NYC-WTC_000232127

NYC 9/11 Public Portal Document

Part II - Environmental Community Monitoring Plan 133-135 Greenwich & 21-23 Thames Streets Airtek Project 05-0701 - Rev 2 September 16, 2005

The precision check for manual methods is based on a comparison of the concentrations measured by two samplers that collected data side-by-side during the same specific time period. To ensure that the two collocated samplers duplicate similar conditions during monitoring specific rules are enforced: The two collocated PM2.5 samplers must be within 4 meters of each other and particulate matter samplers must be at least 1 meter apart to preclude airflow interference. This 1-meter separation is based on the low volume of sampling. Currently, the PM2.5 ERM monitors have a sampling volume of 16.67 L/min. At low concentrations, agreement between the measurements of collocated samplers, since they are expressed as percent differences, may be relatively poor. For this reason, collocated measurements are selected for use in the precision calculations only when both measurements are above 60 g/m’ for PM2.5. The accuracy check for manual methods involves checking the flow rate of the sampler each calendar quarter.

3.5 Quality Assurance for Gaseous Pollutants These are some of the measures AIRTEK staff take to ensure the quality of data from the continuous gas analysis systems. A "monitoring system" for a given pollutant at a given site usually consists of an inlet tube (called a "probe"), an automatic electronic analyzer and a data acquisition system (possibly connected to multiple instruments) and/or a strip chart recorder.

• Traceability of standards:

o Gaseous pollutant concentration standards (in compressed-gas cylinders or in permeation tubes) traceable to a NIST-traceable reference material (NTRM) or to a NIST-certified gas manufacturer’s internal standard (GMIS)

o Ultraviolet photometers (for ozone) certified against a NIST-certified reference UV photometer at EPA

o mass flow meters (inside mulligas dilution/gas phase titration calibrators) certified traceable to NIST standards

o flow calibrators (bubble meters and/or dry flow calibrators) certified NIST- traceable

o temperature, pressure, etc. certified NIST-traceable

• Multipoint calibrations: The sample collection staff notes the monitoring system's response to multiple known concentrations, adjusting the system if necessary to read correctly. This is done quarterly, after maintenance or repair and when a zero/span check is out of range.

• Zero/span checks: The sample collection staff or an automated system records the monitoring system’s response to pure air, then to a concentration near its upper range limit (at least once every 2 weeks).

• Precision checks: The sample collection staff or an automated system records the monitoring system’s response to a known concentration of a roughly consistent value (every 2 weeks). (In practice, this is usually combined with the zero/span check.)

Performance audits:

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