Real-time measurement of trace metals on fine particles by laser-induced plasma techniques

Physical and chemical characterization of airborne particles on-line and in real time can provide direct measurement regarding the dynamics, phase partition, and the transformation of aerosols and chemical species associated with the aerosol particles. This information is extremely useful for a wide range of applications such as emission control and process optimization. A compact laser-based instrument has been developed at the Oak Ridge National Laboratory for measurement of elemental composition on aerosol particles. Laser-induced plasma spectroscopy (LIPS) was employed as the principle in the design of the field-portable instrument. It was found that the LIPS technique itself was insufficient to detect trace metals (i.e., mercury and chromium) in aerosols at a level commonly found in source emissions. The LIPS technique could achieve a detection of aerosol mercury at 9.8 ng m(-3), and chromium at 98 ng m(-3) with a precision of +/-1%. We have enhanced the detection sensitivity for the LIPS measurement of these two species by coupling the spectroscopic technique with an aerosol beam-focusing device. The signal enhancement was about two orders of magnitude over traditional nonfocusing approach. The reported elemental detection level of our instrument was for aerosols of a number median diameter of 300 nm and the geometric standard deviation of 1200 nm. Each measurement was accomplished in an interval approximately 1-2 min. (C) 2000 Elsevier Science B.V. All rights reserved.