PCDDs/PCDFs in ambient air (<1 fg m(-3)) - the CTDEP long term sampling (30 d) method.

The Connecticut Department of Environmental Protection (CTDEP) commenced monitoring for PCDDs/PCDFs (polychlorinated dibenzodioxins and polychlorinated dibenzofurans) in ambient air in 1987 and adopted the long term (30 d) sampling approach in 1993. The CTDEP method represents the first use of isotopically labeled PCDDs/PCDFs as field surrogates to monitor the behavior of native PCDDs/PCDFs present in actual ambient air samples. This feature first introduced in 1987 was later adopted by US EPA in revisions to sampling methods for PCDDs/PCDFs in ambient air (EPA Method TO9A) as well as development of EPA Reference Method 23 for measurement of PCDDs/PCFDs in stationary source emissions. Results are provided here for a total of twenty-three (23) samples (reported as pairs) representing twelve (12) 30 d sampling events conducted at a site located in metropolitan Hartford CT. Samples were collected in winter months during calendar years 2002-2008. PCDDs/PCDFs concentration data (pgm(-3)) are reported as both congener sums (Cl(4)-Cl(8)) and 2378-substitued congeners. Total PCDDs/PCDFs concentrations for these twelve (12) sampling events ranged from 0.68 pg m(-3) (2003) to 4.18 pg m(-3) (2004) with a mean concentration of 2.04 pg m(-3). Method performance was monitored through use of collocated samples, in field isotopically labeled compounds, isotopically labeled laboratory applied internal standards and field blank samples. Method performance consistently exceeded goals established in USEPA Method TO9A for these same parameters. Average recoveries of in field labeled PCDDs/PCDFs ranged from 97.5% to 104.2%. Average (mean) recoveries for each of the ten (10) isotopically labeled internal standards ranged from 77.0% ((13)C-OCDF) to 95.5% ((13)C-2,3,7,8-TCDF). Method precision defined as % RPD data for collocated sampler pairs ranged from 8% to 14% for PCDDs and from 5% to 12% for PCDFs. The mean RPD for all PCDDs/PCDFs combined is 9.6%. Field monitoring results demonstrate method sensitivity for all PCDDs/PCDFs congeners and 2378-substituted congeners to be well below concentrations typically found for these compounds in ambient air (all reported data represent measured concentrations). Quantities (pg) found in field blanks represent the major determinant to achieving further enhancements in method sensitivity for selected congeners (OCDD<42 fg m(-3); 1,2,3,4,6,7,8-HpCDD<5.7 fg m(-3); and 1,2,3,4,6,7,8-HpCDF<2.1 fg m(-3)). The CTDEP method represents a highly sensitive and reliable technique for monitoring of PCDDs/PCDFs congeners and other persistent organic pollutants (POPs) at ultra trace levels in ambient air (fg m(-3)).

Atmospheric concentrations of PCDDs/PCDFs in Metropolitan Hartford Connecticut--current levels and historical data.

The State of Connecticut (CT) has established an Ambient Air Quality Standard (AAQS) for PCDDs/PCDFs expressed as 2, 3, 7, 8-TCDD equivalents on an annualized basis of 1.0 pg/m(3) TEQ. This AAQS represents the maximum concentration permitted in ambient air from all known sources of PCDDs/PCDFs including background contributions. Atmospheric concentrations of PCDDs/PCDFs are currently monitored at a single site located in Hartford Connecticut. The data collected at this site are compared annually to the AAQS and ultimately used to demonstrate compliance with the AAQS. Samples were collected at Brainard Airport in Hartford, CT. during each of two winter sampling campaigns. These sampling campaigns that were conducted during the winter months of 2003-2004 and 2004-2005 each consisted of two 30 day sampling events conducted in consecutive fashion. Results are provided for a total of eight (8) samples (reported as pairs) representing a total of four (4) 30 day sampling events. The mean concentration for the eight sample set of 0.013 pg/m(3) TEQ represents 1.4% of the CT DEP (Connecticut Department of Environmental Protection) AAQS guideline of 1.0 pg/m(3) TEQ. The highest values were observed during the January 20-February 18, 2005 sampling event (0.0193 and 0.0204) while the lowest TEQ values were observed during the December 21, 2004-January 20, 2005 sampling event (0.0124 and 0.0127). All measured values were significantly below the AAQS of 1.0 pg/m(3). The mean concentration for total PCDDs/PCDFs (Cl4-Cl8) measured in the eight sample set was 2.62 pg/m(3). This value is higher than concentrations measured historically at other locations in the State of Connecticut including urban settings such as Bridgeport, Wallingford and Hartford. The ambient PCDDs/PCDFs profile for the Brainard Airport Site is consistent with profiles typically attributable to combustion sources. The PCDDs/PCDFs profile is remarkably similar to profiles observed at the majority of sites used by the State of Connecticut during prior PCDDs/PCDFs monitoring programs. Congener profile analyses of samples collected in the Hartford Metropolitan area including most notably samples collected in consecutive winter seasons at the Brainard Airport site suggest a common set of source contributions to PCDDs/PCDFs levels measured in ambient air at these locations.