Airborne ²¹⁰Pb Particle Size Measurements During and After the WTC Collapse

N.H Harley¹; P. Chittaporn¹; A. Kong²; and I.M. Fisenne² (¹New York University School of Medicine; ²USDHS, Environmental Measurements Laboratory)

A pilot version of our particle size sampler, the Integrating Miniature Particle Size sampler (IMP) has been operative at Fernald, OH, as part of the exposure assessment research we are doing under EMSP. For quality control we deploy size samplers at 2 homes in New Jersey. One is on a terrace within sight of, and 3 km. north west from the World Trade Center Towers. Two weeks following 9/11, a size sampler was deployed on the roof of the New York City EML Laboratory, 2 km. North of the towers, and was operative from September 24 in 3 to 5 month sampling intervals until 2004. The NJ sampler was operational continuously from 2000. One 4 month sample was collected from 8/19/2001 to 1/17/2002, bridging the WTC collapse. All radon decay products attach to the ambient aerosol and the long lived Po-210 decay product from deposited Pb-210 is alpha counted and used as the atmospheric tracer to measure the airborne aerosol particle size distribution. These samplers contained 6 stages, an inlet impactor covered with ZnS, 4 fine mesh stainless steel screens from 200 to 500 mesh, and an exit Millipore backup filter to capture all residual particles. The samples were alpha counted in low background alpha counters and the size distribution obtained with a deconvolution program. The median size on the New Jersey terrace changed from 250 nm to 150 nm in the samples collected before and after the 9/11 building collapse, and the distribution was more disperse following the event. In NYC the median changed from 150 nm in the September to December sample, to less than 10 nm with less dispersion in the subsequent sample. *(Work Supported by USDOE EMSP Contract DE FG07 97ER62522)

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