ON LINE MONITORING OF BENZENE AIR CONCENTRATIONS WHILE DRIVING IN TRAFFIC BY MEANS OF ISOTOPIC DILUTION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

There is no shortage of information about the average benzene concentr ations in urban air, but there is very little about microenvironmental exposure, such as in-vehicle concentrations while driving in various traffic conditions, while refuelling, or while in a parking garage. Th e main reason for this lack of data is that no analytical instrumentat ion has been available to measure on-line trace amounts of benzene in such situations. We have recently proposed a highly accurate, high-spe ed cryofocusing gas chromatography/mass spectrometry (GC/MS) system fo r monitoring benzene concentrations in air. Accuracy of the analytical data is achieved by enrichment of the air sample before trapping, wit h a stable isotope permeation tube system. The same principles have be en applied to a new instrument, specifically designed for operation on an electric vehicle (Ducato Elettra, Fiat). The zero emission vehicle and the fully transportable, battery-operated GC/MS system provide a unique possibility of monitoring benzene exposure in real everyday sit uations such as while driving, refuelling, or repairing a car. All pow er consumptions have been reduced so as to achieve a battery-operated GC/MS system. Liquid nitrogen cryofocusing has been replaced by a pack ed, inductively heated, graphitized charcoal microtrap. The instrument has been mounted on shock absorbers and installed in the van. The who le system has been tested in both fixed and mobile conditions. The max imum monitoring period without external power supply is 6 h. The full analytical cycle is 4 min, allowing close to real-time monitoring, and the minimum detectable level is 1 mu g/m(3) for benzene. In-vehicle m onitoring showed that, when recirculation was off and ventilation on, i.e., air from outside the vehicle was blown inside, concentrations va ried widely in different driving conditions: moving from a parking lot into normal traffic on an urban traffic condition roadway yielded an increase in benzene concentration from 17 to 62.3 mu g/m(3) even if th e actual distance was small. A larger increase was observed when a car was left with the engine running at a distance 2 m from the zero emis sion vehicle: We measured an increment of benzene concentrations from 15.2 to 174.4 mu g/m(3) with a car equipped with a catalytic converter , and from 19.1 to 386.3 mu g/m(3) with a car without such a converter .