Environ. Sci. Technol. 2007, 41, 82-87 deposited during the peak period of combustion. The Elemental and Molecular Evidence temporal trends of soot-BC observed in our lake cores do of Soot- and Char-Derived Black not agree with published historical reconstructions Carbon Inputs to New York City’s based on fuel consumption and estimated emission factors. Atmosphere during the 20th Century Introduction P A T R I C K L O U C H O U A R N , * , † , ‡ Black carbon (BC) is a generic term that was initially S T E V E N N . C H I L L R U D , ‡ introduced by Novakov (1) to illustrate the role of soot in S T E P H A N E H O U E L , ‡ , # B E I Z H A N Y A N , § atmospheric sulfur chemistry. Goldberg (2) further charac- D A M O N C H A K Y , ‡ C O R N E L I A R U M P E L , | terized BC based on particle size and formation conditions C L A U D E L A R G E A U , ⊥ G E R A R D B A R D O U X , | as a spectrum of highly recalcitrant organic residues re- D A N W A L S H , ‡ A N D R I C H A R D F . B O P P § maining after organic matter combustion (whether biomass Department of Earth and Environmental Sciences, Columbia or fossil fuel). With time, the BC definition has evolved into University, Geoscience Building, Room 110, P.O. Box 1000, a continuum model which represents combustion byproducts 61 Route 9, West Palisades, New York 10964-8000, ranging from slightly charred materials, retaining original Lamont-Doherty Earth Observatory of Columbia University, structural information of the parent material, to highly Palisades, New York 10964, Earth and Environmental condensed refractory soot (3, 4). Simple particle size dif- Sciences, Rensselaer Polytechnic Institute, Troy, New York ferentiation between char and soot has been augmented with 12180, Laboratoire Bioge´ochimie et EÄ cologie des Milieux methods employing optical, physical, chemical, and/or Continentaux, Site du Centre INRA Versailles-Grignon, thermal treatments to separate noncombustion organic Baˆtiment Eger, 78850 Thivernal-Grignon, France, and carbon (OC) from BC. Although BC is often referred to as Laboratoire de Chimie Bioorganique et Organique Physique, being primarily elemental carbon in the form of graphite, it UMR CNRS 7618 BIOEMCO, EÄ cole Nationale Supe´rieure de is seldom pure and normally includes varying proportions Chimie de Paris, France of other atoms (5). Urban centers are major sources of combustion-derived particulate BC and OC to the atmosphere, and their expansion in the 20th Century has led to environmental impacts of BC Soot black carbon (here expressed as GBC) is present in that range from local health effects on humans (6, 7) to sediments of Central Park and Prospect Park Lakes, New potentially global influence on the earth’s radiation budget York City (NYC), and peaks in the middle of the 20th (5, 8). The energy and transportation sectors have been Century at the highest values (1-3% dry weight) ever recognized as major emitters of fine carbonaceous particles, reported in urban lakes. During that period ( 1940-1970), or soot-BC, which can redistribute over vast areas (9). the GBC represents up to 28% of the total organic∼ Researchers have attempted to reconstruct temporal trends carbon (OC). Radionuclide-normalized whole core inventories of soot-BC using historical data on fuel consumption and of accumulated GBC are similar in the two lakes which estimated fuel-specific BC emission factors (9-11). However, are separated by 15 km, suggesting that emissions of fine emission factors are poorly constrained, resulting in the soot particles may∼have accumulated homogeneously recognition of the need for additional reconstruction ap- proaches (5). Ice cores provide the potential for obtaining over at least the urban center of NYC. The distribution of the history of long-range transport of fine-particles of BC polycyclic aromatic hydrocarbons (PAHs) in the sediments emitted from multiple source regions over time. Urban lake is decoupled from that of GBC. The highest levels of total cores, on the other hand, may record the history of BC and PAHs correspond to peak coal use for space heating in other combustion-associated contaminants, including PAHs NYC in the early 1900s. In contrast, GBC concentrations were and metals, near their sources (12-16). They can provide a highest in the mid 1900s, a period when oil combustion chronology of deposition of combustion-derived carbon- dominated local fossil fuel use and incineration of municipal aceous aerosols, over the past 100-150 years, a period of solid waste (MSW) was common practice in NYC. accelerated industrialization characterized by major changes Decreases in GBC levels observed in more recently in combustion technologies and fuel use. Furthermore, deposited sediments are consistent with improvements in reconstructing atmospheric deposition of BC in urban lakes can constrain historical exposure to combustion-derived particle emissions control systems. Non-soot BC (char) aerosols for health studies of urban populations. was identified by a high carbon to nitrogen (C/N) ratio that This study uses two lakes within the airshed of NYC to persisted after correction for GBC. This likely tracer of establish the history of BC emissions since the end of the MSW incineration was estimated to contribute an additional 19th century and focuses on two components of BC: 35% of total organic carbon found in the sediments thermally recalcitrant soot-BC and thermally labile char ∼ residues derived from inefficient combustion processes, such * Corresponding author phone: (409) 740-4710, fax: (409) 740- as municipal solid waste (MSW) incineration. 4787, e-mail: [email protected]. Present address: Depts. of Ocean- ography and Marine Sciences, Texas A&M University, 5007 Avenue U, Galveston, Texas 77551. Materials and Methods † Columbia University. Push cores were collected in 1996 from Central Park Lake ‡ Lamont-Doherty Earth Observatory of Columbia University. (CPF) and in 2002 from Prospect Park Lake (PPL7), located § Rensselaer Polytechnic Institute. respectively, in NYC’s boroughs of Manhattan and Brooklyn. | Site du Centre INRA Versailles-Grignon. ⊥ UMR CNRS 7618 BIOEMCO. The lake history and chronology of contaminant inputs to # Present address: University of Colorado at Boulder, Department Central Park Lake have been described previously (12, 16). of Chemistry and Biochemistry, 215 UCB, Boulder, CO 80309. We are not aware of any previous study describing the 82 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 41, NO. 1, 2007 10.1021/es061304+ CCC: $37.00 © 2007 American Chemical Society Published on Web 11/29/2006 TABLE 1. Organic Carbon (OC), Nitrogen (N), Organic Carbon/Nitrogen Atomic Ratio ((C/N)a), and Black Carbon (CTO-BC and GBC) Values for Four Reference Materials (2 Soot Samples and 2 Estuarine Sediments)a OC N CTO-BC GBC BC (Lit) (%dw) (%dw) (C/N)a (%dw) (%dw) (%dw) diesel soot (SRM 2975) 86.5 ( 1.7 0.42 ( 0.09 240 ( 52 64.4 ( 0.8 63.7 ( 8.7 63 ( 4.1c-68.2 ( 0.9d n-hex soot (U. of Denver) 92.8 ( 1.0 bdb 43.8 ( 2.3 42.2 ( 1.5 41.1 ( 0.8e-44 ( 5.3c NY/NJ sediment (SRM 1944) 4.4 ( 0.4 0.22 ( 0.01 23 ( 2 0.96 ( 0.04 0.82 ( 0.07 0.66 ( 0.16d-0.80 ( 0.02d Balt Harbor (SRM 1941b) 3.1 ( 0.1 0.26 ( 0.01 14 ( 1 0.41 ( 0.08 0.41 ( 0.04 0.51 ( 0.14e-0.58 ( 0.05d a CTO-BC: Chemothermal oxidation method (Gustafsson et al. (21)); GBC: chemothermal oxidation method with prior demineralization and hydrolysis (Gelinas et al. (22)); BC Lit: literature values for soot BC in the reference materials listed. b bd: below detection level. c Nguyen et al. (23). d Gustafsson et al. (21). e Hammes et al. (4). environmental geochemistry of PP Lake sediments. Both lakes exact soot-BC standards exist at present (4, 20), accuracy were constructed in the 1860s as part of the 19th Century can only be assessed by comparing results from similar Park works in Metropolitan NYC. They have surface areas of treatments of selected reference materials. Soot-BC was approximately 7.1 104 m2 and 2.4 105 m2, respectively, measured on several BC-containing NIST standard reference × × and a drainage to surface area ratio of 10-15 within a heavily materials using both the GBC and CTO methods and the ∼ urbanized environment (12). Both lakes are shallow with a results were compared to published data (Table 1). Based on deepest water column of 1.2 and 1.8 m where CPF and PPL7 replicate analyses (n ) 4) of each sample, the precision of were collected, respectively. the GBC method averages 9% (range 4-14%). These data Upon recovery, core CPF was sliced into 2 cm sections also demonstrate that both methods produce results that over its entire length (52 cm). PPL7 was sliced into 1 cm are consistent with values previously reported in the litera- sections from 0 to 10 cm, 2 cm sections from 10 to 30 cm, ture. Furthermore, comparison between GBC and CTO-BC and 4 cm slices for the remainder of the core (30-54 cm). on a series of natural sediment samples, NIST reference All sections were oven dried at 35 °C under a flow of air materials, and soot, produces a strong relationship with a filtered through a column of florisil. Dried samples were then slope of 1 over 2 orders of magnitude in soot-BC concentra- ground and homogenized with a mortar and pestle.