Performance evaluation of the active-flow personal DataRAM PM2.5 mass monitor (Thermo Anderson pDR-1200) designed for continuous personal exposure measurements
Introduction
Exposure to ambient particulate matter (PM) has recently received considerable attention as the result of epidemiological findings showing associations between ambient PM, PM10 and PM2.5 concentrations (particles with diameters less than 10 and 2.5 μm, respectively) and mortality (Ozkaynak and Thurston, 1987; Schwartz and Dockery, 1992; Dockery et al., 1993; Pope III et al., 1991; Katsouyanni et al., 1995; Pope et al., 1995; Schwartz et al., 2002). Findings from these health studies have raised concerns about the sufficiency of the National Ambient Air Quality Standard (NAAQS) for PM, in terms of the regulated level, the upper size cut of the particles, the adequacy of measuring only particle mass, and the applicability of fixed-site monitoring to personal exposure. These concerns have been difficult to address, since little is known about the relationship between outdoor particle concentrations and actual human exposure. Several studies have indicated that outdoor and even indoor concentrations may be poor estimators of personal exposures to PM10 or PM2.5 and its components. For example, daytime personal PM10 exposures were found to be approximately 50% higher than corresponding indoor and outdoor levels (Thomas et al., 1993), while personal SO42− and H+ exposures were found to be higher than indoor, but lower than outdoor concentrations (Suh et al., 1994). Understanding patterns of individual exposures to PM can be significantly improved by the use of personal monitors, as these samplers incorporate the effects of factors such as indoor pollutant sources and human activity patterns.
A variety of personal samplers have been developed to-date. Amongst those commercially available are: the PM2.5 Personal Exposure Monitor (PEM Model 200 MSP Corp., Minneapolis, MN, 4 liters per minute (l/min−1)) (Buckley et al., 1991); a personal PM2.5 sampler with cyclone (GK2.05 KTL Cyclone, BGI Inc., Waltham, MA, 4 l/min −1) used in the European 6-city EXPOLIS study and others (Koistinen et al., 1999); the Institute of Occupational Medicine sampler (IOM Personal Inhalable Dust Sampler, SKC inc., Eighty Four, PA, PM10) (Mark et al., 1986); a High Flow Personal Sampler (HFPS) for PM2.5 (Adams et al., 2001) with a flow rate of 16 l/min−1 that allows for shorter sampling periods; and a Personal Cascade Impactor Sampler (PCIS) that provides size-fractionated PM personal data at 9 l/min−1 (Misra et al., 2002). In all of the aforementioned personal samplers, particle mass concentrations are determined based on gravimetric analysis of filter and/or impaction substrates on which PM are collected over periods of several hours or an entire day. Although federal air quality standards for PM in the United States are based on integrated 24-h and annual mass concentrations, recent studies have provided evidence of adverse health effects from short-term exposures to PM (US EPA, 1996; Schwartz and Neas, 2000; Delfino et al., 1998; Peters et al., 2001). Nevertheless, the values of key metrics influencing personal exposure to PM, such as the emission strengths of outdoor and indoor particle sources, “personal cloud” generation, and other micro-environmental factors, fluctuate on time scales that are substantially shorter than several hours. Individual activity patterns influencing exposure, such as amount of time spent indoors, outdoors and in commute, also vary on time periods considerably shorter than several hours.
Several recent articles have hypothesized about the health significance of brief airborne particle excursions on a time scale of a few minutes to several hours, suggesting that these excursions might explain some of the excess mortality (Michaels (1996), Michaels (1997); Michaels and Kleinman, 2000). This hypothesis is based on a number of acute human exposure studies (∼25) cited in Michaels and Kleinman (2000) and recent animal studies (Godleski et al., 1999; Clarke et al., 2000) that show evidence of adverse health effects due to such brief excursions. Two recent asthma panel studies of 22–24 asthmatic children examined effects of hourly PM10 data and found maximum 1-h PM10 showed the strongest associations with asthma symptoms (Delfino et al (1998), Delfino et al. (2002)). The need for developing personal monitors that measure particle concentration in shorter time intervals (on the order of 1–2 h, or less) is therefore of paramount importance to environmental health, as it leads to substantial improvements in exposure assessment to ambient particulates.
The objective of the study presented in this paper was to evaluate the performance of the active-flow, personal DataRAM (MIE pDR-1200; Thermo Electron Corp., Franklin, MA) for providing real-time mass concentration measurements and to assess the effect of particle size and humidity on the relationship between the response of the pDR and the actual aerosol mass concentration. The active pDR, like previous DataRAM models (MIE pDR-1000AN; Thermo Electron Corp., Franklin, MA) (Liu et al., 2002), is an integrating nephelometer that measures continuously the amount of light (with wavelength, λ, equal to 880 nm) scattered by particles drawn though a sensing zone at a flow rate of 4 l/min−1. The amount of light scattered is converted to particle concentration readings using well-established light scattering theory (Kerker, 1969) and factory calibrations. In this paper, we present results from a field evaluation of this instrument conducted in Southern California from 6 December, 2002 to 19 February, 2003. The pDRs were tested while stationary (not worn by subjects for personal monitoring) and thus, the current study addresses the accuracy and precision of the instrument's measurement technique, but does not address reliability or durability issues that may be encountered in actual field use. The performance of the active pDR was compared to other collocated continuous and time-integrated PM2.5 samplers, which is not practical for actual personal sampling.
Section snippets
Thermo MIE personal DataRAM
The active pDR (shown in Fig. 1) is an integrating nephelometer (scattering coefficient range=1.5×10−6–0.6 m−1 at wavelength 880 nm). It has maximum external dimensions of 153 mm (6.0 in) H×92 mm (3.6 in) W×63 mm (2.5 in) D, weighs 0.5 kg and operates in a temperature range of −20–70°C and relative humidity range from 10% to 95%. It records in units of μg m−3, as calibrated by the manufacturer using a fine ISO test dust (specific gravity, 2.5–2.6; MMD, 2–3 μm). For this study, the pDRs were programmed to
Precision of the active pDR monitors
The precision of the collocated pDR monitors for measurement of the ambient PM2.5 mass concentration was found to be very high. Figs. 2a and b illustrate the degree of correlation found among the 15-min average readings of three collocated pDRs. The three pDR readings were highly correlated with R2 greater than 0.99 and slopes within ±10% of unity in all cases. In our collocated precision tests, the pDRs were not necessarily zeroed regularly in order to more closely approximate field operations
Summary and conclusions
The field study of the active pDR monitors showed the instruments to be of sufficient precision and accuracy to be useful for personal exposure studies. The precision of the instruments is very high (2.1%) and notably higher than the passive pDR configuration. Comparison to other proven continuous monitors revealed good agreement at lower relative humidities. Results at higher RH followed predictable theoretical and empirical trends that provide an accurate correction of pDR readings if RH is
Acknowledgements
This work was supported in part by the Southern California Particle Center and Supersite (SCPCS), funded by the US EPA under the STAR program, and the National Institute of Environmental Health Sciences of the National Institute of Health, Grant # ES-11615. Although the research described in this article has been funded in part by the United States Environmental Protection Agency through Grants # 53-4507-0482 and #53-4507-7721 to the University of Southern California, it has not been subjected
References (36)
- et al.
Investigation of the entry characteristics of dust samplers of a type used in the British nuclear industry
Atmospheric Environment
(1986) - et al.
Development and evaluation of a personal cascade impactor sampler (PCIS)
Atmospheric Environment
(2002) - et al.
Field evaluation of a modified dataram mie scattering monitor for real-time PM2.5 mass concentration measurements
Atmospheric Environment
(2000) Optical properties of aerosols of mixed composition
Atmospheric Environment
(1984)- et al.
Correlations between gravimetry and light-scattering photometry for atmospheric aerosols
Atmospheric Environment
(1994) - et al.
Design and validation of a high-flow personal sampler for PM2.5
Journal of Exposure Analysis and Environmental Epidemiology
(2001) - et al.
Calibration, intersampler comparison, and field application of a new PM10 personal air sampling impactor
Aerosol Science and Technology
(1991) - et al.
Comparison of real-time instruments used to monitor airborne particulate matter
Journal of the Air and Waste Management Association
(2001) - et al.
Inhaled concentrated ambient particles are associated with hematologic and bronchoalveolar lavage changes in canines
Environmental Health Perspectives
(2000) - et al.
Aerosol light scattering measurements as a function of relative humidity
Journal of the Air and Waste Management Association
(2000)
Symptoms in pediatric asthmatics and air pollutiondifferences in effects by symptom severity, anti-inflammatory medication use, and particulate averaging time
Environmental Health Perspectives
Association of asthma symptoms with peak particulate air pollution and effect modification by anti-inflammatory medication use
Environmental Health Perspectives
An association between air pollution and mortality in six US cities
New England Journal of Medicine
Photometer measurement of polydisperse aerosols
Journal of Aerosol Science
Short-term effects of air-pollution on health—a European approach using epidemiological time-series data-the APHEA project- background, objectives, design
European Respiratory Journal
The Scattering of Light
Fine particle (PM2.5) measurement methodology, quality assurance procedures and pilot results of the EXPOLIS study
Journal of the Air and Waste Management Association
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