VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

been much higher than the lower limit given above, perhaps even approaching concentrations of condensed water vapor that are observed in dense fogs (i.e., thousands of pg/m’).

Thus, individuals engulfed in the initial dust/smoke cloud may have been exposed for several hours to concentrations of both fine and coarse inhalable particles anywhere in the range from milligrams per cubic meter (> 1,000 pg/m’) to perhaps hundreds of milligrams per cubic meter (> 100,000 pg/m^). However, it does not appear that people outside the lower Manhattan area (except possibly very briefly for those on Governor’s Island or in Brooklyn Heights) experienced such extreme PM exposures. This estimation is based, for example, on hourly PM2 5 levels observed at several NYSDEC monitoring sites (Figure 7) during September 11 to 13. Of most note, as seen in Figure 7, PMj 5 concentrations at NYC sites generally remained under 25 pg/m’ during most of September 11 and 12. However, hourly PMj j concentrations did increase to the 50-100 pg/m’ range for a few hours on September 12 and 13 at PS 64, which is located about 2.5 km northeast of Ground Zero, and at PS 199, which is located in Queens several miles east-northeast of Ground Zero. These PM2 5 increases most likely reflected east­ northeast dispersal of not only windblown fine PM from settled dust but also probably of newly formed fine PM generated by the intense fires (> 1000 °F) at WTC Ground Zero. This would be consistent with dispersal to the east-northeast of the WTC plume, as indicated by the ORD modeled trajectory plotted for September 13 (shown in Figure 8). The increased hourly PM2 5 levels at PS 64 and PS 199 (reaching 166 and 100 pg/m’ at 9 a.m. September 13) indicate that the WTC plume likely briefly fiimigated the surface for a few hours at those and/or intervening locations during the morning of September 13.

Changes in wind direction later in the day on September 13 resulted in rotation of the WTC plume back to a flow predominantly to the south-southwest (mainly over New York Harbor) through September 14 and 15, as indicated in Figures 9 and 10. Note the very low PM2 5 hourly values (almost all < 6 pg/m^) at NYSDEC monitoring sites throughout the NYC area following rain associated with a frontal passage and, also, likely reflecting in part decreased vehicular traffic in the aftermath of September 11 events.

During the next several days, ORD plume dispersion modeling indicates that the plume rotated in such a manner as to result in transport in varying directions, including sometimes to the north-northwest (over northern New Jersey and NYC areas), but there was little indication of the plume fumigating the surface, based on surface PM measurements at preexisting PM monitoring sites. During the rest of September and on into October, 24-hour PM2 5 values at preexisting NYSDEC monitoring sites did not exceed the daily PM2.5 NAAQS (65 pg/m^ 24-h). In fact, daily PM2 5 values from most pre-existing fixed sites throughout the NYC area did not show marked elevations in comparison to historical PM2 5 levels for NYC areas, with the occurrence through mid- to late October (from time to time or from site to site) of a few 24-hour PM2 5 values approaching the 24-hour AQILOC (40 pg/m’) not being notably out of line with past frequency of such excursions in NYC.

Starting September 21, the EPA/ORD WTC perimeter monitoring sites at Sites A, C, and K (within 100-200 meters of Ground Zero) allowed tracking of WTC-related ambient PM emissions in the immediate WTC vicinity. The ORD monitoring data, shown in Figure 11 (top) showed widely varying PM concentrations across the WTC perimeter sites from day to day, with

DRAFT-DO NOT QUOTE OR CITE 30 October 2002

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