Variations of anthropogenic CO 2 in urban area deduced by radiocarbon concentration in modern tree rings Andrzej Z. Rakowski a,b, * , Toshio Nakamura a , Anna Pazdur b a Center for Chronological Research, Nagoya University, Chikusa, Nagoya 464-8602, Japan b Radiocarbon Laboratory, Institute of Physics, Silesian University of Technology, ul. Boleslawa Krzywoustego 2, 44-100 Gliwice, Poland Available online 12 February 2008 Abstract Radiocarbon concentration in the atmosphere is significantly lower in areas where man-made emissions of carbon dioxide occur. This phe- nomenon is known as Suess effect, and is caused by the contamination of clean air with non-radioactive carbon from fossil fuel combustion. The effect is more strongly observed in industrial and densely populated urban areas. Measurements of carbon isotope concentrations in a study area can be compared to those from areas of clear air in order to estimate the amount of carbon dioxide emission from fossil fuel combustion by using a simple mathematical model. This can be calculated using the simple mathematical model. The result of the mathematical model followed in this study suggests that the use of annual rings of trees to obtain the secular variations of 14 C concentration of atmospheric CO 2 can be useful and efficient for environmental monitoring and modeling of the carbon distribution in local scale. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Radiocarbon concentration; Tree rings; Carbon dioxide; Fossil fuel component 1. Introduction Changes in radiocarbon concentrations in the atmosphere can be attributed to natural and anthropogenic causes, and it is important to distinguish the two. Naturally caused changes need to be estimated for reliable radiocarbon dating, while the changes caused by human activity are important in envi- ronmental studies. Anthropogenic causes include fossil fuel combustion (Suess, 1955; Kuc and Zimnoch, 1998; Rakowski et al, 2001, 2004a,b), nuclear weapon tests (Nydal and Lo ¨vseth, 1983; Levin and Hesshaimer, 2000), and nuclear power generation (McCartney et al., 1988a,b). One of the most significant anthropogenic factors is the Suess effect, which was observed in radiocarbon concentra- tions of annual tree rings by Suess (1955). The effect accounts for a gradual decrease in radiocarbon concentrations in the at- mosphere since about 1850. This is attributed to the emission of carbon dioxide from fossil fuel combustion. Because the half-life of radiocarbon is much less than the ages of most carbonaceous deposits, the isotope is virtually absent in areas of high carbon dioxide emissions. In stratosphere, where most radiocarbon is produced through the action of cosmic rays, and in troposphere, natural carbon dioxide containing radiocarbon is mixed with that derived from fossil fuel combustion. This produces a dilution of radiocarbon in the atmosphere that is transferred to other carbon reservoirs in biosphere and hydro- sphere. In spite of its global nature, the Suess effect cannot be evaluated directly from radiocarbon measurements mostly due to a nuclear weapons testing. It can only be estimated using mathematical models of the global carbon cycle (Oeschger et al., 1975). After 1945, nuclear weapons testing caused increases in the concentrations of radiocarbon in the atmosphere. During the atomic tests, neutrons were released with sufficient ener- gies (thermal) to generate significant amounts of radiocarbon. A maximum of radiocarbon concentration occurred in 1963, at a magnitude two times higher than the natural concen- trations before 1850 (Nydal and Lo ¨vseth, 1983). Since 1963 radiocarbon concentrations have been decreasing, a trend * Corresponding author. Center for Chronological Research, Nagoya Univer- sity, Chikusa, Nagoya 464-8602, Japan. Tel.: þ48 32 2372488; fax: þ48 32 2372254. E-mail address: andrzej.rakowski@polsl.pl (A.Z. Rakowski). 0265-931X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2007.12.007 Available online at www.sciencedirect.com Journal of Environmental Radioactivity 99 (2008) 1558e1565 www.elsevier.com/locate/jenvrad