Abstract. Arid regions are a major source of mineral dust aerosol. Transport from these sources can have a great impact on aerosol climatology in distant regions. In order to assess the impact of dust on climate we must understand how dust properties change after long distance transport from sources. This study addresses the changes in columnar aerosol properties when mineral dust outbreaks from western Africa arrive over the eastern Caribbean after transport across the Atlantic Ocean, a transit of 5–7 days. We use data from the NASA Aerosol Robotic Network (AERONET) located at five Caribbean and two western Africa sites to characterize changes in columnar aerosol properties: aerosol optical depth (AOD), size distribution, single scattering albedo, and refractive indexes. We first characterized the local aerosol climatology at each site and then using air mass back trajectories we identified those days when trajectories over Caribbean sites back-tracked to western Africa. Over the period 1996–2014 we identify 3174 days, an average of 167 days per year, when the air mass over the Caribbean sites could be linked to at least one of the two western Africa sites. For 1162 of these days, AOD data are available for the Caribbean sites as well as for the corresponding western Africa sites about 5–7 days earlier, when the air mass passed over these sites. We identified dust outbreaks as those air masses yielding AOD  ≥  0.2 and an Ångström exponent below 0.6. On this basis of the total 1162 days, 484 meet the criteria for mineral dust outbreaks. We observe that the AOD at 440 nm decreases by about 0.16 or 30 % during transport. The volume particle size distribution shows a similar decrease in the volume concentration, mainly in the coarse mode. The single scattering albedo, refractive indexes, and asymmetry factor remain unchanged. The difference in the effective radius over western Africa sites with respect to Caribbean sites ranges between 0 and −0.3 µm. Finally we conclude that in about half of the cases only non-spherical dust particles are present in the atmosphere over the western Africa and Caribbean sites, while in the other cases dust particles were mixed with other types of aerosol particles.

Over the last decades, the impact of mineral dust from African deserts on human health and climate has been of great interest to the scientific community. In this paper, the climatological analysis of dusty events of the past 20 years in the Caribbean area has been performed using a particulate approach. The focus is made on June 2020 extreme event dubbed “Godzilla”. To carry out this study, different types of data were used (ground-based, satellites, model, and soundings) on several sites in the Caribbean islands. First, the magnitude of June 2020 event was clearly highlighted using satellite imagery. During the peak of this event, the value of particulate matter with an aerodynamic diameter of less than 10 μμm (PM10) reached a value 9 times greater than the threshold recommended by the World Health Organization in one day. Thereafter, the PM10, the aerosol optical depth, and the volume particle size distribution analyses exhibited their maximum values for June 2020. We also highlighted the exceptional characteristics of the Saharan air layer in terms of thickness and wind speed for this period. Finally, our results showed that the more the proportion of particulate matter with an aerodynamic diameter of less than 2.5 μμm (PM2.5) in PM10 increases, the more the influence of sea salt aerosols is significant.

Desert dust coming from North African sources is a major phenomenon of the atmosphere related to its impact on the earth climate and human health. A great part of this particle product is transferred in a westward flux, over the Atlantic Ocean in form of outbreaks. Depending on the season, transport conditions and meteorological configuration along the pathway, high dust concentrations can reach either the northeast coast of South America or the islands of the Caribbean region. Their arrival corresponds with bad local air quality and numerous admittances into hospital emergency rooms. The control of health risk requires a dust-level forecast using satellite, model and ground measurements data. In this study, we investigate a correlation between PM10 measurements performed in 2015 by air quality networks at two sites, one in Dakar located on the West African coast and the other in Guadeloupe, a French Caribbean Island. The PM10 dust concentrations for both sites have been obtained using the same certified instruments (TEOM). Only Guadeloupe dust events presenting a daily mean PM10 of up to 35 µg/m 3 with back trajectories crossing in the vicinity of Dakar and verifying trajectories coming from Dakar, crossing close to Guadeloupe, have been taken into account. An air masses transport delay deduced by the HYSPLIT trajectory model was applied and a non-correlation between the two sites PM10 (correlation coefficient R = 0.3) was observed. Using the same trajectories and back trajectories, proximity conditions and HYSPLIT delay, the two sites' Aeronet photometric measurements (AOT1020) have been compared. A good correlation confirmed by a correlation coefficient, R = 0.88, was obtained between the Dakar AOT 1020 and the Guadeloupe AOT 1020. On the twelve dusty days of 2015 within eligible conditions of the pathway, an 80% decrease of AOT1020 during the transfer over the Atlantic Ocean was found.

Abstract. Mineral dust aerosol can be a major driver of aerosol climatology in regions distant from the sources. This study addresses the change of columnar aerosol properties when mineral dust arrives to the Caribbean Basin after transport from Africa over the Atlantic Ocean. We use data from NASA Aerosol Robotic Network (AERONET) sites in five Caribbean and two West African sites to characterize changes in aerosol properties: aerosol optical depth, size distribution, single scattering 15 albedo, and refractive indexes. After obtaining local aerosol climatology in each area, the air mass connections between West Africa and Caribbean Basin have been investigated by means of air mass back trajectories. Over the period 1996-2014 we identify 3174 connection days, on average, 167 connection days per year. Among these, 1162 pairs of data present aerosol data in Caribbean sites with corresponding aerosol observations in Western Africa sites ~5-7 days before. Of these 1162 days, 484 meet the criteria to be characterized as mineral dust outbreaks. Based on these days we observe the following 20 changes in aerosol-related properties in transiting the Atlantic: AOD decreases about 0.16 or -30%; the volume particle size distribution shape shows no changes; single scattering albedo, refractive indexes, and asymmetry factor remain unchanged; the difference in the effective radius in West African area with respect to Caribbean Basin is between 0 and +0.3 µm; and half of the analyzed cases present predominance of non-spherical particles in both areas.

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