Concentrations and sources of trace elements in particulate air pollution,Dar es Salaam,Tanzania, studied by EDXRF

Trace elements in near‐ground atmospheric aerosols were investigated in Dar es Salaam, Tanzania. Particles were collected at two sites, one urban and one rural, during two months with different meteorological conditions. The samplers, dichotomous impactors, segregate the particles into two size fractions, fine (PM_2.5, d_a < 2.5 µ m) and coarse (2.5 < d_a < 10 µ m). A sharp cyclone was used to sample finer particles (PM₁, d_a < 1 µ m). Meteorological parameters were also examined at both sites. An EDXRF spectrometer, based on three‐axial geometry, was used for quantitative elemental analysis. Concentrations of elements heavier than phosphorus were determined. Also, the content of black carbon on the filters was measured with a reflectometer. The elemental concentrations were compared with respect to season and geographical location in the city. The levels of different species in Dar es Salaam were also compared with similar data from other African and European countries. This showed low values of Pb with respect to the size of the city and no legislation on the use of leaded petrol, that often is the main source of lead. High values of Cl were also found, as would be expected in a coastal city. The coarse particles in the air, originating from soil, had a different composition in Dar es Salaam than in Gaborone, Botswana, and the concentration of black carbon was higher than in other cities. On the basis of the data collected, source assignments were made and the following sources found; sea‐spray, soil, city road dust, biomass burning, industries and traffic. Comparing the concentrations of different elements in PM_2.5 and PM₁ revealed that black carbon, Zn, Pb, K and Br are present only in the smallest particles. Copyright © 2004 John Wiley & Sons, Ltd.