Erosion, transport and deposition of atmospheric dust are largely determined by the nature and state of the earth's surface (the dust source) and the physical characteristics of the atmosphere. The state of the atmosphere is subject to important temporal variations related to diurnal and seasonal cycles and to synoptic conditions. The dynamic evolution of particulate concentrations measured at Brussels showed a significant peak in PM10 during 24–25 March 2007. The 4-day backward trajectories calculated for this peak attributed its cause to a dust storm that had occurred 2 days earlier in the Sahara. Chemical analysis showed a significant similarity to Saharan dust composition, primarily oxides of Si, Fe, and Al. On 29 March, another peak with a very high PM concentration and an elevated PM2.5-to-PM10 ratio was recorded in Brussels. Analysis of its PM profile showed that it was mainldy caused by formation of secondary aerosols.