Abstract-
I. INTRODUCTIONollutant and toxic gases affect human health in multiple scenarios. Their effects can vary from localized, low intensity to systemic with potential life threats, depending mainly on exposure time and concentrations. Hazardous gas, like explosives or flammable ones are also source of increasing concern for security reasons due to their possible use in terrorists attacks to military installations. Some of them are currently in use or are foreseen to be used as energy carrier for automotive transports and so their diffusion is expected to grow significantly, for example, hydrogen powered car refilling stations could become very common in the near future [1]. The capability to detect and monitor the presence of such substances in the work or living environments, being indoor or outdoor, is thus of paramount importance in multiple applicative scenarios and should be considered as a potential life saving assets. Unfortunately, the characteristics of chemical signal propagation make the use of single measurement point solutions unfeasible and mostly inefficient. Actually, propagation of chemical plumes in real environments is primary related to complex fluid dynamics effects (e.g. turbulence) with diffusion being negligible in many circumstances [2]. Actually, diffusion velocities of gas molecules are too slow to transport chemical signals under many conditions. As such, gas concentrations in real environment can easily become very difficult to predict both in space and time domain.Just as an example, the plume generated by an H 2 spill in a hydrogen based car refilling station could move in rather unpredictable paths and the probability of a single solid state chemical sensor to be hit by it with a significant concentration in a timely way could be considered negligible.Recently researchers began to tackle these scenarios with novel approaches that refer to two main classes. A first approach is based on the use of a moving detector. Together with appropriate modeling information these detectors can follow random paths exploring a particular environment before being hit by a chemical plume [3][4]. After that, by using chemical spills search algorithms, often biomimetic, they try to detect the source of contamination (source declaration problem). The other approach, basically rely on the use of multiple, low cost and autonomous distributed fixed detectors, that try to cooperate in reconstructing a chemical image of the sensed environment [1] [5][6][7]. Both approaches could maximize probabilities to detect and quantify appropriately the presence of hazardeous or toxic gas in environment with different specificities.Advantages of distributed approach are identifiable in flexibility, scalability, enhanced signal to noise ratio, robustness and self healing. Several sensors node can be placed in different locations, each one with its own characteristics in terms of environmental conditions (air flow, temperature, humidity, different gas concentration, etc.) contributing to describe more thoroughly t...
