VAPOR-PRESSURES AND PREDICTED PARTICLE GAS DISTRIBUTIONS OF POLYCHLORINATED BIPHENYL CONGENERS AS FUNCTIONS OF TEMPERATURE AND ORTHO-CHLORINE SUBSTITUTION

Parameters are given for calculating saturation liquid-phase vapor pressures (p(L)o, Pa) of 180 polychlorinated biphenyl (PCB) congeners as functions of temperature and ortho-chlorine substitution. These are slopes (m(L)) and intercepts (b(L)) of the equation log p(L)o = m(L)/T + b(L). Values of m(L) and b(L) were obtained from gas chromatographic retention data for 32 PCB congeners. These slopes varied regularly with homolog (number of total chlorines) and also with the number of ortho-chlorines. From this information, m(L) and b(L) values were estimated for 148 other PCBs whose vapor pressures had been reported at only a fixed temperature. Vapor pressure data were applied to predicting the adsorption of PCBs to aerosols at 10 and 25-degrees-C, using the Junge-Pankow equation. Particulate percentages increased with homolog number, from 2-5% for trichlorobiphenyls to >90% for octachlorobiphenyls at 10-degrees-C. Within each homolog, PCBs with fewer ortho-chlorines (and consequently lower p(L)o had increased particulate percentages. These results suggest that the more highly toxic mono- and non-ortho-PCBs are associated to a greater degree with particles in ambient air, and consequently more likely to be removed by precipitation and dry deposition.