Arizona Dust Research Articles

Topographic shielding and funneling for dust events associated with the North American Monsoon in the Sonoran Desert, central Arizona, USA

Dust storms are linked to large scale accidents and fatalities in the Central Sonoran Desert, specifically in the central Gila River Valley of the United States during the North American Monsoon. This study analyzes three events where the underlying topography impacts large summertime dust storms and their movement. All three examples demonstrate the shielding or, conversely, funneling effects associated the underlying terrain. The funneling between isolated mountain complexes, such as White Tank Mountains, the Sierra Estrella, the Sacaton Mountains, the San Tan Mountains, and the South Mountain Complex can combine to create substantially higher dust concentrations. Conversely, dust flow into these isolated mountain complexes can also lead to shielding, or blocking, of the dust such that area behind the topographic features experiences less dust while the windward side of the barriers have accented dust concentrations. These dust storm/topography studies provide a first opportunity to identify topographic influences on central Arizona dust storms. Significance statementThe purpose of this study is to identify Topographic elements of the central Sonoran Desert located in the Arizona region of the Southwestern United States that impact the movement of dust storms. Using IDW interpolation to analyze PM10 concentration levels and wind speeds, we find that stand-alone mountain complexes can provide significant dust shielding and funneling that effect the overall trajectory of a dust storm in this region.

Trajectory analysis of central Sonoran Desert dust storms

Dust storms are a major cause of central Sonoran Desert weather fatalities. Through back-trajectory analysis of North American Monsoon dust storms in central Sonoran Desert of the United States. This study is specific to central Arizona (USA) from 2009 to 2022 using the HYSPLIT model. Our findings have shown that dust storms originate from southerly or near-southerly regions. The dust storms displaying the highest concentrations of particulates show a preference to originate from the southwest. This coincides with the development of a 500 hPa ridge to the east of the study area. The highest concentration storms’ back-trajectories display the lowest heights above the ground. Given their southwestern origin, these storms travel upslope along the seasonally dry river beds of the Gila River and its tributaries. Weaker dust storms originate over a wider area with a shift to a southerly direction. Such origination indicates that weaker dust storms are traveling downslope through the washes and channels of the dry Santa Cruz River. As dust concentrations drop, storm direction drifts east and dust height is suspended higher. This paper highlights the spatial variations in central Arizona dust storms, showing the likeliest paths of the strongest events and assists in identifying aeolian dust origins.

Investigating the dependence of mineral dust depolarization on complex refractive index and size with a laboratory polarimeter at 180.0° lidar backscattering angle

Abstract. In this paper, the dependence of the particles' depolarization ratio (PDR) of mineral dust on the complex refractive index and size is for the first time investigated through a laboratory π-polarimeter operating at 180.0∘ backscattering angle and at (355, 532) nm wavelengths for lidar purposes. The dust PDR is indeed an important input parameter in polarization lidar experiments involving mineral dust. Our π-polarimeter provides 16 accurate (<1 %) values of the dust lidar PDR at 180.0∘ corresponding to four different complex refractive indices, studied at two size distributions (fine, coarse) ranging from 10 nm to more than 10 µm and at (355, 532) nm wavelengths while accounting for the highly irregular shape of mineral dust, which is difficult to model numerically. At 355 nm, the lidar PDR of coarser silica, the main oxide in mineral dust, is equal to (33±1) %, while that of coarser hematite, the main light absorbent in mineral dust, is (10±1) %. This huge difference is here explained by accounting for the high imaginary part of the hematite complex refractive index. In turn, Arizona dust exhibits higher depolarization than Asian dust, due to the higher proportion in hematite in the latter. As a result, when the strong light-absorbent hematite is involved, the dust lidar PDR primarily depends on the particles' complex refractive index, and its variations with size and shape are less pronounced. When hematite is less or not involved, the dust lidar PDR increases with increasing sizes, though the shape dependence may then also play a role. The (355, 532) nm wavelength dependence of the dust lidar PDR then allows discussing on the involved particle sizes, thus highlighting the importance of dual-wavelength (or more) polarization lidar instruments. We believe these laboratory findings will help improve our understanding of the challenging dependence of the dust lidar PDR with complex refractive index and size to help interpret the complexity and the wealth of polarization lidar signals.

Influence of particle properties and environmental factors on the performance of typical particle monitors and low-cost particle sensors in the market of China

The performance of particle measurements based on three types of principles, including tapered element oscillating microbalance (TEOM), beta attenuation monitor (BAM) and light scattering, were investigated with different types of particle (braize, arizona dust and polystyrene spheres), particle sizes (1.1, 2.0, 2.5 and 3.0 μm), and environmental factors (temperature, relative humidity and relatively high particle concentration). Specifically, two middle-cost monitors (LY, LL) and three low-cost sensors (PT, YT, SF) with light scattering were considered.Good correlations with gravimetric were all observed on three principle instruments with three particle types at laboratory tests, except for less concerned intercepts did not meet the requirements of standard HJ 653–2013. Particle properties showed negligible effect on the instrumental measurements based on BAM and TEOM, commonly as high-cost monitors. Interestingly, middle-cost monitors were found to be more sensitive to particle properties versus low-cost sensors using calibration dusts with various properties. Moreover, obvious impacts of particle sizes were observed for all tested light-scattering monitors and sensors. In addition, different trends of sensors measuring PM10/PM2.5/PM1.0 with the increase of particle sizes indicated the poor particle recognition of light scattering principle. Expectedly, poor correlations of sensors were observed in ambient experiments compared with laboratory experiments due to the effect of complex environmental factors. Relative humidity (RH) and temperature (T) were proposed to express synergistic effects on measurements by sensors. Meanwhile, poor correlation and zero drift of YT sensors after high particle concentration exposure experiments revealed high particle concentrations would result in the pollution of low-cost sensors due to the lack of self-cleaning function. In conclusion, to evaluate the performance of sensors for future standard instrumental developments more accurately, both indoor and outdoor assessments should be taken out. The data acquired in this study could provide information for future evaluation of the performance of particle monitors and sensors based on light scattering principle.

Quantifying the impact of cropland wind erosion on air quality: A high-resolution modeling case study of an Arizona dust storm

Dust storms fueled by wind erosion of desert and cropland soils in south-central Arizona have caused numerous highway accidents and health risks by creating hazardous air quality conditions. Despite much speculation that a major fraction of windblown dust during these storms originates at an active or abandoned cropland surface over the region, its quantification is largely missing in the literature. This study estimated the contribution of cropland wind erosion to the regional air quality degradation, in terms of concentration of particulate matter with diameter 10 μm and smaller (PM10), during a typical springtime dust storm, by conducting high-resolution (1 km horizontally) simulations utilizing the Weather Research and Forecasting-FENGSHA (a dust emission model)-Community Multiscale Air Quality (WRF-FENGSHA-CMAQ) modeling framework. The dust model for this study employed up-to-date and very high-resolution data on land use, soil texture, and vegetation index. The modeling system used in this study simulated reasonably well a regional dust storm (that raised concerns for air quality and highway safety) of 08–09 April 2013 compared against ground (station) observations of PM10 and satellite observations of dust optical depth and vertical structure of aerosol subtypes. The model evaluations also included the use of radar observations.Furthermore, the model results from this study revealed that the cropland wind erosion was responsible for 55% and 51% of total PM10 over Phoenix (33.35°N–33.85°N, 112.36°W–111.485°W) and western Pinal County (32.50°N–33.35°N, 112.2°W–111.2°W), respectively, during the simulated dust storm. The large contributions suggest that the inclusion and accurate representation of cropland dust sources are crucial in preparing emission inventories and in air quality modeling for the region. Such representation is particularly important in view of the projected future aridity over this region (that is already under a long-term drought), which may lead to fallowing of currently active farmlands, making them potential hotspots of dust emission. The modeling approach developed for this work can be used to carry out more comprehensive studies, over extended spatial and temporal extents, to identify the sources of windblown dust and quantify their climatological dust emission potentials for this region or elsewhere. Such studies are highly desirable to help decision-making processes to reduce windblown dust and the associated health and safety risks.

An improved on-line measurement method of particulate matter concentration using tri-wavelength laser light scattering

Continuous monitoring of particulate matter (PM) from stationary source emissions is essential to reduce air pollution. The measurement accuracy of the widely used light scattering method is seriously affected by the particle characteristics, especially particle size. Based on the dependence of the scattered light on the particle size and incident wavelength, an improved on-line measurement method of PM mass concentration using tri-wavelength laser light scattering was proposed. Laboratory measurements on silica particles, Arizona dust, and fly ash from coal-fired power plants using this method were performed with a coupled laser. The experimental and theoretical results of silica particles showed an apparent power-law relationship between the PM mass concentration sensitivity (PMCS) and the average particle size. A linear function can approximate the relationship between the ratio of scattered light intensities at different wavelengths (RSDW) and the average particle size. The relationship between PMCS and RSDW established by particle size was introduced into the on-line correction of particle mass concentration measurement. The measurements of silica particles, Arizona dust, and fly ash obtained excellent correction effects. Compared with the uncorrected light scattering method, the average measurement deviations of mass concentration for three samples are reduced from 49.75% ± 1.11%, 48.62% ± 2.62% and 46.48% ± 0.83% to 8.11 ± 1.99%, 4.34 ± 2.26%, and 2.99 ± 0.55%, respectively.

Sensitivity Analysis of the Surface Acoustic Wave Sensor towards Size-Distributed Particulate Matter

To study the sensitivity of the surface acoustic wave (SAW) sensor towards particulate matter (PM), an analytic model has been built based on single particle perturbation theory of full size range and the lognormal size distribution of the PM. The sensitivity of the frequency shift to 1 nanogram of PM has been calculated. The model shows that the frequency shift is a result of the competition between the negative perturbation by mass loading and the positive perturbation by elastic coupling, determined by particle size distribution parameters, material, and SAW frequency. To verify the model, the relationship of the frequency shift of a 315 MHz SAW to the concentration of aerosols generated by two kinds of powders of different sizes was measured. The experiment is in agreement with the model: the sensor has shown negative sensitivity towards aerosols generated by the finer particles of 1 μm, 3 μm polytetrafluoroethylene (PTFE), and A1 Arizona dust and positive sensitivity towards aerosols generated by the coarser particles of 10 μm PTFE and A4 Arizona dust; and the negative sensitivity is about 1 order higher than the positive.

Development of Dust Storm Modeling for Use in Freeway Safety and Operations Management: An Arizona Case Study

Extreme weather conditions such as strong winds, hail, heavy rainfall, heavy snowfall, and high air temperature impact roads, traffic, and operational decisions. Strong winds in arid regions may pick up fine dust particles and create massive blowing plumes dramatically reducing the visibility. This reduced visibility severely impairs driving ability causing catastrophic crashes. The purpose of this research was to investigate the impacts of dust storms on freeway safety and operations. Interstates 8, 10, 15, 17, 19, and 40 running through Arizona were studied in relation to dust loading and crash risks. To achieve this, nine severe Arizona dust storms (2009–2016) were modeled using Weather Research and Forecasting (WRF) model coupled with a chemistry module (WRF-Chem). WRF is a mesoscale numerical weather prediction system with a software architecture allowing for parallel computation. When coupled with a chemistry module (WRF-Chem), it could be used to model the fate and transport of the particulate matter. Dust hot spots were calculated based on Getis-Ord Gi* statistical method and were correlated to dust storm caused crashes. It was shown that a positive Gi* accompanied by dust loading of at least 50 kgm–2 will result in a crash with a 90% confidence level. The outcome of this research could be used by local and federal transportation agencies to communicate warnings to drivers for improved safety.

Simulating the meteorology and PM10 concentrations in Arizona dust storms using the Weather Research and Forecasting model with Chemistry (Wrf-Chem)

ABSTRACTNine dust storms in south-central Arizona were simulated with the Weather Research and Forecasting with Chemistry model (WRF-Chem) at 2 km resolution. The windblown dust emission algorithm was the Air Force Weather Agency model. In comparison with ground-based PM10 observations, the model unevenly reproduces the dust-storm events. The model adequately estimates the location and timing of the events, but it is unable to precisely replicate the magnitude and timing of the elevated hourly concentrations of particles 10 µm and smaller ([PM10]).Furthermore, the model underestimated [PM10] in highly agricultural Pinal County because it underestimated surface wind speeds and because the model’s erodible fractions of the land surface data were too coarse to effectively resolve the active and abandoned agricultural lands. In contrast, the model overestimated [PM10] in western Arizona along the Colorado River because it generated daytime sea breezes (from the nearby Gulf of California) for which the surface-layer speeds were too strong. In Phoenix, AZ, the model’s performance depended on the event, with both under- and overestimations partly due to incorrect representation of urban features. Sensitivity tests indicate that [PM10] highly relies on meteorological forcing. Increasing the fraction of erodible surfaces in the Pinal County agricultural areas improved the simulation of [PM10] in that region. Both 24-hr and 1-hr measured [PM10] were, for the most part, and especially in Pinal County, extremely elevated, with the former exceeding the health standard by as much as 10-fold and the latter exceeding health-based guidelines by as much as 70-fold. Monsoonal thunderstorms not only produce elevated [PM10], but also cause urban flash floods and disrupt water resource deliveries. Given the severity and frequency of these dust storms, and conceding that the modeling system applied in this work did not produce the desired agreement between simulations and observations, additional research in both the windblown dust emissions model and the weather research/physicochemical model is called for.Implications: While many dust storms can be considered to be natural, in semi-arid climates such storms often have an anthropogenic component in their sources of dust. Applying the natural, exceptional events policy to these storms with strong signatures of anthropogenic sources would appear not only to be misguided but also to stifle genuine regulatory efforts at remediation. Those dust storms that have resulted, in part, from passage over abandoned farm land should no longer be considered “natural”; policymakers and lawmakers need to compel the owners of such land to reduce its potential for windblown dust.

Heterogeneous atmospheric degradation of pesticides by ozone: Influence of relative humidity and particle type

In the atmosphere pesticides can be adsorbed on the surface of particles, depending on their physico-chemical properties. They can react with atmospheric oxidants such as ozone but parameters influencing the degradation kinetics are not clear enough. In this study the heterogeneous ozonolysis of eight commonly used pesticides (i.e., difenoconazole, tetraconazole, cyprodinil, fipronil, oxadiazon, pendimethalin, deltamethrin, and permethrin) adsorbed on hydrophobic and hydrophilic silicas, and Arizona dust at relative humidity ranging from 0% to 80% was investigated. Under experimental conditions, only cyprodinil, deltamethrin, permethrin and pendimethalin were degraded by ozone. Second-order kinetic constants calculated for the pesticides degraded by ozone ranged from (4.7 ± 0.4) × 10−20 cm3 molecule−1 s−1 (pendimethalin, hydrophobic silica, 55% RH) to (2.3 ± 0.4) × 10−17 cm3 molecule−1 s−1 (cyprodinil, Arizona dust, 0% RH). Results obtained can contribute to a better understanding of the atmospheric fate of pesticides in the particulate phase and show the importance of taking humidity and particle type into account for the determination of pesticides atmospheric half-lives.

Heterogeneous Photo-oxidation of SO2 in the Presence of Two Different Mineral Dust Particles: Gobi and Arizona Dust.

The impact of authentic mineral dust particles sourced from the Gobi Desert (GDD) on the kinetic uptake coefficient of SO2 was studied under varying environments (humidity, O3, and NOx) using both an indoor chamber and an outdoor chamber. There was a significant increase in the kinetic uptake coefficient of SO2 (γSO42-,light) for GDD particles under UV light compared to the value (γSO42-,dark) under dark conditions at various relative humidities (RH) ranging from 20% to 80%. In both the presence and the absence of O3 and NOx, γSO42-,light and γSO42-,dark greatly increased with increasing RH. The resulting γSO42-,light of GDD particles was also compared to that of Arizona Test Dust (ATD) particles. The γSO42-,light values of GDD were 2 to 2.5 times greater than those of ATD for all RH levels. To understand the photocatalytic act of dust particles, both GDD and ATD were characterized for the metal element composition of fresh particles, the aerosol acidity of aged particles, and the hygroscopic properties of both fresh and aged particles. We conclude that the difference in the formation of sulfate between GDD and ATD particles is regulated mainly by the quantity of the semiconductive metals in dust particles and partially by hygroscopic properties.

Estimating Water and Solid Impurities in Jet Fuel from ISO Codes

An original mathematical approach to estimate the quantity of impurity particles in jet fuel from a vector of ISO numbers is proposed. The main goal of this study is to design a model that relates the proportion of free water (in parts per million by volume, ppmv) and the content of solid contaminant (mg/L) to the corresponding ISO numbers, traditionally used in jet fuel industry. This model is also applied to obtain the combination of ISO numbers corresponding to the alarm values standardized in ppmv and mg/L units. The new method provides estimations for the free water and solid impurities (simulated by the addition of Arizona dust in laboratory) separately, using sequences of ISO numbers corresponding to the sizes of 4, 6, 14, and 30 μm. It is based on the assumption that the granulometric distribution of water (and that of the solid contaminant) is always fixed, i.e., adding more or less percentage of water (or solid contaminant), the number of particles of a given size will vary proportionally. Using this assumption and starting with an ISO code vector (or a set of them obtained by subsequent measurements), a new procedure is proposed to split it into two vectors, corresponding to the ISO codes of water and Arizona dust, respectively. Finally, the contents of free water and solid contaminant are calculated from those two ISO code vectors and validated using design of experiment techniques. This procedure allows us to translate the standardized alarms measured using free water (ppmv) and solid contaminants (mg/L) into ISO numbers.

Comparison of aerosol and bioaerosol collection on air filters

Air filters efficiency is usually determined by non-biological test aerosols, such as potassium chloride particles, Arizona dust or di-ethyl-hexyl-sebacate (DEHS) oily liquid. This research was undertaken to asses, if application of non-biological aerosols reflects air filters capacity to collect particles of biological origin. The collection efficiency for non-biological aerosol was tested with the PALAS set and ISO Fine Test Dust. Flow rate during the filtration process was 720 l/h, and particles size ranged 0.246–17.165 μm. The upstream and downstream concentration of the aerosol was measured with a laser particle counter PCS-2010. Tested bioaerosol contained 4 bacterial strains of different shape and size: Micrococcus luteus, Micrococcus varians, Pseudomonas putida and Bacillus subtilis. Number of the biological particles was estimated with a culture-based method. Results obtained with bioaerosol did not confirmed 100% filters efficiency noted for the mineral test dust of the same aerodynamic diameter. Maximum efficiency tested with bacterial cells was 99.8%. Additionally, cells reemission from filters into air was also studied. Bioaerosol contained 3 bacterial strains: Micrococcus varians, Pseudomonas putida and Bacillus subtilis. It was proved that the highest intensity of the reemission process was during the first 5 min. and reached maximum 0.63% of total number of bacteria retained in filters. Spherical cells adhered stronger to the filter fibres than cylindrical ones. It was concluded that non-biological aerosol containing particles of the same shape and surface characteristics (like DEHS spherical particles) can not give representative results for all particles present in the filtered air.

An aerosol flow tube study of the interaction of N 2O 5 with calcite, Arizona dust and quartz

The interaction of N 2O 5 with dispersed samples of Arizona Test Dust (ATD), Calcite (CaCO 3) and quartz (SiO 2) was investigated at varying relative humidity using an aerosol flow reactor. Reactive uptake coefficients, γ, obtained at close to zero relative humidity were (4.8 ± 0.7) × 10 −3 for CaCO 3, (8.6 ± 0.6) × 10 −3 for Quartz and (9.8 ± 1.0) × 10 −3 for ATD. In the case of calcite, evidence was obtained for an enhanced rate of uptake at relative humidities above ≈ 50%. The results are compared to literature values obtained using bulk substrates and to previous aerosol uptake data on Saharan dust.

The heterogeneous reaction of HNO3on mineral dust and γ-alumina surfaces: a combined Knudsen cell and DRIFTS study

The kinetics of the interaction of HNO3 with natural mineral dusts (Saharan, Chinese and Arizona dust) and γ-alumina surfaces has been studied at T = 298 K using a Knudsen cell reactor coupled to a mass spectrometer for kinetic studies on the gas uptake as well as DRIFT spectroscopy for studies of the surface products. The uptake of HNO3 on each surface was found to be fast with initial uptake coefficients of γ ≈ 0.1. Nitrate and water have been identified as reaction products. The formation rate of surface nitrate, however, was slower with uptake coefficients ranging from 8 × 10−3 < γ < 5.4 × 10−2 depending on the chemical nature of the surface. From these results a two-step mechanism for the reactive uptake of HNO3 onto mineral oxides, consisting of fast adsorption of gas-phase HNO3 followed by a slower surface reaction of HNO3(ads) with surface OH-groups is inferred. Furthermore, it was found that the reactivity of mineral dust towards HNO3 decreased with increasing exposure. However, the original reactivity could be recovered by water exposure and may therefore be conserved under atmospheric conditions.

Heterogeneous Reactivity of Gaseous Nitric Acid on Al2O3, CaCO3, and Atmospheric Dust Samples: A Knudsen Cell Study

The heterogeneous reaction between HNO3 and various authentic and synthetic mineral dust/mineral oxide surfaces has been investigated using a low-pressure Knudsen reactor operating at 298 K. The surfaces used were Saharan dust from Cape Verde, Arizona dust, CaCO3, and Al2O3. In all cases, a large irreversible uptake was observed. An uptake coefficient of γ = (11 ± 3) × 10-2 was determined for Saharan dust, and γ = (6 ± 1.5) × 10-2 was obtained for Arizona dust. The uptake coefficients for HNO3 on heated CaCO3 and on unheated CaCO3 are given by γ = (10 ± 2.5) × 10-2 and (18 ± 4.5) × 10-2, respectively, and are in good agreement with previous results. CO2 and H2O were formed as gas-phase products. Measurements of the uptake coefficient of HNO3 on grain-size selected samples of Al2O3, γ = (13 ± 3.3) × 10-2, and systematic variation of sample mass enabled us to show that the geometrical surface area of the dust sample is appropriate for calculation of uptake coefficients in these experiments. The high reactiv...

Temporal and spatial characteristics of Arizona dust storms (1965–1980)

AbstractHourly meteorological data for four first order stations (Phoenix, Tucson, Winslow and Yuma) were used to identify dust storms which occurred in Arizona from 1965 to 1980. Supporting data on diurnal dust storm frequencies for three Air Force bases in southern Arizona were also used in the analysis. In this study, dust storms have been defined as blowing dust events when visibility is reduced to si‐6 km. Data, however, were also collected for all events when visibility was sll‐3 km which is the dust storm definition used by Orgill and Sehmel (1976).In general, Yuma experiences the most dust storms per year followed closely by Phoenix, with Tucson and Winslow having very few events. Dust storms at Phoenix, on average, tend to be more severe than those experienced at the other sites. The most intense and frequent dust storms in Arizona occur during the summer months and are associated with strong downdrafts generated by intense thunderstorm activity. Several less intense dust storms of longer duration also occur at most sites during the late winter and early summer months with peak occurrence in April. These events are usually associated with cyclonic storm activity including cold frontal passages and upper level cut‐off lows which are common throughout the state at this time of year.Phoenix and Tucson are dominated by late, afternoon dust storms (1700–1800 h) especially during the summer months. Start times are much more irregular at Yuma and Winslow but modes are evident al 0900 h and 1200 h respectively.Phoenix and Tucson experience relatively short duration dust storms averaging 66 and 15 minutes, respectively. Although these dust storms are relatively short, they are rather intense, which is indicated by low visibilities associated with these dust storms. In contrast, storms at Yuma and Winslow are typically longer, lasting more than two hours (160 and 202 minutes, respectively).The dust storm frequency patterns based on visibility criteria pose an important question as to whether higher annual sediment fluxes result from many low‐to‐intermediate magnitude events or fewer, higher magnitude events. This question cannot be readily answered at the present time because of the lack of sediment load data during dust storms. Although meteorological conditions may play a major role in dust storm generation, detailed research is required to evaluate the relative importance of antecedent moisture conditions, surface soil and vegetation conditions, and anthropogenic factors.