NYC-WTC_000232249

NYC 9/11 Public Portal Document

5.1 PMio Monitoring (“Real-Time”/Continuous)

5.1.1 Beta - Attenuation PMio Monitors (All Sites)

The monitors selected to continuously measure PMio are beta-attenuation monitors manufactured by Met One Instraments, Inc. (Met One). The Met One E-BAM will be used for continuous PMio measurements. The instrument operates on the principle of beta attenuation.

The E-BAM has not been officially designated by USEPA as either Reference or Equivalent Method. However, the E-BAM design is descended directly from the BAM-1020 (which has received USEPA’s designation as an Automated Equivalent Method - EQPM-0798-100), modified to provide portable battery operation and produce measurements in real-time (averaging times less than 1 hour). The accuracy and precision of the E-BAM are consistent with USEPA requirements for Class III designation for PMio Class III equivalent method instruments include any candidate instruments that cannot qualify as Class 1 or Class 11 instruments. These may either be filter-based integrated samples not meeting Class I or Class n criteria, or filter or non-filter based continuous or semi-continuous samplers. Other methods include all non-FRM or non-equivalent measurement methods capable of characterizing fine particles that may not be or have not yet been classified as an equivalent method. Existing manual and continuous analyzers in this category include the dichotomous sampler, IMPROVE samplers, nephelomethers, beta attenuation monitors, and Tapered Element Oscillating Microbalances (TEOMs). Such instruments are not precluded from becoming equivalent on a site-specific, regional or national basis.

The beta attenuation process uses a small source of beta particles (carbon-14, 60 microcuries) is coupled to a sensitive detector that counts the emitted beta particles. The dust particles are collected on a filter tape that is placed between the beta source and the detector. Dust on the filter will intercept some of the beta particles. The reduction of beta particles is proportional to the amount of dust on the filter, which allows the mass of dust to be determined from the beta particle counts. The dust mass is combined with the air volume collected during the filter exposure time to determine the PM concentration.

The E-BAM monitors will be equipped with particle size selective inlets. The design of the inlets is such that particles larger than the desired size range will be removed from the air flow, based on the air flow rate. The units will be equipped with an inlet head to separate PMjo. Sampling flow rate is critical to maintain the proper particle size cut points of the inlets. Flow rates are maintained at 16.7 liters per minute (LPM) in the E-BAM monitors using an integral flow meter, pressure sensor, and ambient temperature sensor on board each monitor.

The data from the E-BAM units will be recorded by digital data loggers using the analog signal outputs of the monitors. The PMio data from the E-BAM monitors will be recorded as 5-minute, hourly, and daily (midnight-to-midnight) averages.

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