One of the most complex challenges in the field of industrial odour emissions is the characterization of passive area sources, which emit contaminants even if not endowed with their own gas flow. Two primary sampling devices have been developed for this scope: Wind Tunnel (WT), with a unidirectional airflow without vertical mixing, and Flux Chamber (FC), with a turbulent well-mixed flow. Essentially, two are the debated issues about the sampling instrumentation. The first concerns which device is more suitable for accurately describing the real fluid dynamic behaviour at the liquid-gas interface. The second issue involves the extent to which the emission rates, estimated by the two sampling systems, differ. This study addresses these debates providing experimental data on the real atmospheric motion near liquid surfaces, aiding the choice between WT and FC. Field tests reveal that atmospheric conditions can make the fluid dynamics similar to either WT or FC, with the general scenario showing an intermediate wind behavior. Thus, it is not possible to a priori determine the most suitable device. Concerning the second issue, this research presents an experimental comparison of VOCs (Volatile Organic Compounds) emission rates between a recently developed WT and a US-EPA design FC. These trials indicate that for soluble compounds, WT and FC yield comparable results. However, for gas-phase controlled species (low-solubility VOCs), WT tends to overestimate emissions compared to FC, with the ratio of specific emission rates ranging from 2 to 4.5. The developed theoretical mass transfer model aligns well with observed values, except for toluene due to its non-ideal mixture with water.

The estimation and characterization of diffuse emissions of volatile organic compounds (VOCs) is a crucial issue for industry and environmental regulators. Compared to channelled ones, diffuse emissions derive from complex (non-point) sources, such as wastewater treatment plants, storage tanks, and process unit components. Such sources are typically influenced by dynamic factors such as operational activities and weather conditions. Therefore, this complexity makes the localization and quantification of diffuse VOC emissions a crucial challenge from a technical and regulatory perspective. Recently, the technical standard EN 17628:2022 has been published, which provides a framework to address this issue, proposing five different techniques for the localization, identification, and quantification of diffuse emissions. Nevertheless, while it represents a step forward in this field, the standard shows some shortcomings for a proper implementation, potentially causing divergent interpretations of the guidelines. The accuracy of the measurements is highly dependent on the configuration and morphology of the site, but especially on the meteorological data implemented to calculate the emitted flux. In addition, these techniques, despite being well-established, are particularly complex from both a technical–scientific and logistical–economic point of view. An emerging method, Quantitative Optical Gas Imaging (QOGI) appears to theoretically overcome some issues, but requires further studies to ensure accurate and reproducible quantification of emissions. This review aims to highlight the advantages, disadvantages, and potential developments of the various techniques described in the standard for the characterization of diffuse VOC emissions in the industrial sector.

The characterization of passive area sources, emitting odours due to wind-driven convection, poses significant challenges. The present experimental study aims to evaluate the performance, in terms of fluid dynamics and mass transfer, of a recently developed wind tunnel, with a more compact design and reduced weight, compared to the one proposed by the Italian regulations. The results show that the new design outperforms the Italian standard in several aspects. From a fluid dynamic point of view, the new wind tunnel exhibits a slightly more homogenous and uniform velocity distribution, and it does not reveal airflow preferential channels inside the central body. The pressure tests highlight that the presence of fillers in the new wind tunnel does not significantly alter the pressure inside the hood and therefore the gas–liquid equilibrium conditions; actually, the slight overpressure may help to prevent the infiltration of external air. Finally, mass transfer tests on the standard device show a vertical concentration gradient along the outlet duct, highlighting concentration values that differ up to a factor of two depending on the measurement point. The new design has almost completely solved this issue, thanks to the use of fillers that promote mixing of the outlet flow.

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.

Quantitative Optical Gas Imaging (QOGI) is increasingly adopted to support Leak Detection And Repair (LDAR) programs and process safety monitoring; however, its quantitative performance strongly depends on operating and environmental conditions. This study presents a controlled laboratory assessment of the performance of a QOGI system, with particular focus on methane emission rates close to the declared Minimum Leak Detection Rate (MDLR) of the instrument. Fourteen experimental configurations are investigated by systematically varying key parameters, including measurement distance, wind conditions, thermal contrast between the gas plume and the background, framing, and viewing angle.The results show that, under favorable operating conditions, QOGI provides a stable and highly consistent response, with good linearity between measured and actual emission rates. From a statistical perspective, the median is identified as the most robust central tendency index when a limited number of acquisitions is available, making it particularly suitable for practical field applications. Measurement distance is identified as the primary driver of performance, while correct wind configuration is essential to avoid systematic bias. Thermal contrast further enhances stability, whereas observation geometry has a marginal influence when the plume is fully captured.Overall, the study identifies an optimal operating window in which QOGI delivers reliable and decision-useful quantitative information, providing practical guidance for its effective deployment in process safety, LDAR applications, and regulatory contexts.