Field evaluation of the differential TEOM monitor for continuous PM2.5 mass concentrations

The performance of a prototype differential TEOM monitor (Rupprecht and Patashnick Co., NY) and its ability to measure the "actual" ambient near-continuous PM-2.5 mass in an area often high in semivolatile particulate matter has been evaluated. Measurements were made within a mobile particle instrumentation trailer (PIU) located in Claremont, CA-a "receptor" site in the Los Angeles Basin. The Differential TEOM monitor has been developed to directly measure ambient PM mass concentrations while accounting for collection artifacts, including loss of semivolatile aerosols and temperature changes. The Differential TEOM monitors used in this study were self-referencing, providing mass concentration measurements at 5 min intervals. To reference the semicontinuous mass measured by the Differential TEOM monitor, its 24 h time-integrated mass concentrations were compared to those determined by collocated filter-based samplers, i.e., MOUDI (Model 110) and Partisol (Model 2025). A HEADS was used to evaluate ammonium nitrate losses from the time-integrated samplers. The results show that PM-2.5 mass measurements using the Differential TEOM monitor are consistent with those of the MOUDI and Partisol, while differences can be generally explained by loss of ammonium nitrate from the reference samplers. The field results also demonstrate the ability of the Differential TEOM monitor to track adsorption and desorption processes from its sample filter. Although adsorption and evaporation can be dynamic processes, and difficult to estimate, the results of this study also suggest that the Differential TEOM monitor provides a very good estimate of the "actual" ambient particulate mass present on a near-continuous basis.