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

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 1760 fg m(-3) with an average of 1235 fg m(-3), consistent with their counterparts from other urban areas. From the measured concentrations, it was also observed that: (i) Houston exhibited low 2,3,7,8TCDD and 2,3,7,8-TCDF concentrations, (ii) the fall and winter VIP 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(degrees)-based) models were used to describe the distribution of the 2,3,7,8-substituted congeners for Houston. It was determined that P-L(degrees) estimates using retention indices were more accurate than those obtained with entropy-based approaches. The research demonstrates that PM2.5 and PM10 can be used instead of total suspended particle to estimate K-p, although it was shown that PM10 is more appropriate for relating the particulate fraction to K-oa. Finally, the research demonstrates that K-p-P-L(degrees) partitioning models are improved by adding relative humidity as a variable to the correlation analysis. (C) 2004 Elsevier Ltd. All rights reserved.