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DETERMINING UNCERTAINTY IN PHYSICAL PARAMETER MEASUREMENTS BY MONTE CARLO SIMULATION
Citation:
Coy, D., G. Kew, M. Mullins, AND P. Piserchia. DETERMINING UNCERTAINTY IN PHYSICAL PARAMETER MEASUREMENTS BY MONTE CARLO SIMULATION. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/D-86/052 (NTIS PB86164902), 1986.
Description:
A statistical approach, often called Monte Carlo Simulation, has been used to examine propagation of error with measurement of several parameters important in predicting environmental transport of chemicals. These parameters are vapor pressure, water solubility, octanol-water partition coefficient, and 'volatilization from water' (based on the ratio of laboratory-measured volatilization rate constant to oxygen reaeration rate constant for a specific system). Column chromatographic and high pressure liquid chromatographic (HPLC) methods tend to under-predict aqueous solubility and vapor pressure and overpredict octanol-water partition coefficient. Measurement error proves not to be normally distributed, with differing bias for each parameter. For 'volatilization from water', determination of the ratio of rate constants for compounds whose Henry's Law constant equals or exceeds 1,000 torr/mole/liter typically report 95% confidence limits equal to 5 to 10 percent of the ratio. Analysis of a regression approach often used to determine the ratio suggests underestimation of both the ratio and its variance. Monte Carlo Simulation did not confirm underestimation of the ratio but suggests variances may be under-estimated by a factor of 2.3. Using the statistical approach in other cases might allow an investigator to choose levels of a parameter (e.g. a drinking water standard) knowing the uncertainty associated with the choice, or the converse.