Field comparison of dry deposition samplers for collection of atmospheric mineral dust: results from single-particle characterization

Abstract

Abstract. 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.

Investigation of an Intense Dust Outbreak in the Mediterranean Using XMed-Dry Network, Multiplatform Observations, and Numerical Modeling

“…This and the discrepancy between the model and measured deposition indicate the need to apply more sophisticated size depending deposition schemes. These could for example include ultra-Stokesian effects [57], which might affect deposition velocities by 10% for particles with d >10 µm, or could be non-Stokesian deposition models (a list is given e.g., by Waza et al [31]), which might modify effective deposition velocities by more than an order of magnitude. While these models are available in principle, the choice and implementation might be difficult due to their diversity [31] and missing information on boundary conditions (e.g., relevant friction velocities).…”

“…Aerosol dry deposition was collected at three locations for this study: on the flat roof of the Engineering department building (Ecotekne campus) at Lecce ( A novel dry deposition collector with an active rain protection was used. The geometry of its sampling head follows the 'flat-plate' design as described by Waza et al [31]. The function of the spacers in the given design was replaced by an external mounting frame, thus reducing the disturbance of the flow field between the plates.…”

“…Image acquisition was done at 100-150 nm/pixel resolution, and particle size was estimated from their projected cross-sectional area. Particle mass and aerodynamic diameter were estimated from their size assuming preferential flat orientation and a density based on the approximate composition from chemistry (for details refer to Waza et al [31]). X-Ray fluorescence analysis time was chosen to allow for a minimum of 40,000 X-ray counts per particle.…”

Does Satellite Chlorophyll‐a Respond to Southernmost Patagonian Dust? A Multi‐year, Event‐Based Approach

“…One collector is a pyramidal receptacle (CP), with a 2025-cm 2 collection surface suited for measuring vertical dust flux (e.g., Cosentino, Gaiero, et al, 2020;Gaiero et al, 2003Gaiero et al, , 2013Orange et al, 1990;Skonieczny et al, 2011). The other is a Buffalo Spring Number Eight (BSNE) (Fryrear, 1986), with a 10-cm 2 collection surface suited for measuring horizontal dust flux (e.g., Cosentino, Gaiero, et al, 2020;Waza et al, 2019). Both collectors were placed 5 m above ground to avoid collecting local saltation material.…”

“…Individual events are associated with dust-emitting surface areas ranging between 8.3 and 78.4 km 2 , while emission rates range between 1.0 and 34.3 Gg hr −1 (Table S3). BSNE efficiency is between 35% and 45% with no (Goossens & Offer, 2000) or little (Waza et al, 2019) wind speed dependency between 1 and 5 m s −1 . However, wind speed was above this range most of the time in Rio Grande, so that these emission rates should be considered minimum estimates.…”