Al and Fe in PM 2.5 and PM 10 suspended particles in south-central Florida: The impact of the long range transport of African mineral dust

Aluminum and iron were measured in daily samples collected at urban and rur al sites near Ft. Myers, Florida, in 1995-1996 using a dichotomous sampler. Al and Fe concentrations were low during most of the year but they increas ed dramatically during summer when African dust was advected into Florida. The ratio of fine (less than 2.5 mum diameter) to coarse (2.5-10 mum) Al an d Fe is relatively constant in African dust events with the fine accounting for a third to a half of the total. Also the mass ratio of Al-to-Fe is rel atively constant at 1.8, a value similar to average crustal material. In co ntrast, in non-African dust the fine-to-coarse and Al-to-Fe ratios are extr emely variable and generally much lower than those during African events wh en dust concentrations ranged up to 86 mug m(-3). The timing and magnitude of the Ft. Myers dust peaks closely matched those measured concurrently in Miami, 200 km to the southeast. Large areas of the eastern United States ar e frequently impacted by African dust every summer. Although dust concentra tions can reach very high values it seems unlikely that African dust events alone will cause a violation of the Environmental Protection Agency's stan dards for PM 2.5 or PM 10. However, African dust in conjunction with emissi ons from local and regional sources could conceivably present a problem wit h compliance. The probability of such an occurrence is heightened by the fa ct that dust concentrations are highest in the summer when pollution levels are often at a maximum in the eastern states.