Arizona Test Dust Research Articles

Resuspension of inhalable particles from clothing: A manikin-based chamber study

Clothing plays a significant role in facilitating inhalation exposure to particulate matter (PM). Nevertheless, there is a lack of studies investigating PM resuspension from clothing. This study aims to quantify size-resolved PM resuspension rate (RR) from clothing while exploring the effects of factors influencing this process. In a controlled chamber, we deposited Arizona Test Dust on a seated and clothed thermal manikin. The seated manikin was then placed in a resuspension chamber to perform arm movements using a consistent test mechanism. We evaluated the size-resolved resuspension rates in the diameter range 0.3–10 μm as a function of long-sleeve clothing type (cotton shirts vs. polyacrylic sweaters), relative humidity (RH) (35 vs. 70 %), dust loading (204 vs. 321 mg/m2), and movement intensity (0.25, 0.5, and 0.75 Hz). The short-term PM10 concentration in the breathing zone was 1.25 times higher than in the bulk air during resuspension. The size-dependent RR varied between 0.01 h−1 and 0.06 h−1. Higher RR was associated with higher movement intensity and dust loading on clothing, while a small dependence was found on clothing type and RH. The results offer a valuable dataset for enhancing current inhalation exposure models related to indoor aerosols and for developing targeted interventions to reduce exposure to particles associated with clothing.

Development of a two-stage virtual impactor for the generation of micrometer-scale monodisperse aerosols

Monodisperse particles are useful across a wide range of industrial applications, such as LCD displays, solar cells and rechargeable batteries, due to their uniformly small sizes. However, generating high volumes of monodisperse particles remains challenging. In this study, it was aimed to generate monodisperse aerosols by classifying micrometer-scale solid aerosol particles within a narrow size range. Accordingly, a new particle-size classification device with two virtual impactors connected in series and clean air cores was developed. The first-stage virtual impactor had a slightly larger cutoff size than the second-stage, and the major flow discharged from the first-stage was directed to the second-stage. The target particle size range was altered by changing the nozzle sizes in the first and second stages or by adjusting the flow rate. Subsequently, the classification performance of the two-stage virtual impactor was simulated and validated through an experiment using Arizona test dust. The implemented combinations of cutoff sizes for the first and second stages were 3.0 and 2.0 μm, 3.9 and 2.7 μm, or 6.7 and 4.8 μm. As a result, monodisperse aerosol particles were classified at a geometric standard deviation of 1.04–1.14 and a particle size range of 2–6.7 μm. The two-stage virtual impactor developed herein may be useful for various research and performance evaluations, as it can classify micrometer-scale solid particle aerosols that exhibit high monodispersity.

Assessing the oxidative potential of dust from great salt Lake

Great Salt Lake (GSL) is one of the world's largest inland bodies of saltwater. Climate change, drought, and water diversions have led to the GSL reaching historically low levels, exposing over 1945 km2 of lakebed. Dust events can transport particulate matter (PM) from the GSL's exposed lakebed to the adjacent urban areas, presenting air quality and health concerns. In this study, we assessed the oxidative potential (OP) of dust from the exposed GSL bed compared to dust samples collected from other regional playas and to reference Arizona test dust. The oxidative potential of PM10 (particles ≤10 μm in aerodynamic diameter) derived from these dusts was assessed by two acellular assays: the ascorbic acid (OPAA) and dithiothreitol (OPDTT) and two extraction solvents: phosphate buffer saline and Gamble's simulated lung fluid. All samples were also analyzed for elemental composition. Our results show that the concentration of As and Li in most of the GSL dust samples exceeded the Environmental Protection Agency (EPA) soil residential regional screening levels, and the OPAA and OPDTT of dust samples from GSL playas were generally higher than the OP of other regional playas. Our findings also indicated that the OP of the GSL dust was associated with metals, including Cu, Mn, Fe, and Al. This is the first study evaluating the oxidative potential of dust from the GSL, which improves our understanding of how increasing aridity, particularly desiccation of saline lakes, affects air quality and public health.

Iron content in aerosol particles and its impact on atmospheric chemistry.

Atmospheric aerosol effects on ecological and human health remain uncertain due to their highly complex and evolving nature when suspended in air. Atmospheric chemistry, global climate/oceanic and health exposure models need to incorporate more realistic representations of aerosol particles, especially their bulk and surface chemistry, to account for the evolution in aerosol physicochemical properties with time. (Photo)chemistry driven by iron (Fe) in atmospheric aerosol particles from natural and anthropogenic sources remains limited in these models, particularly under aerosol liquid water conditions. In this feature article, recent advances from our work on Fe (photo)reactivity in multicomponent aerosol systems are highlighted. More specifically, reactions of soluble Fe with aqueous extracts of biomass burning organic aerosols and proxies of humic like substances leading to brown carbon formation are presented. Some of these reactions produced nitrogen-containing gaseous and condensed phase products. For comparison, results from these bulk aqueous phase chemical studies were compared to those from heterogeneous reactions simulating atmospheric aging of Fe-containing reference materials. These materials include Arizona test dust (AZTD) and combustion fly ash particles. Also, dissolution of Fe and other trace elements is presented from simulated human exposure experiments to highlight the impact of aerosol aging on levels of trace metals. The impacts of these chemical reactions on aerosol optical, hygroscopic and morphological properties are also emphasized in light of their importance to aerosol-radiation and aerosol-cloud interactions, in addition to biogeochemical processes at the sea/ocean surface microlayer upon deposition. Future directions for laboratory studies on Fe-driven multiphase chemistry are proposed to advance knowledge and encourage collaborations for efficient utilization of expertise and resources among climate, ocean and health scientific communities.

Comprehensive performance evaluation of six bioaerosol samplers based on an aerosol wind tunnel

Choosing a suitable bioaerosol sampler for atmospheric microbial monitoring has been a challenge to researchers interested in environmental microbiology, especially during a pandemic. However, a comprehensive and integrated evaluation method to fully assess bioaerosol sampler performance is still lacking. Herein, we constructed a customized wind tunnel operated at 2–20 km/h wind speed to systematically and efficiently evaluate the performance of six frequently used samplers, where various aerosols, including Arizona test dust, bacterial spores, gram-positive and gram-negative bacteria, phages, and viruses, were generated. After 10 or 60 min of sampling, the physical and biological sampling efficiency and short or long-term sampling capabilities were determined by performing aerodynamic particle size analysis, live microbial culturing, and a qPCR assay. The results showed that AGI-30 and BioSampler impingers have good physical and biological sampling efficiencies for short-term sampling. However, their ability to capture aerosols at low concentrations is restricted. SASS 2300 and BSA-350 wet-wall cyclones had excellent enrichment ratios and high microbial cultivability in both short-term and long-term sampling; however, they were not suitable for quantitative studies of aerosols. Polycarbonate filter samplers showed outstanding performance in physical and long-term sampling but lacked the ability to maintain microbial activity, which can be improved by gelatin filter samplers. However, limitations remain for some fragile microorganisms, such as E. coli phage PhiX174 and coronavirus GX_P2V. In addition, the effects of wind speed and direction should be considered when sampling particles larger than 4 µm. This study provides an improved strategy and guidance for the characterization and selection of a bioaerosol sampler for better measurement and interpretation of collected ambient bioaerosols.

Prebiotic synthesis of mineral-bearing microdroplet from inorganic carbon photoreduction at air-water interface.

The origin of life on Earth is an enigmatic and intricate conundrum that has yet to be comprehensively resolved despite recent significant developments within the discipline of archaeology and geology. Chemically, metal-sulfide minerals are speculated to serve as an important medium for giving birth in early life, while yet so far direct evidence to support the hypothesis for the highly efficient conversion of inorganic carbon into praxiological biomolecules remains scarce. In this work, we provide an initial indication that sphalerite, employed as a typical mineral, shows its enormous capability for promoting the conversion of inorganic carbon into elementary biomolecule formic acid (HCOOH) in airborne mineral-bearing aerosol microdroplet, which is over two orders of magnitude higher than that of the corresponding conventional bulk-like aqueous phase medium in the environment (e.g. river, lake, sea, etc.). This significant enhancement was further validated by a wide range of minerals and clays, including CuS, NiS, CoS, CdS, MnS, elemental sulfur, Arizona Test Dust, loess, nontronite, and montmorillonite. We reveal that the abundant interface of unique physical-chemical features instinct for aerosol or cloud microdroplets reduces the reaction energy barrier for the reaction, thus leading to extremely high HCOOH production (2.52 × 1014 kg year-1). This study unfolds unrecognized remarkable contributions of the considered scheme in the accumulation of prebiotic biomolecules in the ancient period of the Earth.

Performance evaluation of particulate matter removal by surfactant foams

Surfactant foams can be repeatedly formed and ruptured, providing an extensive surface area which can be utilized for the contaminant removal. In order to mitigate the expenses associated with filter maintenance in the filter-equipped device, the particulate matter removal was attempted by the surfactant foam in this study, aiming to assess the feasibility as an alternative technology for improving air quality. Two types of particulate matter (Arizona test dust (ATD) and incense stick) and two types of surfactants (SLS-30 and LAO) were adopted to evaluate the removal efficiency of particulate matter under different surfactant concentrations (0.05, 0.1, and 0.2 wt%) and different flow systems (with and without internal airflow). Overall, ATD were better removed than incense stick due to the larger size which resulted in the greater sedimentation and subsequent contact with foams. Also, SLS-30 showed better removal performance than LAO as the surfactant concentration increased from 0.05 wt% to 0.2 wt%. These findings can be attributed to foam generation properties, in which SLS-30 demonstrated superior foam generation capabilities as the surfactant concentration increased, providing a larger surface area for PM adsorption as well as suppressing the remaining headspace in the chamber. The findings in this study presents the advantageous utilization of foams as an adsorbent for PM as well as a filling material in the limited space, thereby enabling enhanced PM removal capabilities.

Next-generation ice-nucleating particle sampling on board aircraft: characterization of the High-volume flow aERosol particle filter sAmpler (HERA)

Abstract. Atmospheric ice-nucleating particle (INP) concentration data from the free troposphere are sparse but urgently needed to understand vertical transport processes of INPs and their influence on cloud formation and properties. Here, we introduce the new High-volume flow aERosol particle filter sAmpler (HERA) which was specially developed for installation on research aircraft and subsequent offline INP analysis. HERA is a modular system consisting of a sampling unit and a powerful pump unit, and it has several features which were integrated specifically for INP sampling. Firstly, the pump unit enables sampling at flow rates exceeding 100 L min−1, which is well above typical flow rates of aircraft INP sampling systems described in the literature (∼ 10 L min−1). Consequently, required sampling times to capture rare, high-temperature INPs (≥ −15 ∘C) are reduced in comparison to other systems, and potential source regions of INPs can be confined more precisely. Secondly, the sampling unit is designed as a seven-way valve, enabling switching between six filter holders and a bypass with one filter being sampled at a time. In contrast to other aircraft INP sampling systems, the valve position is remote-controlled via software so that manual filter changes during flight are eliminated and the potential for sample contamination is decreased. This design is compatible with a high degree of automation, i.e., triggering filter changes depending on parameters like flight altitude, geographical location, temperature, or time. In addition to presenting the design and principle of operation of HERA, this paper describes laboratory characterization experiments with size-selected test substances, i.e., SNOMAX® and Arizona Test Dust. The particles were sampled on filters with HERA, varying either particle diameter (300 to 800 nm) or flow rate (10 to 100 L min−1) between experiments. The subsequent offline INP analysis showed good agreement with literature data and comparable sampling efficiencies for all investigated particle sizes and flow rates. Furthermore, the collection efficiency of atmospheric INPs in HERA was compared to a straightforward filter sampler and good agreement was found. Finally, results from the first campaign of HERA on the High Altitude and LOng range research aircraft (HALO) demonstrate the functionality of the new system in the context of aircraft application.

Vibrational spectroscopy as a probe of heterogeneities within geochemical thin films on macro, micro, and nanoscales.

Minerals play a critical role in the chemistry occurring along the interface of different environmental systems, including the atmosphere/geosphere and hydrosphere/geosphere. In the past few decades, vibrational spectroscopy has been used as a probe for studying interfacial geochemistry. Here, we compare four different vibrational methods for probing physical and chemical features across different mineral samples and length scales, from the macroscale to nanoscale. These methods include Attenuated Total Reflection - Fourier Transform Infrared (ATR-FTIR), Optical Photothermal Infrared (O-PTIR), Atomic Force Microscopy-Infrared (AFM-IR) and micro-Raman spectroscopy. The emergence of these micro-spectroscopic probes has offered new insights into heterogeneities within geochemical thin films and particles. These developments represent an important step forward for analyzing environmental interfaces and thin films as often these are assumed to be physically and chemically homogeneous. By comparing and integrating data across these measurement techniques, new insights into sample differences and heterogeneities can be gained. For example, interrogation of the various mineral samples at smaller length scales is shown to be particularly informative in highlighting unique chemical environments, including for chemically complex, multicomponent samples such as Arizona Test Dust (AZTD), as well as differences due to crystal orientation.

The Kinetics of Adsorption and Desorption of Selected Semivolatile Hydrocarbons and H2O Vapor on Two Mineral Dust Materials: A Molecular View.

A flowing gas experiment using a Knudsen flow reactor was performed on a series of seven semivolatile probe gases interacting with two often used mineral dust materials, namely, coarse Arizona test dust (ATD-C) and kaolinite. The semivolatile probe gases used were applinate (acetate ester), pipol (ethyl ester of 2-methylvaleric acid), benzylacetate (acetate ester of benzylalcohol), menthol (alcohol), toluene, limonene, and γ-terpinene (terpene hydrocarbon). Uptake experiments under molecular flow conditions resulted in absolute coverages and initial uptake coefficients γ0 based on the geometric sample surface. Integration of a simple Langmuir adsorption model afforded an analytical solution of the desorption kinetics of the semivolatile hydrocarbon upon spontaneous desorption from the solid mineral dust substrate at ambient temperature. Numerical fitting of the desorption rate resulted in adsorption (ka) and desorption (kd) rate constants, where 1/kd represented the surface residence time of the adsorbed semivolatile. The major conclusions are as follows: (a) Desorption at short ("prompt") and long time scales reveal stronger binding to ATD compared to kaolinite for all tested organic probe gases. (b) No difference in the desorption yields and kinetics was observed for H2O vapor on either substrate. (c) Prompt desorption at ambient temperature starts with the immediate detection of probe gases adsorbed on the vessel walls of the sample compartment, followed by the slower growth and decay of semivolatiles adsorbed on the substrate, leading to ka and kd. (d) Surface residence times at ambient temperatures for semivolatile organics vary from 50 to 40 000 s for toluene/ATD and menthol/ATD, respectively. For H2O vapor, 3000 s was measured on both kaolinite and ATD. (e) Large initial uptake coefficients γ0 in the range of 0.25-0.77 were measured for all semivolatiles except toluene, whose values were lower by roughly one order of magnitude. Rapid saturation was observed in all cases except for limonene, which appeared to undergo chemical reactions on both mineral substrates.

Suspended matter filtration causes a counterintuitive increase in UV-absorption.

In water treatment, filtration is often a first step to avoid interference of chemical or UV-disinfection with suspended matter (SPM). Surprisingly, in testing a ballast water filter with 25 and 40μm mesh screens, UV-absorption (A, 254nm) of filtered water increased with the largest increase in the finest screen. The hypothesis that filtration partly removes large particles and partly replaces them with small unfiltered ones, leading to an overall increase in absorption, was tested by measuring particle counts, particle-size distributions (PSD) and by modeling the Mass Normalized Beam Attenuation Coefficient (A/SPM) before and after filtration. An independent model verification was made by measuring and modeling A/SPM of three differently sized Arizona test dust suspensions. It is concluded that filtration is a good pretreatment for chemical disinfection systems because it removes the suspended matter mass, but that the production of smaller particles increases UV-absorption and hence may reduce disinfection performance.

Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization of o- and p-aminophenols under simulated aerosol and cloud conditions (pH 1–7, and ionic strength 0.01–1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4–0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products of o- and p-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions.

Operating resistance prediction of non-flat HEPA filters

The operating resistance of a high-efficiency particulate air (HEPA) filter is affected by the environment and cannot be obtained through the dust holding capacity (DHC) test in the laboratory. For non-flat HEPA filters, studies on the effect of non-uniform deposition of particles on operating resistance were insufficient. We proposed an equivalent permeability coefficient (EPC) method to calculate the operating resistance of the filter and took particle size distribution into account. After comparing with the DHC test data using Arizona test dust (A2 fine dust), it was proved that this method can achieve a relative error of <4%. We found >60% of the particles were deposited in the bottom 2/5 of the V-shaped structures. And the uneven deposition of particles could reduce the operating resistance. Then, we realized the optimal design of structural parameters of V-shape and cylinder filters. • Proposed a novel operating resistance prediction model of HEPA filters. • The uneven particle deposition is beneficial to reduce the operating resistance. • Optimized the structural parameters of the HEPA filters.

Heterogeneous reaction of NO2 with feldspar, three clay minerals and Arizona Test Dust

Heterogeneous reaction of NO2 with mineral dust aerosol may play important roles in troposphere chemistry, and has been investigated by a number of laboratory studies. However, the influence of mineralogy on this reaction has not been well understood, and its impact on aerosol hygroscopicity is not yet clear. This work investigated heterogeneous reactions of NO2 (∼10 ppmv) with K-feldspar, illite, kaolinite, montmorillonite and Arizona Test Dust (ATD) at room temperature as a function of relative humidity (<1% to 80%) and reaction time (up to 24 hr). Heterogeneous reactivity towards NO2 was low for illite, kaolinite, montmorillonite and ATD, and uptake coefficients of NO2, γ(NO2), were determined to be around or smaller than 1×10−8; K-feldspar exhibited higher reactivity towards NO2, and CaCO3 is most reactive among the nine mineral dust samples considered in this and previous work. After heterogeneous reaction with NO2 for 24 hr, increase in hygroscopicity was nearly insignificant for illite, kaolinite and montmorillonite, and small but significant for K-feldspar; in addition, large increase in hygroscopicity was observed for ATD, although the increase in hygroscopicity was still smaller than CaCO3.

Abrasion testing of anti-reflective coatings under various conditions

PV modules can quickly accumulate a light hindering layer of dust on the front glass, especially in arid regions. This soiling needs to be removed regularly, often using dry brushes as water is usually not easily available to wash the panels. Repeated cleaning negatively affects the anti-reflective coating (ARC) on the glass, leading to permanent transmittance loss and therefore a reduced energy yield. Within this work, two different ARCs and a reference glass are investigated regarding their resistance against harsh abrasion with a dry linear brushing abrasion cycle tester for laboratory and mobile use. The reduction of the spectral transmission is studied as a function of brushing cycles (0, 100, 1000) and integral relative transmittance loss has been calculated. Furthermore, a sensitivity analysis is performed for additional test parameters being type of dust, brush speed and weight. In particular, the type of dust shows a significant influence on the abrasion behavior. Less influential are the brush weight and the speed in the range used here. The dusts used in this setup were Feldspar, Calcite, Corundum and Arizona test dust in different particle size distributions. Using the hard Corundum dust, 1000 brush cycles lead to a relative loss in transmittance of about 3%. The application potential of the presented linear abrasion test for quality assessment and benchmarking of commercial glass coatings will be discussed. In particular, the implementation of region-specific test dusts in laboratory test procedures is of high interest for further standardization activities. • Linear brush abrasion test setup was used to test two different Anti-Reflective Coatings (ARCs). • Huge differences in transmittance loss between the coatings detected. • Investigation of the impact of test parameters brush speed, weight, brush cycles and type of dust. • Dust type and hardness are the most important influencing factors on the transmittance loss while brush speed and weight show no significant impact. • Method can be used for the development of site-specific ARC.

Effects of heterogeneous reaction with NO2 on ice nucleation activities of feldspar and Arizona Test Dust

Mineral dust is an important type of ice nucleating particles in the troposphere; however, the effects of heterogeneous reactions on ice nucleation (IN) activities of mineral dust remain to be elucidated. A droplet-freezing apparatus (Guangzhou Institute of Geochemistry Ice Nucleation Apparatus, GIGINA) was developed in this work to measure IN activities of atmospheric particles in the immersion freezing mode, and its performance was validated by a series of experimental characterizations. This apparatus was then employed to measure IN activities of feldspar and Arizona Test Dust (ATD) particles before and after heterogeneous reaction with NO2 (10±0.5 ppmv) at 40% relative humidity. The surface coverage of nitrate, θ(NO3−), increased to 3.1±0.2 for feldspar after reaction with NO2 for 6 hr, and meanwhile the active site density per unit surface area (ns) at -20°C was reduced from 92±5 to <1.0 cm−2 by about two orders of magnitude; however, no changes in nitrate content or IN activities were observed for further increase in reaction time (up to 24 hr). Both nitrate content and IN activities changed continuously with reaction time (up to 24 hr) for ATD particles; after reaction with NO2 for 24 hr, θ(NO3−) increased to 1.4±0.1 and ns at -20°C was reduced from 20±4 to 9.7±1.9 cm−2 by a factor of ∼2. Our work suggests that heterogeneous reaction with NO2, an abundant reactive nitrogen species in the troposphere, may significantly reduce IN activities of mineral dust in the immersion freezing mode.

An evaluation of the heat test for the ice-nucleating ability of minerals and biological material

Abstract. Ice-nucleating particles (INPs) are atmospheric aerosol particles that can strongly influence the radiative properties and precipitation onset in mixed-phase clouds by triggering ice formation in supercooled cloud water droplets. The ability to distinguish between INPs of mineral and biological origin in samples collected from the environment is needed to better understand their distribution and sources. A common method for assessing the relative contributions of mineral and biogenic INPs in samples collected from the environment (e.g. aerosol, rainwater, soil) is to determine the ice-nucleating ability (INA) before and after heating, where heat is expected to denature proteins associated with some biological ice nucleants. The key assumption is that the ice nucleation sites of biological origin are denatured by heat, while those associated with mineral surfaces remain unaffected; we test this assumption here. We exposed atmospherically relevant mineral samples to wet heat (INP suspensions warmed to above 90 ∘C) or dry heat (dry samples heated up to 250 ∘C) and assessed the effects on their immersion mode INA using a droplet freezing assay. K-feldspar, thought to be the dominant mineral-based atmospheric INP type where present, was not significantly affected by wet heating, while quartz, plagioclase feldspars and Arizona Test Dust (ATD) lost INA when heated in this mode. We argue that these reductions in INA in the aqueous phase result from direct alteration of the mineral particle surfaces by heat treatment rather than from biological or organic contamination. We hypothesise that degradation of active sites by dissolution of mineral surfaces is the mechanism in all cases due to the correlation between mineral INA deactivation magnitudes and their dissolution rates. Dry heating produced minor but repeatable deactivations in K-feldspar particles but was generally less likely to deactivate minerals compared to wet heating. We also heat-tested biogenic INP proxy materials and found that cellulose and pollen washings were relatively resistant to wet heat. In contrast, bacterially and fungally derived ice-nucleating samples were highly sensitive to wet heat as expected, although their activity remained non-negligible after wet heating. Dry heating at 250 ∘C leads to deactivation of all biogenic INPs. However, the use of dry heat at 250 ∘C for the detection of biological INPs is limited since K-feldspar's activity is also reduced under these conditions. Future work should focus on finding a set of dry heat conditions where all biological material is deactivated, but key mineral types are not. We conclude that, while wet INP heat tests at (&gt;90 ∘C) have the potential to produce false positives, i.e. deactivation of a mineral INA that could be misconstrued as the presence of biogenic INPs, they are still a valid method for qualitatively detecting very heat-sensitive biogenic INPs in ambient samples if the mineral-based INA is controlled by K-feldspar.

Laboratory calibration of a light scattering soiling sensor

In this study, laboratory calibration of a commercial soiling sensor was carried out using Doha dust and the Arizona Test Dust A2 Fine. Soiling conditions ranging from 0.3 to 10 g m−2 in dust loading were created by aerosol deposition and sieve deposition methods using the two dust types. Transmission loss under each soiling condition was determined using a PV reference cell and a solar simulator, and the corresponding light scattering reading from the deposited dust was also obtained. A strong linear correlation with high reproducibility was found between the actual transmission loss and the light scattering reading. For both dust types, the actual transmission loss was approximately 2.4 times the soiling sensor’s reading with aerosol deposition and about 2.6 with sieve deposition. The difference in the correction factor may be attributed to the difference in dust property and the impact of the deposition method on the morphology of deposited dust. The calibration results can be directly applied to the commercial soiling sensor tested in this study for soiling caused by dusts similar to those used in this study. The findings also show that sieve deposition may be used in place of the more desirable aerosol deposition method for local dust calibration of soiling sensors, but it is necessary to evaluate the particle size distribution of the deposited dust for assessing the accuracy of the calibration result.

An experimental method for efficiently evaluating the size-resolved sampling efficiency of liquid-absorption aerosol samplers

Aerosol samplers are critical tools for studying indoor and outdoor aerosols. Development and evaluation of samplers is often labor-intensive and time-consuming due to the need to use monodisperse aerosols spanning a range of sizes. This study develops a rapid experimental methodology using polydisperse solid aerosols to evaluate size-resolved aerosol-to-aerosol (AtoA) and aerosol-to-hydrosol (AtoH) sampling efficiencies. Arizona Test Dust (diameter 0.5–20 µm) was generated and dispersed into an aerosol test chamber and two candidate samplers were tested. For the AtoA test, aerosols upstream and downstream of a sampler were measured using an online aerodynamic particle sizer. For the AtoH test, aerosols collected in sampling medium were mixed with a reference sample and then measured by the laser diffraction method. The experimental methodology were validated as an impressive time-saving procedure, with reasonable spatial uniformity and time stability of aerosols in the test chamber and an acceptable accuracy of absolute mass quantification of collected particles. Evaluation results showed that the AGI-30 and the BioSampler sampler had similar size-resolved sampling efficiencies and that efficiencies decreased with decreasing sampling flow rate. The combined evaluation of AtoA and AtoH efficiency provided more comprehensive performance indicators than either test alone. The experimental methodology presented here can facilitate the design and choice of aerosol sampler.

The effect of (NH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;)&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;SO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; on the freezing properties of non-mineral dust ice-nucleating substances of atmospheric relevance

Abstract. A wide range of materials including mineral dust, soil dust, and bioaerosols have been shown to act as ice nuclei in the atmosphere. During atmospheric transport, these materials can become coated with inorganic and organic solutes which may impact their ability to nucleate ice. While a number of studies have investigated the impact of solutes at low concentrations on ice nucleation by mineral dusts, very few studies have examined their impact on non-mineral dust ice nuclei. We studied the effect of dilute (NH4)2SO4 solutions (0.05 M) on immersion freezing of a variety of non-mineral dust ice-nucleating substances (INSs) including bacteria, fungi, sea ice diatom exudates, sea surface microlayer substances, and humic substances using the droplet-freezing technique. We also studied the effect of (NH4)2SO4 solutions (0.05 M) on the immersion freezing of several types of mineral dust particles for comparison purposes. (NH4)2SO4 had no effect on the median freezing temperature (ΔT50) of 9 of the 10 non-mineral dust materials tested. There was a small but statistically significant decrease in ΔT50 (−0.43 ± 0.19 ∘C) for the bacteria Xanthomonas campestris in the presence of (NH4)2SO4 compared to pure water. Conversely, (NH4)2SO4 increased the median freezing temperature of four different mineral dusts (potassium-rich feldspar, Arizona Test Dust, kaolinite, montmorillonite) by 3 to 9 ∘C and increased the ice nucleation active site density per gram of material (nm(T)) by a factor of ∼ 10 to ∼ 30. This significant difference in the response of mineral dust and non-mineral dust ice-nucleating substances when exposed to (NH4)2SO4 suggests that they nucleate ice and/or interact with (NH4)2SO4 via different mechanisms. This difference suggests that the relative importance of mineral dust to non-mineral dust particles for ice nucleation in mixed-phase clouds could potentially increase as these particles become coated with (NH4)2SO4 in the atmosphere. This difference also suggests that the addition of (NH4)2SO4 (0.05 M) to atmospheric samples of unknown composition could potentially be used as an indicator or assay for the presence of mineral dust ice nuclei, although additional studies are still needed as a function of INS concentration to confirm the same trends are observed for different INS concentrations than those used here. A comparison with results in the literature does suggest that our results may be applicable to a range of mineral dust and non-mineral dust INS concentrations.