Assessment of the regional fossil fuel CO 2 distribution through Δ 14 C patterns in ipê leaves: The case of Rio de Janeiro state, Brazil Guaciara M. Santos a, ⁎ , Fabiana M. Oliveira b , Junghun Park c , Ana C.T. Sena a , Júlio B. Chiquetto d , Kita D. Macario b , Cassandra S.G. Grainger a,e a Department of Earth System Science, University of California, Irvine, USA b Institute of Physics, Universidade Federal Fluminense, Niterói, Brazil c Korea Institute of Geoscience and Mineral Resources, Geochemical Analysis Center, Daejeon, South Korea d Institute of Advanced Studies, University of São Paulo, Sao Paulo, Brazil e Public Library of Science journal, San Francisco, USA ABSTRACT ARTICLE INFO Article history: Received 6 February 2019 Received in revised form 15 May 2019 Accepted 19 June 2019 Available online 26 June 2019 Fossil fuel-derived CO 2 (Cff) emission patterns and their point sources across the Rio de Janeiro megacity and state were estimated from a single regional-scale Δ 14 C distribution map based on isotopic measurements of ipê leaves (Tabebuia, a popular flowering deciduous perennial tree). Data from multi-year sampling (i.e., 2014–2016) was renormalized to reflect 14 C signatures of the 2015 calendar year. Spatial variability in Δ 14 C ranges from a maximum of 27.1 ± 0.4‰ (city of Petrópolis, a higher-elevation municipality) to a minimum of -43.6 ± 1.4‰ (i.e., approximately 27.6 ± 1 ppm of Cff — Santo Cristo, a district within the Rio de Janeiro city). Overall, higher Δ 14 C values correlate well with green habitats and high elevation areas, while lower values are associated with Cff emissions in densely populated areas with higher industrial and traffic footprints. Cff emissions are higher where local air circulation is poor, such as the area surrounding Guanabara Bay. Other areas with significantly higher Cff emissions were the Paraíba Valley and Mountain regions. These results may be explained by atmospheric transport of CO 2 from neighboring states, such as São Paulo and Minas Gerais, and by the predominant west winds and the limited regional air flow created by large topographic features. Lower Cff emissions were observed in the Northwest and Lakes regions, which are dominated by agriculture and tourism activities. Our results highlight the potential of directly estimating Cff for studying urban landscapes in the southern region of Brazil through 14 C time-integrated distribution mapping of ipê leaves. The method could also be used to augment greenhouse gas (GHG) emissions inventory studies trends in partitioning Cff from CO 2 of bio-template sustainable sources. Keywords: Ipê leaves Stable isotope analysis Radiocarbon Fossil fuel emissions GHG inventory 1. Introduction Researchers have confirmed that the continuing global rise in atmospheric CO 2 content is caused by anthropogenic CO 2 emissions [1]. Most of those contributions are associated with the burning of fossil fuels (coal, petroleum, and natural gas, among others). While many sources of CO 2 may have similar isotopic composition as the atmosphere itself, fossil fuel-derived CO 2 (Cff) is highly depleted in radiocarbon (i.e., Δ 14 C= -1000‰) and negative carbon isotopic signatures (δ 13 C -28‰, in average) compared to cleaner air-CO 2 (δ 13 C= -8‰). Therefore, 14 C and carbon isotopic measurements of bottom-up point sources of air-CO 2 can improve our understanding of fossil fuel-derived CO 2 emissions in urbanized areas [2]. The isotopic ef- fects due to Cff admixture on the C levels in air-CO 2 allow inferences into its overall emissions, and therefore can provide significant informa- tion that is helpful in establishing mitigation measures at the local, regional, and national levels. Sophisticated studies (e.g. [3–9]) typically rely on higher-frequency or continuous measurements of trace gas concentrations (including CO 2 and CO), higher frequencies of measurements of 14 C in ambient air, and ancillary measurements of atmospheric dynamics (i.e., boundary layer height), or satellite observations of atmospheric column CO 2 . In these studies, isotopic analysis is preferably carried out on air-CO 2 samples captured in pre-evacuated flasks [10,11], or zeolite molecular sieve traps [12]. Later, air-filled containers are shipped to laboratories for CO 2 extraction and cryogenic purification, so that specific isotopic mea- surements can be performed. Although these sampling methods are de- sirable, as they can better document the atmospheric isotopic changes, they can be challenging and extremely costly. They require special han- dling, distribution, and recovering of containers. Furthermore, suitable vacuum line systems for mass-production of CO 2 extractions are also necessary. City and Environment Interactions 1 (2019) 100001 ⁎ Corresponding author at: Department of Earth System Science, University of California, Irvine, Irvine, CA, USA. E-mail address: gdossant@uci.edu. (G.M. Santos). http://dx.doi.org/10.1016/j.cacint.2019.06.001 2590-2520/© 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). Contents lists available at ScienceDirect City and Environment Interactions journal homepage: www.elsevier.com/locate/cacint