Abstract
The use of general purpose steady state Gaussian models (e.g. AERMOD) for predicting Odour exposure levels around the vicinity of an industrial site has been considered an accepted practice for many countries around the world for more than a decade now.
This tendency has been reduced lately in Southern Europe due the widely known shortcomings of steady- state plume models to accurately assess dispersion under a range of ‘complex’ conditions (e.g. topography; coastal flows, calm and stable conditions; cold flows; heterogeneous land usage). In such circumstances, there is a real danger that odour impact risk can be either under or overestimated, which has a substantial influence on the development of pragmatic, cost efficient odour mitigation management. Environmental consultancies in Spain have started using CALPUFF, a US EPA guideline model as an alternative means to provide a more effective way of simulating these complex conditions.
The main difference in the applications of the model among Environmental professionals in Spain seems to be the types of meteorological data inputs to the CALPUFF model. In the experience of the authors three types of met data are commonly used to drive CALPUFF in Spain: single station AERMOD observational met data, CALMET gridded windfields produced with TAPM derived surface and upper air files, and CALMET gridded windfields produced with a combination of observational data and TAPM derived surface and upper air files.
These configurations are commonly named as: CALPUFF ‘Lite’ (AERMOD surface and upper air met data), CALPUFF ‘NoObs’ (3D windfields produced with prognostic met data only), and CALPUFF ‘Hybrid’ (3D windfields produced by CALMET with blended prognostic and observational met data).
This paper evaluates how predictions with each met data type compare for odour assessment purposes for a complex study site, and whether the use of any of the met data sets offers any advantage in gaining a better understanding of odour exposure and impact risk. The modelled odour impact was validated by means of “Odour ambient measurements” using German standard VDI 3940.
According to the German standard VDI 3940 Part 1, a group of trained Olfactory panellists, selected in compliance to Olfactometry standard EN13725, observes the odour impression at a given measurement grid surrounding an emitting site. This statistical approach gives a reasonable impression of the odour impact in the vicinity of an emitting site and can be correlated to the Odour plume extent.
The results of this case study provide a compelling case to use a mix of TAPM met data, and surface observational met data to define odour management requirements and assess regulatory compliance.
