The EU Horizon 2020 call ‘’Science with & for Society’’ funded the D-NOSES project (Distributed Network for Odour Sensing, Empowerment and Sustainability), which aims to develop a methodology based on participatory strategies and collaboration among different stakeholders using an extreme citizen science approach. This paper presents the findings of this approach applied to a Chilean case study concerning a small community impacted by a municipal wastewater treatment plant. Results of odour observations gathered by citizens during a three-month period are compared with the traditional odour impact evaluation techniques such as field inspections. An adapted odour annoyance index showed a better accuracy for each assessment square compared to the odour impact characteristics. It also points out challenges of citizen participation and opportunities of combining both approaches.