The development of a static sampler for the measurement of inspirable aerosol in the ambient atmosphere (with special reference to PAHs). Final report of IOM work on CEC Contract 7261 04/424/08

The aim of the work described in this report was to develop a new static aerosol sampler for use in the environments around coking plants, to collect an appropriate fraction of aerosol in a form that can subsequently be assessed for polycyclic aromatic hydrocarbons (PAHs). It was agreed at the outset that the new instrument should collect the inhalable fraction, corresponding to that which is breathed in by humans.At the beginning, it became clear that the quantitative definitions of inhalability as contained within existing conventions do not apply over the full range of windspeeds appropriate to the ambient atmosphere. Therefore the first task was to perform a set of experiments, using a full-scale tailor’s mannequin in the large wind tunnel at the Institute of Occupational Medicine, for particles with aerodynamic diameter up to about 100 /an and windspeeds up to about 10 m/s. At the larger particle sizes and higher windspeeds, these new data exhibited a windspeed dependency not accounted for in the existing inhalability conventions. As a direct result of this new work, a revised inhalability convention has been adopted by the International Standards Organisation. This was used in the present work as the working criterion for the new sampler.A flowrate of 70 2/min was chosen for the new instrument, based on a compromise between the need to obtain high flow at high pressure drop (such as across a loaded silver membrane filter) and the need to produce a compact, portable device. Once this flowrate was established, a sampling head was developed matching the new inhalability criterion. It is of the ‘rotating-head’ type, consisting of a 25 mm circular orifice in a tapered conical head which rotates steadily through 360 � about a vertical axis (so that there is no preferred orientation with respect to the wind). Below the 47 mm filter, a Tenax adsorbent granular bed serves to collect the gaseous PAHs. The sampling head, drive mechanism, pump, and flow metering and control are all incorporated into a portable weatherproof cabinet. Field trials in the ambient atmospheric environment near a coke works in England showed that the instrument performed well up to expectations. “”