An Innovative Sampler as a Reference Standard for Measurement of Particulate Matter Mass in Ambient Air

Ambient particulate matter (PM) mass exposure is determined by collecting the PM on a sample filter over a period of 24 hours. Because the composition of ambient PM is constantly changing, the PM mass measured using the reference method may not be representative of the PM levels in the atmosphere, primarily due to the loss of collected semi-volatile material that is present in the atmosphere during the collection period. In addition, by obtaining a single value over a 24-hour period, the method may not properly recognize the true exposure risks that occur during short term spikes in the ambient PM levels. Rupprecht & Patashnick Co., Inc. (R&P) proposes to resolve these issues through the use of an innovative advance to their popular TEOM¿ Ambient Particulate Monitor. The TEOM¿ mass monitor is a filter-based, inertial micro-balance that provides direct mass measurements of the collected material in near real time. The innovation, the Differential TEOM¿ System, is a self-referencing system that utilizes an electrostatic precipitator (ESP) to periodically remove the ambient PM from the sample stream to allow the system to measure sampling artifacts caused by the presence of semi-volatile compounds such as ammonium nitrate or semi-volatile organics. The Phase I research project compared the results obtained using the initial prototype Differential TEOM¿ monitor operating at ambient temperature with results from an early test Differential TEOM¿ monitor operating at a fixed control temperature and with reference method results, with all samples collected at R&P¿s facilities in Albany, NY. The real-time comparison showed that the performance of the ambient Differential TEOM¿ monitor accurately reflects the mass concentration measured using the other sample methods. The work proposed for the Phase II research project is to deploy and optimize four prototype Differential TEOM¿ monitors to collect PM10 and PM2.5 mass over a 12-month period, permitting the evaluation of the instruments over multiple seasons. The units will operate at ambient temperature, providing a measure of the ambient PM mass as it exists in the atmosphere at the time of collection. The instruments will be co-located, allowing precision determination, and the results will be compared to measurements obtained using other PM sampling equipment, including the current reference method and speciation monitors. Results obtained to date suggest that the Differential TEOM¿ could be used as a new reference standard for ambient particulate matter mass measurements by accounting for the presence of semi-volatile compounds.