AN INVESTIGATION INTO THE DIFFERENCES IN COMPOSITION OF FORMALDEHYDE ATMOSPHERES GENERATED FROM DIFFERENT SOURCE MATERIALS AND THE CONSEQUENCES FOR DIFFUSIVE SAMPLING

The results of an investigation into the differences in formaldehyde a tmospheres generated from different source materials are presented. It was initiated after discrepancies were found between the results obta ined from pumped and diffusive sampling methods when using formalin as the source material for formaldehyde atmosphere generation. The compo sitions of formaldehyde vapours produced from various source materials have been determined using infrared (IR) spectroscopy and chemical an alysis. These showed that those atmospheres generated from paraformald ehyde yield almost entirely formaldehyde monomer, whereas those genera ted from formalin yield a mixture of formaldehyde monomer and methoxym ethanol. This has the effect of varying the effective molecular weight of the formaldehyde species in the atmosphere, thereby changing the e ffective sampling rate of diffusive sampling devices. Results in this study suggest that there is a possibility that diffusive samplers will give erroneous results if they are used in field environments where t he formaldehyde atmosphere differs in composition from that used in th e laboratory calibration. This emphasizes the need to be certain bf th e nature and composition of any pollutant vapour in order that the sam pling device can be appropriately calibrated. Crown copyright (C) 1996 Published by Elsevier Science Ltd.