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 2,3,7,8-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 (Koa-based and -based) models were used to describe the distribution of the 2,3,7,8-substituted congeners for Houston. It was determined that 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 Kp, although it was shown that PM10 is more appropriate for relating the particulate fraction to Koa. Finally, the research demonstrates that Kp− partitioning models are improved by adding relative humidity as a variable to the correlation analysis.