Abstract:
Atmospheric polycyclic aromatic hydrocarbons are ubiquitous environmental
pollutants, which may be present both in the gaseous phase and adsorbed onto the
surface of particles. Denuders are sampling devices which have been effectively
employed in such partitioning applications. Here we describe and characterise a novel
miniature denuder consisting of two multi-channel silicone rubber traps (each 178 mm
long, 6 mm o.d. containing 22 silicone tubes), separated by a quartz fibre filter for
particle phase collection. The denuder only requires a small portable personal
sampling pump to provide sampling flow rates of ~0.5 L min-1. Theoretical
considerations indicated that the air flow through the denuder was expected to be
laminar, and the linear velocity arising from longitudinal diffusion was found to be
negligible. The calculated particle transmission efficiency through the denuder was
found to be essentially 100 % for particles > 50 nm, whilst the experimental overall
efficiency, as determined by CPC and SMPS measurements, was 92 ± 4 %. The size
resolved transmission efficiency was < 60 % for particles below 20 nm and 100 % for
particles larger than 200 nm. Losses could have been due to diffusion and
electrostatic effects. Semi-volatile gaseous analytes are pre-concentrated in the
silicone of the trap and may be thermally desorbed using a commercially available
desorber, allowing for total transfer and detection of the collected analytes by GC36
MS. This enhances detection limits and allows for lower sampling flow rates and
shorter sampling times, which are advantageous for studies requiring high temporal
resolution.
