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Article

Dry and Wet Atmospheric Deposition Composition in Southwest Florida: Environmental and Health Implications

by
Razvan Barcan
1,
Zoie R. Kassis
1,
Christopher M. Teaf
2,
Ashley Danley-Thomson
3,
Douglas J. Covert
4 and
Thomas M. Missimer
1,*
1
U.A. Whitaker College of Engineering, Florida Gulf Coast University, 10501 FGCU Boulevard South, Fort Myers, FL 33965-6565, USA
2
Institute of Science & Public Affairs, Florida State University, Tallahassee, FL 32306, USA
3
Department of Bioengineering, Civil and Environmental Engineering, U.A. Whitaker Engineering, Florida Gulf Coast University, 10501 FGCU Boulevard South, Fort Myers, FL 33965-6565, USA
4
Hazardous Substance and Waste Management Research, Inc., 2976 Wellington Circle West, Tallahassee, FL 32309, USA
*
Author to whom correspondence should be addressed.
Atmosphere 2023, 14(1), 102; https://doi.org/10.3390/atmos14010102
Submission received: 17 November 2022 / Revised: 22 December 2022 / Accepted: 28 December 2022 / Published: 3 January 2023
(This article belongs to the Section Biosphere/Hydrosphere/Land–Atmosphere Interactions)
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Abstract

:
Southwest Florida is one of the most rapidly growing regions of the United States and has been impacted over the past decade with water-quality issues and some associated health problems. The ionic ratios of the dust measured in southwest Florida vary significantly from those on the Florida east coast and in the Caribbean. The metals concentrations reported herein are enriched in potassium and calcium from local sources. Atmospheric deposition of metals and nutrients appears to have potential impacts on both indirect health problems and environmental issues of concern, particularly harmful algal blooms. However, no significant past research has been performed on measurement of the concentration of either metals including the micronutrient iron or nutrient concentrations occurring in atmospheric dry and wet fallout in southwest Florida. Measurements of the composition of key metals and nutrients were made over a one-year period. Concentrations of total phosphorus in the dust ranged from 0–80.5 mg/kg with an average of 4 mg/kg and in rainfall from 1–15.8 чg/L with an average of 4 mg/kg. Nitrate ranged from 0–746 чg/L with an average of 114.4 чg/L in rainfall in a soluble form, and from 1.3 to 718 mg/kg with an average of 209.9 mg/kg in an insoluble form. Ammonia was measured to range from 1.4 to 658 mg/kg with an average of 101.4 mg/kg in rainfall. Iron was found in the dust at concentrations ranging from 0–81 mg/kg with an average of 3.8 mg/kg and in rainfall from 0–125.7 mg/kg with an average of 3.0 mg/kg. While the measured nutrient and iron concentrations are not likely to initiate a harmful algal bloom, they are likely to sustain an existing bloom. Global climate change may exacerbate the atmospheric aerosol issue by increased wind speeds over Africa associated with longer term drought conditions caused by atmospheric temperature increases.

1. Introduction

Over a timescale duration of thousands to tens of thousands of years, geological studies have shown that atmospheric-transported aerosols deposits represent a major source of nutrients and other components of soil [1]. Under modern global warming and anthropogenic changes in the surface of the Earth, transport of aerosols has become a major environmental and health issue. While a substantial database exists on the composition and concentration of the transported dust in some regions, little is known concerning the changes in composition away from the oceans and shorelines, particularly in areas influenced by Saharan dust transport to North America. No past studies have been conducted in southwestern Florida to define the composition of atmospheric aerosols.
Atmospheric dust aerosols are composed of suspended particles of varying composition, including inorganic and organic materials, originating from wind-entrainment in local and distant environments [2,3,4,5,6]. Once the dust has entered the atmosphere, it can be transported thousands of kilometers before being deposited on the ocean or land surface [7,8,9,10], where it contributes to the formation of soils, influences terrestrial plant growth, and contributes to ocean and lake biological productivity [11,12,13,14,15,16,17]. In general, the larger-sized dust particles (>10 µm in diameter) are deposited closer to the source due to their high settling velocity, while smaller-sized particles are capable of traversing long distances and undergo an extended lifetime in the atmosphere based on a diminished rate of gravitational settling [18].
Circulation of aerosols in the atmosphere is very complex, beginning at the source areas, and then interacting with both atmospheric processes and undergoing chemical reactions [19]. A variety of physical and chemical processes act upon the dust as it is transported, and deposition can occur as direct dry fallout or can be entrained in rainfall as wet deposition.
Back-trajectory studies of trans-Atlantic aerosols in southern Florida suggest three main sources of dust, which include Africa, Asia, and local anthropogenic factors, with the highest mineral concentrations occurring during the summertime in the months of June to August [20,21,22]. Huneeus et al. [23] estimated that the regions of North Africa are the source area for dust transport of about 800 Tgyr−1 (800 million metric tons/yr). However, models used to simulate dust movement show a large variation in possible transport volumes from North Africa with a range of 204 to 2888 Tgyr−1 (204 to 2888 million metric tons/yr) [23]. The plume of dust occurs from the source areas in a nearly continuous pathway across the Atlantic Ocean to the southeastern United States (Figure 1) [24]. The distribution of dust is continuously monitored by the NOAA and NASA, as it poses significant weather impacts to the region. The African continent constitutes the largest source of mineral dust aerosols along the entire East Coast of the United States including the southeastern part of the country [20]. South Florida experiences an average mineral dust deposition rate of about 9.1 mg/cm2/yr, and it is estimated that 60–80% of the soil covering the Florida Keys has been derived from African soil [13,25].
It is also well known that phosphate from African dust has had an important impact on downwind regions, such as the Amazon rain forest with an influx of 22,000 metric tons per year [15,17]. African dust has also significantly impacted tree growth and soils formation in the Florida Keys [16].
Southwestern Florida has been adversely affected by freshwater and marine harmful algal blooms which have been particularly intense over the past two decades. The primary sources of the nutrient loading that lead to the freshwater algal blooms has been attributed to a combination of discharge from Lake Okeechobee and basin runoff, which includes agricultural and urban origins [26]. Atmospheric fallout of nutrients was measured in the past to assess potential impacts on the nutrient budget of Lake Okeechobee [27] and the Everglades [28,29]. Because of the abundance of nutrient flux into estuaries and nearshore areas of southwest Florida, any additional inputs of nutrients may be critical in terms of prolonging the impacts of both freshwater and marine harmful algal blooms. Therefore, measurement of the wet and dry deposition of nutrients is an important environmental issue in southwestern Florida, especially as climate change occurs causing increased water temperature and possibly increased atmospheric aerosol influx [30,31].
Historical studies, coupled with anecdotal evidence, indicate that mineral dust aerosols may pose a risk to human health in sensitive individuals through direct respiratory contact with dust constituents [10,18,32,33,34,35]. The particulate matter component of the dust is a known contributor to adverse respiratory health effects [33,36,37,38,39,40]. Its composition and presence of bioactive microbes within the dust can also collectively impact human and environmental health [41,42]. Human exposure to atmospheric aerosols (i.e., Particulate Matter, PM) has been demonstrated to affect heart rate and associated cardiac health [43], blood pressure and associated atherosclerosis [44], cognitive decline including the onset of Alzheimer’s disease [45], and premature birth [37]. However, Schlesinger et al. [46] suggested that “There continues to be major gaps to knowledge about the relative toxicity of particles from various sources, and the relationship between toxicity and particle physicochemical properties”. Another health issue associated with African dust is the attachment of microbes (some pathogenic) on the inorganic substances, but that is not the primary subject of this paper [41,43].
The composition of atmospheric dry and wet fallout has not been measured in southern Florida, and correlation with local respiratory health issues as has been shown in the Miami area [39]. Previous studies were mostly focused on the east coast of Florida and the Keys as these areas are at the forefront of the trans-Atlantic tradewinds that carry the dust. It is the purpose of this research to present new data on wet and dry dust chemistry from a station in southwestern Florida and link it with environmental issues and some limited health information.

2. Methods

2.1. Sample Collection

Dust aerosols and rainfall samples were collected on a monthly basis (or greater frequency in the case of rainfall) using a specialized collection system located at the Emergent Technologies Institute at Florida Gulf Coast University located in southwest Florida near the City of Fort Myers (Figure 2 and Figure 3). A wet-dry fallout collection system was used to collect rainfall and dust. This device is specially designed to collect atmospheric dust in either in the dry mode or in rainfall. We modified the system to be powered by a solar panel collection mechanism that allows for gravitational settling of dust aerosols as well as rainfall collection at specific times of interest. The platform is located in an open field away from obstructions and interferences to minimize contamination. The freshly accumulated aerosol dust was removed by flushing the container with deionized water. During rainfall periods, the dry collector bucket is covered, and the rainfall collector bucket opens. This is achieved by the use of a sensor that detects rainfall.

2.2. Sample Preparation

Three stages of sampling and mixing were used to achieve a uniform dust distribution and prepare the samples for analysis. The original undigested samples of dust were stored in individual containers for each month when the sample was collected. A portion of each sample was digested and prepared for analysis using an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) device. Analysis preparation consisted of digesting and reconstituting 10 mL of a sample (dust with deionized water) in 5 mL of nitric acid (15 M) aqueous solution. Following digestion, the solution was heated to 90–100 °C for 5 h with boiling chips to allow for nucleation sites and prevent superheating and flash boiling.
After 5 h, the water content was allowed to evaporate, leaving behind a concentrated 5 mL solution comprised of dust and acid. Lastly, the leftover solution was flushed with 45 mL of deionized water prior to ICP-MS analysis.
Monthly or at a greater frequency (event based), rainfall samples were also analyzed to determine metals composition using the ICP-MS and nutrients concentrations using a nutrient auto-analyzer. For analysis of the metals, the rainfall samples were treated with nitric acid to ensure that all of the metals were dissolved. The water analyzed for nutrients was filtered to remove any particulate materials prior to analysis.

2.3. Inductively Coupled Plasma Mass Spectrometer (ICP-MS) Analyses of Metals

A Perkin-Elmer, NexION 2000 ICP-MS was used to detect and analyze the metallic analytes present in the collected samples. The ICP-MS analysis method consisted of four main stages, including the introduction system, the ICP torch, the interface, and the mass spectrometer (MS). The introduction system utilizes a pump to transport the analyte inside a nebulizer that turns the liquid into a fine mist before entering the spray chamber. Argon gas is inserted into the ICP torch where an RF coil increases the gas temperature to approximately 6000 °C, essentially converting it into plasma. The mist from the spray chamber enters the plasma and the analyte becomes ionized. During the interface stage, a fraction of the ionized aerosol undergoes filtration and removal of polyatomic interferences prior to entering the mass spectrometer for analysis.
The ICP-MS was first optimized using the NexION Setup Solution to achieve standardization for the analytes being tested. Analytes were selected based on the historical data of dust composition found in the literature [3,13].
The ICP-MS was then optimized with a blank solution prior to examining the analytes present in the dust/acid solution. ICP-MS was used to measure the concentrations of the digested samples of dust derived from aerosol and rainfall samples for iron (Fe), sulfur (S), copper (Cu), magnesium (Mg), lead (Pb)carbon (C), aluminum (Al), chromium (Cr), silicon (Si), calcium (Ca), phosphorous (P), and potassium (K). Additional testing was performed for aerosol dust surface analysis of undigested aluminum (Al), potassium (K), and iron (Fe). A blank sample was first prepared to set the zero-absorbance limit and the standard was diluted into a series of known concentrations prior to running the samples. This method of analysis is equivalent to the historical approach used to obtain the concentration data for aluminum (Al), potassium (K), and iron (Fe). Surface dust analysis follows the procedure for ICP-MS testing as presented in Section 2.2., but it excludes the process of digestion in nitric acid. As such, the ICP-MS measures the analytes present on the surface of the dust particles without taking into consideration the analytes present inside the particles that would otherwise be exposed through digestion.

2.4. Nutrients Measured in the Rainfall Samples

Nutrient concentrations for nitrous oxide (N2O), nitrite (NO2), nitrate (NO3), and ammonia (NH3) were measured in the rainfall samples and undigested dust samples using a SEAL AA500 Analytical Calorimetric Nutrient Analyzer. The colorimetric nutrient analyzer utilizes five main components (tungsten lamp, collimator, prism, slits, and detector) to determine the concentration level of the sample based on the sample ability to absorb light. Prior to the analysis, the sample is combined with a reagent to yield a specific sample color. The collimator converts the incoming light into parallel beams. Light is then delimited by the primary slit prior to being diffracted into individual wavelengths upon exiting the prism. Based on the sample solution being tested, a specific wavelength is selected through the secondary slit. Light then passes through the sample before reaching the detector. According to Beer-Lambert law, the amount of light being absorbed by the sample is directly proportional to the sample concentration. The analyzer uses this principle to yield the concentration of the sample based on the sample absorbance of light.

3. Results

3.1. Measured Concentrations of Metals and Some Nutrients in the Digested Dust

A summary of the digested dust data is shown in Table 1 with the measured dates and concentrations given in Figure 4. Twelve elements were measured in the dust at the ETI location. Based on the average concentration, the most abundant element found was sulfur, followed by magnesium, potassium, calcium, aluminum, silicon, carbon, boron, phosphorus, iron, copper, and chromium. The most significant constituents to the environment based on water quality impacts are phosphorus and iron, while silicon, aluminum, potassium, chromium and copper may have health impacts depending on the concentrations being inhaled.
The measured constituent that produced peak deposition during summer was sulfur at ~6000 µg/kg, followed by calcium, aluminum, potassium, carbon, silicon, boron, phosphorus, chromium, and copper (Figure 4). Iron deposition occurred in highest concentrations during winter and spring, but also occurred in the summer months at lower concentrations. Magnesium displayed highest concentrations during winter and spring, followed by lower uniform concentrations throughout the year. Copper and chromium showed a relatively even distribution of measurable concentrations throughout the year with occasional peaks in the spring/summer.

3.2. Concentrations of Undigested Dust Aerosols in Rainfall Using the Colorimetric Nutrient Analyzer and ICP-MS Analysis

Samples of rainfall were analyzed in an undigested mode for nutrients and metals using the nutrient auto-analyzer and the ICP-MS machine. A summary of the data collected is presented in Table 2 and the measurements made in time are presented in Figure 5. The metals concentrations were quite low based on low solubility in the rainwater. The concentration of potassium was highest with an average of 364 µg/L.
The monthly distribution of aluminum and iron showed relatively similar concentration patterns with the highest values during early summer (June) and winter (January–February) followed by lower concentrations through the remaining year (Figure 5). The highest potassium values occurred in June and were found in lower concentrations throughout the year. The nutrients (nitrogen species) were highest in the early summer (June) followed by lower concentrations during the remaining summer months, and increased concentrations in the late fall and through the winter months. This trend follows the general rainfall accumulation pattern at the site, which has over 70% occurring in the months of June, July, August, and September.

3.3. Concentrations from Digested Monthly Rainfall Samples Using the Colorimetric Nutrient Analyzer and ICP-MS Analysis Instruments

Concentrations are reported for all samples analyzed with some statistical analyses in Table 3 and temporal data presented in Figure 6. The highest metals concentrations were aluminum, calcium, magnesium, silicon, and potassium. Aluminum concentrations peaked during summer and late October (Figure 6a). Magnesium displayed highest concentrations during late spring with increased activity in the summer (Figure 6f). Potassium concentrations occurred at lower levels, with peak uniform concentrations during late summer and throughout the fall season (Figure 6d). Nutrient concentrations displayed highest values during late spring and throughout summer with occasional lower spikes during late winter, possibly caused by local sources of dust (Figure 6h–j). Calcium and silicon concentrations were prominent throughout the spring and summer months (Figure 6b,e). Iron was detected in rain samples collected during spring at 120–130 чg/L but absent during the rest of the year.

4. Discussion

To explore the potential impacts of Saharan dust deposition and other locally derived aerosols on the local environment and residents of southwest Florida, the new data collected on the chemistry of dry and wet fallout was placed within the context of past information collected in southern Florida at other locations between the point of origin (Saharan Africa) and the collection site. We have compared the dry and wet fallout composition data collected in southwest Florida to Saharan dust composition, Florida East Coast sampling stations, and have discussed the impacts on the environment, and potential impacts on local public health.

4.1. Historical Accounts on Trans-Atlantic Dust Aerosols Reaching the United States, including Dust Properties

Based on past studies of long-distance transport of atmospheric dust, it is highly likely that Saharan dust affects the southwest Florida area. From 2004 to 2018, the University of Arizona conducted a study to determine the most common sources of trans-Atlantic dust aerosols by analyzing the concentration and chemical nature of fine aerosol constituents (≤PM2.5) using ten monitoring stations positioned along the East Coast of the United States [6]. Dust aerosol sources were grouped into four possible categories: Africa, Asia, Mix (comprised of African and Asian dust), and other local sources. For this study, a dust event was representative of any measured fine particulate concentration exceeding a threshold of two standard deviations from the mean concentration of dust detected at each station each month. Data revealed that African aerosols were more predominant from North Carolina to the South, whereas the Asian aerosols were more common from North Carolina to the North. Aerosols pertaining to the “Other” category were significantly lower in concentration and dispersed throughout the East Coast [6].
Saharan dust contained the greatest number of fine particles (approx. 2.5 μm or less in diameter; PM2.5) across the entire East Coast with South Florida containing the highest concentration of fine dust (10.27 μm/m3) as compared to the Asian and other sources (2.69 μm/m3 and 0.86 μm/m3, respectively). Other studies also suggest that Saharan fine dust aerosols are responsible for approximately 40% of soil deposits spanning from Florida to Virginia [6]. The fine soil concentration was calculated based on the individual concentration values of aluminum, silicon, calcium, iron, and titanium.
These data are also supported by additional studies conducted by Joseph M. Prospero in 1988 at the University of Miami where Advanced Very High-Resolution Radiometer (AVHRR) measurements were used to analyze the distribution of aerosol optical thickness (AOT) of dust plumes spanning across the Atlantic [2]. Findings revealed highest values of AOT occurring during the month of July. This coincides with the aerosol data collected from 1974 to 1996 in Miami where a seasonal deposition rate with peak concentrations was recorded during the summer months of June, July, and August. One-third to one-half of the African dust deposits in Miami were comprised of dust particles with an aerodynamic diameter ranging from 2.0 to 2.5 µm [2].
Earlier atmospheric turbidity measurements (20 August–23 September 1974) showed a progressive decrease in large mineral aerosol concentrations spanning from West Coast of Africa toward the Caribbean and South Florida, where aerosols appeared reddish-brown, characteristic of Saharan dust [7]. Dust color picks up different shades of grey as it travels North across the Atlantic mainly due to humus from vegetated lands but also due to combustion-related pollution constituents from industrialized cities such as New York and Boston [25].
The concentration of Saharan dust varies from 100 µg/m3 near the West Coast of Africa to 1 µg/m3 towards the Caribbean and as little as 1 × 10−5 µg/m3 over the Antarctic. Across the Equator, dust aerosols undergo a sudden increase in concentration due to the Intertropical Convergence Zone where the Northeasterly Trades and Southeasterly Trades converge [25,47].
This annual cycle of aerosol transport was also confirmed by the Aerosol Optical Depth (AOD) data measured at Key Biscayne, Florida, which displayed the highest levels of AOD during July of 2010 [16].
Surface meteorological equipment including SYNOP (surface synoptic observation stations) and a pyranometer were also used to analyze yearly changes (2007–2014) in surface radiation flux over South Florida [16]. These data were used to determine sub-annual radiation patterns caused by trans-Atlantic mineral dust aerosols. The average yearly Photosynthetically Active Radiation (PAR) results showed increased intensity during May-August and declined intensity during winter as the mineral aerosol dust concentration decreases. These data are consistent with the decrease in direct surface radiation levels during summer months based on historical direct normal irradiance measured in South Florida [16]. Previous studies have shown that Optical Depth and its variations of wavelength follow a direct correlation to the in situ studies of aerosol size distribution of the Saharan dust [48].

4.2. Trajectory Patterns and Origins of Trans-Atlantic Dust Aerosols Reaching the United States

Observed dust trajectories show that Saharan dust does impact all of southern Florida including the study area (Figure 1). A large number of other satellite images taken by NOAA show that southwest Florida is within the dust plume area extending the entire width of the Atlantic Ocean from Africa into the Gulf of Mexico [24]. Through satellite imagery, it was determined that Saharan dust accounts for 50% of trans-Atlantic dust emissions, followed by Central and East Asia at 20%. The Gobi Desert and the surrounding arid areas comprised of alluvial deposits are among the primary sources of dust from East Asia. The plume emerging from West Africa is comprised of Saharan dust, whereas the South plume is likely attributable to anthropogenic factors such as biomass burning [48]. Another source of AOT is the Arabian Sea where the dust is being transported by wind from the Middle East region [20,24].
Moderate to high concentrations of aerosol dust were detected by the NASA Total Ozone Mapping Spectrometer (TOMS) satellite based on the spectral contrast of 340 and 380 nm during January 1984 and July 1985 [20]. The dust plume located across the West African Coast and east and central equatorial Atlantic most likely originated from the desert plains of the Chad basin and the salt-lake chotts of Tunisia and Northern Algeria where a significant amount of sediment movement occurs every year as it is subject to deflation [20]. Other potential dust sources suggested by TOMS are the Western regions of the Ahaggar Mountains, the Arabian Peninsula, and the Northeastern regions of Sudan. The Tarim Basin is also a possible source of dust plumes visible over western China. Although most of these sources contain environments and ecosystems that are believed to support favorable conditions for mineral dust formation (wadi sediments, lake sediments, alluvial fans, etc. in an arid climate), the precise terrain types responsible for the formation of the plumes remain difficult to extrapolate. It is also important to note that other major arid regions such as the Gobi Desert show no formation of dust plumes despite the presence of arid environmental conditions. However, this can be explained by recognizing that such locations contain coarser soils that exceed the average particle size limit (10 µm) necessary for significant wind entrainment and plume formation. Additional factors that may influence the formation of dust plumes include soil moisture, surface conditions, the characteristics of the local wind patterns, and the distribution of the soil particles [20].
Earlier studies (1965–1984) have recorded some of the highest concentration values of mineral aerosols over the Western North Atlantic Ocean and the Caribbean (Barbados Island [49,50,51]. Barbados Island was selected for aerosol research since it is the closest landmass windward from Africa [51].
To characterize the composition of the dust, samples were collected and analyzed quantitatively and qualitatively using different techniques such as x-ray diffraction, emission spectroscopy, neutron activation, and atomic absorption spectroscopy [52]. Pre-1971 aerosol concentration measurements in Barbados were collected by suspending nylon meshes in the wind at a region east of the island. With the introduction of electrical power in 1971, measurements in Barbados were obtained by sampling 1–2 m3 of aerosols every minute using filters and electric pumps. The concentration of mineral content was then measured by extracting the water-soluble components and heating the filter to 500 °C [53].
Aerosols were directly linked to severe drought events taking place in North Africa starting in the late 1960s and reaching unprecedented levels of severity in the early 1970s and early 1980s, resulting in major crop failures and elevated death rates. The highest dust concentration peaks were recorded in 1972–1973 and 1983–1984 (approx. 20–27 µg/m3) compared to the highest precipitation departures in North Africa described in terms of 1.3–1.8 standard deviations from the mean [53]. With climate change causing more variability in precipitation, the pulses of extreme concentration in Saharan dust may intensify in the future.
In Barbados, the troposphere can reach as much as 100% radiative absorption levels when Saharan aerosols are present (virtually no light passage). The Saharan Aerosol outbreak is characterized by atmospheric inversion, whereby the dust creates a warm layer through radiative absorption above the cooler layer present at lower altitudes. This inversion inhibits deep convection development, maintaining a cloud-free environment over large areas of the Atlantic Ocean. Atmospheric inversion is visible through satellites and can be used to trace the development of Saharan dust aerosols [52]. Considering the regular annual cycle of aerosol transport with maximum dust concentrations occurring during summer and dropping to a minimum in the winter, the summer mineral dust aerosols were four times less concentrated prior to the African drought, while the winter dust aerosols exceeded the pre-drought concentration values by a factor of ten [52].
The mass production of mineral dust aerosols in Africa was measured in 1982–1983 (prior to the African drought event from 1983–1984) using a network of eleven sun-photometer stations spread throughout the Saharan region. Turbidity measurements were also conducted in Agadez, a city in Niger located 1930 km from the Saharan Desert. This location was strategically selected to allow enough time and distance for a homogeneous mixture of mineral aerosols to be characterized. Data revealed an average fine aerosol mass of 80 × 106 to 90 × 106 tons/yr. being generated in the Saharan region with 60% of its mass traveling towards the Gulf of Guinea in the South, 28% traveling westward across the Atlantic, and the remainder 12% towards Europe in the North [53,54]. This accounts for approximately 24 × 106 metric tons/yr of African mineral dust deposition along the East Coast of the United States.

4.3. Historical Accounts on the Chemical Nature of Trans-Atlantic Aerosols in Florida and Comparison to Data Collected in Southwestern Florida: Metals and Nutrients

Independent studies were conducted on biweekly dust collections (PM2.5) during 1979–1995 from different sites pertaining to national parks and wilderness areas in the southwestern and eastern United States. The soils were found to contain significant levels of aluminum, iron, silicon, titanium, and calcium. These data concur with additional measurements collected in the summer of 1979 on aerosol dust carried by wind from the Gulf of Mexico into central Illinois where chemical analyses revealed high concentrations of Si, Al, and other crustal elements [4]. Calcium enrichment in the form of CaCO3 was found in rainwater samples following African dust events and accounted for a significant increase in rainwater pH (~30% increase in pH [55].
Between mid-June of 1982 and mid-June of 1983, the total aluminum concentration derived from aerosol minerals over Miami was 0.10 g/m2/yr based on 18 analyzed events for dissolved and particulate Al. This accounts for a total Al deposition rate of 126 mg/m2/yr., corresponding to 8% of the total mineral dust deposits in Miami [49]. The summer months exerted the highest Al deposition rates with the lowest pH rain values due to extensive rainfall 140–150 cm and increased Saharan dust events during summer. As expected, precipitation yielded increased aluminum deposits with decreased aerosol mineral concentration [49].
Rain samples collected in Miami during intense summer dust events appeared like a fine red-brown mud, indicating a significant presence of iron [49]. During winter periods when dust events are sparse, the rain samples appeared rough and gray-colored, indicative of particles derived from local anthropogenic sources. Since dust aerosols cover large areas, similar mineral soil deposits with uniform chemical traits were discovered in multiple locations from the northwestern part of Florida to the Florida Keys as well as Barbados and Jamaica. Data revealed similar summer highs and uniform concentrations of aluminum and iron that were equivalent to the dust analyzed in Miami. Dust collections were found to contain an aluminum deposition range of 0.1 g/m2/yr, which is equivalent of a mineral dust deposition rate of approximately 1.25 g/m2/yr or the same rate as aeolian minerals deposition in the North Atlantic [49]. The deposition rate of Al in rainfall samples collected at five distinct collection sites in Florida from 1993 to 1994 ranged between 0.062 and 0.148 g/m2/yr, with prominent deposits occurring during the summer months [56]. The Al deposits were equivalent to a mineral dust deposition rate of 0.78 to 1.9 g/m2/yr [49].
The average concentrations of fine dust at the monitoring station located in South Florida (EVER1, located in the Everglades) was 10.27 ± 4.89 µg/m3 for African dust, 2.69 ± 1.46 µg/m3 for Asian dust, and 0.86 ± 0.90 µg/m3 for other sources. From these results, it is evident that African dust represents the major component of fine dust aerosols in South Florida. Latitudinal trajectory data indicated a progressive decrease in fine African dust concentrations from South Florida to Maine [6].
The study conducted at the University of Arizona in 2004 provides an average chemical mass ratio analysis of the fine dust aerosols (PM) in Southeast Florida at the EVER1 station in the Florida Everglades. These data in terms of ion ratios are compared to dust analyses made in this investigation in Southwest Florida (Table 4). The chemical ratios analyzed (Si:Al, Al:Ca, Fe:Ca, and K:Fe) displayed no particular source patterns but exhibited distinct values based on station location [6]. The African dust contained the highest Al:Ca ratio (4.55) in relation to the Asian and “Other” sources (1.5 and 1.1, respectively). The Asian and “Other” sources displayed a higher ratio of Si:Al (2.03 and 2.67, respectively) relative to the African aerosols (1.9). The Fe:Ca ratio measurement was largest in the African dust aerosols; 2.34 [3].
The digested dust and digested rainfall data collected in SW Florida displays potassium concentrations that are 2–3 orders of magnitude larger than the potassium detected at the EVER1 station. Furthermore, the digested rainfall data in SW Florida contains more than 20 times the concentration of aluminum detected at the EVER1 station in 2004, possibly originating from dust fallout. Compared to the digested dust collected in SW Florida, the samples measured at the EVER1 station contained at least 3 orders of magnitude more iron. The lower concentration of iron in SW Florida dust suggests other anthropogenic sources being involved. The higher concentrations of K and S in some samples may also be associated with the operation of a waste to energy incinerators located about 15 km to the north of the sampling site and perhaps some emissions from road traffic (e.g., diesel truck sources).
The elements and compounds extracted from aerosol dust samples originating in Southwest Florida followed a seasonal pattern of peak concentrations recorded during the spring and mid-summer months with decreased concentrations at the beginning of the fall season. This trend was also noticeable amongst the most common dust constituents (Al, K, Fe, and NO3) recorded in historical measurements of Saharan dust analysis conducted in South Florida, the Caribbean, the Amazon, and Tropical North Atlantic [4,56].
Given the relatively industrialized location of the collection site (near a limestone aggregate mine), it is possible that local and regional inland anthropogenic sources may have contributed to the elevated calcium concentration peaks recorded in the summer. Calcium carbonate (CaCO3) is an important component of limestone processing, and it has the potential of being released into the air upon extracting the limestone from the ground and loading it into trucks. However, the occurrence of extreme atmospheric concentrations of calcium carbonate is unlikely for several reasons. First, the mining facility is required to adopt air pollution control measures when processing limestone (i.e., wetting the material, installing wind covers, reducing the drop height of the extracted material, using specialized dust collectors, etc.) [57], and secondly, data acquired at the ETI indicates a non-uniform concentration of calcium and carbon from the samples collected in 2020 and 2021. If limestone mining operations were influencing the concentrations, it would be expected that calcium and carbon analytes should maintain a more uniform level of concentration throughout the collection period.
Cations (i.e., Si, Al, K, and Ca) are likely to originate from trans-Atlantic dust since they comprise the primary blocks of the Saharan mineral dust deposits previously studied in southeast Florida [2,25]. The seasonal trends of dust samples collected in Southwest Florida are comparable to the historical accounts where optical depth measurements of Saharan dust displayed seasonal deposition rates with peak concentrations during summer (June, July, and August) [2,5]. Clear satellite impacts show the Saharan dust plume occurring over the study area, particularly in summer months. Some ions (i.e., Si, Cu, Fe) derived from digested dust samples displayed increased concentrations starting in November and extending throughout the winter season. A similar pattern was also observed in aerosol measurements of aluminum (Al), iron (Fe), nitrous oxide (N2O), nitrogen dioxide (NO2) and nitrate (NO3). This occurrence does not reflect the historical accounts whereby atmospheric dust concentrations were lowest during the winter months [16,20]. It is possible that air contaminants derived from natural or anthropogenic activities surrounding the collection site may have influenced the dust composition to a certain extent, influencing the concentration levels during late fall and winter. The anthropogenic activities most common in the area are agriculture, including vegetable crops and some citrus. Dry season (winter and spring) fires may also contribute some dust. The winter season also has an increase in vehicular traffic associated with the tourist season when population can double in the study area. This could account for the higher values of N2O. As such, it is possible that these values may not necessarily reflect true concentration values of Saharan dust constituents. Furthermore, the collection apparatus used to collect dust samples is located near ground level (1.25 m above ground) where air quality tends to be more affected by entrained low level dust. In addition, the setup lacks a filtration system to help mitigate the possibility of contamination from biological organisms and biological residue that might have interacted with the collection device. Consequently, it is advisable that further studies be conducted using an improved version of the currently used collection system that operates at a higher altitude using dust-specific filtration systems on the order of microns.
The dust composition in terms of ion ratios at the EVER 1 Station on the Florida East Coast as compared to those found at the Southwest Florida Station is shown in Table 4. The digested dust sample ratios at the Southwest Florida Station had a considerably different set of ratios, particularly for K:Fe and Fe:Ca, while the Al:Ca ratio was more in line with those measured on the East Coast of Florida. Localized sources of dust in the form of particulate CaCO3 may have influenced the composition. The source of the high concentration of potassium in the dust is unknown, but may be related to the application of fertilizers in farm fields located in the general vicinity and within forest fire smoke. It could also be related to suspended mineral dust in combination with organic contamination as potassium plays an important role in plant photosynthesis and energy production. While no fertilized farms fields are located in close proximity to the sampling location, during strong wind events potassium associated with fertilizers could be carried to the sampling location. In addition, there are no local sources of clay minerals located at land surface in near vicinity to the sampling location but some dust from the mining operation could entrain clays that occur within the lower soil horizon.
As illustrated in Figure 4, Figure 5 and Figure 6, cationic constituents (i.e., K, Al, and Mg) and nitrates from rainfall samples were generally detected more frequently throughout the year in relation to aerosol dust constituents. No apparent trends of seasonal concentrations were observed for potassium in the rainfall samples (refer to Figure 6). Rainfall magnesium exhibited higher readings during spring, whereas aluminum readings were highest in the summer and winter months (refer to Figure 6). Although industrial anthropogenic sources may contribute to elevated concentrations of aluminum in the atmosphere, based on the seasonality and isolated concentration peaks of aluminum detected at the ETI center (refer to Figure 4 and Figure 5), it is reasonable to assume that aluminum readings originate from trans-Atlantic dust. Peak readings of rainfall nutrients (NO2, NO3, NH3) were more concentrated during spring and summer; however, lower spikes were also recorded occasionally throughout the year with no apparent seasonal trend (refer to Figure 6).
Concentrations of nitrate, sulfate, potassium, total organic carbon (TOC), and elemental carbon (EC) in the fine dust aerosols from South Florida are summarized in Table 5 [6] and compared with the concentrations found in southwestern Florida. For the Everglades site, at an average concentration range of 0.45–0.48 μg/m3, no unique concentration of nitrate could be used to distinguish between the African, Asian, or “Other” dust types. The “Other” source exhibited the highest concentration of sulfate (2.64 μg/m3), possibly derived from local pollution sources. The concentration of potassium in both, African and “Other” aerosols, 0.22 and 0.23 μg/m3, respectively, exceeded the Asian dust concentration of 0.1 μg/m3 by a factor of more than 2. Elemental Carbon (EC) exhibited significantly higher concentration values in the Asian and “Other” sources at 0.27 and 0.44 μg/m3, respectively compared to the African source. EC was nearly undetectable at 0.04 μg/m3.
The concentrations of nitrate, potassium, and total carbon found in the dust samples collected at the Everglades station show a degree of similarity. At the Everglades site, the average nitrate concentrations are equivalent among the three dust sources. Sulfate was not measured in this study. The average undigested potassium was more than double of that found in the three dust types at the Everglades site which may be indicative of airborne fertilizer sources at the SW Florida site, but the digested dust value was more in line with the Everglades station values. There is no reasonable explanation of this discrepancy. The total carbon value measured at the SW Florida site was relatively similar to that determined for the African dust found at the Everglades site and more that an order of magnitude below the other dust sources.

4.4. Potential Environmental Impacts and Indirect Health Impacts of Aerosol Deposition in Southwest Florida and the Surrounding Area

Considerable research is ongoing in southwestern Florida to accurately measure all aspects of the nutrient budget that could facilitate or increase the duration of harmful algal blooms that produce toxins that impact human health. In addition, discussion with respiratory specialists suggest that the number of serious respiratory diseases have been rising over the last several decades. These diseases include CPOD, severe allergies, and asthma. This same pattern is observed in Caribbean islands and the east coast of Florida (see Section 1).
In southwestern Florida there are a number of potential direct and indirect environmental impacts of atmospheric aerosol fallout. The data collected indicate significant concentration of nutrients and the micronutrient Fe in both dry and wet fallout. For the past several decades there has been an increase in the frequency of red tide events in the Gulf of Mexico for extended periods occurring in shallow coastal waters [58]. In addition, harmful blooms of cyanobacteria have plagued the freshwaters from Lake Okeechobee to the Caloosahatchee River estuary and in canals and made-made lakes [59]. The measured nutrient and Fe concentrations measured indicate that atmospheric fallout in southwestern Florida and the nearshore area cannot be ignored when determining nutrient budget balances and primary productivity studies. While the concentrations of nutrients and iron measured are not likely to initiate a harmful algal bloom, they are likely to help sustain one.
African dust contains a number of components that can impact the duration of algal blooms of both marine and freshwater species. Additional local sources of nutrients and Fe in the dry and wet fallout also add to the impacts of the Saharan dust. The enhanced influx of phosphorus, nitrogen, and iron in the dust deposition from the combined distant and local sources and in rainfall tends to increase biological productivity [60,61]. While the phosphorus and nitrogen species may have a more direct impact, iron deposition may be in the reduced (direct impact) or oxidized form, which may not produce a direct impact at the water surface. However, in any areas of anoxic conditions or hypoxia, the iron may be reduced to a reduced state that would allow utilization by organisms that produce harmful algal blooms in the Gulf of Mexico and estuarine areas [62]. Once the particulate iron is deposited on the marine bottom, it may also be reduced and diffuse back into the water column and be available for algal uptake. While the macronutrients and iron inputs in the marine environment are unlikely to directly produce harmful algal blooms, they may serve to prolog events by supplying these key nutrients.
Harmful algal blooms are common in Lake Okeechobee with impacts to the Caloosahatchee River [59,63,64]. In Lake Okeechobee and deep man-made lakes and canals in southwest Florida, there is a common occurrence of anoxic water associated with the decay of organic material. The fluid mud in Lake Okeechobee is an example of a layer that is anoxic and could reduce the iron oxide to a more biologically active form [65]. Therefore, atmospheric deposition of nutrients and iron have a significant impact on harmful algal bloom dynamics.
The exacerbation of harmful algal blooms (HAB) caused by atmospheric aerosol deposits can expose the population of southwest Florida to the toxins secreted by red tide organisms which produce brevetoxins and by cyanobacteria which produce microcystin and other cyanotoxins [66,67,68]. These health impacts are under active investigation in southwest Florida.

4.5. Potential Direct Health Impacts of Aerosols in Southwest Florida

Saharan dust exposure and all dust exposure in general is known to have adverse impacts to human health, particularly with regard to respiratory diseases [4,10,13,14,18,32,33,34,35,37,69]. Fine particles on the order of PM2.5 and smaller can remain suspended in the atmosphere for weeks prior to inhalation exposure and have the potential to penetrate deeper into the respiratory pathways, increasing the risk of pulmonary diseases such as pneumonia, pneumonitis, chronic obstructive pulmonary disease (COPD), pneumoconiosis, silicosis, and asbestosis [70]. The inhaled particulates that are resistant to degradation can stimulate collagen deposition inside the lungs. The potential for toxicity is not well understood but seems to be influenced by the presence of specific minerals, the shape of the particles, toxic components, the presence or absence of mineral coating, and particle surface characteristics [70]. The fine particle size characteristics of the African dust creates a potential health concern and may contribute to observed morbidity rates, especially in people with pre-existing respiratory conditions.
A direct association between African dust transport and acute exacerbations of COPD was documented in Miami, Florida [39]. Studies in Africa, Europe, and many Caribbean islands have found a variety of health impacts caused by exposue to African dust, including pre-mature birth, heart rate and associated cardiac health, blood pressure and associated atherosclerosis, and cognitive decline, onset of Alzheimer’s disease (see Introduction for references). Discussions with doctors have provided antidotal information that severe respiratory illness has increased significantly over the past decade in southwest Florida. However, the development of statistics on the rate of increase and the impact of the dust composition and concentration is beyond the scope of this research. Additional research is merited based on the composition of the dust found in this study and a recent study of mercury deposition on local plant leaves that is likely associated with aerosol fallout [71]. Quantification of the dust fallout (mass) also needs to be assessed.

5. Conclusions

Historical accounts of trans-Atlantic dust transport indicate that Northwest Africa contributes to the highest mineral concentration (14.2 µg/m3) over the tropical North Atlantic and is the largest contributor of aerosol dust (790–840 Mt/year) reaching the Americas, with seasonal deposition rates reaching peak concentrations during the summer months of June, July, and August. Southwest Florida is impacted by African dust through both wet and dry deposition. However, the ratios of many inorganic constituents including K:Fe, Al:Ca, Si:Al, and Fe:Ca are substantially different (larger) in southwest Florida compared to those found in African dust from the source areas to the Florida East Coast. This supports a conclusion of a greater influence from local anthropogenic sources related to passage of the dust across Florida.
Local environmental problems in southwest Florida, such as increased frequency and duration of marine and freshwater algal blooms, may be influenced by the combined African dust and local dust sources, based in the concentrations of nutrient and Fe, presumed to be in oxide form, found in the wet and dry fallout. The measured aerosol fallout is enriched in phosphorus, nitrogen species, and iron which can influence algal bloom duration and extent. While the form of the iron being deposited is an oxide, it can be converted to a more biologically available form under reducing conditions which occur within the fluid mud in Lake Okeechobee, in manmade lakes and waterways, and in marine benthic sediments. Therefore, both the macronutrient and micronutrient influxes (e.g., iron) may prolong the duration and significance of harmful algal blooms. Due to climatic changes, the long-term impacts of aerosol fallout in southwest Florida may increase because of increased wind speeds over arid regions of Africa and increased atmospheric temperature, therefore promoting greater impacts on harmful algal bloom dynamics.
Based on this research, it would be prudent to increase the number of measurement stations for dust composition and concentration, develop better dust collection techniques in southwest Florida, and develop a regional clinical database on respiratory health issues. In addition, the southwest Florida data should be included in the historical database for trans-Atlantic dust in order to improve awareness and allow the scientific community to better assess the impacts of atmospheric aerosols on the environment, climate change, and health considerations in southwest Florida.

Author Contributions

R.B. conceived the project, collected and analyzed samples, and wrote the original text. Z.R.K. collected and analyzed samples and drafted the graphics. C.M.T. and D.J.C. added information on the health aspects of the dust. A.D.-T. and T.M.M. managed the research and contributed to the text. T.M.M. funded the research and provided the final text modifications and edits. All authors have read and agreed to the published version of the manuscript.

Funding

The funded was provided from the research account for the Eminent Scholar Research work performed by Thomas M. Missimer as provided by the State of Florida and Florida Gulf Coast University.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data collected for this research are contained in the paper. The raw data can be provided upon request.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Derry, L.A.; Chadwick, O.A. Contributions from Earth’s atmosphere to soils. Elements 2007, 3, 333–338. [Google Scholar] [CrossRef]
  2. Prospero, J.M. Atmospheric dust studies. Bull. Am. Meteorolog. Soc. 1968, 49, 645–652. [Google Scholar] [CrossRef] [Green Version]
  3. Savoie, D.L.; Prospero, J.M. Aerosol concentration statistics for the Northern Tropical Atlantic. J. Geophys. Res. 1977, 82, 5954–5964. [Google Scholar] [CrossRef]
  4. Prospero, J.M. Long-range transport of mineral dust in the global atmosphere: Impact of African dust on the environment of the southeastern United States. Proc. Natl. Acad. Sci. USA 1999, 96, 3396–3403. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  5. Talbot, R.W.; Harriss, R.C.; Browell, E.V.; Gregory, G.L.; Sebacher, D.I.; Beck, S.M. Distribution and geochemistry of aerosols in the tropical North Atlantic troposphere—Relationship to African dust. J. Geophys. Res. 1986, 91, 5173–5183. [Google Scholar] [CrossRef]
  6. Aldhaif, A.M. Sources, frequency, and chemical nature of dust events impacting the United States East Coast. Atmos. Environ. 2020, 231, 117456. [Google Scholar] [CrossRef]
  7. Carlson, T.N.; Prospero, J.M. The large-scale movement of Saharan air outbreaks over the northern equatorial Atlantic. J. Appl. Meterol. 1972, 11, 283–297. [Google Scholar] [CrossRef]
  8. Prospero, J.M. Mineral and sea salt aerosol concentrations in various ocean regions. J. Geophys. Res. 1979, 84, 725–730. [Google Scholar] [CrossRef]
  9. Westphal, D.L. A case study of mobilization and transport of Saharan Dust. J. Atmos. Sci. 1987, 45, 2145–2175. [Google Scholar] [CrossRef]
  10. Prospero, J.M.; Carlson, T.N. Vertical and areal distribution of Saharan dust over the western equatorial North Atlantic Ocean. J. Geophys. Res. 1996, 77, 5255–5265. [Google Scholar] [CrossRef]
  11. Muhs, D.R.; Budahn, J.; Prospero, J.M.; Carey, S.N. Geochemical evidence for African dust inputs to soils of western Atlantic islands: Barbados, the Bahamas, and Florida. J. Geophys. Res. 2007, 112, F02009. [Google Scholar] [CrossRef] [Green Version]
  12. Muhs, D.R.; Budahn, J.; Prospero, J.M.; Skipp, G.; Herwitz, S.R. Soil genesis on the island of Bermuda in the Quaternary: The importance of African dust transport and deposition. J. Geophys. Res. 2012, 117, F03025. [Google Scholar] [CrossRef] [Green Version]
  13. Glaser, P.H.; Hansan, B.C.S.; Donovan, J.J.; Givnish, T.J.; Stricker, C.A.; Volin, J.C. Holocene dynamics of the Florida Everglades with respect to climate, dustfall, and tropical storms. Proc. Natl. Acad. Sci. USA 2013, 110, 17211–17216. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  14. Talbot, R.W.; Andreae, M.; Berresheim, H.; Artaxo, P. Aerosol chemistry during the wet season in Central Amazonia: The influence of long-Range transport. J. Geophys. Res. 2013, 95, 16955–16969. [Google Scholar] [CrossRef]
  15. Yu, M.; Chin, M.; Yuan, T.; Bian, H.; Remer, L.A.; Prospero, J.M.; Omar, A.; Winker, D.; Yang, Y.; Zhang, Y.; et al. The fertilizing role of African dust in the Amazon rainforest: A first multi-year assessment based on data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite observations. Geophys. Res. Lett. 2015, 42, 1984–1991. [Google Scholar]
  16. Harley, G.L.; King, J.; Maxwell, J.T. Trans-Atlantic connections between North African dust flux and tree growth in the Florida Keys, United States. Earth Interact. 2017, 21, 1–22. [Google Scholar] [CrossRef]
  17. Prospero, J.M.; Barkley, A.E.; Gaston, C.J.; Gatineau, A.; Campos y Sansano, A.; Panechou, K. Characterizing and quantifying African dust transport and deposition to South America: Implications for the phosphorus budget in the Amazon Basin. Global Biochem. Cycles 2020, 34, e2020GB006536. [Google Scholar] [CrossRef]
  18. Querola, X.; Tobias, A.; Pérez, N.; Karanasiou, A.; Amato, F.; Stafoggia, M.; Garcia-Pando, C.P.; Ginoux, P.; Forastierre, F.; Gumy, S.; et al. Monitoring the impact of desert dust outbreaks for air quality for health studies. Environ. Internat. 2019, 130, 104867. [Google Scholar] [CrossRef]
  19. Tanaya, T.Y.; Orito, K.; Sekiyama, T.T.; Shibata, S.; Chiba, M.; Tanaka, H. MASINGAR, a global tropospheric aerosol chemical transport model coupled with MRI/JMA98 GCM. Pap. Meteorol. Geophys. 2003, 53, 119–138. [Google Scholar] [CrossRef] [Green Version]
  20. Prospero, J.M. Long-term measurements of the transport of African dust to the southeastern United States. J. Geophys. Res. 1999, 104, 15917–15928. [Google Scholar] [CrossRef] [Green Version]
  21. Prospero, J.M.; Lamb, P.J. African droughts and dust transport to the Caribbean: Climate change implications. Science 2003, 302, 1024–1027. [Google Scholar] [CrossRef] [PubMed]
  22. Gioda, A.; Mayoral-Bracero, O.L.; Scatena, F.N.; Weathers, K.C.; Mateus, V.L.; McDowell, W.H. Chemical constituents in clouds and rainwater in Puerto Rico rainforest: Potential sources and seasonal drivers. Atmos. Environ. 2013, 68, 208–220. [Google Scholar]
  23. Huneeus, N.; Schulz, M.; Balkanski, Y.; Griesfeller, J.; Prospero, J.; Kinne, S.; Bauer, S.; Boucher, O.; Chin, M.; Dentener, F.; et al. Global dust model intercomparison in AeroCom phase I. Atmos. Chem. Phys. 2011, 11, 7781–7816. [Google Scholar] [CrossRef] [Green Version]
  24. National Atmospheric and Space Administration (NASA). Atmospheric Composition Maps, Dust Aerosol Optical Thick Map, 09-02-021. 2021. Available online: https://earthobservatory.nasa.gov/global-maps/MODAL2_M_AER_OD (accessed on 2 September 2021).
  25. Parkin, D.W.; Phillips, D.R.; Sullivan, R.; Johnson, L.R. Airborne dust collections down the Atlantic. Quart. J. R. Met. Soc. 1972, 98, 798–808. [Google Scholar] [CrossRef]
  26. Havens, K.E.; Ji, G.; Beaver, J.R.; Fulton, R.S., III; Teacher, C.E. Dynamics of cyanobacteria blooms are linked to the hydrology of shallow Florida lakes and provide insight into possible impacts of climate change. Hydrobiologia 2019, 829, 43–59. [Google Scholar] [CrossRef]
  27. Peters, N.E.; Reese, R.S. Variations of weekly atmospheric deposition for multiple collectors at a site on the shore of Lake Okeechobee, Florida. Atmos. Environ. 1995, 29, 179–187. [Google Scholar] [CrossRef]
  28. Grimshaw, H.J.; Dolske, D.A. Rainfall concentrations and wet atmospheric deposition of phosphorus and other constituents in Florida, U.S.A. Water Air Soil Pollut. 2002, 137, 117–140. [Google Scholar] [CrossRef]
  29. Redfield, G.W. Atmospheric deposition of phosphorus to the Everglades: Concepts, constraints, and published deposition rates for ecosystem management. Sci. World J. 2002, 2, 1843–1873. [Google Scholar] [CrossRef]
  30. Havens, K.E.; Paerl, H.W. Climate change at a crossroad for control of harmful algal blooms. Environ. Sci. Technol. 2015, 49, 12605–12606. [Google Scholar] [CrossRef]
  31. Paerl, H.W.; Gardner, W.S.; Havens, K.E.; Joyner, A.R.; McCarthy, M.J.; Newell, S.E.; Qin, B.; Scott, J.T. Mitigating cyanobacterial harmful algal blooms in aquatic ecosystems impacted by climate change and anthropogenic nutrients. Harmful Algae 2016, 54, 213–222. [Google Scholar] [CrossRef] [Green Version]
  32. Prospero, J.M.; Blades, E.; Naidu, R.; Mathison, G.; Thani, H.; Lavoie, M.C. Relationship between African dust carried in the Atlantic trade winds and surges in pediatric asthma attendances in the Caribbean. Int. J. Biometeorol. 2009, 52, 823–832. [Google Scholar] [CrossRef] [PubMed]
  33. Prospero, J.M.; Collard, F.-X.; Molinié, J.; Jeannot, A. Characterizing the annual cycle of African dust transport to the Caribbean Basin and South America and its impact on the environment and air quality. Glob. Bichem. Cycles 2014, 29, 757–773. [Google Scholar] [CrossRef]
  34. Terradellas, R.; Nickovic, S.; Zhang, X.-Y. Airborne Dust: A Hazard to Human Health, Environment and Society. In World Meteorological Organization; Bulletin nº 2015; p. 64. Available online: https://public.wmo.int/en/resources/bulletin/airborne-dust-hazard-human-health-environment-and-society (accessed on 9 September 2021).
  35. Venero-Fernández, S.J. Saharan dust effects on human health: A challenge for Cuba’s researchers. MEDICC Rev. 2016, 18, 32–34. [Google Scholar] [PubMed]
  36. Akpinar-Elci, M.; Martin, F.E.; Behr, J.G.; Diaz, R. Saharan dust, climate variability, and asthma in Grenada, the Caribbean. Int. J. Biometeorol. 2015, 59, 1667–1671. [Google Scholar] [CrossRef] [PubMed]
  37. Viel, J.-F.; Mallet, Y.; Raghoumandan, C.; Quénel, P.; Kadhel, P.; Rouget, F.; Multigner, L. Impact of Saharian dust episodes on preterm births in Guadeloupe (French West Indies). Occup. Environ. Med. 2019, 76, 336–340. [Google Scholar] [CrossRef]
  38. Kotsyfakis, M.; Zarogiannis, S.G.; Patelarou, E. The health impact of Saharian dust exposure. Int. J. Occup. Med. Environ. Health 2019, 32, 749–760. [Google Scholar] [CrossRef]
  39. Gutierrez, M.P.; Zuidema, P.; Mirsaeidi, M.; Campos, M.; Kumar, N. Association between African dust transport and acute exacerbations of COPD in Miami. J. Clin. Med. 2020, 8, 2496. [Google Scholar] [CrossRef]
  40. U.S. Environmental Protection Agency (USEPA). Integrated Science Assessment for Particulate Matter; U.S. Environmental Protection Agency: Washington, DC, USA, 2020. Available online: https://www.federalregister.gov/documents/2020/01/27/2020-01223/integrated-science-assessment-for-particulate-matter (accessed on 12 December 2021).
  41. Schuerger, A.C.; Smith, D.J.; Griffen, D.W.; Jaffe, D.A.; Wawrik, B.; Burrows, S.M.; Christner, B.C.; Gonzalez-Martin, C.; Lipp, E.K.; Schmale, D.H., III; et al. Science questions and knowledge gaps to study microbial transport and survival in Asian and African dust plumes reaching North America. Aerobiologia 2018, 34, 425–435. [Google Scholar] [CrossRef]
  42. Waters, S.M.; Purdue, S.K.; Armstrong, R.; Detrés, Y. Metagenomic investigation of African dust events in the Caribbean. FMES Microbiology Letters 2020, 367, fnaa051. [Google Scholar] [CrossRef]
  43. Pieters, N.; Plusquin, M.; Cox, B.; Kicinski, M.; Vangrpnsvold, J.; Nawrot, T.S. An epidemiological appraisal of the association between heart rate variability and particulate air pollution: A meta-analysis. Heart 2012, 98, 1127–1135. [Google Scholar]
  44. Auchincloss, A.H.; Diez Roux, A.V.; Dvonch, J.T.; Brown, P.T.; Barr, R.G.; Daviglus, M.L. Associations between recent exposure to ambient fine particulate matter and blood pressure in Multi-Ethnic Study of Athersclerosis (MESA). Environ. Health Perspect. 2008, 116, 486–491. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  45. Kilian, J.; Kitazawa, M. The emerging risk of exposure to air pollution on cognitive decline and Alzheimer’s disease—Evident from epidemiological and animal studies. Biomed. J. 2018, 41, 141–162. [Google Scholar] [CrossRef] [PubMed]
  46. Schlesinger, R.B.; Kunzil, N.; Hidy, G.M.; Gotschi, T.; Jerrett, M. The health relevance of ambient particulate matter characteristics: Coherence of toxicological and epidemiological inferences. Inhal. Toxicol. 2006, 18, 95–125. [Google Scholar] [CrossRef] [PubMed]
  47. Carlson, T.N. Atmospheric turbidity in Saharan dust outbreaks as determined by analysis of satellite brightness data. Monthly Weather Review 1979, 107, 322–335. [Google Scholar] [CrossRef]
  48. Levin, Z.; Joseph, J.H.; Mekler, Y. Properties of Sharav (Khamsin) dust—Comparison of optimal and direct sampling. J. Atmos. Sci. 1980, 37, 882–891. [Google Scholar] [CrossRef]
  49. Prospero, J.M.; Nees, R.T.; Uematsu, M. Deposition rate of particulate and dissolved aluminum derived from Saharan Dust in precipitation at Miami, Florida. J. Geophys. Res. 1987, 92, 14723–14731. [Google Scholar]
  50. Prospero, J.M.; Savoie, D.L.; Carlson, T.N.; Nees, R.T. Monitoring Saharan aerosol transport by means of atmospheric turbidity. In Saharan Dust: Mobilization, Transport, Deposition; Morales, C., Ed.; Chapter 8; SCOPE Report 14; John Wiley & Sons: New York, NY, USA, 1979; pp. 171–187. [Google Scholar]
  51. Prospero, J.M.; Nees, R.T. Impact of the North African drought and El Niño on mineral dust in the Barbaros trade winds. Nature 1986, 320, 735–738. [Google Scholar] [CrossRef]
  52. Prospero, J.M.; Nees, R.T. Dust concentration in the atmosphere of the Equatorial North Atlantic: Possible relationship to the Sahelian Drought. Science 1977, 196, 1196–1198. [Google Scholar] [CrossRef] [Green Version]
  53. D’Almeida, G.A. A model for Saharan dust transport. J. Clim. Appl. Meteor. 1986, 25, 903–916. [Google Scholar] [CrossRef]
  54. Reiff, J.; Forbes, G.S.; Spieksma, F.T.M.; Reynders, J.J. African dust reaching northwestern Europe: A case study to verify trajectory calculations. J. Clim. Appl. Meteorol. 1986, 25, 1543–1567. [Google Scholar]
  55. Loye-Pilot, M.D.; Martin, J.M.; Morelli, J. Influence of Saharan dust on rain acidity and atmospheric input to the Mediterranean. Nature 1986, 321, 427–428. [Google Scholar]
  56. Landing, W.M.; Perry, J.J., Jr.; Guentzel, J.L.; Gill, G.A.; Pollman, C.D. Relationships between the atmospheric deposition of trace elements, major ions, and mercury in Florida: The FMS project (1992–1993). Water Air Soil Pollut. 1995, 80, 343–352. [Google Scholar] [CrossRef]
  57. U. S. Office of Mining Efficiency and Renewable Energy. ITP Mining: Energy and Environmental Profile of the U. S. Mining Industry; Chapter 9; Washington, DC, USA, 2002. Available online: https://www.energy.gov/eere/amo/downloads/itp-mining-energy-and-environmental-profile-us-mining-industry-december-2002 (accessed on 20 December 2021).
  58. Brand, L.E.; Compton, A. Long-term increase in Karenia brevis abundance along.the Southwest Florida Coast. Harmful Algae 2007, 6, 232–252. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  59. Rosen, B.H.; Davis, T.W.; Gobler, C.J.; Kramer, B.J.; Loftin, K.A. Cyanobacteria of the 2016 Okeechobee Waterway Harmful Algal Bloom; Open-File Report 2017-1054; U.S. Geological Survey: Reston, VA, USA, 2017. [CrossRef] [Green Version]
  60. Griffin, D.W.; Kellogg, C.A. Dust storms and their impact on ocean and human health. EcoHealth 2004, 1, 284–295. [Google Scholar] [CrossRef]
  61. Lenes, J.M.; Darrow, B.A.; Walsh, J.J.; Prospero, J.M.; He, R.; Weisberg, R.H.; Vargo, G.A.; Heil, C.A. Saharan dust and phosphatic fidelity: A three-dimensional biogeochemical model of Trichodesmium as a nutrient source for red tides on the West Florida Shelf. Cont. Shelf Res. 2008, 28, 1091–1115. [Google Scholar] [CrossRef]
  62. Conley, D.J.; Carstensen, J.; Vaquer-Sunyer, R.; Duarte, C.M. Ecosystem thresholds with hypoxia. In Eutrophication in Coastal Ecosystems: Towards Better Understanding and Management Strategies 12 Selected Papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006; Andersen, J.H., Conley, D.J., Eds.; Developments in Hydrology: Nyborg, Denmark; Springer: Dordrecht, The Netherlands, 2009; pp. 21–29. [Google Scholar] [CrossRef]
  63. Kramer, B.J.; Davis, T.W.; Meyer, K.A.; Rosen, B.H.; Goleski, J.A.; Dick, G.J.; Oh, G.; Gobler, C.J. Nitrogen limitation, toxin synthesis potential, and toxicity of cyanobacteria populations in Lake Okeechobee and the St. Lucie River Estuary, Florida, during the 2016 state of emergency event. PLoS ONE 2018, 13, e0196278. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  64. Rosen, B.H.; Loftin, K.A.; Graham, J.L.; Stahlhut, K.N.; Riley, J.M.; Johnston, B.D.; Senegal, S. Understanding the Effect of Salinity Tolerance on Cyanobacteria Associated with a Harmful Algal Bloom in Lake Okeechobee, Florida; Scientific Investigations Report 2018-5092; U. S. Geological Survey: Reston, VA, USA, 2018. [CrossRef]
  65. Missimer, T.M.; Thomas, S.; Rosen, B. Legacy phosphorus in Lake Okeechobee sediment: A review with new perspectives. Water 2020, 13, 39. [Google Scholar] [CrossRef]
  66. Hoagland, P.; Jin, D.; Beet, A.; Kirkpatrick, B.; Reich, A.; Ullman, S.; Fleming, L.E.; Kirkpatrick, G. The human health effects of Florida red tides: An expamded analysis. Environ. Internat. 2014, 68, 144–153. [Google Scholar]
  67. Ibelings, B.W.; Backer, L.; Kardinaal, W.E.A.; Chorus, I. Current approaches to cyanotoxin risk assessment and risk management around the globe. Harmful Algae 2014, 40, 63–74. [Google Scholar] [CrossRef] [Green Version]
  68. Stumpf, R.P.; Li, Y.; Kirkpatrick, B.; Litaker, R.W.; Hubbard, K.A.; Currier, R.D.; Harrison, K.K.; Tomlinson, M.C.; Anil, A.C. Quantifying Karenia brevis bloom severity and respiratory irritation impact along the shoreline of southwest Florida. PloS ONE 2022, 17, e0260755. [Google Scholar] [CrossRef]
  69. Rodriguez, R.I.; Ortiz-Martinez, M.G.; Jiménez-Vélez, B.D. Organic extracts from African dust storms stimulate oxidative stress and induce inflammatory responses in human lung cells through Nrf2 but not NF-kB. Env. Toxicol Pharm 2015, 39, 845–856. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  70. Zhang, X.; Zhao, L.; Tong, D.Q.; Wu, G.; Dan, M.; Teng, B. A systematic review of global dust and associated human health effects. Atmosphere 2016, 7, 158. [Google Scholar] [CrossRef]
  71. Greenplate, R.; Thomas, S.; Danley-Thomson, A.; Missimer, T.M. Phytoremediation potential of the coastal plain willow Salix Carolina for mercury and other heavy metals. Environ. Sci. Pollut. Res. 2022. in review. [Google Scholar]
Atmosphere 14 00102 g001 550
Figure 1. Optical thickness of African dust across the Atlantic Ocean southeastern United States, Including Florida [26].
Figure 1. Optical thickness of African dust across the Atlantic Ocean southeastern United States, Including Florida [26].
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Atmosphere 14 00102 g002 550
Figure 2. Map showing the location of the sample collection station. A close-up of the dry and wet sampling device is shown in Figure 3.
Figure 2. Map showing the location of the sample collection station. A close-up of the dry and wet sampling device is shown in Figure 3.
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Atmosphere 14 00102 g003 550
Figure 3. Closeup of the dry/wet sampling device. Note that the bucket used to gather dry fallout is open when it is not raining. The rain sensor closes the dry bucket and opens the wet bucket during rainfall.
Figure 3. Closeup of the dry/wet sampling device. Note that the bucket used to gather dry fallout is open when it is not raining. The rain sensor closes the dry bucket and opens the wet bucket during rainfall.
Atmosphere 14 00102 g003
Atmosphere 14 00102 g004a 550Atmosphere 14 00102 g004b 550
Figure 4. Composition of dust including concentrations of Fe, Si, Al, K, Ca, and Mg measured using bulk digestion and ICP-MS measurements of samples collected throughout the year. Note that where the error bars cannot be seen, they are very small relative to the concentration.
Figure 4. Composition of dust including concentrations of Fe, Si, Al, K, Ca, and Mg measured using bulk digestion and ICP-MS measurements of samples collected throughout the year. Note that where the error bars cannot be seen, they are very small relative to the concentration.
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Figure 5. Concentrations of undigested aerosols (soluble fractions) including Fe, Al, and K) and nutrients (N2O, NO2, and NO3) in rainfall at the ETI collection site. Note that where the error bars are difficult to see, they are small compared to the concentration.
Figure 5. Concentrations of undigested aerosols (soluble fractions) including Fe, Al, and K) and nutrients (N2O, NO2, and NO3) in rainfall at the ETI collection site. Note that where the error bars are difficult to see, they are small compared to the concentration.
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Figure 6. Concentrations of selected metals (Al, Si, Fe, K, Ca, Mg) and nutrients (P, NO2, NO3, NH3) in rainfall water that were digested using acid. Note that where the error bars are difficult to see, they are small compared to the concentration.
Figure 6. Concentrations of selected metals (Al, Si, Fe, K, Ca, Mg) and nutrients (P, NO2, NO3, NH3) in rainfall water that were digested using acid. Note that where the error bars are difficult to see, they are small compared to the concentration.
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Table
Table 1. Data parameters for digested aerosol dust results using ICP-MS analysis with concentrations in µg/kg.
Table 1. Data parameters for digested aerosol dust results using ICP-MS analysis with concentrations in µg/kg.
ConstituentMinimumMaximumAverageStandard Deviation
B0.0330.727.582.0
C0.0897.245.4181.3
Si0.0853.3263.8282.4
P0.080.54.415.9
S0.05752.1664.21626.8
K0.03251.1422.0983.6
Ca0.03813.5371.01024.4
Al0.03599.7324.6765.2
Cu0.018.21.63.3
Cr0.031.80.84.1
Mg3.1220265632783.1
Fe0.081.03.914.0
Table
Table 2. Data parameters for undigested aerosol dust results (soluble fractions) in rainfall using the Colorimetric Nutrient Analyzer and ICP-MS analysis. All values are in µg/L.
Table 2. Data parameters for undigested aerosol dust results (soluble fractions) in rainfall using the Colorimetric Nutrient Analyzer and ICP-MS analysis. All values are in µg/L.
ConstituentMinimumMaximumAverageStandard Deviation
Al0.0231.43.8
Fe0.00.90.10.2
Pb0.00.00.00.0
K0.09467.9364.41298.3
N2O0.0746.9118225.4
NO20.0207.33.626.7
NO30.0746.8114.4218.5
Table
Table 3. Concentrations for digested rainfall dust using the Colorimetric Nutrient Analyzer and ICP-MS analysis methods. All values in µg/L.
Table 3. Concentrations for digested rainfall dust using the Colorimetric Nutrient Analyzer and ICP-MS analysis methods. All values in µg/L.
ConstituentMinimumMaximumAverageStandard Deviation
K10.233678.380.2
Al203.811254.82405.72265.5
Mg6.1852.998.4151.2
NO20.432.85.20.1
NO31.3718.5209.9210.2
NH31.4658101.4111.5
P0.115.83.13.1
Si0.0517.3116.8158.5
Fe0.0125.73.319.1
Ca0.0974.124.0129.2
Table
Table 4. The ratios of K:Fe, AL:Ca, Si:Al, and Fe:Ca pertaining to the three categories of fine dust sources (African, Asian, and Other) measured at the EVER1 station in South Florida [6] compared to the composition ratios for the digested dust and digested rainfall in SW Florida (this study).
Table 4. The ratios of K:Fe, AL:Ca, Si:Al, and Fe:Ca pertaining to the three categories of fine dust sources (African, Asian, and Other) measured at the EVER1 station in South Florida [6] compared to the composition ratios for the digested dust and digested rainfall in SW Florida (this study).
Ion RatiosAfricanAsianOther
(Anthropogenic)		SW Florida (Digested Dust)SW Florida (Digested Rainfall)
K:Fe0.391.037.15129.6823.56
Al:Ca4.551.501.100.87100.12
Si:Al1.922.032.670.810.05
Fe:Ca2.340.880.540.010.14
Table
Table 5. The average concentration of nitrate, sulfate, potassium, organic carbon (OC), and elemental carbon (EC) pertaining to the three categories of fine dust sources (African, Asian, and “Other”) measured at the EVER1 station in South Florida [6] compared to the average concentrations found in this study. All concentrations are in mg/m3.
Table 5. The average concentration of nitrate, sulfate, potassium, organic carbon (OC), and elemental carbon (EC) pertaining to the three categories of fine dust sources (African, Asian, and “Other”) measured at the EVER1 station in South Florida [6] compared to the average concentrations found in this study. All concentrations are in mg/m3.
AnalyteAfricanAsianOtherUndigested Dust (SW FL)Digested Dust (SW FL)
NO30.450.480.480.0090.532
SO42.011.992.64--
K0.220.10.230.5810.12
TOC0.681.050.66--
EC0.040.270.44-0.022
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Barcan, R.; Kassis, Z.R.; Teaf, C.M.; Danley-Thomson, A.; Covert, D.J.; Missimer, T.M. Dry and Wet Atmospheric Deposition Composition in Southwest Florida: Environmental and Health Implications. Atmosphere 2023, 14, 102. https://doi.org/10.3390/atmos14010102

AMA Style

Barcan R, Kassis ZR, Teaf CM, Danley-Thomson A, Covert DJ, Missimer TM. Dry and Wet Atmospheric Deposition Composition in Southwest Florida: Environmental and Health Implications. Atmosphere. 2023; 14(1):102. https://doi.org/10.3390/atmos14010102

Chicago/Turabian Style

Barcan, Razvan, Zoie R. Kassis, Christopher M. Teaf, Ashley Danley-Thomson, Douglas J. Covert, and Thomas M. Missimer. 2023. "Dry and Wet Atmospheric Deposition Composition in Southwest Florida: Environmental and Health Implications" Atmosphere 14, no. 1: 102. https://doi.org/10.3390/atmos14010102

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