NYC-WTC_000232249

NYC 9/11 Public Portal Document

7.0 METEOROLOGICAL MONITORING Due to the complex nature of wind movement in an around buildings in the urbanized setting of Lower Manhattan, monitoring of wind velocity and direction on a continuous basis is warranted. Data available from regional National Weather Stations (NWS) such as Newark Airport, LaGuardia and Kennedy Airports can be used to complement the localized data but is likely NWS data may not always representative of conditions in and around the 130 Liberty Street site. A meteorological station will be deployed in the immediate vicinity of the site. The actual station will initially be located at roof top level at the deconstruction site.

The on site meteorological station will be connected directly to the computer station situated at ground level. Data will transmitted continuously and recorded as 5-minute average values. Data from the roof top station will be logged continuously at the unit’s data logger and also transmitted via telemetry to the street level computer station.

The meteorological monitoring component of the air sampling and monitoring program will consist of equipment designed to continuously record wind speed, wind direction, standard deviation of wind direction, precipitation, and air temperature from a 10-foot tripod or roof mount tower. Monitoring will be done from the roof of the building at 130 Liberty Street until deconstruction activities warrant its physical removal when the roof is removed or access is denied due to ongoing constniction activities. The 130 Liberty Street roof mounted station, will then be collocated with one of the air monitoring stations..

Meteorological variables and their importance in air quality modeling and ambient air monitoring is provided below as follows:

• Wind Speed: The wind speed is a major determinant of the travel distance and travel time of the contaminant. For example, in the air quality models, concentration is inversely proportional to the wind speed. Wind speed also affects the volatilization of contaminants from a work zone and thus influences the ambient air concentrations.

Wind Direction: The wind direction indicates the direction in which contaminants will be transported. For example, ambient air quality models use hourly averages of wind direction to determine which location specific concentrations. The observed wind directions during ambient air sampling will be used to designate samples as upwind, downwind, or crosswind relative to potential contaminant emissions sources.

• Standard Deviation of Wind Direction: can be used to perform stability calculations for ah’ contaminant transport calculations.

• Barometric Pressure: can be used in the calibration of the high-volume samples.

• Ambient Temperature: The ambient temperature is used in determining the rise of a buoyant plume. A plume rise calculated by an air quality model determines the final height above ground of the centerline of the pollutant plume from a point source. Ambient temperature can be helpful in quantifying the degree of contaminant volatilization.

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