Assessing the accuracy of commercially available gas sensors for the measurement of ambient ozone and nitrogen dioxide.

The objective of the National Institute for Occupational Safety and Health (NIOSH) accuracy criterion is to ensure that measurements from monitoring devices are within ±25% of the true concentration of the analyte with 95% certainty. To determine whether NO and O sensors meet this criterion, three commercially available units (Cairclip O/NO, Aeroqual NO, and Aeroqual O sensors) were co-located three times with validated instruments (NO chemiluminescence [NO] and photometric O analyzers [O]) at an outdoor monitoring station. As cofactors of sensor performance such as temperature (T) and relative humidity (RH) potentially influence the response of NO and O sensors, corrections for cofactors were made by using T, RH, and the sensor measurements to predict measurements made by NO and O during the first co-location period (training dataset). The developed models were tested in the merged data obtained from the second and third co-location periods (testing dataset). In the training and testing datasets, the mean NO as measured by NO was 4.6 ppb (range = 0.4-35 ppb) and 9.4 ppb (range = 1-37 ppb), respectively. The mean O in the training and testing datasets as measured by O was 38.8 ppb (range = 1-65 ppb) and 35.7 ppb (range = 1-61 ppb), respectively. None of the sensor measurements in the training dataset were within the NIOSH accuracy criterion (mean error ≥25%). After correcting for cofactors of sensor performance, the accuracy of the Cairclip O/NO and the Aeroqual O sensors considerably improved when tested with the testing dataset (mean error = -1% and 14%, respectively). However, the Aeroqual NO sensor had an error that was not within ±25%. Raw measurements from the tested sensors may be unsuitable for assessing workers' exposure to NO and O. Corrections for cofactors of Cairclip O/NO and Aeroqual O sensor performance are required for more accurate occupational exposure assessment.