Polycyclic aromatic hydrocarbons pahs

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds containing two to eight rings that arise from the incomplete combustion of fossil fuels and wood. Forest fires and volcanoes contribute to the PAH burden, but by far, anthropogenic sources are responsible for the majority of the PAH input to the atmosphere, which in turn contributes to depositional loadings to aquatic and terrestrial systems. The largest anthropogenic sources of PAHs are vehicular emissions from both gasoline and diesel powered vehicles, coal and oil combustion, petroleum refining, natural gas consumption, and municipal and industrial/municipal incinerators. Once they enter the atmosphere, PAHs redistribute between the gas and particle phases and are subject to removal mechanisms such as oxidative and photolytic reactions, and wet and dry deposition.

Gigliotti et al. (2000) and Gigliotti (2003) report PAH data from Liberty Science Center, New Brunswick, and Sandy Hook. Thirty-six PAHs were analyzed at both sites including phenanthrene and benzo[a]pyrene (BaP) whose concentrations ranged from 0.18 to 31.5 ng m-3 and from below detection limit to 1.4 ng m-3, respectively. PAH concentrations at the suburban site were about two times higher than concentrations measured at the coastal site, consistent with the closer proximity of New Brunswick to urban/industrial regions than Sandy Hook. The seasonal trends of particu-late PAH concentrations indicate that PAH sources such as fuel consumption for domestic heating and vehicular traffic drive their seasonal occurrence. Gas-phase concentrations of methylated phenan-threnes and pyrene and particle-phase concentrations of most high molecular weight PAHs were higher during the winter. In contrast, phenan-threne and fluoranthrene show the opposite seasonal trend with concentrations peaking in the summer months. Because temperature accounted for less than 25 percent of the variability in atmospheric concentrations of these two PAHs in

Figure 27.7. Particle-phase benzo[a]pyrene concentrations (ngm 3) measured at Liberty Science Center (triangles), New Brunswick (diamonds) and Sandy Hook (squares).

the Clausius-Clapeyron plots, seasonal variability could not be attributed to temperature-controlled air-surface exchange. PAH concentrations in the NewJersey coastal atmosphere indicate the importance of local and regional sources originating from urban/industrial areas to the north, northeast, and southwest. As expected, PAH concentrations at the Liberty Science Center in the heart of the urban-industrial region of the estuary were nearly always greater than those measured at NewBrunswick and Sandy Hook.

Gas-phase phenanthrene concentrations are highest at the Liberty Science Center and typically lowest at the coastal Sandy Hook site (Fig. 27.6). On average, the concentrations of phenanthrene are about 2.5 times lower at Sandy Hook than at New Brunswick. Phenanthrene concentrations at Sandy Hook vary between ~ 2-5 ng m-3 in the summer but may increase to perhaps 5-10 ngm-3 in the colder months.

In contrast to phenanthrene, which is found almost exclusively in the gas phase, Figure 27.7 shows the measured particulate concentrations of BaP, which is found almost exclusively in the particle phase. BaP is a well-known product of fossil fuel combustion. The concentrations of particulate BaP (typically ten times lower than phenanthrene concentrations) are perhaps five to ten times higher in the winter atmosphere than in summer, and are considerably higher at the urban-industrial and suburban sites than at the coastal Sandy Hook site.

Table 27.3 is a summary of the dry particle deposition, wet deposition, and gas absorption of PAHs on an annual basis (|g m-2 yr-1) to the estuary as represented by the Liberty Science Center, New Brunswick, and Sandy Hook sites. The gaseous PAH concentrations at New Brunswick were included in the calculation of gas absorption into the estuary even though the site is physically removed from the estuary.

As with PCBs, these are the first comprehensive estimates of PAH deposition to the New York/New Jersey Harbor Estuary and the Lower Hudson River Estuary. Comparing only wet and dry particle deposition amongst the systems (Table 27.4), the New York/New Jersey Harbor Estuary is loaded at a rate of approximately two to ten times the rates reported for the Great Lakes from IADN (Hoff et al., 1996; Hillery et al., 1998) and Chesapeake Bay from CBADS (Baker et al., 1997)from the 1990s. The

Table 27.3. PAH deposition fluxes |g m-2 yr-1
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