Transport of North African dust to Big Bend, Texas, during the 1999 Big Bend Regional Aerosol and Visibility Study

Episodes of high fine-particle (PM2.5) dust concentrations were observed at Big Bend, Texas, during July and August 1999, corresponding to the first half of the Big Bend Regional Aerosol and Visibility Observational (BRAVO) Study. Particulate elemental composition suggested a non-local, North African origin for these dust plumes. We employed a Monte Carlo particle dispersion model to study the three-dimensional transport of air parcels from several North African source regions to Big Bend from July through October 1999. The model analysis confirmed that air parcels originating in Africa frequently reached Texas during July and August, but not during September and October. The modeling also reproduced the episodic nature of the plumes; each "event" lasted approximately five days, as seen in both the modeling results and in aerosol data. Additional observational data, including aerosol size distributions, sun photometer data, and compositional analysis of individual particles by scanning electron microscopy, were used to further characterize the North African dust and to distinguish it from local dust sources.