VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

concentrations at some other nearby lower Manhattan sites exceeded EPA’s 40 micrograms per cubic meter (pg/m^) 24-hour Air Quality Index (AQI) level ofconcern for susceptible subgroups. The high PM concentrations recorded very near WTC Ground Zero during late September and early October may imply increased chronic health risks for the most highly exposed individuals (e.g, persons spending extended periods of time within the WTC work zone without wearing protective respirators). By mid- to late October, PM values across lower Manhattan had largely returned to levels typical ofNew York City and other US urban areas, with only afew WTC or nearby sites occasionally approaching or exceeding the AQI level ofconcern.

Many individuals were exposed for a few hours to very high PM concentrations in the initial dust cloud that spread over lower Manhattan on September 11. Also, high levels of airborne particles were detected during the first several days after September 11 at a few already existing PM monitoring sites scattered across the New York City area. Hourly or daily fine particle (less than 2.5 pm in diameter, PM2 5) values at some new sites set up by EPA or New York State exceeded 40 pg/m’ (though the AQI applies only to the daily averages).

PM2.5 measurements from newly established monitoring sites around the WTC perimeter varied widely, depending on wind direction. Daily average (24-hr) PM2 5 concentrations on some days exceeded 200 pg/m^ at one WTC perimeter site or another during late September and early October. However, PM2 5 concentrations decreased rapidly with distance from the WTC, with few PM2 5 values exceeding the 40 pg/m’ AQI at monitoring locations ranging from 3 to 10 blocks away from the WTC. During the entire period following September 11, PM2 5 values recorded at lower Manhattan sites away from the WTC perimeter were not markedly different than during periods before or since, as the New York metropolitan area routinely experiences PM2 5 values near and above the AQI.

Concentrations of various elements (e.g., calcium, sulfur, silicon, lead, and other metals) in WTC PMj 5 particles also were enriched above typical background levels on an episodic basis at sites mainly on or near the WTC perimeter, including on some days extending into late October and into November.

The issue of alkalinity of WTC dust and its potential as a possible health concern for exposed individuals is raised by observations by the United States Geological Survey (USGS) and academic researchers of high pH (> 11.0) of aqueous solutions of settled WTC dust not leached by rainfall. After late September, indoor exposures to such dust probably warrant more concern than outdoor exposures for possible acute irritative effects or more chronic health effects, not only because of the basic nature of some constituent particles but also because of other unusual features, such as slender microscopic glass fibers with toxic materials attached to them or very fine particles composed of imusual combinations of silica coalesced with lead or other toxic materials.

DRAFT-DO NOT QUOTE OR CITE 4 October 2002

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