VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

recovery operations, which could serve as a “WTC signature” for tracking the movement of the WTC plume and its potential impacts on ground-level air quality in the NYC area. Along with the addition of several more New York State-operated PM sampling sites in lower Manhattan and elsewhere as part of an extended air monitoring network set up by NYSDEC, the ORD 290 Broadway site helped to ensure reasonably good coverage (within feasibility constraints) of lower Manhattan neighborhoods surrounding the WTC Ground Zero work zone. In addition to the ORD monitoring sites (A, C, K, and 290 Broadway), Figure 2 shows the location of New York State-operated PM2 5 and PM|q sampling sites.

This expanded monitoring coverage greatly enhanced federal/state government capabilities for tracking trajectories of WTC-generated plumes, areas potentially affected by the plumes, and possible WTC-related PM exposures in the NYC area. For example, notable PM increases at ORD Site A (on the WTC Ground Zero north perimeter), coupled with PM elevations at the NYSDEC site at Chambers St. and West St. about 5 blocks north of the WTC (labeled BMCC for Borough of Manhattan Community College in Figure 2) and/or at the Canal St. Post Office would be indicative of a northerly trajectory of the WTC plume and potential surface-level exposures of population groups in the vicinity of those monitoring sites and intermediate locations. Alternatively, marked increases PM levels at Site A, coupled with PM elevations at 290 Broadway and/or PS 64 (~ 2.5 km northeast of the WTC), would be consistent with a northeasterly WTC plume trajectory. Also, any increases in PM levels at Site C, coupled with elevations at Park Row and/or preexisting PM sites at PS 199, the Maspeth Library in Queens, or PS 274 in Brooklyn would be consistent with an easterly WTC plume trajectory; whereas PM increases at ORD Sites C or K, along with PM elevations at Battery Park, would indicate a southerly plume movement. PM increases at multiple ORD sites proximal to the WTC perimeter and in several neighborhoods in various directions from the WTC could also conceivably occur under meteorological conditions involving low wind speeds and thermal stability conditions, producing low mixing layer heights and a more well-defined WTC plume traversing across lower Manhattan or other NYC areas. On the other hand, if PM concentrations at other sites across lower Manhattan or other areas in NYC tend to vary with each other (i.e., go up and down together) and are similar in values, this would imply that they are responding more to urban or regional background sources rather than to emissions from the WTC sites.

To aid in assessing the potential effects of WTC-related air pollutants on air quality in NYC areas, ORD has also embarked on the modeling of the dispersal of WTC Ground Zero­ generated plumes, based on prevailing meteorological conditions (e.g., wind speed and direction). This includes: (a) initially, classical Gaussian plume modeling, providing regional- scale hour-by-hour plots that roughly delineate the likely spread and direction of the WTC plume, and (b) more recent initiation of detailed local-scale computational fluid dynamic modeling which is expected to provide improved, detailed estimation of the dispersal of emissions from Ground Zero in the street canyons of lower Manhattan. Some preliminary results of the regional-scale plume modeling are discussed below and compared with PM monitoring results for certain days of particular interest. It is important to note that the preliminary results of the regional-scale modeling primarily allow the estimation of the likely direction and width of the WTC plume at particular times, but they do not alone enable one to conclude if or where the plume may have touched down and resulted in surface-level increases in pollutant levels. They alone also do not allow one to conclude what the PM concentrations would have been, only what

DRAFT-DO NOT QUOTE OR CITE 27 October 2002

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