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Show Determining nitrogen oxide emissions from a stationary source acceptable to the EPA must conform to their Method 7 (typical sample train schematic figure 5). The sampling probe is placed at any location in the stack system and a grab sample is collected in an evacuated flask containing a solution of sulfuric acid and hydrogen peroxide, which immediately reacts with the nitrogen oxides. This is then analyzed colorimetrically by wet absorbance with a spectophotometer for nitrogen oxide concentration. A total of 12 samples are necessary for the three required tests, each having four points. Collaborative tests have produced accuracy of about + 6.5% with an experienced sampling team. Obviously, the volume and absolute humidity of the exhaust gas stream must be taken into account for calculation of the mass emission rate. The authors have also had experinece of the simple colorimetric method (Draeger tube) in which a flue gas sample is manually pumped through a throw away glass phial of chemicals. A color change takes place in the chemicals depending on the NOx concentration. While this method is wonderfully convenient, requires no skill and is very inexpensive, it requires a multitude of readings before credible results can be obtained. In reality, industrial users of nitrogen oxides emissions data must continue to rely on the results obtained with proprietary, commercially available, portable nitrogen oxides instrumentation. It would seem desirable to have new instruments which are more convenient and easier to operate with non-analytically trained personnel, yet still maintaining all the other good features such as durability, portability, accuracy, repeatability and credance. 13/9 |