of balloons in the troposphere and in the stratosphere. LOAC is an original OPC performing observations at two scattering angles. The first one is around 12°, and is almost insensitive to the refractive index of the particles; the second one is around 60° and is strongly sensitive to the refractive index of the particles. By combining measurement at the two angles, it is possible to retrieve the size distribution between 0.2 and 100 µm and to estimate the nature of the dominant particles (droplets, carbonaceous, salts and mineral particles) when the aerosol is relatively homogeneous. This typology is based on calibration charts obtained in the laboratory. The uncertainty for total concentrations measurements is ±20 % when concentrations are higher than 1 particle cm−3 (for a 10 min integration time). For lower concentrations, the uncertainty is up to about ±60 % for concentrations smaller than 10−2 particle cm−3. Also, the uncertainties in size calibration are ±0.025 µm for particles smaller than 0.6 µm, 5 % for particles in the 0.7–2 µm range, and 10 % for particles greater than 2 µm. The measurement accuracy of submicronic particles could be reduced in a strongly turbid case when concentration of particles > 3 µm exceeds a few particles cm−3. Several campaigns of cross-comparison of LOAC with other particle counting instruments and remote sensing photometers have been conducted to validate both the size distribution derived by LOAC and the retrieved particle number density. The typology of the aerosols has been validated in well-defined conditions including urban pollution, desert dust episodes, sea spray, fog, and cloud. Comparison with reference aerosol mass monitoring instruments also shows that the LOAC measurements can be successfully converted to mass concentrations.

New polarization and brightness curves as a function of scattering angle are studied at λ=632.8 and 543.5nm using PROGRA2 instruments (Propriétés Optiques des Grains Astronomiques et Atmosphériques) for four different kinds of soot and for two samples of carbon-black levitating in the cloud. The soot samples are also studied on the deposited surface. Two of the soot samples are issued from incomplete combustion of Toluene liquid solvent under two different combustion conditions. Two others are issued from a solid polymer. Polymethyl Methacrylate or PMMA under two different combustion conditions. These new studies are done using new more sensitive cameras than previous ones, allowing darker agglomerates to be detected.

Mineral sand is a major component of aerosols in the atmosphere. It is necessary to have a laboratory database to interpret the remote sensing measurements of light scattered by such grains. For this purpose, the PROGRA2 experiment is dedicated to the retrieval of polarization and brightness phase curves, in the visible wavelength domain, of various grains that can be found in Earth's atmosphere and in space. The measurements of the scattered light by levitating clouds of grains are conducted at two wavelengths, 632.8 and 543.5 nm, with PROGRA2-VIS. Large grains (at least tens of micrometers) are studied in microgravity conditions during parabolic flights; smaller (micrometer-sized) grains are lifted by an air draught in ground-based conditions. The PROGRA2-SURF instrument allows measurements on the grains deposited on a plane surface, at the same wavelengths. New data for the scattering properties are presented for sands of various origins, including fine clay. The polarimetric phase curves for levitating grains are close to each other for all the samples (except for black sands); small discrepancies are mainly due to grains' light absorption differences. The polarization curves for levitating grains differ strongly from those of deposited grains (dry or wet). In particular, these curves can be used to interpret remote sensing measurements to distinguish between grains at ground and grains transported by winds.

Measuring linear polarization of light scattered by a cloud of particles can help retrieve their physical properties. We present an extensive study of polarimetric measurements of sand grains that can be found on the surface and in the atmosphere of the Earth. Different techniques of measurements are compared using the Laboratoire de Météorologie Physique nephelometer on the ground and the Propriétés Optiques des Grains Astronomiques et Atmosphériques on the ground and in microgravity during parabolic flights. The techniques used on the ground bias the measurements. When the grains are lifted by an air draft, differentiation is produced in the size distribution and the nature of the floating particles. When the grains are carried along with the airflow, some grains become oriented along the flow direction at air speeds greater than a few meters per second, producing abnormal negative polarization. On the other hand, measurements conducted under microgravity permit the retrieval of the representative optical properties of the lifted sand grains with sizes greater than tens of micrometers.

Measuring linear polarization of light scattered by a cloud of particles can help to retrieve their physical properties. Here we start an extensive study of polarimetric measurements of sand grains that can be found on the surface and in the atmosphere of Earth. Different techniques of measurements are compared using the LaMP nephelometer and PROGRA2 on ground and in microgravity during parabolic flights. The techniques used on ground bias the measurements. When the grains are lifted by air draught, differentiation is produced in the size distribution and nature of floating particles. When the grains are carried along with air flow, some grains become oriented along the flow direction at air speeds greater than a few m/s, producing abnormal negative polarization. On the other hand, measurements conducted under microgravity permit retrieval of the bulk optical properties of lifted sand grains with size greater than tens of micron.

Measuring linear polarization of light scattered by a cloud of particles can help to retrieve their physical properties. Here we start an extensive study of polarimetric measurements of sand grains that can be found on the surface and in the atmosphere of Earth. Different techniques of measurements are compared using the LaMP nephelometer and PROGRA2 on ground and in microgravity during parabolic flights. The techniques used on ground bias the measurements. When the grains are lifted by air draught, differentiation is produced in the size distribution and nature of floating particles. When the grains are carried along with air flow, some grains become oriented along the flow direction at air speeds greater than a few m/s, producing abnormal negative polarization. On the other hand, measurements conducted under microgravity permit retrieval of the bulk optical properties of lifted sand grains with size greater than tens of micron.