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 with SerdolitW AD-4 sorbent was tested for weekly integrated benzene measurements. Measuring was carried out under highly differing pollution levels and meteorological conditions. The mean uncertainty range for the benzene concentration interval of 0]18 mgrm3 was calculated as 0.3 mgrm3. The coefficient of variation was 13%. Including the uncertainty of both the active and the passive technique, it can be interpreted as an upper limit. The detection limit was determined as 0.3 mgrm3, providing a technique for monitoring benzene concentrations under rural conditions. The mean experimentally determined uptake rate was 0.34"0.04 cm3rmin for shielded sampling in a protective chamber Sigma-2.. The uptake rate had no relationship with air humidity and benzene level. In contrast, a correlation with air temperature was detected. On a weekly basis the seasonal effect of an annual temperature cycle amounted to "10% in benzene concentration. A corresponding temperature correction by employing weekly averages reduced the deviation of weekly passive values from active measurement. No influence of ambient air velocity on the uptake rate was found up to a weekly average of 3.5 mrs if an appropriate wind shielding was employed. This was achieved by the original PE-end cap as well as by the Sigma-2 device.