Assessment of the regional fossil fuel CO2 distribution through Δ14C patterns in ipê leaves: The case of Rio de Janeiro state, Brazil

Abstract 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 ipe 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 Petropolis, 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 Paraiba Valley and Mountain regions. These results may be explained by atmospheric transport of CO 2 from neighboring states, such as Sao 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 ipe 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.