One year of high-volume PM2.5 filter samples were collected from 2004 to 2005 at one rural site and three urban sites in the Southeastern Aerosol Research and Characterization (SEARCH) network. These filters were analyzed for both organic tracers and carbon isotopes. Sources for primary carbon were previously apportioned based on molecular marker-based chemical mass balance modeling (CMB-MM). In this study, these primary sources were further classified into two categories as having fossil and contemporary origins. 14C data were used to estimate the relative contributions of fossil and contemporary contents in total carbon (TC). Combined these two sets of independent results, fossil and contemporary contributions to secondary carbon source, which was estimated by the unexplained OC in CMB-MM, were calculated. The fossil secondary organic carbon (SOCF) and the contemporary secondary organic carbon (SOCC) ranged from 0.56 to 3.20 microgC/m3 and 0.82 to 4.09 microgC/m3, respectively. SOCF was higher at urban sites and exhibited small seasonal variation at all sites, probably resulting from higher fossil precursor emissions in urban areas. In contrast, SOCC was higher at the rural site and exhibited obvious seasonal variation at all sites. During the whole year SOCF was the major secondary organic carbon (SOC) contributor at the urban sites, while SOCC dominated SOC at the rural site. In summer isoprene-derived SOC showed a large contribution to SOCC and exhibited significant positive correlation with SOCC, indicating the importance of isoprene-derived secondary organic aerosol (SOA) formation during summer. It is interesting to note that the secondary items, including SOCF, SOCC, secondary sulfate, and secondary ammonium, exhibited significant correlations between the monitoring sites, suggesting the regional impact of secondary aerosol in the southeastern United States.
Previous work has shown that certain parts of the Great Lakes region are polluted with Dechlorane Plus (DP), a highly chlorinated flame retardant that was used as a replacement for Dechlorane/Mirex. It was suspected that a source of DP to the environment might be its manufacturing facility located in the city of Niagara Falls, New York. To confirm this source location and to determine DP's spatial distribution, 26 tree bark samples were collected in triplicate from the northeastern United States, and the concentrations of DP and several brominated flame retardants (BFRs) were measured. Most concentrations of DP in tree bark were found to be much higher than those of the BFRs. The highest DP concentrations were > 100 ng g(-1) bark in the city of Niagara Falls, dropping rapidly width distance from the potential source. A simple one-dimensional, Gaussian diffusion model was used to explain the spatial distribution of DP and to locate the source. The calculated source location was < 7 km away from the DP manufacturing plant it! Niagara Falls, New York.