Elemental Constituents of Miami Aerosol as Function of Particle Size Kenneth A. Hardy* Florida International University, Miami, Fla. 33 101
Roland Akselsson’, John W. Nelson, and John W. Winchester Florida State University, Tallahassee, Fla. 32301
Results are presented of proton-induced x-ray emission analysis of aerosol samples taken in Miami, Fla., in the summer of 1974. Elemental concentrations and elemental ratios as a function of particle size are shown for 13 elements. These size distributions allow the determination of the sources of several elements observed in the Miami aerosol. Data from north Florida and Bermuda are compared.
The city of Miami provides an opportunity to observe elemental constituents of the aerosol as it may be modified from the predominantly marine atmosphere background by urban nonindustrial activity. Major sources of the elements are the tropospheric land-derived particles and added sea spray particles carried by prevailing southeasterly winds, soil dust constituents raised by human activity in the city, automotive emissions that contain lead and halogen elements, and emissions from stationary combustion sources that include oil- and gas-fired power plants and refuse incinerators. The present study was undertaken to evaluate the relative importance of these major sources for 14 elemental constituents as a function of particle size. The results have practical importance in identifying sources and processes that control total suspended particulate matter and the levels of fine particulate matter in a respirable size range. The elemental constituents of respirable size range particulate matter is of public health interest, as this determines human susceptibility to specific pollution processes. Experimental
Samples of the aerosol were taken a t three locations in Miami, Fla., in midsummer, 1974, as part of an initial evaluation of air particulate matter in south Florida. Particles were classified into six size classes from 4 pm by single orifice cascade impactors of the Battelle design ( I ) , and elemental analyses were carried out using protoninduced x-ray emission (2-4). Concentrations are reported here for the elements S, C1, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, Br, and Pb. Sampling sites chosen for this study were: MIA, a downtown Miami location 2 km from the seacoast, on a rooftop 10 m above street level in an area with heavy traffic during working hours; FIU, a lightly populated location at the Florida International University campus 15 km from the seacoast, on a rooftop 10 m above a mostly asphalt-covered ground surface exposed to considerable local traffic; SWD, a quiet residential location in southwestern Dade County 2 km from the seacoast, on a platform 6 m above ground level in a grass- and tree-covered area. Weather during the sampling period was typical of subtropical maritime environments with winds varying from south to east a t 3-5 m/s. Contrary to the normal weather pattern, there was little rainfall during this study. Sampling locations are shown in the map of Figure 1. Present address, University of Lund, Solvegatan 14, 22362 Lund, Sweden. 176
Environmental Science & Technology
Sampling commenced on July 8 simultaneously at the three sites and was completed on July 18, 1974. During this time eight separate samples were collected at each site. Flow rates of 1 l./min through the cascade impactors were maintained by a critical flow orifice and were checked before and after each sampling period. Seven sampling periods were of 24-h duration, and one was of 72-h duration, which yielded seven samples of approximately 1.4 m3 and one of approximately 4.3 m3. Particle size fractions were collected in the ranges of equivalent aerodynamic diameter >4, 4-2,2-1, 1-0.5, and 0.5-0.25 pm by impaction on paraffin-coated ultrathin polystyrene film supported by glass disks. Particles of equivalent aerodynamic diameter
