A Unique Stack Simulator Facility at the National Physical Laboratory

We report the capabilities of a Stack Simulator facility developed at the National Physical Laboratory (NPL) and describe its use in two case studies involving the testing of an NPL calibration transfer strategy for process control mass spectrometers and the trial of a Proficiency Testing (PT) scheme. In the former it was shown that under real stack conditions the calibration transfer strategy improved the quantitative accuracy of a Quadrupole Mass Spectrometer (QMS) from an error of 70 % down to 4 %. In the trial of a PT scheme involving four Source Testing Association (STA) members it was found that three of the members could quantify NO/O2/CO/SO2 test mixtures to within the requirements of the Waste Incineration Directive (WID) whilst the fourth could not, reporting an SO2 concentration in error by -26 %. The error source was traced back to a bias in the members’ calibration gas.