Alternatives to the Gravimetric Method for Quantification of Diesel Particulate Matter near the Lower Level of Detection

Abstract

This paper is part of the Journal of the Air & Waste Management Association's 2010 special issue on combustion aerosol measurements. The issue is a combination of papers that synthesize and evaluate ideas and perspectives that were presented by experts at a series of workshops sponsored by the Coordinating Research Council that aimed to evaluate the current and future status of diesel particulate matter (DPM) measurement. Measurement of DPM is a complex issue with many stakeholders, including air quality management and enforcement agencies, engine manufacturers, health experts, and climatologists. Adoption of the U.S. Environmental Protection Agency 2007 heavy-duty engine DPM standards posed a unique challenge to engine manufacturers. The new standards reduced DPM emissions to the point that improvements to the gravimetric method were required to increase the accuracy and the sensitivity of the measurement. Despite these improvements, the method still has shortcomings. The objectives of this paper are to review the physical and chemical properties of DPM that make gravimetric measurement difficult at very low concentrations and to review alternative metrics and methods that are potentially more accurate, sensitive, and specific. Particle volatility, size, surface area, and number metrics are considered, as well as methods to quantify them. Although the authors believe that an alternative method is required to meet the needs of engine manufacturers, the methods reviewed in the paper are applicable to other areas where the gravimetric method detection limit is approached and greater accuracy and sensitivity are required. The paper concludes by suggesting a method to measure active surface area, combined with a method to separate semi-volatile and solid fractions to further increase the specificity of the measurement, has potential for reducing the lower detection limit of DPM and enabling engine manufacturers to reduce DPM emissions in the future.

Validation of a Novel Air Toxic Risk Model with Air Monitoring

“…The understanding and treatment of diesel particles is an area of active work. ( 30,31 ) Modeled concentrations of diesel particulates were compared to the OEHHA cancer inhalation unit risk factor that was developed under the California regulatory framework ( 5 ) to provide environmental health protection and represents a “reasonable estimate” of the carcinogencity of diesel exhaust particulates. At present this value has not been adopted by the U.S. EPA or the Minnesota Department of Health, and while diesel particles are generally recognized as being carcinogenic, there is no consensus on the magnitude of the inhalation unit risk factor.…”

Investigation of solid particle number measurement: Existence and nature of sub-23nm particles under PMP methodology

“…An alternative system commonly used by researchers to remove volatile particles is a catalytic stripper (CS) (AbdulKhalek & Kittelson, 1995;Kittelson et al, 2005;Park et al, 2003;Swanson & Kittelson, 2010a;Swanson & Kittelson, 2010b). In contrast to the PMP system, the CS uses a different approach to remove volatile particles.…”

Toward Developing A New Occupational Exposure Metric Approach for Characterization of Diesel Aerosols

“…The complexity of the DPM aerosols suggests that a comprehensive assessment should not be limited to the measurement of a single physical property. From a source characterization standpoint, the surface area of DPM nanoparticles emitted by a diesel engine was recently identified as a physical parameter appropriate for evaluating biological response (Ramachandran et al 2005;Alfoldy, et al 2009;Giechaskiel et al 2009;Hesterberg et al 2010;Swanson et al 2010). The variability in number concentration of the emitted DPM particles under different engine configurations and operating conditions calls for the evaluation of that property too.…”