Trace hazardous metals detection with an atmospheric microwave-generated plasma
Conference
·
OSTI ID:20067633
A 1.5 kW atmospheric microwave plasma at 2.45 GHz is being developed as an excitation source for real-time detection of hazardous metals in smokestack exhaust. there is currently an important need for metals continuous emissions monitors (CEMs) to meet current and future clean air regulations. A number of plasma generation methods for metals atomic emission spectroscopy are being tested for this application including inductively coupled plasmas (ICPs), laser sparks, dc electrode sparks, and microwave discharges. The microwave plasma has a significant advantage to continuously operate robustly in large volumes of fast flowing ({ge} 14 l/minute) air or undiluted stack exhaust. Good performance has been achieved on an incinerator to sensitively ({approximately}1 {micro}g/m{sup 3}) and accurately (<45% relative to EPA method-29) detect lead, chromium, and beryllium. However, it has been found that the excitation of other hazardous metals such as mercury, cadmium, and arsenic is very dependent on the oxygen content of the gas matrix. In a pure nitrogen or noble gas plasma the detection of mercury 253.65 nm, cadmium 228.89 nm, and arsenic 193.73 nm can approach that of Pb, Cr, and Be. However, the intensity of these lines if significantly reduced as oxygen is added. less than 1% addition of oxygen can dramatically reduce the detection limit of these metals while not effecting other metals such as lead. In addition, the 228.89 nm cadmium line reverses to an absorption feature for a certain range of oxygen content. Experimental measurements will be presented of the performance of this microwave plasma with Hg, Cd, and As as a function of oxygen additive. An attempt will be made to explain the behavior in terms of the possible UV absorption and atomic excitation mechanisms in the plasma.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (US)
- OSTI ID:
- 20067633
- Country of Publication:
- United States
- Language:
- English
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