Wintertime spatio-temporal variation of ultrafine particles in a Belgian city

► Ultrafine particles (UFPs) measured simultaneously at 4 sampling points in a Belgian city. ► Dynamics of UFP at all sites with respect to meteorological and traffic conditions assessed. ► Dominant effect of traffic conditions on the UFP concentrations observed. ► Central monitoring site represented well the UFP at other sites within 1 km2 grid area.