During the spring of 1998, smoke produced by biomass burning in Central America was transported northward, where it eventually affected the continental United States. To quantify this event, this study analyzes the presence of aerosols using the Total Ozone Mapping Spectrometer (TOMS) aerosol index. Unusually large amounts of UV-absorbing aerosols were present over parts of Central America during 1998 compared to a climatology created from the 13-year Nimbus 7 TOMS data set (1979--1992). The role of transport is studied by computing trajectories for air parcels initialized in the area with the most widespread fires. Comparison of the TOMS aerosol index maps and the parcel trajectories indicates that the trajectories adequately represent the smoke transport. Analysis of the TOMS data, the meteorological observations, and the trajectories indicates that the source region of the smoke is influenced by two prevailing transport regimes: one northward and one westward. The transport alternates between the two flow patterns. Statistical analysis of the transport shows that May 1998 and the climatology contain similar patterns of northward and westward flow regimes. The northward flow regime in 1998, however, is among the strongest of the 20-year period analyzed. The combination of unusually large smoke production and stronger than normal northward transport led to significant smoke concentrations over large areas of the central and southern United States. ¿ 2001 American Geophysical Union