Jeffrey L. Ambs

Measurement of total PM2.5 mass (nonvolatile plus semivolatile) with the Filter Dynamic Measurement System tapered element oscillating microbalance monitor

[1]xa0Field studies have been performed in Lindon, Utah (February 2003) and Rubidoux, California (July 2003) to determine if the Rupprecht and Patashnick (R&P) Filter Dynamic Measurement System (FDMS) determines total fine particulate mass, including the semivolatile ammonium nitrate and organic material. Collocated measurements were made with the FDMS, a conventional tapered element oscillating microbalance (TEOM) monitor with a heated filter, an R&P differential TEOM monitor, the Brigham Young University (BYU) Real-Time Total Ambient Mass Sampler (RAMS), the BYU particle concentrator-organic sampling system (PC-BOSS), a PM2.5 Federal Reference Method (FRM), a PM2.5 speciation sampler, an R&P continuous nitrate monitor, and two Sunset continuous carbon monitors (one to measure quartz filter-retained particulate carbon and one to measure particulate semivolatile carbonaceous material lost from the particles on a filter during sampling). The RAMS and PC-BOSS samplers have been shown to determine fine particulate material, including both the semivolatile and the nonvolatile components. Linear regression analysis at the Lindon site between the FDMS (X) and the PC-BOSS (Y), and the FDMS (X) and the RAMS (Y), resulted in zero-intercept slopes of 1.01 ± 0.06 (r2 = 0.63) and 1.00 ± 0.01 (r2 = 0.69), respectively. At the Rubidoux sampling site, linear regression analysis between the PC-BOSS (X) and the FDMS (Y) gave a zero-intercept slope of 0.96 ± 0.02 (r2 = 0.90). Linear regression analysis between the FDMS (X) and the RAMS (Y) resulted in a zero-intercept slope of 0.99 ± 0.01 (r2 = 0.80). Measurements made at the two sites indicate that the FDMS and the R&P differential TEOM monitors do measure total fine particulate mass, including the semivolatile ammonium nitrate and organic material. Both the heated TEOM monitor and PM2.5 FRM did not measure the semivolatile material. The difference between the FDMS and a heated TEOM monitor was explained by the semivolatile ammonium nitrate and organic material measured by the various chemical composition monitors.

Development of a Sample Equilibration System for the TEOM Continuous PM Monitor

ABSTRACT In recent years, scientific discussion has included the influence of thermodynamic conditions (e.g., temperature, relative humidity, and filter face velocity) on PM retention efficiency of filter-based samplers and monitors. Method-associated thermodynamic conditions can, in some instances, dramatically influence the presence of particle-bound water and other light-molecular-weight chemical components such as particulate nitrates and certain organic compounds. The measurement of fine particle mass presents a new challenge for all PM measurement methods, since a relatively greater fraction of the mass is semi-volatile. The tapered element oscillating microbalance (TEOM) continuous PM monitor is a U.S. Environmental Protection Agency (EPA) PM10 equivalent method (EQPM-1090-079). Several hundred of these monitors are deployed throughout the United States. The TEOM monitor has the unique characteristic of providing direct PM mass measurement without the calibration uncertainty inherent in mass surrogate methods. In addition, it provides high-precision, near-real-time continuous data automatically. Much attention has been given to semi-volatile species retention of the TEOM method. While using this monitor, it is desirable to maintain as low an operating temperature as practical and to remove unwanted particle-bound water. A new sample equilibration system (SES) has been developed to allow conditioning of the PM sample stream to a lower humidity and temperature level. The SES incorporates a special low-particle-loss Nafion dryer. This paper discusses the configuration and theory of the SES. Performance results include high time-resolved PM2.5 data comparison between a 30 °C sample stream TEOM monitor with SES and a standard 50 °C TEOM monitor. In addition, 24-hr integrated data are compared with data collected using an EPA PM2.5 Federal Reference Method (FRM)-type sampler. The SES is a significant development because it can be applied easily to existing TEOM monitors.

Measurement of Both Nonvolatile and Semi-Volatile Fractions of Fine Particulate Matter in Fresno, CA

An intensive sampling campaign was performed in Fresno, CA during December 2003 measuring fine particulate matter including both the semi-volatile and nonvolatile fractions of the aerosol. Both the newly developed R&P FDMS Monitor and a PC-BOSS have been shown to measure total PM 2.5 concentrations including semi-volatile nitrate and organic material. Good agreement was observed between the PC-BOSS and the R&P FDMS Monitor in this study with linear regression analysis resulting in a zero-intercept slope of 1.00 ± 0.02 and an R 2 = 0.93. Several real-time measuring systems including the R&P Differential TEOM, the Met One BAMS, and a GRIMM Monitor were also employed and comparisons of total PM 2.5 mass were made with the R&P FDMS Monitor. Agreement among these various monitors was generally good. However, differences were sometimes seen. Reasons for observed differences in the real-time mass measurement systems are explained by the composition and complexity of the measured aerosol, most importantly the composition of semi-volatile material. A newly automated ion chromatographic system developed by Dionex was also field tested and compared to both R&P 8400N Nitrate and integrated PC-BOSS inorganic species measurements. Sulfate and nitrate determined by the Dionex and PC-BOSS systems agreed. However, nitrate measured by the 8400N was low during fog events compared to the other two systems.

Field Evaluation of the Differential TEOM Monitor for Continuous PM2.5 Mass Concentrations Special Issue of Aerosol Science and Technology on Findings from the Fine Particulate Matter Supersites Program

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.

Long-term field characterization of tapered element oscillating microbalance and modified tapered element oscillating microbalance samplers in urban and rural New York State locations.

Abstract Long-term field comparisons of continuous and integrated filter measurements of mass concentrations of par-ticulate matter (PM) with an aerodynamic diameter less than or equal to 2.5 μm (PM2.5) were performed at rural and urban sites in New York State. Two versions of the continuous tapered element oscillating microbalance (TEOM) mass monitor are deployed at each site, in addition to Federal Reference Method filter samplers. Data are grouped into monthly averages to retain and demonstrate seasonal differences. Strong seasonal dependence is observed—the TEOM monitors with the heated sensors are biased systematically low with respect to the Federal Reference Method measurements during the cold season. For the rural site, the average bias for the sample equilibration system (SES)-equipped and standard TEOM monitors is 14 and 24%, respectively. At this location, the TEOM monitor measurements were biased low for all 34 months. For the urban site, the average bias for the SES and standard TEOM monitors is 8 and 18%, respectively. At this location, the TEOM monitor measurements are as likely to be biased high as low during the warm-season months. The hour averaged data from the two versions of the TEOM monitor are also compared, and also indicate that the SES-equipped version of the TEOM monitor captures 7-11% more PM2.5 mass at these locations.

Laboratory Characterization of Modified Tapered Element Oscillating Microbalance Samplers

Abstract Laboratory tests with generated aerosols were conducted to test the efficacy of two recent design modifications to the well-established tapered element oscillating microbalance (TEOM) continuous particulate matter (PM) mass monitor. The two systems tested were the sample equilibration system-equipped TEOM monitor operating at 30 °C, which uses a Nafion dryer as part of the sample inlet, and the differential TEOM monitor, which adds a switched electrostatic precipitator and uses a self-referencing algorithm to determine “true PM mass.” Test aerosols included ammonium sulfate, ammonium nitrate, sodium chloride, copper (II) sulfate, and mixed aerosols. Aerosols were generated with an atomizer or a vibrating orifice generator and were equilibrated in a 450-L slow flow chamber before being sampled. Relative humidity in the chamber was varied between 10 and 90%, and step changes in humidity were executed while generating aerosol to test the response of the instruments. The sample equilibration system-equipped TEOM monitor does reduce, but not totally eliminate, the sensitivity of the TEOM mass monitor to changes in humidity. The differential TEOM monitor gives every indication of being a very robust technique for the continuous real-time measurement of ambient aerosol mass, even in the presence of semi-volatile particles and condensable gases.

Particle Collection Characteristics of a Prototype Electrostatic Precipitator (ESP) for a Differential TEOM System

A differential tapered element oscillating microbalance (TEOM) system that includes an electrostatic precipitator (ESP) that is alternately switched on and off has been developed to improve the measurement of airborne particulate matter mass. Preliminary results showed that it has the potential to overcome the difficulties inherent in PM mass measurement and holds the promise of the measurement of PM mass as it exists in ambient air at ambient temperature. A critical aspect of this device is that the ESP totally removes particles from the air stream. In this study a prototype ESP developed by Rupprecht and Patashnick (R&P) Co., Inc. was evaluated for particulate removal efficiency. Laboratory tests were conducted to determine the removal efficiencies for different-sized particles by generating ultrafine (< 0.1 μ m) and fine (> 0.1 μ m) particles. The ultrafine particles were generated using a 5% solution of sodium chloride, while the fine particles were generated with the different sizes (0.5 μ m and 1 μ m) of polystyrene latex particles. The discrete size intervals of generated ultrafine particles were obtained from an electrical differential mobility analyzer (DMA). The transmitted ultrafine and fine particles passing through the ESP were then detected using a condensation particle counter (CPC) and a LAS-X, respectively. The overall particle collection efficiency of the ESP was calculated from the differential particle collection efficiencies and the specific particle size distributions of the test aerosols. The results showed that the collection efficiencies of the ESP were essentially constant over the range of corona current levels tested, indicating that those were not strong functions of the applied potential if the field strength was sufficiently high.