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 rural 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 increased dramatically during summer when African dust was advected into Florida. The ratio of fine (less than 2.5 μm diameter) to coarse (2.5–10 μm) Al and 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 relatively constant at 1.8, a value similar to average crustal material. In contrast, in non-African dust the fine-to-coarse and Al-to-Fe ratios are extremely variable and generally much lower than those during African events when dust concentrations ranged up to 86 μg 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 are frequently impacted by African dust every summer. Although dust concentrations can reach very high values it seems unlikely that African dust events alone will cause a violation of the Environmental Protection Agency’s standards for PM 2.5 or PM 10. However, African dust in conjunction with emissions from local and regional sources could conceivably present a problem with compliance. The probability of such an occurrence is heightened by the fact that dust concentrations are highest in the summer when pollution levels are often at a maximum in the eastern states.