Validation and modelling of a novel diffusive sampler for determining concentrations of volatile organic compounds in air

The monitoring of volatile organic compounds (VOCs) is important for a variety of air quality issues including ozone formation, secondary aerosol production and human health. VOCs are regulated in workplace and ambient air. A novel diffusive sampler that combines radial and axial diffusion has been developed that improves upon existing commercially available designs. The POcket Diffusive (POD) sampler has been validated under laboratory and field conditions for the measurements of VOCs in ambient air. Laboratory tests varied sampling conditions of temperature (-30 to 40 C), humidity (10 to 80 %), wind velocity (0.1 to 4 m.s-1), and concentration (0.5 – 50 µg.m-3) for a number of specific VOCs. An overall uncertainty of circa 9 % for the measurement of benzene is calculated for the validation tests, in compliance with the data quality objectives of the EU air quality directive 2008/50/EC. A semi-empirical diffusion model has been developed to estimate sampling rates for compounds that were not tested, and for conditions outside of tested ranges during validation. The diffusion model (and validation tests) shows a low influence of environmental conditions on the sampling rate for the POD sampler. Average reproducibility values of circa 3 % are reported with overall sampling uncertainties ranging from 9 % to 15 %, for the whole range of tested conditions, depending on the compound. The sampler is easy to handle, contains an adsorbent cartridge that is compatible with existing thermal desorption systems and can be adjusted to anticipated conditions. The flexibility to measure in environments ranging from clean to heavily polluted workplace situations can be achieved by using diffusive bodies with different porosities. This approach may reduce the possibility of measurements that are below detection limits or influenced by saturation effects. Field tests, conducted in parallel with independent quality controlled canister sampling, confirmed the ease of use and quality of VOC measurements with the POD sampler, for compounds that were, and were not, evaluated during laboratory tests.JRC.H.2-Air and Climat