Real-time measurements of coal mine dust mass concentration (DMC) are needed for health and ventilation on-demand applications. The currently used method requires capturing aerosol on filters by means of a vacuum pump and Fourier Transform Infrared Spectroscopic (FTIR) analysis so that end-of-work-shift measurements are accomplished. We are developing a photoacoustic spectrometer (PAS) equipped with a tunable quantum cascade laser (QCL) to measure speciated DMC in real-time. The QCL is sequentially tuned to four wavelengths to quantify the DMC of respirable crystalline silica (RCS), kaolinite, coal, and calcite. In addition to absorbing light strongly at one wavelength, each dust type also absorbs a little laser light at the other three wavelengths, as has been determined in our laboratory dust chamber measurements for each dust type taken separately. A matrix of measurements has been developed to quantify the relationship between speciated DMC and aerosol light absorption at the four wavelengths. The inverse of this matrix is used to obtain speciated DMC from PAS measurements for a mixture containing all four dust types. We present individual and mixed dust measurements to demonstrate the current state of the art in PAS sampling of speciated DMC.
