Special issue  

Compared to other European regions, the metropolitan area of Barcelona sees relatively high particulate matter due to high anthropogenic emissions, a dry and warm Mediterranean climate and low dispersive conditions due to a unique topographical situation. During the autumn of 2010, the SAPUSS experiment took place, involving measurements of aerosols with multiple techniques occurring simultaneously in order to deduce point source characteristics and to understand the atmospheric processes responsible for their modifications. The unique approach is the large variety of instrumentations deployed simultaneously in a number of monitoring sites used including: a main traffic road, two urban background sites, a regional background site and two towers within the city (150 m and 545 m above sea level, 150 m and 80 m above ground, respectively). The purpose of this issue is to contribute to the advancement of our understanding of the sources and the evolution of aerosols in the atmosphere. This integrated study would also be of interest for other similar sites worldwide.