Gas-particle partitioning of PCDD/Fs in daily air samples

Abstract

Eight short-term (24-48h) air samples were taken at Lancaster, UK, to study the gas-particle partitioning of PCDD/Fs. Sampling dates in autumn 1997 were selected with a view to minimising temperature fluctuation during the sampling events. ΣCl4-8DD/Fs (ΣTEQ) for the first 6 samples were 1.1-3.6 pgm-3 (15-44fg TEQm-3), typical of a rural site; two other samples had ΣCl4-8DD/Fs of 18 and 7.9pgm-3, with 320 and 100fg TEQm-3. The observed gas-particle distributions varied from 0-34% particle-bound for Cl(2/3)DD/Fs to >70% for Cl6-8DD/Fs. Measured particle-bound fractions were compared to theoretical estimates of their distribution based on the Junge-Pankow model using three different reported sets of vapour pressures. The best correlation was obtained using vapour pressures derived from measured GC-retention time indices (Eitzer and Hites, 1988). Plotting log partition coefficient (K(p)) versus log sub-cooled liquid vapour pressure (p(L)) gave excellent correlations with slopes of roughly -1 for all homologue groups. 2,3,7,8-substituted congeners showed slopes of -1 for the first five sampling events. It is proposed that kinetic factors at the low ambient temperatures, coupled with additional emissions during the last sampling events resulted in non-equilibrium partitioning. © 2000 Elsevier Science B.V.