Determination of a calibration method for nitrogen dioxide monitors.

The study established a detailed method by which passive air-sampling monitors for NO2, operating on the principle of diffusion may be calibrated. This procedure assures a timely, precise and accurate direct calibration method which may be utilized in monitoring potential exposures to nitrogen dioxide. The specific monitor investigated was the Monotox monitor (Model Compur (4100) manufactured by MDA scientific, Inc. The work involved three major areas of study: 1. Evaluation of the working lifetime of a nitric oxide (NO) to nitrogen dioxide (NO2) converter apparatus to determine its potential use in the calibration method. 2. Characterization of the stability of manufactured NO2 calibration-gas to assess its potential use in the calibration method. 3. Evaluation of the monitor response time, the response of the monitor (at various NO2 concentrations as a function of the expected response), and the reproducibility of these responses for purposes of developing a precise and accurate direct calibration method. The results of the research efforts addressing these three areas were utilized in determining the most reliable and accurate method for the calibration of direct reading NO2 monitors. The conclusions derived from this study are: 1. At a NO concentration level of 5 ppm, the conversion apparatus has a working lifetime of approximately 6 hours at a flow rate of 20 mL/min (or a total volume of 7.2 L). 2. The manufactured NO2 calibration-gas appeared to be stable for a period of approximately 3 months. 3. The Montox monitor response time (to an equilibrium value) varies with the NO2 challenge concentration; for example, the device requires approximately 3 minutes reaching equilibrium at a nitrogen dioxide concentration of 1.4 ppm. The Monotox response is generally comparable to that of an infrared analyzer. This study established a reliable calibration method for passive air-sampling of NO2 using the Monotox monitor. The method utilizes an NO2 calibration-gas and provides the operator with a useful calibration procedure by which reliable field data can be collected. The calibration method developed performs successfully and efficiently.