<p><strong>Abstract.</strong> The present study offers the first chemical characterization of the submicron (PM<sub>1</sub>) 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<sub>1</sub> determined by a TEOM-FDMS (tapered element oscillating microbalance&ndash;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<span class="thinspace"></span>µg<span class="thinspace"></span>m<sup>−3</sup>, levels of NR PM<sub>1</sub> 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<sub>1</sub> concentrations higher than 15<span class="thinspace"></span>µg<span class="thinspace"></span>m<sup>−3</sup>), sea breeze phenomena and Saharan desert dust outbreaks (PM<sub>10</sub> up to 900<span class="thinspace"></span>µg<span class="thinspace"></span>m<sup>−3</sup>). 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&ndash;40<span class="thinspace"></span>%), whereas sulfate particles were predominant (40<span class="thinspace"></span>%) for days under oceanic influence. Overall, measurements showed that about three-quarters of the total PM<sub>1</sub> were explained by NR PM<sub>1</sub>, BC (black carbon) and Fe (a proxy for dust) concentrations, leaving approximately one-quarter for other refractory species. A mean value of 4.6<span class="thinspace"></span>% for the Fe<span class="thinspace"></span>∕<span class="thinspace"></span>PM<sub>1</sub> 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<span class="thinspace"></span>% of the total organic fraction. A new organic aerosol (OA) source, representing on average 3<span class="thinspace"></span>% 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<span class="thinspace"></span>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<span class="thinspace"></span>%) and was representative of regional (approximately three-quarters) but also local (approximately one-quarter) sources due to enhanced photochemical processes.</p>