Overcoming traceability challenge in air quality measurements by developing reference gas mixtures of CO2 in a typical indoor/outdoor range for future relevant IoT technology applications

Abstract

High-resolution air quality monitoring using inexpensive sensor systems has attracted a lot of attention in the context of smart cities. However, in order to preserve metrological traceability, these systems must be regularly recalibrated.  The necessity of quality control, dependability, and traceability of analytical data has received a lot of attention lately. IoT sensors can also be used to monitor the condition of equipment and ensure that it conforms with safety rules, given the rapid advancement of new technologies and their numerous everyday uses. Therefore, the primary motivation for our study endeavour was to provide reference gas mixtures to calibrate those sensors optimally in the future while keeping traceability to SI units, which is an important and demanding duty of gas standard laboratories at NMIs. Given the significance of metrological issues in the current context, the national measurement and calibration centre (SASO-NMCC) developed the methodology for preparing such primary standard gas mixtures (PSMs) through standardized gravimetric method in order to improve measurement capabilities and provide a level of confidence regarding greenhouse gas standards. Compatibility check, as per ISO 6143:2001, for the gas chromatography thermal conductivity detector (GC-TCD) with respect to the gravimetric assigned values with its associated combined uncertainty is also presented for each produced PSM. The relative expanded uncertainty of the carbon dioxide standard mixture, taking into account the contributions from verification analysis by GC-TCD, was less than 0.7 % for the prepared range of (0.00499 ± 0.00006) to (0.1996 ± 0.000424) mol/mol. This is comparable to the average of 0.25 % relative uncertainties presented on international standards mixtures.