African smoke particles act as cloud condensation nuclei in the wintertime tropical North Atlantic boundary layer over Barbados

The number concentration and properties of aerosol particles serving as cloud condensation nuclei (CCN) are important for understanding cloud properties, including in the tropical Atlantic marine boundary layer (MBL), where marine cumulus clouds reflect incoming solar radiation and obscure the low-albedo ocean surface. Studies linking aerosol source, composition, and water uptake properties in this region have been conducted primarily during the summertime dust transport season, despite the region receiving a variety of aerosol particle types throughout the year. In this study, we compare size-resolved aerosol chemical composition data to the hygroscopicity parameter κ derived from size-resolved CCN measurements made during the Elucidating the Role of Clouds–Circulation Coupling in Climate (EUREC4A) and Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) campaigns from January to February 2020. We observed unexpected periods of wintertime long-range transport of African smoke and dust to Barbados. During these periods, the accumulation-mode aerosol particle and CCN number concentrations as well as the proportions of dust and smoke particles increased, whereas the average κ slightly decreased (κ=0.46±0.10) from marine background conditions (κ=0.52±0.09) when the submicron particles were mostly composed of marine organics and sulfate. Size-resolved chemical analysis shows that smoke particles were the major contributor to the accumulation mode during long-range transport events, indicating that smoke is mainly responsible for the observed increase in CCN number concentrations. Earlier studies conducted at Barbados have mostly focused on the role of dust on CCN, but our results show that aerosol hygroscopicity and CCN number concentrations during wintertime long-range transport events over the tropical North Atlantic are also affected by African smoke. Our findings highlight the importance of African smoke for atmospheric processes and cloud formation over the Caribbean.</p

Interhemispheric transport of viable fungi and bacteria from Africa to the Caribbean with soil dust

Daily aerosol samples collected in trade winds at Barbados, West Indies, throughout 1996–1997 yielded significant concentrations of viable (culture-forming) bacteria and fungi only when African dust was present. Air masses from the North Atlantic, North America, and Europe yielded no cultivable organisms. The strong association of cultivable organisms with African dust suggests various factors that might be relevant to viability. Although we did not specifically look for pathogens, these same mechanisms could protect them as well. Our results suggest that arid regions could be an important source for the long-range transport of viable microorganisms. The transport of microorganisms to Barbados follows a clear meteorological and seasonal pattern, which suggests that it should be possible to model the transport process and to predict events. Microorganism and dust concentrations were unusually great in 1997, possibly in response to the strong El Niño. This suggests that the long-range transport of microorganisms might be particularly responsive to climate variability in general

Relationship between African dust carried in the Atlantic trade winds and surges in pediatric asthma attendances in the Caribbean

Asthma is epidemic in developed and developing countries including those in the Caribbean where it is widely believed that African dust, transported in high concentrations in the Trade Winds every year, is a major causative factor. The link between asthma and dust in the Caribbean is based largely on anecdotal evidence that associates sharp increases in the occurrence of asthma symptoms with hazy conditions often caused by dust. Here we report on a 2-year study of the relationship between the daily concentrations of dust measured in on-shore Trade Winds at Barbados and pediatric asthma attendance rates at Queen Elizabeth Hospital (QEH). We looked for large increases in QEH daily attendances in relation to daily dust concentrations as previously suggested by anecdotal observations. We could not find any obvious relationship although there may be more subtle linkages between dust and asthma. Our measurements show, however, that the concentration of dust in the size range under 2.5 microm diameter is sufficiently high as to challenge United States Environmental Protection Agency air quality standards for respirable particles. Thus, African dust may constitute a health threat of a different nature, producing symptoms less obvious than those of asthma

Is Summer African Dust Arriving Earlier to Barbados? The Updated Long-Term In Situ Dust Mass Concentration Time Series from Ragged Point, Barbados, and Miami, Florida

Abstract Surface dust mass concentrations, extracted from filters collected at Miami, Florida, and Ragged Point, Barbados, since 1974 and 1973, respectively, provide a rare, unusual, and important metric of the intercontinental transport of North African dust. The daily-resolved time series, updated through December 2018 for Miami and through December 2015 along with May–September 2016 and January–March and June–August 2017 for Barbados, indicate summer-mean dust mass concentrations have mostly decreased this decade at Miami, but not at Barbados, where instead the events containing the highest dust mass concentration events may be shifting to earlier in the year

Daily nitrate, sulfate, and sea salt aerosol mass concentrations measured at Ragged Point, Barbados from 1990-2011 and aerosol and meteorological model predictions from EQUATES

Here we present the nitrate, non-sea salt (nss)-sulfate, and sea salt mass concentrations measured at Ragged Point, Barbados that corresponds to the manuscript “Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic on Barbados are attributed to clean air policies, African smoke, and anthropogenic emissions”Sulfate and nitrate aerosols degrade air quality and modulate radiative forcing and the hydrological cycle. Emissions of sulfur dioxide (SO2) and nitrogen oxide (NOx) and meteorological factors determine how widespread these impacts are. To determine these impacts in the context of long-range transport to distant sites, we measured sulfate and nitrate aerosol from 1990-2011 at Ragged Point in Barbados. Non-sea salt (nss)-sulfate rapidly decreased by ~30% in the 1990s tracking reductions in SO2 in the U.S. and Europe. However, concentrations began to rise again in 2000 concurrently with increases in SO2 emitted from Africa and the oxidation of SO2 to sulfate as inferred from the EQUATES project data ran within the CMAQ model. Nitrate remained constant throughout the 21 years but spike in 2008 and 2010 when favorable transport of African smoke to the site occurred. These findings provide insight into the impact of changing emissions on the aerosol burden over remote regions that can inform model predictions of current and future aerosol loadings.This data is associated with the article: Gaston, C.J., Prospero, J.M., Foley, K., Pye, H.O.T., Custals, L., Blades, E., Sealy, P., Christie, J.A. Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic on Barbados are attributed to clean air policies, African smoke, and anthropogenic emissionsIn the file Daily Ragged Pt nitrate_sulfate_sea salt concentrations.csv we provide the daily nitrate, sulfate, sodium and calculated sea salt (as sodium * 3.252) mass concentrations, which have been filtered for days when the sampling pump run time <10%. Negative values have also been excluded. In the file Monthly EQUATES Aerosol_Gas_and_met 2002_2011.csv provides the predicted values of particulate nitrate, sulfate, calculated non-sea salt sulfate, sodium, and calculated dust mass concentrations. Particle data is segregated into fine particulate matter (PMF, including Aiken and accumulation modes) and coarse (PMC). Gas phase sulfur dioxide, carbon monoxide, hydrogen peroxide, benzene, and hydroxyl radical concentrations. Meteorological data includes relative humidity, temperature, precipitation, wind speed and wind direction

Coupling Sr-Nd-Hf Isotope Ratios and Elemental Analysis to Accurately Quantify North African Dust Contributions to PM 2.5 in a Complex Urban Atmosphere by Reducing Mineral Dust Collinearity

Tracking Saharan-Sahelian dust across the globe is essential to elucidate its effects on Earth's climate, radiation budget, hydrologic cycle, nutrient cycling, and also human health when it seasonally enters populated/industrialized regions of Africa, Europe, and North America. However, the elemental composition of mineral dust arising locally from construction activities and aeolian soil resuspension overlaps with African dust. Therefore, we derived a novel "isotope-resolved chemical mass balance" (IRCMB) method by employing radiogenic strontium, neodymium, and hafnium isotopes to accurately differentiate and quantitatively apportion collinear proximal and synoptic-scale crustal and anthropogenic mineral dust sources. IRCMB was applied to two air masses that transported African dust to Barbados and Texas to track particulate matter (PM) spikes at both locations. During Saharan-Sahelian intrusions, the radiogenic content of urban PM increased with respect to Sr/ Sr and Hf/ Hf but decreased in terms of Nd/ Nd, demonstrating the ability of these isotopes to sensitively track African dust intrusions even in complex metropolitan atmospheres. The principal aerosol strontium, neodymium, and hafnium end members were concrete dust and soil, soil and motor vehicles, and motor vehicles and North African dust, respectively. IRCMB separated and quantified local soil and distal crustal dust even when PM concentrations were low, opening a promising source apportionment avenue for urbanized/industrialized atmospheres

Diverging trends in aerosol sulfate and nitrate measured in the remote North Atlantic in Barbados are attributed to clean air policies, African smoke, and anthropogenic emissions

Sulfate and nitrate aerosols degrade air quality, modulate radiative forcing and the hydrological cycle, and affect biogeochemical cycles, yet their global cycles are poorly understood. Here, we examined trends in 21 years of aerosol measurements made at Ragged Point, Barbados, the easternmost promontory on the island located in the eastern Caribbean Basin. Though the site has historically been used to characterize African dust transport, here we focused on changes in nitrate and non-sea-salt (nss) sulfate aerosols from 1990–2011. Nitrate aerosol concentrations averaged over the entire period were stable at 0.59 µg m−3 ± 0.04 µg m−3, except for elevated nitrate concentrations in the spring of 2010 and during the summer and fall of 2008 due to the transport of biomass burning emissions from both northern and southern Africa to our site. In contrast, from 1990 to 2000, nss-sulfate decreased 30 % at a rate of 0.023 µg m−3 yr−1, a trend which we attribute to air quality policies enacted in the United States (US) and Europe. From 2000–2011, sulfate gradually increased at a rate of 0.021 µg m−3 yr−1 to pre-1990s levels of 0.90 µg m−3. We used the Community Multiscale Air Quality (CMAQ) model simulations from the EPA's Air QUAlity TimE Series (EQUATES) to better understand the changes in nss-sulfate after 2000. The model simulations estimate that increases in anthropogenic emissions from Africa explain the increase in nss-sulfate observed in Barbados. Our results highlight the need to better constrain emissions from developing countries and to assess their impact on aerosol burdens in remote source regions

Godzilla mineral dust and La Soufrière volcanic ash fallout immediately stimulate marine microbial phosphate uptake

During the “Godzilla” dust storm of June 2020, unusually high fluxes of mineral dust traveled across the Atlantic from the Sahara Desert, reaching the Caribbean Basin, Gulf Coast, and southeastern United States. Additionally, an eruption of the La Soufrière volcano on St. Vincent in April 2021 generated substantial ashfall in the southeastern Caribbean. While many studies have analyzed mineral dust’s ability to relieve nutrient limitation of phosphorus (P) in the P-stressed North Atlantic, less is known about the impact of extreme events and other natural aerosols on fluxes of P into seawater and from seawater into marine microbial cells. We quantified P and iron (Fe) content in mineral dust from the Godzilla dust storm and volcanic ash from the La Soufrière eruption collected at Ragged Point, Barbados. We also performed seawater incubations to assess the marine microbial response to aerosol deposition. Using environmentally-relevant concentrations of atmospheric particles for within the ocean’s mixed layer allowed us to draw realistic conclusions about how these deposition events impacted P cycling in situ. Volcanic ash has lower P content than mineral dust, and P in volcanic ash is far less soluble (~1%) than assumed in current atmospheric deposition models. Adding mineral dust and the volcanic ash leachate in concentrations representing different deposition scenarios increased soluble reactive phosphorus (SRP) concentrations in coastal seawater by ~7-32 nM. Phosphate uptake rate was stimulated in coastal seawater after either mineral dust or volcanic ash deposition at aerosol concentrations relevant to the Godzilla dust event, with ash eliciting the fastest uptake rate. Furthermore, high concentrations of both the mineral dust and volcanic ash led to slightly elevated alkaline phosphatase activity (APA) compared to the relevant controls, indicating higher potential for use of dissolved organic phosphorus (DOP) as a P source. Quantifying these aerosols’ impacts on P cycling is a significant step towards achieving a better understanding of their potential roles in relieving nutrient limitation and fueling the biological carbon pump