| Abstract: | The Methods Standardization Branch of the Environmental Protection Agency, National Environmental Research Center, has undertaken a program to standardize methods used in measuring air pollutants covered by the national primary and secondary air quality standards. This paper presents the results of a collaborative test of the method specified for carbon monoxide. The test involved analysis of CO in air samples (in cylinders) by participating laboratories. Three concentrations, covering the range of the method which is, 0 to 58 mg/m3, were analyzed dry and humidified on each of three days by 15 collaborators. The method of analysis, nondispersive infrared spectrometry (NDIR), involved an NDIR instrument in combination with different procedures for eliminating water vapor interference. A statistical analysis of the data obtained produced the following results: 1. The checking limit for duplicates (replication error) is 0.5 mg/m3. 2. The repeatability (variation within a laboratory) is 1.6 mg/m3. 3. The reproducibility (variation between laboratories) varies nonlinearly with concentration; i.e., a minimum of 2.3 mg/m3 at a concentration of 20 mg/m3 and ranges as high as 4.3 mg/m3 in the concentration range of 0 to 58 mg/m3. 4. The reproducibility at the level of the national primary ambient air quality standard, 10 mg/m3-8-hour average, is 2.5 mg/m3 or 25%. 5. The minimum detectable sensitivity is estimated to be 0.3 mg/m3. 6. Compensation for water vapor interference is satisfactorily accomplished using drying agents and refrigeration methods. The use of narrow-band optical filters alone may not provide adequate compensation. 7. The accuracy obtained depends upon the availability of reliable calibration gases. Based on the results of this study, the method produces results that average 2.5% high. Future papers will contain test results for methods to measure other air pollutants. |
