Evaluation of atmospheric gaseous passive samplers through comparison with active in situ measurements

Abstract

The precise measurement of atmospheric trace gases, including sulphur dioxide (SO2), nitrogen dioxide (NO2) and ozone (O3), is crucial for assessing total changes in the atmosphere that may lead to health complications and exacerbate global warming. The quantification of these species by using passive samplers is a generally acknowledged and frequently utilised method. In some cases, however, it is essential to establish a scaling or correction factor to improve the accuracy and precision of passive samplers in relation to active in situ measurements, which are frequently quality checked and calibrated. Scaling factors for certain gaseous species (SO2 NO2 and O3) measured with passive samplers developed and designed by the Atmospheric Chemistry Research Group at the North-West University have previously been calculated. These scaling factors, however, have not undergone evaluation or revision in a considerable amount of time. Therefore, the general aim of this study was to reassess the scaling factors derived from prior research to determine the necessity for adjustments to enhance the precision and accuracy of the passive sampling method. This reassessment was conducted by deploying passive samplers for measurement of atmospheric SO2 NO2 and O3 at Welgegund atmospheric measurement station, which is a comprehensively equipped regional site, between August 2012 and June 2018. Simultaneously, active in situ measurement data for these species were measured at Welgegund. The statistical relationships between passive and active in situ data were evaluated to validate and amend (if necessary) these scaling factors. This study established the scaling factor for SO2 at 0.9, formerly calculated as 1.0. The scaling factor for NO2 found in this study was 1.7, previously recorded as 1.5. The scaling factor for O3 was established at 1.4 in this study, while the previous scaling factor utilised was 1.3. The scaling factors computed in this investigation are reasonably similar to the previously observed values. However, comprehensive statistical analysis performed in this study showed that it is advisable to update the scaling factors to the newly determined values to enhance the efficacy of the passive sampling approach within the context of the South African environment.