Uncertainty in Air Emissions Measurement from an Alumina Refinery
The Worsley Alumina Air Emissions Impact study has involved measurements of approximately 600 substances in emissions from 30 stacks and vents from 22 refinery emissions sources. These data have been modelled to predict ground level concentrations for assessment of the impact of the emissions on the surrounding environment and neighbouring communities.
A key component of the study is the provision of estimates of uncertainty in the emissions measurements for incorporation into the uncertainty determinations for health risk studies. Unfortunately, emissions measurements are generally not accompanied by uncertainty estimates, primarily due to the high cost associated with acquisition of precision and accuracy data from actual stack emissions measurements. Also, formal uncertainty assessments are not included in stationary source testing methods from agencies such as the US EPA. As a consequence, Worsley Alumina instigated a program to determine the uncertainty associated with measurement of concentrations of key emissions including SO2, NOx, particulates, metals (including mercury, hexavalent chromium, arsenic, cadmium and nickel), aldehydes, ketones, PAHs, dioxins and furans, and odours. An assessment of the accuracy of velocity measurements using field data from a number of refinery sources was also carried out to facilitate calculation of the uncertainty in the emission rate determinations of these substances. The results of these calculations are presented in this paper.
This study also included an interlaboratory comparison of the analysis of organic emissions including alcohols, amines, thiols, sulfides, phenols and VOCs found in alumina refinery emissions. These substances have been assessed as less significant in terms of potential health impacts compared with the key emissions described above but are of importance in terms of their potential contribution to refinery odour. These data (which are presented in this paper) have been used to identify deficiencies in the measurements of these substances such that additional method development can be considered to improve the capability of the measurements for alumina refinery applications.