You are here:
DISSOCIATION OF SULFUR HEXAFLUORIDE TRACER GAS IN THE PRESENCE OF AN INDOOR COMBUSTION SOURCE
Citation:
Guo*, Z, R B. Mosley*, S Wasson*, R C. Fortmann, AND J. McBrian. DISSOCIATION OF SULFUR HEXAFLUORIDE TRACER GAS IN THE PRESENCE OF AN INDOOR COMBUSTION SOURCE. JOURNAL OF THE AIR AND WASTE MANAGEMENT ASSOCIATION 51(4):616-622, (2001).
Description:
As an odorless, non-toxic, and inert compound, sulfur hexafluoride (SF6) is one of the most widely used tracer gases in indoor air quality studies in both controlled and uncontrolled environments. This compound may be subject to hydrolysis under elevated temperature to form acidic inorganic compounds such hydrogen fluoride and sulfuric acid. Thus, in the presence of unvented combustion sources such as kerosene heaters, natural gas heaters, gas log fireplace, candles, and lamps, the SF6 breakdown may interfere with measurements of the emissions from these cources. Tests were conducted in a research house with a vent-free natural gas heater to investigate these potential interferences. It was observed that the heater operation caused about 5% reduction of SF6 concentration, which can be an error source for the ventilation rate meqasurement and consequently the estimated pollutant emission rates. Further analysis indicates that this error can be mush greater than the observed 5% under certain test conditions because it is a function of the ventilation flow rate. Reducing the tracer gas concentraqtion has no effect on this error. A simple theoretical model is proposed to estimate the magnitude of this error. The second type of interference comes from the primary and secondary products of the SF6 breakdown, mainly sulfuric acid, sulfur dioxide, hydrogen fluoride, and fine particulate matter. In the presence of -5ppm SF6, the total airborne concentrations of these species increased by a factor of 4 to 10. The tests were performed at relatively high SF6 concentrations, which is necessary to determine the interferences quantitatively. The second type of interference can be significantly reduced if the SF6 concentration is kept at low ppb level.