VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

high hourly or daily PM2.5 levels being seen at one or another perimeter site downwind from Ground Zero on given days. As seen in Figure 11, exceedances of the 24-hour PM2.5 NAAQS level (65 pg/m’) occurred at some Ground Zero perimeter sites during late September and into October, but on only a few occasions thereafter. A general downward trend in daily PM concentrations, as well as a decreasing range of 24-hour variations, were seen for PM2 5 concentrations at these WTC perimeter sites from early October, 2001, onward. The range of 24-hour values among these ORD sites generally remained below the AQILOC of 40 pg/m^ during December, 2001, and January, 2002 (as depicted by black bar in lower right of Figure 11 top panel). In contrast to the results seen for the ORD/WTC perimeter sites, distinctly lower PM2.5 concentrations were observed at the 290 Broadway site about six blocks northeast of Ground Zero. The 24-h PM2 5 concentrations recorded there by VAPS sampling exceeded 65 pg/m’ (daily PM2 5 NAAQS level) only once, on October 4; and the 24-h AQI LOC (40 pg/m’) for highly susceptible persons was approached or exceeded at the 290 Broadway site on only a few occasions (e.g., Sept. 27; Oct. 3, 4, 5; Oct 20; Nov. 15-16). These daily values often reflect high hourly values occurring overnight mainly during early morning hours before 7 or 8 a.m. The overall pattern of results from ORD perimeter monitoring stations near the WTC, coupled with distinctly lower PM2 5 concentrations monitored by ORD on the 16* floor at 290 Broadway (about 6 blocks northeast of the WTC) suggest occasional short-term increments in fine PM values at WTC Ground Zero and, at times, along the WTC fire plume path (with areas impacted shifting with prevailing winds).

For example, when low wind speeds and mixing layers associated with a high pressure system over New York City area occurred during October 3-5, generally increased region-wide PM2 5 levels were observed across much of northern New Jersey and New York City, with some additional PM increments being superimposed at a few monitoring sites within modeled WTC plume dispersion areas. During such weather conditions, plumes tend to be more well-defined than if there were turbulence and are more identifiable for longer distances (see Stull 2000, for example). In particular, 24-hour PM2 5 at WTC Site A (on north perimeter of Ground Zero) reached 400 pg/m^ on October 3-4, but 24-hour PM2 5 values dropped off to 90 pg/m^ at the 290 Broadway site several blocks northeast of WTC and to 53 pg/m^ at PS 64 about 1.5 km further to the northeast of WTC Ground Zero and only reached 60 pg/m’ at Site K (on southwest perimeter of Ground Zero). This was consistent with prevailing winds (to the northeast) and the modeled plume dispersion depicted in Figure 12 for October 4.

Daily average PM2 5 data obtained at additional sites in lower Manhattan (Chambers St., Park Row, and the U.S. Coast Guard Station at Battery Park) are shown in the lower half of Figure 11. These sites are located from 3 to 10 blocks to the north, east, and south fi-om the WTC (see Figure 2). It can readily be seen in Figure 11 that concentrations of PM2 5 were much lower than found at the WTC perimeter, indicating a very rapid decline with distance from Ground Zero. PM2 5 concentrations at these three sites can also be seen to go up and down together. Correlation coefficients between pairs of these sites are all > 0.9; and the concentrations are all very similar, suggesting that these sites were responding mainly to variations in urban and regional background sources rather than to WTC emissions. None of the daily PM2 5 values exceeded the 65 pg/m’ PM2.5 24-hr NAAQS. Only a few daily PM2 5 values, as seen in Figure 11 and listed in the WTC Environmental Data Trend Report (EPA, 2602a) for the NYSDEC lower Manhattan sites to the north, east, and south of the WTC even approached

DRAFT-DO NOT QUOTE OR CITE 31 October 2002

NYC-WTC_000149112