A comprehensive program of combined field sampling and laboratory analyses: for selected isomers of PCDDs/PCDFs in the ambient atmosphere of the South Coast Air Basin has been completed. The program was conducted by ENSR Corporation, Acton, MA with the support of ENSECO- Cal Labs who conducted the analytical portion of the program. State-of-the-art sampling and analyses techniques (HRGUHRMS) were employed to conduct a preliminary assessment of atmospheric burdens of PCDDs/PCDFs. The parameters of interest included fifteen PCDDs/PCDFs isomers of primary toxicological significance (2,3,7,8-substituted). The monitoring network, comprised of eight stations, included a number of sites situated in primarily residential areas (San Bernardino, El Toro, and Reseda), as well as several sites in the vicinity of suspected sources of PCDDs/PCDFs (Cal Trans, Commerce, North Long Beach, West Long Beach). Samples were collected via a regional network operated during each of four calendars quarters or seasons. A total of nine sampling sessions were completed during the calendar period of December 1987 to March 1989. Typically, 5 to 7 stations were in contemporaneous operation during a particular session. Sampling times were typically 24 hours in duration. The highest concentrations of PCDDs/PCDFs. congener class sums (Cl4 -C18) and 2,3,7,8-substituted species were noted during a period predominated by off-shore air flows in December 1987, suggesting a regional air mass and transport phenomena. Concentrations of the PCDDs/PCDFs were diminished markedly in subsequent sessions where airflow patterns were primarily offshore or of coastal origin. PCDDs/PCDFs congener profiles (C14-C18) and 2,3,7,8-substituted isomeric patterns strongly suggest combustion source influences in the majority of the sessions and samples examined. Ambient PCDDs/PCDFs concentrations expressed as toxic equivalent sums were the highest during the December 1987 session and lower thereafter. The El Toro site, located south of Los Angeles, consistently showed the lowest measured PCDDs/PCDFs concentrations, as well as the lowest TEF weighted sum. 1,2,3,4,6;7,8-HpCDD was the most predominant 2,3,7,8-substituted species and most prevalent PCDD after OCDD. 2,3,7,8-TCDD was absent from almost all of the samples examined. Detection limits typically ranged from lo-20 fg/m3.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
Stay involved, sign up with CARB's Research Email Distribution List