Mesure des concentrations d'ammoniac (NH3) dans l'environnement urbain de la décharge d'Akouédo (Abidjan) : Évaluation des performances des capteurs passifs

Abstract

This study, carried out within the framework of the European DACCIWA project (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa provided the first-ever measurements of atmospheric ammonia (NH3) concentrations near the Akouédo landfill (Abidjan, Côte d’Ivoire). Simultaneous passive sampling was conducted from February 2015 to March 2017 using INDAAF sensors and ALPHA badges. The analysis of the samples by ion chromatography made it possible to evaluate the discrepancies between these two types of sensors and to study the temporal variation of the concentrations in this polluted environment. A strong correlation (r = 0.90, R² = 0.82) was observed between the two sensors, indicating similar temporal variations in concentration. Moderate discrepancies between these sensors were observed (MAE = 11.55 ppb; RMSE = 13.16 ppb), especially during pollution peaks. The average bias of -28.3% suggests that the ALPHA badge tends to overestimate concentrations compared to the INDAAF sensor. The two sensors exhibited similar temporal dynamics, although concentrations measured by ALPHA (16.4–73.2 ppb, mean = 40.8 ppb) were consistently higher than those from INDAAF (8.0–59.0 ppb, mean = 29.2 ppb). The observed monthly and seasonal variability is characterized by a peak in concentrations in June, during the rainy season. The strong concordance between the measurements from the two passive samplers makes them a robust and reliable solution for characterizing the variability of ammonia pollution in a tropical environment.