Variability of mineral dust concentrations over West Africa monitored by the Sahelian Dust Transect

Kaly, François; Marticorena, Béatrice; Chatenet, B.; Rajot, Jean-Louis; Janicot, Serge; Niang, Awa; Yahi, Houda; Thiria, Sylvie; Maman, A.; Zakou, A.; Coulibaly, Bréhima; Coulibaly, M.; Koné, I.; Traoré, Salifou; Diallo, Aboubacry; Ndiaye, T.

doi:10.1016/j.atmosres.2015.05.011

Cited by 33 publications

(65 citation statements)

References 46 publications

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“…These results are consistent with the 5-year measurements of wind direction reported by Kaly et al (2015) in Mbour for the dry season. From back-trajectory analysis (Fig.…”

Section: Geographical Origins Of Chemical Speciessupporting

confidence: 82%

“…The total PM 1 mean concentration (including BC and Fe) is 8.2 µg m −3 (maximum halfhourly average: 143 µg m −3 ), a value which is about 10 times lower than the PM 10 mean concentration of 103.5 µg m −3 over the same period. This PM 10 average is consistent with the range of monthly averages reported by Kaly et al (2015) at Mbour for the March-June period of 2006-2010 (between 63 and 126 µg m −3 ). When compared to similar studies conducted around the world, Mbour clearly appears much less polluted than megacities such as Beijing (Sun et al, 2012) or the Paris area during winter (Petit et al, 2014).…”

Section: Estimation Of Absorbing Compound Concentrations In Pmsupporting

confidence: 78%

“…Our measurements during IOP-1 are generally consistent with monthly average frequencies of Mbour surface wind directions reported by Kaly et al (2015) between 2006 and 2010. Indeed, their climatology has shown that spring months are generally influenced by winds coming predominantly from two main sectors, north to east (0-90 • , prevailing in March-April) and northwest to southwest (315-225 • , dominant in May-June).…”

Section: Classification Of Air Massessupporting

confidence: 77%

“…Kaly et al (2015), based on 5 years of observations (2006)(2007)(2008)(2009)(2010) at Mbour, defined the dry season as the period during which no precipitation occurs from November to April and the wet season from May to October, where significant precipitation is measured, with a transition during April-May. In the work of Mortier et al (2016), who analyzed data from 2006 to 2012 at Mbour, the seasons are defined based on RH levels: from December to March-April (RH < 40 %) for the dry season and from June to September (RH ∼ 80 %) for the wet season.…”

Section: Classification Of Air Massesmentioning

confidence: 99%

“…The Mbour station, as part of the international AERONET network (Holben et al, 1998), is routinely equipped with active and passive remote sensing instruments for cloud, aerosol and meteorological monitoring (CIMEL sun/sky photometer, CIMEL microlidar, flux meters and a weather station). Since the AMMA campaigns in 2006, Mbour is also one of the three ground-based stations of the "Sahelian Dust Transect" where PM 10 mass concentrations are measured continuously (every 5 min) thanks to a tapered element oscillating microbalance (TEOM; Marticorena et al, 2010;Kaly et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

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Chemical characterization and source apportionment of submicron aerosols measured in Senegal during the 2015 SHADOW campaign

Rivellini¹,

Chiapello²,

Tison³

et al. 2017

Atmos. Chem. Phys.

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Abstract. The present study offers the first chemical characterization of the submicron (PM 1 ) fraction in western Africa at a high time resolution, thanks to collocated measurements of nonrefractory (NR) species with an Aerosol Chemical Speciation Monitor (ACSM), black carbon and iron concentrations derived from absorption coefficient measurements with a 7-wavelength Aethalometer, and total PM 1 determined by a TEOM-FDMS (tapered element oscillating microbalance-filtered dynamic measurement system) for mass closure. The field campaign was carried out over 3 months (March to June 2015) as part of the SHADOW (SaHAran Dust Over West Africa) project at a coastal site located in the outskirts of the city of Mbour, Senegal. With an averaged mass concentration of 5.4 µg m −3 , levels of NR PM 1 in Mbour were 3 to 10 times lower than those generally measured in urban and suburban polluted environments. Nonetheless the first half of the observation period was marked by intense but short pollution events (NR PM 1 concentrations higher than 15 µg m −3 ), sea breeze phenomena and Saharan desert dust outbreaks (PM 10 up to 900 µg m −3 ). During the second half of the campaign, the sampling site was mainly under the influence of marine air masses. The air masses on days under continental and sea breeze influences were dominated by organics (36-40 %), whereas sulfate particles were predominant (40 %) for days under oceanic influence. Overall, measurements showed that about threequarters of the total PM 1 were explained by NR PM 1 , BC (black carbon) and Fe (a proxy for dust) concentrations, leaving approximately one-quarter for other refractory species. A mean value of 4.6 % for the Fe / PM 1 ratio was obtained. Source apportionment of the organic fraction, using positive matrix factorization (PMF), highlighted the impact of local combustion sources, such as traffic and residential activities, which contribute on average to 52 % of the total organic fraction. A new organic aerosol (OA) source, representing on average 3 % of the total OA fraction, showed similar variation to nonrefractory particulate chloride. Its rose plot and daily pattern pointed to local combustion processes, i.e., two open waste-burning areas located about 6 and 11 km away from the receptor site and to a lesser extent a traditional fish-smoking location. The remaining fraction was identified as oxygenated organic aerosols (OOA), a factor that prevailed regardless of the day type (45 %) and was representative of regional (approximately three-quarters) but also local (approximately one-quarter) sources due to enhanced photochemical processes.

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“…These results are consistent with the 5-year measurements of wind direction reported by Kaly et al (2015) in Mbour for the dry season. From back-trajectory analysis (Fig.…”

Section: Geographical Origins Of Chemical Speciessupporting

confidence: 82%

Section: Estimation Of Absorbing Compound Concentrations In Pmsupporting

confidence: 78%

Section: Classification Of Air Massessupporting

confidence: 77%

Section: Classification Of Air Massesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Chemical characterization and source apportionment of submicron aerosols measured in Senegal during the 2015 SHADOW campaign

Rivellini¹,

Chiapello²,

Tison³

et al. 2017

Atmos. Chem. Phys.

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Mineral dust over west and central Sahel: Seasonal patterns of dry and wet deposition fluxes from a pluriannual sampling (2006–2012)

et al. 2017

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Total and wet mineral dust deposition has been monitored since 2006 at three Sahelian stations in Senegal, Mali, and Niger, respectively at the weekly and the event time scale. Average annual deposited mass fluxes range from 75 to 183 g m−2 yr−1, from west to east. Deposition fluxes exhibit a clear seasonal cycle in Mali and Niger. High wet deposition fluxes result from an optimum phasing between dust concentration and precipitation: the maximum occurring at the beginning of the wet season, after the maximum of dust concentration and before the precipitation maximum. The contribution of wet to total deposition varies from 67% in Mali to 8% in Senegal. It is the main factor of variability of the deposition fluxes from year to year and at the seasonal scale in Niger and Mali. Wet deposition fluxes in Mali and Niger are mainly due to the wash out of dust emitted by convective systems. In Senegal, the deposition fluxes are lower and dominated by dry deposition (92% of the annual deposition flux). This is due to the low occurrence of convective systems producing local dust emissions and intense wet deposition. The dry deposition fluxes are primarily driven by the variability of the dust concentration. The dry deposition velocities derived from our measurements are consistent with those estimated by theoretical models. Scavenging ratios computed from the measured wet deposition fluxes, dust concentrations, and precipitation are anticorrelated with precipitation amounts. This suggests that most of the atmospheric dust is scavenged at the very beginning of the precipitation events.

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Dust Uplift Potential in the Central Sahel: An Analysis Based on 10 years of Meteorological Measurements at High Temporal Resolution

et al. 2017

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A 10 year data set of wind speed and precipitation recorded in two Sahelian stations located in Niger and Mali is used to investigate the duration and the diurnal and seasonal cycles of high wind speeds and Dust Uplift Potential (DUP). The results indicate that high wind speeds, those greater than the threshold wind velocity required to initiate wind erosion (TWV) over a bare soil occurred in the middle and late morning during the dry and wet seasons but also at nighttime during the wet season. However, the morning wind speeds are only slightly greater than TWV leading to low DUP. On the opposite, the high wind velocities associated to the nocturnal mesoscale convective systems crossing the Sahel during the wet season are responsible for the highest potential wind erosion events. This leads to a strong seasonality of DUP with more than 70% occurring in less than 90 days, from mid‐April to mid‐July. The duration of the high wind speed events is very short since more than 80% last for less than 3 h, suggesting that the frequency of the observations performed in SYNOP meteorological stations is not sufficient to correctly quantify the contribution of such events to DUP. Finally, by combining precipitation and DUP, we estimated that precipitation should have a relatively limited role in terms of inhibition of wind erosion in this region with precipitation only affecting 25% of total DUP.

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Variability of mineral dust concentrations over West Africa monitored by the Sahelian Dust Transect

Cited by 33 publications

References 46 publications

Chemical characterization and source apportionment of submicron aerosols measured in Senegal during the 2015 SHADOW campaign

Chemical characterization and source apportionment of submicron aerosols measured in Senegal during the 2015 SHADOW campaign

Mineral dust over west and central Sahel: Seasonal patterns of dry and wet deposition fluxes from a pluriannual sampling (2006–2012)

Dust Uplift Potential in the Central Sahel: An Analysis Based on 10 years of Meteorological Measurements at High Temporal Resolution

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