A low cost transportable instrument based on microsystem technologies for benzene monitoring in outdoor air: a comparative infield test using a standard GC tool

In order to allow for efficient control of environmental pollution, especially in cities with a large amount of vehicular traffic, capillary outdoor air quality monitoring is of paramount importance. Nowadays, most of the instrumentation used in air quality monitoring stations for benzene detection is derived from laboratory equipment, and is therefore expensive, bulky and operatively complex for in-field installation. To allow for capillary distribution over the monitored area, air quality monitoring tools should be able to perform real-time and precise measurements, but also be cheap, easy to install and require little maintenance. In this work, a solid state metal oxide semiconductor gas sensor was used in a simplified gas-chromatographic (GC) architecture. The main improvements were the overall simplicity of the pneumatic circuit, the use of an inexpensive packed separation column, the implementation of auto-calibration and, most of all, the use of a MOX gas sensor fabricated directly on a silicon microhotplate as detector, allowing the use of filtered outdoor air as a carrier gas. The results of field tests of the prototype are presented, during its use in a monitoring station in Bologna equipped with a standard GC instrument for the outdoor detection of benzene. Comparative measurements collected by both devices over several months of continuous operation showed very good agreement between the measured benzene concentrations.