VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

only lasted a few hours. Concentrations of sulfur and silicon at this time were notably elevated at the DOE site as compared to days immediately before and after. Also, ORD data collected by both the nephelometer and the aetholometer sited on the Federal Building at 290 Broadway indicated substantial elevations of PM and light-absorbing components within the space of a few hours early in the morning of October 4. Hourly PM2 5 levels at PS 64 were also elevated (some in excess of 100 pg/m’) during or shortly after the same hours on October 4, suggesting brief surface fumigation by the WTC plume to the north-northeast of Ground Zero.

It has been suggested that the high concentrations of sulfur observed at the DOE building on Varick Street were related to transport fi’om power plants either in the Northeast or in the Ohio Valley. During this early October period, there were most probably some increases in the concentration of sulfur associated with regional scale transport of sulfates derived from distant sources. However, the extremely high abundance of sulfur at Site A on the Ground Zero perimeter observed by ORD and the ratio of sulfur observed at Site A compared with that observed at Site K suggests that Ground Zero was a large source of sulfur on October 3 and could have also contributed to sulfur readings at the DOE rooftop site.

The peak elevations of airborne fine PM silicon limited to October 3-4 at Site A and at 290 Broadway are notable, suggesting high temperature volatilization of silicon from glass and/or cement by intense WTC fires on those dates and transport of the WTC plume in a north to northeasterly direction. This is consistent both with the plume trajectory plotted in Figure 12 and the marked increases in silicon levels reported by Cahill et al. (2002) at the DOE Varick Street site, to the north-northeast of the WTC, including unusual measured elevations of silicon in very fine (0.09-0.50 pm) and, possibly, inferred ultrafine (< 0.01 pm) PM size ranges (silicon otherwise typically being mainly associated with coarse fraction particles > 2.5 pm). There were also marked increases in ORD-observed concentrations of various metals on October 3-4, reinforcing the conclusion that the DOE Varick Street data for October 3 reflected emissions fi’om intense Ground Zero fires. The very brief increase in PM2 5 values and high levels of silicon at the DOE site on October 3 apparently did not occur again at that site, based on preliminary EPA evaluation of the Cahill et al. raw data provided by DOE (Figure 19). Interestingly, Lioy et al. (2002) reported lead and other substances as being unusually congealed together with silicon in particles from the WTC settled dust, likely due to the vaporization of silicon, lead, and/or other metals by intense heat, followed by their condensation and coagulation into particles with unusual composition.

The above high-resolution measurements suggest that WTC emissions in late September and early October varied greatly at times over 24-hour periods and that some of the more notable emissions probably occurred in discrete events which resulted in air pollutant elevations that lasted only a few hours (mainly overnight during cooler early morning hours before temperature increases after sunrise). Such events were likely related to activities of rescue and recovery operations at the WTC, such as removal of large pieces of debris perhaps resulting in increased oxygen flow and brief flareups of fires within the WTC rubble pile. Further high temporal resolution analyses, including more detailed local-scale WTC plume plots, will be needed to better understand the specific lower Manhattan areas impacted by short-term WTC emission events and the implications of these sporadic events for potential human exposures and health impacts.

DRAFT-DO NOT QUOTE OR CITE 36 October 2002

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