Standardisation and performance evaluation of passive sampler preparation for the detection of reactive gases (NO2, NH3, HNO3, O3 and SO2) in ambient air

This study, conducted within the European DACCIWA FP7 programme (2014–2017), presents a standardised and controlled protocol for the preparation, deployment, and laboratory analysis of International Network to study Deposition and Atmospheric chemistry in Africa (INDAAF) passive samplers used to monitor reactive gases (NO2, NH3, HNO3, O3, SO2) in ambient air. The updated procedure documents and standardises the cleaning of reusable components, the preparation of impregnation solutions, the controlled drying and storage of filters, and the standardisation of field handling and ion chromatography analysis. From 2013 to 2017, a total of 5620 passive samplers were produced and deployed across urban monitoring sites in West and Central Africa. Based on these urban deployments, a new evaluation of the analytical performance of the INDAAF passive sampler is presented in this study. Detection limits derived from the urban dataset were approximately 0.05 ± 0.02 ppb for HNO3, 0.15 ± 0.07 ppb for NO2, 0.5 ± 0.1 ppb for NH3, 0.04 ± 0.02 ppb for SO2, and 0.07 ± 0.05 ppb for O3. Reproducibility, expressed as the coefficient of variation between duplicate samplers, was 12% for HNO3, 7% for NO2, 10% for NH3, 12% for SO2, and 8% for O3, indicating good measurement stability and consistency. The performance evaluation based on co-located NH3 measurements using INDAAF samplers and UKCEH ALPHA reference badges showed strong agreement (r = 0.92), confirming the reliability of the standardised protocol under real field conditions.