OVER 100 YEARS OF URBAN COMBUSTION RECORDED IN CENTRAL PARK LAKE SEDIMENTS

Saturated hydrocarbons (SH) and polycyclic aromatic hydrocarbons (PAHs) have been quantified in a sediment core (CPF) from Central Park Lake, New York City. Analyses of radionuclides Pb-210 and Cs-137 were used to assign approximate dates to each individual section in core CPF. Ratios of 1,7- to 2,6- dimethylphenanthrane (1,7/2,6-DMP), retene to chrysene (Ret/Chy) and fluoranthene to fluoranthene plus pyrene (Fl/(Fl+Py)) have parallel trends throughout the core. Results show that the ratio of U/R is sensitive to petroleum inputs, Ret/Chy is responsive to contributions from softwood combustion, while both indicators of Fl/(Fl+Py) and 1,7/2,6-DMP can be used to discriminate pyrogenic PAH sources amongst wood, coal and petroleum combustion. Combined usage of these ratios suggests that in New York City, wood combustion dominated a hundred years ago, shifting to coal usage from the 1900s to the 1950s, whereas petroleum usage began around the 1920s and has dominated since the 1940s. Mass balance equations based on above source-sensitive indicators have been used to estimate the relative contributions from each specific pyrogenic sources. Temporal profiles of estimated petroleum combustion-derived PAH fluxes resemble the historical petroleum consumption data provided by EIA data (Energy Information Administration in Department of Energy). Calculated coal-derived PAH flux peaked ~ 1916, declined since then until the 1960s, different with the two-peak trend (the 1920s and the 1940s) provide by EIA data. The absence of the second peak in the calculated coal fluxes in core CPF is probably due to the shift from coal to oil as major residence heating fuel during the 1930s. It was widely believed that the decreased PAH concentrations and fluxes in global sediments during the last half century resulted mainly from major energy shift from coal to petroleum, our data, however, show that this shift occurred prior to 1950 and did not result in obvious decline in TPAH fluxes in Manhattan. The sharpest decreases in TPAH fluxes in NYC occurred in the 1970s, most like as a result of a decline in petroleum usage caused by oil embargo of OPEC and the particle emission control related to the installation of catalytic converters in motor vehicles.