For the protection of health, the recommendations of the World Health Organization and the European directives (directive 2008/50/EC) recommend not to exceed more than 35 times a year the daily limit value of PM10: 50 µg/ m³. Many studies carried out in the Caribbean zone use this threshold as an indicator of the presence of African sand mists. In partnership with the University of the West Indies and the University of Valladolid, the KaruSphère laboratory has evaluated a new PM10 dust detection threshold, i.e. 35 µg/m³. For the first time, 10 years of optical photometric data and in situ measurements of PM10 have been coupled and analyzed simultaneously in 3 Caribbean islands: Guadeloupe, Martinique and Puerto Rico. This work made it possible to characterize the atmospheric circulation in the Atlantic zone and to highlight the transition periods between the high and the low dust season. This study clearly demonstrates that the sand mist detection threshold generally taken into account, 50 µg/m³, is unsuitable for the Caribbean basin. Indeed, in the Lesser Antilles, 55% of dust events occur with PM10 concentrations below 50 µg/m³.