A field campaign focused primarily on free tropospheric aerosol measurements over Mildura, Australia, at 34 ¿S (Mildura Aerosol Tropospheric Experiment (MATE 98)) was conducted in the austral spring of 1998 to test for the current presence of a seasonal aerosol layering activity observed in the 1970s and to obtain additional characteristics that would lead to a better understanding of the phenomenon. Ground-based lidar as well as balloon-borne optical particle counters and backscattersondes with ozone sensors were employed. The results indicate that large horizontal scale layers are present and show that their structure is highly correlated with excess ozone. Particle concentrations in the layers were sufficient to measurably affect aerosol optical depth. The probable source is distant biomass burning regions, but a detailed understanding of associated smoke transport and evolution as observed over Mildura is incomplete.