Odor Monitoring in the Metal Processing Industry Using IOMS, Olfactometric Analysis and GC analysis in an integrated way

Industrial activities involving metal forming and heat treatments generate complex and variable emission profiles, where both stack and fugitive sources contribute to ambient air quality and odor nuisance. In this context, accurate monitoring of odorous compounds at trace levels is essential for regulatory compliance and social acceptability. This study presents a field application of instrumental odor monitoring technologies in a metalworking facility using mineral oils. In collaboration with ARPA Lombardia, two Instrumental Olfactory Monitoring Systems (IOMS)—WT1 (Ellona, France) and MSEM 3200 (Sensigent, USA)—were installed at the fence line, which in this case coincided with a sensitive residential receptor. The goal was continuous odor detection and correlation with industrial activity. Odor sample bags were collected from stack emissions and analyzed with gas chromatography–mass spectrometry (GC/MS) and dynamic olfactometry, in accordance with EN 13725:2022. The analysis revealed a complex mixture of VOCs, ketones, alcohols, and sulfur-based compounds. The odor concentration at the source reached 6896 ouE/m³, and this value was used to calibrate the IOMS devices through a structured training process involving diluted odor samples. Temporal data analysis highlighted two daily peaks in VOC concentrations during weekdays: in the morning (08:30–10:00) at 0.02–0.036 ppm, and in the evening (19:00–20:00) at 0.032–0.074 ppm. Minimal concentrations were observed during weekends. However, while VOC levels contributed to the background odor, they did not always coincide with odor concentration peaks—reflecting the chemical heterogeneity of VOCs, of which only specific families (e.g., aldehydes, ketones, alcohols) are strongly odor-active. The WT1 device recorded elevated H₂S levels during late afternoon hours (up to 0.036 ppm), whereas the MSEM—equipped with 32 heterogeneous sensors (MOS, EC, polymeric)—captured more stable and persistent odor signals, particularly during night shifts. Moderate odor levels (251–1000 ouE/m³) were widespread throughout the day, while high-intensity peaks (>1000 ouE/m³) occurred mostly in the evening and nighttime, likely associated with thermal processing cycles. The results show the importance of using multiple IOMS units to distinguish between persistent background odors and short-term odor spikes. A citizen complaint campaign is planned to assess the correlation between instrumental data and odor perception. Finally, the study supports the need to develop standardized protocols for IOMS design.