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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 hygrocopicity 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 average κ slightly decreased (κ = 0.46 +/- 0.10) from marine background conditions (κ = 0.52 +/- 0.09) when the 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 in 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. In the file “Dust_Mass_Conc_Royer2022” dust mass concentrations in grams per meter^3 are provided for each day of sampling. These data were used to generate Figure 2a in the manuscript. The file “Particle_Type_#fract_Royer2022” contains data obtained through CCSEM/EDX analysis and used to generate the temporal chemistry plot (Figure 4) provided in the manuscript. The data contains particle numbers for each particle type identified on stage 3 of the sampler, total particle numbers analyzed for the entire stage 3 sample, as well as particle number fractions in % values. In the file “Size-resolved_chem_Royer2022” we provide particle # and number fraction (%) values used to generate size-resolved chemistry plots in the manuscript (Figures 5a and 5b). The file includes all particle numbers and number fractions for sea salt, aged sea salt, dust+sea salt, dust, dust+smoke, smoke, sulfate, and organic particles in each size bin from 0.1 through 8.058 um during cumulative clean marine periods and CAT Event 1 as described in the manuscript. The file “K_at_0.16S_Royer2022” contains κ values calculated at 0.16% supersaturation (S) throughout the entire sampling period. These data were specifically used to generate the plot in Figure 7a. The file “CCN#_at_0.16S_Royer2022” contains cloud condensation nuclei (CCN) values calculated at 0.16% supersaturation (S) throughout the entire sampling period. These data were used to create the CCN portion of the plot in Figure 7b. 

Abstract. The number concentration and properties of aerosol particles serving ascloud condensation nuclei (CCN) are important for understanding cloudproperties, including in the tropical Atlantic marine boundary layer (MBL), where marine cumulus clouds reflect incoming solar radiation and obscure thelow-albedo ocean surface. Studies linking aerosol source, composition, andwater uptake properties in this region have been conducted primarily duringthe summertime dust transport season, despite the region receiving a varietyof aerosol particle types throughout the year. In this study, we comparesize-resolved aerosol chemical composition data to the hygroscopicityparameter κ derived from size-resolved CCN measurements made duringthe 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. Weobserved unexpected periods of wintertime long-range transport of Africansmoke and dust to Barbados. During these periods, the accumulation-mode aerosol particle and CCN number concentrations as well as the proportions ofdust and smoke particles increased, whereas the average κ slightlydecreased (κ=0.46±0.10) from marine backgroundconditions (κ=0.52±0.09) when the submicron particles were mostly composed of marine organics and sulfate. Size-resolved chemicalanalysis shows that smoke particles were the major contributor to theaccumulation mode during long-range transport events, indicating that smokeis mainly responsible for the observed increase in CCN numberconcentrations. Earlier studies conducted at Barbados have mostly focused onthe 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. Ourfindings highlight the importance of African smoke for atmospheric processesand cloud formation over the Caribbean. 

Here, we present the data and MixSIAR code that corresponds to the manuscript “Interannual variability in the source location of North African dust transported to the Amazon.” African dust is seasonally transported to the western Tropical Atlantic Ocean (TAO) and South America (SA), including the Amazon Basin. Leading hypotheses suggest that either the Western North African potential source area (PSA) or the Central North African PSA (e.g., Bodélé Depression) is the main source of dust transported to the Amazon. However, these notions remain largely untested with geochemical data. Here, we present a more nuanced hypothesis: both PSAs contribute dust to SA with precipitation and wind patterns determining the dominant source. Our premise is based upon two years of isotopic measurements (strontium and neodymium) of African dust collected in SA integrated into a statistical model in a Bayesian framework. With this approach, we identified strong interannual variability: while the Central PSA supplied 48% in winter 2016, a region within the Western PSA, which we suggest may be located near Niger, Mali, and Algeria accounts for 54% of transport in winter 2014. We propose the variability is due to the strength of the Libyan High and differing amounts of precipitation in the Gulf of Guinea and TAO between the two years. We anticipate that our work will lead to better constraints of dust nutrient deposition and subsequent carbon sequestration in the TAO and Amazon as well as improved model predictions of dust transport. Due to the connection between dust, precipitation, and wind patterns, our work can be used to link changes in climate with past changes in the source and magnitude of dust transported to the Amazon and TAO. This data is associated with the article: Barkley, A.E., Pourmand, A., Longman, J., Sharifi, A., Prospero, J.M., Panechou, K., Bakker, N., Drake, N., Guioiseau, D., Gaston, C.J. Interannual variability in the source location of North African dust transported to the Amazon. Submitted to the Proceedings of the National Academy of Sciences ## Description of the datasets The `data/` folder contains three data sets. `ds01` contains the data collected in this study from 34 samples including the dates of collection and Sr and eNd isotopic ratios. ## Metadata of the trajectory file ds01 is a *csv* file that contain 12 columns. Column 1 presents the date in the format ‘MM:DD:YYYY’ (e.g., 01-30-2014) that sample collection was initiated. Column 2 presents the date ‘MM:DD:YYYY’ (e.g., 01-31-2014) sample collection ended. Column 3 shows the mean 87Sr/86Sr ratio (unitless) measured and Column 4 shows the 95% confidence interval (CI) for each sample run in triplicate. Column 5 shows the 143Nd/144Nd isotopic ratio reported as epsilon neodymium (unitless) and Column 6 presents the 95% CI of the mean epsilon Nd. Columns 7, 9, and 11 show the lead (Pb) isotopic ratios normalized to 204Pb with their corresponding 95% CI in Columns 8, 10, and 12. 

African dust is transported to South America (SA) every winter and spring. Hypotheses suggest that either Western or Central North Africa (e.g., Bodélé Depression) is the main source of transported dust, yet these notions remain largely untested with geochemical data. Using 2 years of isotopic measurements (strontium and neodymium) of African dust collected in SA integrated into a statistical model, we identified strong interannual variability in dust source region. Central North Africa supplied 44% of long‐range transported dust in winter 2016 while the Western region accounted for 53% of dust in winter 2014. We propose the variability is due to differences in the strength of the Libyan High and precipitation over the Gulf of Guinea and Atlantic Ocean between the 2 years. Our findings can improve constraints of dust nutrient deposition and predictions of how changes in climate impact the source and magnitude of dust transported to the Amazon.

 

Abstract Wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area. Gaps in understanding the coupled chemical-meteorological interactions that drive high pollution events make identification of the most effective air-basin specific emission control strategies challenging. To address this, a September 2019 workshop occurred with the goal of planning a future research campaign to investigate air quality in Western U.S. basins. Approximately 120 people participated, representing 50 institutions and 5 countries. Workshop participants outlined the rationale and design for a comprehensive wintertime study that would couple atmospheric chemistry and boundary-layer and complex-terrain meteorology within western U.S. basins. Participants concluded the study should focus on two regions with contrasting aerosol chemistry: three populated valleys within Utah (Salt Lake, Utah, and Cache Valleys) and the San Joaquin Valley in California. This paper describes the scientific rationale for a campaign that will acquire chemical and meteorological datasets using airborne platforms with extensive range, coupled to surface-based measurements focusing on sampling within the near-surface boundary layer, and transport and mixing processes within this layer, with high vertical resolution at a number of representative sites. No prior wintertime basin-focused campaign has provided the breadth of observations necessary to characterize the meteorological-chemical linkages outlined here, nor to validate complex processes within coupled atmosphere-chemistry models.