The need for electronic noses for environmental odour exposure assessment.

This paper focuses on the opportunities for using electronic noses for odour exposure assessment purposes, especially in cases where dispersion modelling is not applicable. Such cases include, for instance, those sources where a detailed characterisation and quantification of the odour emissions for every hour of the simulation time domain is particularly difficult, due to the nature of the source or to the variability of the emissions over time. In such situations, it is useful to determine odour exposure directly at receptors instead. This paper critically discusses the state of the art of electronic nose technology as far as its application to the determination of odour exposure at receptors is concerned. One example of electronic nose application to the monitoring of odours from an Italian municipal solid waste (MSW) landfill is reported, in order to discuss the instrument's potential and limits. The monitoring results are represented by the number of measures that are classified in a specific olfactory class; this information allows the odour exposure at each monitoring site in terms of odour detection frequency to be determined. Besides a quantification of the odour episodes, electronic noses allowed the identification of the landfill gas as the monitored landfill major odour source.

Ammonia diffusion through Nalophan™ bags.

The aim of the work is to verify the diffusion rate of ammonia through the Nalophan™ film that constitutes the sampling bag, considering storage times ranging from 1 to 26 h. The ammonia decay over time was evaluated using gas-chromatography for the quantification of ammonia concentration inside the bag. The research assesses the roles of both of ammonia and water concentration gradients at the polymeric film interface on the diffusion process. The results show that both the ammonia concentration gradient and, in a less pronounced way, the water concentration gradient are the main 'engines' of ammonia diffusion. Double bags seem to represent a simple solution for preventing ammonia losses during storage. Another interesting result concerns the role of the bag surface on the ammonia diffusion rate: the higher the surface/volume (S/V) ratio, the higher the ammonia diffusion rate through the polymeric film.

Comparison of different approaches for odour impact assessment: dispersion modelling (CALPUFF) vs field inspection (CEN/TC 264).

Odour impact assessment has become an important environmental issue. Different approaches can be used in order to evaluate the odour impact on receptors, and therefore to regulate it. Among the different possible regulation approaches, the use of dispersion modelling is suggested or required by several national or regional legislations. The wide diffusion of this approach is probably due to the fact that odour dispersion modelling is relatively cheap and results are easily understandable. Another kind of approach attempts to evaluate the odour impact directly in the field relying on a panel of trained human assessors (field inspection). The growing importance of this odour impact assessment method is proved by the current draft of a European Standard (CEN/TC 264), which defines two different methodologies of field inspection: grid measurement and plume measurement. In this study two different approaches were compared, i.e. odour dispersion modelling and field inspection by plume measurement (with specific adaptation for the studied site), the latter consisting in using a panel of examiners for determining the absence or presence of odour downwind relative to the source, in order to evaluate the plume extent. The comparison was based on application of both methods to the assessment of the odour impact of a plant for the composting of sludge from an Italian food industry. The results show that the odour impacts assessed by the two strategies turned out to be quite comparable, thus indicating that, if opportunely applied, both approaches may be effective and complementary for odour impact assessment purposes.

Development of an electronic nose for environmental odour monitoring.

Exhaustive odour impact assessment should involve the evaluation of the impact of odours directly on citizens. For this purpose it might be useful to have an instrument capable of continuously monitoring ambient air quality, detecting the presence of odours and also recognizing their provenance. This paper discusses the laboratory and field tests conducted in order to evaluate the performance of a new electronic nose, specifically developed for monitoring environmental odours. The laboratory tests proved the instrument was able to discriminate between the different pure substances being tested, and to estimate the odour concentrations giving correlation indexes (R2) of 0.99 and errors below 15%. Finally, the experimental monitoring tests conducted in the field, allowed us to verify the effectiveness of this electronic nose for the continuous detection of odours in ambient air, proving its stability to variable atmospheric conditions and its capability to detect odour peaks.