Variations of uptake rates in benzene diffusive sampling as a function of ambient conditions

Diffusive samplers have found widespread use as a cost-effective technique in measuring ambient benzene concentrations. In a long-term field study the applicability of thermal desorbable Perkin Elmer (PE) diffusive samplers w ith Serdolit(R) AD-4 sorbent was tested for weekly integrated benzene measu rements. Measuring was carried out under highly differing pollution levels and meteorological conditions. The mean uncertainty range for the benzene c oncentration interval of 0-18 mu g/m(3) was calculated as 0.3 mu g/m(3). Th e coefficient of variation was 13%. Including the uncertainty of both the a ctive and the passive technique, it can be interpreted as an upper limit. T he detection limit was determined as 0.3 mu g/m(3), providing a technique f or monitoring benzene concentrations under rural conditions. The mean exper imentally determined uptake rate was 0.34 +/- 0.04 cm(3)/min for shielded s ampling in a protective chamber (Sigma-2). The uptake rate had no relations hip with air humidity and benzene level. In contrast, a correlation with ai r temperature was detected. On a weekly basis the seasonal effect of an ann ual temperature cycle amounted to +/-10% in benzene concentration. A corres ponding temperature correction by employing weekly averages reduced the dev iation of weekly passive values from active measurement. No influence of am bient air velocity on the uptake rate was found up to a weekly average of 3 .5 m/s if an appropriate wind shielding was employed. This was achieved by the original PE-end cap as well as by the Sigma-2 device. (C) 1999 Elsevier Science B.V. All rights reserved.