Mining Project: Feasibility Study For a Novel Field-Portable DPM Monitor

Principal Investigator	Arthur Miller - Request information
Start Date	5/1/2016
Objective	To investigate the feasibility of using alternative measurement approaches to quantify both elemental carbon and organic carbon in filter samples of mine air.
Topic Area	Exposure Monitoring of Dust and Toxic Substances

Research Summary

Diesel engines are one of the primary contributors to the presence of ultrafine and nano aerosols in ambient air and occupational environments. Exposure to diesel emissions has been shown to contribute to various adverse health outcomes of the pulmonary system and cardiovascular system. New technologies are being developed to reduce engine emissions and thereby airborne diesel particulate matter (DPM) levels, yet high exposures persist, especially in underground mines.

In order to reduce worker exposures, it is critical to measure the levels of DPM in active work settings. In mine settings, exposures to DPM are measured by collecting air samples onto filters (usually full-shift samples), and sending them to a lab for analysis by the NIOSH 5040 method. The NIOSH 5040 method is based on a thermal-optical technique and is aerosol type and size independent, but has the significant limitation of being a laboratory method. The time frame to collect samples, analyze them, and get quantitative results is usually days to weeks. This limitation makes it very difficult for mine safety personnel to utilize the results for effectively planning DPM reduction strategies. For this reason, this project research effort will focus on investigating and developing alternative methods for measuring DPM in workplaces.

In the past, several research efforts have focused on investigating and developing alternative methods for measuring DPM in workplaces. Although particulate mass can be estimated from data using assumptions for particle shape and density, this approach does not differentiate the fraction of DPM that is elemental carbon (EC) versus the fraction that is organic carbon (OC). Among the variety of instruments available to estimate carbon concentration in aerosols, two types have been shown to give good correlations with the EC in DPM: light-extinguishing devices and light scattering devices. Light extinguishing instruments (such as the Aethalometer and AirTec) estimate the EC in DPM by measuring the mass concentration of carbon in sampled aerosols, employing the optical light absorption properties of black carbon (BC) at specified wavelengths. These results correlate very well with EC concentrations evaluated by the NIOSH Method 5040. Although these instruments require aerosol-dependent calibration, they are convenient to use and can provide a near real-time measurement.

Light scattering instruments (namely direct-reading photometers), of which there are many, are simple and inexpensive devices that give readings shown to correlate well with total particulate mass concentration measurements; however, as with most of the other real-time methods, they do not differentiate between EC and OC. While the above-mentioned methods have both shown potential for quantitating EC in mine atmospheres, that approach (using EC as a surrogate for DPM/TC) has a significant limitation. A variety of environmental and equipment-related factors lead to a wide variance in EC/OC ratios in the mine air, in both time and space, making it difficult to compare real-time indications of EC with time-weighted average measurements of DPM/TC over a shift, which is how the levels of DPM are measured for regulatory purposes. Therefore, the aim of this proposed research is to investigate the feasibility of using alternative measurement approaches that may be capable of quantifying both EC and OC in mine air.

This research will take place in two phases:

Phase 1. A pilot project to evaluate the use of Fourier transform infrared spectroscopy (FTIR) to quantify EC and OC in filter samples derived from diesel tailpipe emissions and from mine air samples. This phase will help NIOSH researchers understand the efficacy of using an existing spectrometry method that is well-developed and understood (FTIR), along with multi-variate analysis of the spectrometry data, to estimate the EC and OC in airborne diesel emissions.

Phase 2. A full project proposal to further the pilot results and investigate additional spectrometry methods, including Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) and laser-induced breakdown spectrometry (LIBS) for measuring EC and OC in the field. Based on the results of Phase 1, the second phase will entail a three-year study in which the FTIR method is further developed and other spectrometry methods are investigated with the same goal.

The major findings of each task of the project will be published in peer-reviewed journals, transaction volumes, conference proceedings, NIOSH numbered documents, or via web-based dissemination based on intended audience of each output. The ultimate goal is to develop and test a mine-portable method for quantitating EC and OC in mines. Impact will be measured by the adoption of such technology by mine operators.

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