Sources and transport of trace organic contaminants in a mid-Atlantic urban atmosphere

Concentrations of total polychlorinated biphenyls ( t-PCBs) in air and water were measured along a transect from the Inner Harbor of Baltimore to the northern Chesapeake Bay to model the air-water exchange fluxes of these compounds. Volatilization fluxes were highest in February, driven by high winds and elevated dissolved PCB concentrations. Throughout the annual one in nine sampling period, t-PCB volatilization fluxes were similar between the urban (130 mug/m2 ·yr) and rural (120 mug/m2·yr) sites. Approximately 10% of the dissolved t-PCB inventory in the water column in Baltimore Harbor exchanges with the atmosphere each day. From air-water exchange alone, the estimated residence time of dissolved t-PCBs in the harbor is approximately 10 days, indicating air-water exchange is an efficient removal mechanism of t-PCBs from urban coastal waters. Annual flux of t-PCBs volatilizing from Baltimore Harbor is approximately 12% of the gas phase t-PCB inventory over the water, and 40% at the northern Chesapeake Bay site, suggests air-water exchange of t-PCBs has the potential to be a significant source of PCBs to the rural atmosphere.; Gas and particle phase concentrations of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs were quantified in ambient air collected in downtown Baltimore, MD, an urban region, and in Fort Meade, MD, a suburban area, during January and July 2001. Total (gas + particle) concentrations for individual nitro-PAH compounds varied by as much as five times from sample to sample within each month. 2-Nitrofluoranthene and 9-nitroanthracene were the most abundant nitro-PAHs in the air at both sites, accounting for approximately half of the total nitro-PAH concentrations during January and July. Concentrations of nitro-PAHs at Baltimore were on average two to three times higher than those measured at the Fort Meade site. Concentrations for most nitro-PAHs were higher in January than in July, suggesting a reduction in photodecay of nitro-PAHs during January promoted the accumulation of nitro-PAHs. Concentrations of nitro-PAHs produced from gas-phase reactions were significantly correlated with concentrations of oxides of nitrogen (NOx) measured simultaneously at the Fort Meade site. 1-Nitropyrene produced from direct sources and 2-nitrofluoranthene, which is produced from gas-phase reactions (OH and NO3-initiated reactions) were detected in all samples. The relative contribution of gas-phase reactions and direct emission sources of nitro-PAHs were evaluated using source specific concentration ratios of 2-nitrofluoranthene and 1-nitropyrene (2-NF/1-NP). The mean ratios of 2-NF/1-NP at both sites were statistically higher in July than January, indicating gas-phase reactions were an important source of 2-nitrofluoranthene in the summer. However, in January gas-phase reactions were reduced, the NO 3-initiated reaction in particular, and direct emissions may significantly contribute to ambient nitro-PAH levels. Furthermore, the gas-particle partition coefficient (Kp) values for 1-nitropyrene (combustion source) was significantly higher than 2-nitropyrene and 2-nitrofluoranthene (produced from gas-phase reactions). This difference may be caused by enrichment of 1-nitropyrene to the particle during combustion, which becomes non-exchangeable with the gas-phase and thus is not freely available for equilibrium partitioning. (Abstract shortened by UMI.)...