Uncertainty models and influence of the calibration span on ambient air measurements of NO2 by chemiluminescence

Abstract

An assessment of uncertainty in the hourly and annual limit values of NO 2 measurements by molybdenum NO2-to-NO conversion followed by chemiluminescence detection was carried out at 3 different span concentrations (100, 300 and 700 nmol mol (-1)). The uncertainty of the linearity term was calculated for each span concentration by considering (i) a zero-and-span calibration and (ii) a multipoint calibration. Two uncertainty models were applied for the overall uncertainty estimation: (i) the Standard EN 14211 and (ii) a mechanistic model that considers the NO 2 reduction in the converter. The main difference between these models stems from considering or not the possible covariances derived from interactions between NO x and NO concentrations and the converter's efficiency. For both models, the span determined whether or not it was possible to meet the quality objective requested by the EU Air Quality Directives in the annual limit value when no linearity corrections were performed in environments with NO z/NO2 ratios ≤ 0.04. In environments with significant amounts of NO z species (NOz/NO2≥ 0.12), the expanded uncertainty can easily be higher than the data quality objective if bias' corrections are not or cannot be applied.

New Methodology to Evaluate and Optimize Indoor Ventilation Based on Rapid Response Sensors

“…Flow 2.0 can measure, every minute, the air quality indices (AQI) and the air concentration levels of different pollutants: nitrogen dioxide (NO 2 ) and volatile organic compounds (VOCs) in ppb v / v , as well as particulate matter equal to or less than 10 and 2.5 microns (PM 10 and PM 2.5 , respectively) in . Although the manufacturer guarantees the precision and reproducibility of the sensor measurements [ 35 ], the portable gauges were validated in the laboratory in a dynamic reference chamber which generated controlled atmospheres [ 36 , 37 , 38 , 39 ]. The measurements provided by the Flow 2.0 were controlled by measurements taken with the continuous analysers Thermo model 42i for NO–NO 2 –NO x , 48i for CO, 49i for O 3 , and 450i for SO 2 –H 2 S, and Syntech Spectras GC955 gas chromatograph for other chemicals.…”