Improving the efficiency of wind tunnels for odour sampling: analysis and optimization of the outlet conveying system

Odour emissions from passive area sources present a major challenge for environmental monitoring due to the complex chemical and physical mechanisms involved and the lack of standardized sampling methodologies. Wind tunnels (WTs) are widely adopted for this purpose, but significant methodological gaps remain, particularly concerning the gas sampling procedure at the outlet section of the hood. This study investigates the performance of two WTs, one optimized for fluid dynamics and mass transfer and one conventionally used in Italy, under both laboratory and field conditions. The optimized WT demonstrated greater stability and consistency in concentration measurements due to an improved outlet mixing system. To ensure representative sampling in cases where direct access to the WT outlet is limited, two different gas conveyance systems were tested: a Nalophan™ tubular and a Teflon^® grafted tube. Results showed that both configurations provided stable measurements when not occluded, but the Nalophan™ system was susceptible to wind-induced constrictions, leading to transient volatile organic compound accumulation. Field trials confirmed the laboratory findings, showing an optimal sampling time between 5 and 8 min. This study contributes to the development of standardized methodologies for odour sampling, addressing a critical operational gap and supporting recent regulatory advances in odour monitoring.