Isotopic composition of carbon in atmospheric air; use of a diffusion model at the water/atmosphere interface in Velenje Basin

Abstract

CO2 concentrations (partial pressure of CO2, pCO2), and isotope compositions of carbon dioxide in air (δ13CCO2), temperature (T) and relative humidity (H) have been measured in the atmosphere in the Velenje Basin. Samples were collected monthly in the calendar year 2011 from 9 locations in the area where the largest thermal power plant in Slovenia with the greatest emission of CO2 to the atmosphere (around 4M t/year) is located. Values of pCO2 ranged from 239 to 460 ppm with an average value of 294 ppm, which is below the average atmospheric CO2 pressure (360 ppm). δ13CCO2 ranged from -18.0 to -6.4 ‰, with an average value of -11.7 ‰. These values are similar to those measured in Wroclaw, Poland. We performed the comparison of δ13CCO2 values in atmospheric air with Wroclaw since researchers used similar approach to trace δ13CCO2 around anthropogenic sources. The isotopic composition of dissolved inorganic carbon (δ13CDIC) in rivers and lakes from the Velenje basin changes seasonally from -13.5 to -7.1‰. The values of δ13CDIC indicate the occurrence of biogeochemical processes in the surface waters, with dissolution of carbonates and degradation of organic matter being the most important. A concentration and diffusion model was used to calculate the time of equilibration between dissolved inorganic carbon in natural sources (rivers) and atmospheric CO2.