Uncertainty Assessment


The stoichiometric ratio is an exact number and assuming 100 percent purity of the input or output, the uncertainty of the default emission factor is negligible. However, the default factors do not take into account the fractional purities of either the Trona input or soda ash output and, in both cases, are expected to result in consistent over-estimation of emissions. As noted earlier, if no data are available for the purity of the Trona input, it is good practice to assume it is 90 percent and adjust the emission factor shown in Equation 3.14. It is good practice to develop uncertainty estimates based on plant-level data.


Where activity data are obtained from plants, uncertainty estimates can be obtained from producers. This will include uncertainty estimates for Trona used and natural soda ash used. Data that are obtained from national statistical agencies usually do not include uncertainty estimates. It is good practice to consult with national statistical agencies to obtain information on any sampling errors. Where national statistical agencies collect data from the population of soda ash production facilities, uncertainties in national statistics are not expected to differ from uncertainties established from plant-level consultations. Where uncertainty values are not available from other sources, a default value of ±5 percent can be used.

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