Optimization of passive sampler preparation for the detection of reactive gases (NO2, NH3, HNO3, O3, SO2) in ambient air
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This study conducted within the European DACCIWA FP7 program (2014–2017), presents an optimized 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 (NO 2 , NH 3 , HNO 3 , O 3 , SO 2 ) in ambient air. The updated procedure improves the cleaning of reusable components, the preparation of impregnation solutions, the controlled drying and storage of filters, and the standardization of field handling and ion chromatography analysis. From 2013 to 2017, a total of 5026 passive samplers were produced and deployed across urban monitoring sites in West and Central Africa. The protocol optimization led to a systematic enhancement in analytical performance. Detection limits were reduced to approximately 0.05 ± 0.02 ppb for HNO 3 , 0.15 ± 0.07 ppb for NO 2 , 0.5 ± 0.1 ppb for NH 3 , 0.04 ± 0.02 ppb for SO 2 , and 0.07 ± 0.05 ppb for O 3 . Reproducibility also improved, reaching 12% for HNO 3 , 7% for NO 2 , 10% for NH 3 , 12% for SO 2 , and 8% for O 3 , indicating greater measurement stability and consistency. Performance evaluation based on co-located NH 3 measurements using INDAAF samplers and CEH ALPHA reference badges showed strong agreement (R² = 0.84), confirming the reliability of the optimized method under real field conditions.
