Evaluation of VOC measurements in the EXPOLIS study

Personal exposures and microenvironment concentrations of 30 target VOCs we re measured for 401 participants living in five European cities as a part o f the EXPOLIS (Air Pollution Exposure Distributions within Adult Urban Popu lations in Europe) study. Measurements in Basel used an active charcoal (Ca rbotech) adsorbent as opposed to the Tenax TA used in the other study centr es. In addition, within each centre, personal and microenvironment VOC samp ling required different sampling pumps and, because of different sampling d urations, different sampling flow rates. Thus, careful testing of the sampl ing and analysis procedures was required to ensure accuracy and comparabili ty of collected data. Monitor comparison tests using Tenax TA showed a mean VOC concentration ratio of 0.95 between the personal and microenvironment monitors. The LODs for the target VOCs using Tenax TA ranged from 0.7 to 5. 2 mug m(-3). The LODs for the 14 target compounds quantifiable using Carbot ech ranged from 0.9 to 3.2 mug m(-3). Tenax TA field blanks showed no remar kable contamination with the target VOCs, except benzaldehyde, a known arte fact with this adsorbent. Thus, the diffusion barrier system used prevented contamination of Tenax TA samples by passive diffusion during non-sampling periods. Duplicate and parallel evaluations of the Tenax TA and Carbotech showed an average difference of <17% in VOC concentrations within the sampl ing methods, but a systematic difference between the methods (Tenax TA:Carb otech concentration ratio = 1.18-2.36). These field evaluations and quality assurance tests showed that interpretation and comparison of the results i n any VOC monitoring exercise should be done on a compound by compound basi s. It is also apparent that carefully planned and realised QA and QC (QA/QC ) procedures are needed in multi-centre studies, where a common sampling me thod and laboratory analysis technique are not used, to strengthen and simp lify the interpretation of observed VOC levels between participating centre s.