Concentrations and vapor-particle partitioning of polychlorinated dibenzo-p-dioxins and dibenzofurans in ambient air of Houston, TX

摘要

The levels of the 2,3,7,8-substituted congeners of polychlorinated dibenzo-p-dioxins (2,3,7,8-PCDDs) and polychlorinated dibenzofurans (2,3,7,8-PCDFs) were measured in ambient air in Houston, TX between September 2002 and April 2003. Samples collected from five locations showed that the monthly total average 2,3,7,8-PCDD/PCDF concentrations ranged from 808 to 1760fgm~(-3) with an average of 1235 fgm~(-3), consistent with their counterparts from other urban areas. From the measured concentrations, it was also observed that: (ⅰ) Houston exhibited low 2,3,7,8-TCDD and 2,3,7,8-TCDF concentrations, (ⅱ) the fall and winter V/P ratios for Houston were close to one, probably due to elevated winter temperatures, (ⅲ) the highest chlorinated 2,3,7,8-PCDD/PCDFs exhibited the highest concentrations, and (ⅳ) 2,3,7,8-substituted congeners of PCDDs were the major contributors to the International Toxic Equivalent. The last three observations differ from the literature. Gas-particle partitioning (K_(oa)-based and P_L~ο-based) models were used to describe the distribution of the 2,3,7,8-substituted congeners for Houston. It was determined that P_L~ο estimates using retention indices were more accurate than those obtained with entropy-based approaches. The research demonstrates that PM_(2.5) and PM_(10) can be used instead of total suspended particle to estimate K_p, although it was shown that PM_(10) is more appropriate for relating the particulate fraction to K_(oa). Finally, the research demonstrates that K_p—P_L~ο partitioning models are improved by adding relative humidity as a variable to the correlation analysis.