Elemental and Molecular Evidence of Soot- and Char-Derived Black Carbon Inputs to New York City's Atmosphere during the 20th Century

Abstract

Soot black carbon (here expressed as GBC) is present in sediments of Central Park and Prospect Park Lakes, New York City (NYC), and peaks in the middle of the 20th Century at the highest values (1-3% dry weight) ever reported in urban lakes. During that period (approximately 1940-1970), the GBC represents up to 28% of the total organic carbon (OC). Radionuclide-normalized whole core inventories of accumulated GBC are similar in the two lakes which are separated by approximately 15 km, suggesting that emissions of fine soot particles may have accumulated homogeneously over at least the urban center of NYC. The distribution of polycyclic aromatic hydrocarbons (PAHs) in the sediments is decoupled from that of GBC. The highest levels of total PAHs correspond to peak coal use for space heating in NYC in the early 1900s. In contrast, GBC concentrations were highest in the mid 1900s, a period when oil combustion dominated local fossil fuel use and incineration of municipal solid waste (MSW) was common practice in NYC. Decreases in GBC levels observed in more recently deposited sediments are consistent with improvements in particle emissions control systems. Non-soot BC (char) was identified by a high carbon to nitrogen (C/N) ratio that persisted after correction for GBC. This likely tracer of MSW incineration was estimated to contribute an additional '35% of total organic carbon found in the sediments deposited during the peak period of combustion. The temporal trends of soot-BC observed in our lake cores do not agree with published historical reconstructions based on fuel consumption and estimated emission factors.