The effect of the wind velocity on the uptake rates of various diffusive samplers

This paper examines the results of experiments carried out in an exposure chamber to determine the wind effects on the performance of various diffusive sampler types commonly used for measuring gaseous pollutants in air. The resistance to wind of six diffusive samplers, two Palmes tubes, a badge with diffusion membrane, the EMD sampler and two radial diffusive samplers for different pollutants was compared in a range of velocities from 0 to 300 cm s(-1). For all diffusive samplers tested, an increase in uptake rate was observed with increased air velocity usually following a logarithmic function. The consequences are an underestimation in the concentration measured by the diffusive samplers for low wind velocities below 30 cm s(-1) and conversely an overestimation from 60 cm s(-1). The magnitude of wind effects depends on diffusive sampler type and exceeds an uptake rate variation of +/- 20% for the axial diffusion tubes and the EMD sampler. With regard to the characteristics of each diffusive sampler, the dependence of uptake rate on wind velocity was analysed and discussed. The radial diffusive samplers for benzene and particularly the ones having a large and thick porous membrane appear to be the most effective design to minimise the influence of air velocity on passive sampling.