Frequently, passive dry deposition collectors are used to sample atmospheric dust deposition. However, there exists a multitude of different instruments with different, usually not well-characterized sampling efficiencies. As a result, the acquired data might be considerably biased with respect to their size representativity and, as a consequence, also composition. In this study, individual particle analysis by automated scanning electron microscopy coupled with energy-dispersive X-ray analysis was used to characterize different, commonly used passive samplers with respect to their size-resolved deposition rate and concentration. This study focuses on the microphysical properties, i.e., the aerosol concentration and deposition rates as well as the particle size distributions. In addition, computational fluid dynamics modeling was used in parallel to achieve deposition velocities from a theoretical point of view. Scanning electron microscopy (SEM)-calculated deposition rate measurements made using different passive samplers show a disagreement among the samplers. Modified Wilson and Cooke (MWAC) and Big Spring Number Eight (BSNE) – both horizontal flux samplers – collect considerably more material than the flat plate and Sigma-2 samplers, which are vertical flux samplers. The collection efficiency of MWAC increases for large particles in comparison to Sigma-2 with increasing wind speed, while such an increase is less observed in the case of BSNE. A positive correlation is found between deposition rate and PM₁₀ concentration measurements by an optical particle spectrometer. The results indicate that a BSNE and Sigma-2 can be good options for PM₁₀ measurement, whereas MWAC and flat-plate samplers are not a suitable choice. A negative correlation was observed in between dust deposition rate and wind speed. Deposition velocities calculated from different classical deposition models do not agree with deposition velocities estimated using computational fluid dynamics (CFD) simulations. The deposition velocity estimated from CFD was often higher than the values derived from classical deposition velocity models. Moreover, the modeled deposition velocity ratios between different samplers do not agree with the observations.

Mineral dust composition affects a multitude of processes in the atmosphere and adjacent compartments. Dust dry deposition was collected near source in northwest Africa, in Central Asia, and on Svalbard and at three locations of the African outflow regime. Samples were subjected to automated scanning electron microscopy with energy-dispersive X-ray analysis to obtain size and composition of 216,000 individual particles. Results show low temporal variation in estimated optical properties for each location, but considerable differences between the African, Central Asian, and Arctic regimes. No significant difference was found between the K-feldspar relative abundances, indicating comparable related ice-nucleation abilities. The mixing state between calcium and iron compounds was different for near source and transport regimes, potentially in part due to size sorting effects. As a result, in certain situations (high acid availability, limited time) atmospheric processing of the dust is expected to lead to less increased iron solubility for near-source dusts (in particular for Central Asian ones) than for transported ones (in particular of Sahelian origin).

In this paper, individual particle analysis by automated scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) was used to assess the size-resolved information of composition, size distribution, complex refractive index, and mixing state of mineral dust aerosol particles collected using different passive and active samplers. In the study, over 120,000 particles from 53 samples were analyzed. Results show that dust particles are the dominating mineral particle type during this campaign, comprising different classes of silicates, Si-rich (quartz-like), Ca-rich (calcite-like), CaMg-rich (dolomite-like), and CaS-rich (gypsum-like). The results also show that there is no significant difference in composition between suspended and deposited dust particles. By using the particle composition, the size-resolved complex refractive index of dust particles was calculated. The real part of the refractive index varied between 1.71 and 1.53 for wavelengths in the range of 370 to 950 nm. The imaginary part of the refractive index, determined mostly by iron oxide, varied between $3.28\times {10}^{-4}$ and $7.11\times {10}^{-5}$ for wavelengths ranging from 250 nm to 1640 nm. In addition, the refractive index values showed a slight decrease with increasing particle size. We also analyzed the potential for buffering of the acid mobilization of iron by other dust compounds. For particles which contain both iron (Fe) and (unprocessed) calcium (Ca), acids that are able to dissolve insoluble Fe particles can react with the Ca particles before reacting with Fe, but eventually, with longer processing time, the Fe particles could be processed. By analyzing the ratio of sulfate mass to the total aerosol mass of individual particles, the mixing state of sulfate particles to the total dust particles was investigated. The analysis showed that the finer dust particles were associated with higher content of sulfate, while the coarse dust particles correspond to lower sulfate contents, revealing that only fine mode sulfate is more internally mixed with mineral dust aerosol particles.

Ozone (O₃) phytotoxicity is a serious concern all over the globe. O₃ can cause both biochemical and physiological changes to plants that could lead to reduction in growth and yield. Its effect on agricultural crops is usually detected as foliar injury. Although foliar injury has frequently served as physiological basis for monitoring performance of agricultural crops and assessing air quality, its visibility depends on period of exposure, concentration of ozone, and environmental conditions. The present study focused on the determination of biochemical indicators of ozone phytotoxicity including Rubisco (biochemical indicator for carbon assimilation), photo-pigments [carotenoids and chlorophyll (a & b)], and chlorophyll photochemical efficiency on a judiciously selected plant-Nicotiana tabacum (Tobacco), variety: Little Havanna. An enclosed computer controlled growth chamber was used for cultivation of the experimental plant groups (ozone exposed and control). Spectrophotometric measurements of the biochemical indicators were carried out to evaluate the exposure-response behaviour of the plant. Our results showed a significant (P< 0.05) decrease of the biochemical indicators that is reproducible even when foliar injury is not detected. Besides, experiments also showed that chlorophyll a is more sensitive to ozone than chlorophyll b. The instrumental readings were supported by a reduction in total organic nitrogen and starch content and ultimate decrease in growth rate and root: shoot ratio. While significant variations in the intensities of foliar injury can be detected among plants within a group, a reproducible exposure-response data were obtained from instrumental measurements. Such measurements can also serve as basis for the development of implantable sensors for in-situ monitoring of ozone pollution in sensitive crops.

Wind driven dust resuspension is actively and ubiquitously observed at the surface of Mars, however the mechanisms involved, and conditions required are poorly understood (Neakrase et al., 2016). The objective of this laboratory study is to investigate various dust resuspension mechanisms using a unique set of recirculating environmental wind tunnel facilities at Aarhus University (Holstein-Rathlou et al., 2014). This study employs various sensor techniques including digital microscopy and optical reflectance to quantify dust removal as well as Laser Doppler Velocimetry and optical opacity measurement for determining dust concentration (Jakobsen et al., 2019). Importantly in these studies the dust was deposited from suspension within an environmental wind tunnel (Merrison et al., 2008).Already from preliminary experiments significant advancements in our knowledge of dust resuspension have been made. Specifically, for the first time under Martian conditions direct wind driven dust remobilization has been observed (Rondeau et al., 2015). As expected, the process involved dust aggregate detachment and transport. Also for the first time saltation induced dust resuspension has been recreated (i.e. impact induced dust resuspension) from a loose sand bed coated with dust. Interestingly preliminary estimates have shown that both of these mechanisms appear to have similar values of threshold shear stress of around 0.07Pa, this is close to the expected threshold for saltation (Andreotti et al., 2021). It is hoped that both the resuspension flux and threshold can be quantified.These studies are part of an international EU supported research project called ROADMAP (https://roadmap.aeronomie.be/). Three Mars analogue dust prototypes ‘are being used in these experiments. These have been developed and characterized by the ROADMAP team.AcknowledgmentsThis project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004052.ReferencesAndreotti, B., Claudin, P., Iversen, J. J., Merrison, J. P., and Rasmussen, K. R.: A lower-than-expected saltation threshold at Martian pressure and below, Proceedings of the National Academy of Sciences, 118, 2021.Holstein-Rathlou, C., Merrison, J., Iversen, J., Jakobsen, A., Nicolajsen, R., Nørnberg, P., Rasmussen, K., Merlone, A., Lopardo, G., and Hudson, T.: An environmental wind tunnel facility for testing meteorological sensor systems, Journal of atmospheric and oceanic technology, 31, 447-457, 2014.Jakobsen, A. B., Merrison, J., and Iversen, J. J.: Laboratory study of aerosol settling velocities using laser Doppler velocimetry, Journal of Aerosol Science, 135, 58-71, 2019.Merrison, J. P., Bechtold, H., Gunnlaugsson, H., Jensen, A., Kinch, K., Nornberg, P., and Rasmussen, K.: An environmental simulation wind tunnel for studying Aeolian transport on mars, Planetary and Space Science, 56, 426-437, 2008.Neakrase, L., Balme, M., Esposito, F., Kelling, T., Klose, M., Kok, J., Marticorena, B., Merrison, J., Patel, M., and Wurm, G.: Particle lifting processes in dust devils, Space Science Reviews, 203, 347-376, 2016.Rondeau, A., Merrison, J., Iversen, J. J., Peillon, S., Sabroux, J.-C., Lemaitre, P., Gensdarmes, F., and Chassefière, E.: First experimental results of particle re-suspension in a low pressure wind tunnel applied to the issue of dust in fusion reactors, Fusion Engineering and Design, 98, 2210-2213, 2015.

Activities at a European Planetary Simulation Facility   J. P. Merrison, J.J. Iversen, K.R. Rasmussen, A. Waza 1Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus  C, Denmark (merrison@phys.au.dk/ Fax: +45-86120740)  AbstractThis unique and now improved planetary simulation facility is capable of re-creating extreme terrestrial, Martian and other planetary environments. It is supported by EU activities including Europlanet 2024 RI here the latest research and networking activities will be presented. This facility is also used as a test facility by ESA and NASA Mars missions. Specifically it is capable of recreating the key physical parameters such as temperature, pressure (gas composition), wind flow and importantly the suspension/transport of dust, sand or ice particulates. This facility is available both to the scientific and Industrial communities.  Europlanet Transnational Access  This environmental simulator facility is utilized for a broad range of research programs including; the study of other planets (such as Mars), for recreating extreme terrestrial environments, or in specific investigations involving aerosols and other forms of Aeolian particulate transport. The facility is also involved in the Europlanet 2024 Research Infrastructure through which a trans-national access program is allowing numerous research groups access to this facility. Some selected recent and upcoming projects are listed below;Polar CO2 ice on Mars (USA) [5] LIBS system on Mars2020 (ISAE France) [3] Sand transport and ripples on Mars (P. Claudin, B. Andreotti, et al. 2019) Dust aerosols at low pressure. INGV, I [6] Flow Testing of a Sonic Anemometer for the Martian Environment (USA) [4] In-situ utilization on Mars2020 and dust loading. Imperial College UK [7] Other activities include the development, testing and calibration of sensor and planetary lander systems, both for ESA and NASA. Testing for missions ExoMars 2020 and Mars Perseverance were carried out.  Figure 1 The main Planetary Simulation Facility 2022 carrying out a Europlanet2022RI funded experiments involving sand transport under Marian conditions and guests;  Design and operation  The simulator consists of a 38m3 environmental (thermal-vacuum) chamber within which a re-circulating wind tunnel is housed [1]. The wind is generated by a set of two fans which draw flow down the 2m×1m tunnel section and return it above and below. Wind speeds in the range 1-40 m/s have been demonstrated. Cooling is achieved by a novel liquid nitrogen flow system which has achieved temperatures below -160ºC. The inner chamber is thermally isolated from the vacuum chamber. An atmospheric cooling system allowing independent control of the air temperature (tested to -50°C) and a range of particle imaging, microscopy and laser based techniques allow study of aerosols [2].Improved functionalities of this facility (funded by Europlanet 2024RI) include the implementation of; improved pumping capabilities to lower pressure (<10-4mbar) and improved aeroslization systems for dust and ice studies. Additional recent sensor systems include a new Laser Doppler Velocimeter system and an optical transmission (opacity) sensor for studying aerosol properties.  Figure 2 studying resuspended dust using a Laser Doppler Velocimeter and a light transmission (opacity) system.  Sand, dust and ices on Mars  With control of wind flow at low pressure and temperature this facility is well suited for recreating the environment at the surfaces of terrestrial type planets such as Mars, Earth and Titan. The interaction of wind and the planetary surface, specifically the transport of sand and dust is fundamental to understanding the evolution of the planets’ surface and atmosphere. Laboratory studies of the entrainment, flow, deposition and erosion are scarce and empirical in nature. The effects of low atmospheric pressure, composition, temperature can now be studied in detail.This laboratory is part of an EU supported European collaboration called ROADMAP including groups from BIRA in Belgium, CSIC in Spain and UDE in Germany, to study dust aerosols on Mars [Home (aeronomie.be)]Recently Martian Aeolian ripples have been recreated in experiments to investigate the behaviour of wind-driven sand transport under decreasing pressures, from the ambient (1 bar) towards Martian atmospheric conditions, and even to lower pressures than on Mars (2 mbar). In comparison to terrestrial conditions, sand transport at Martian pressures is significantly modified by viscous effects. However, centimeter-scale ripples nevertheless emerge (fig. 2), which match observations made by NASA’s rover Opportunity on the surface of Martian dunes. Fig. 3 Ripples created at low pressure (P. Claudin, B. Andreotti, et al.).  Conclusion  This planetary simulation facility has many unique and recently improved features which make it well suited for both planetary research applications and the development/testing of instrumentation. Details of some of the most recent and upcoming collaborative research activities will be summarized. For information on access to this facility please contact the author.AcknowledgementsThis laboratory is a member of Europlanet 2024 RI which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 871149.The laboratory is also a member of the ROADMAP  project which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004052.References[1] C. Holstein-Rathlou, et al., American Meteorological Society, 31, 447 (2014)[2] S. Alois et al., J. Aerosol Science 106, 1, (2017)[3] Murdoch, N., et al., Planet and Space Sci, 165 (2019) 260-271[4] White, R. D. et al. AIAA Scitech 2020. AIAA2020-0712[5] G. Portyankina et al., Icarus 322,...