Observation of carbon and oxygen isotopic compositions of CO₂ at an urban site in Nagoya using Mid-IR laser absorption spectroscopy

We report the application of Mid-IR laser spectroscopy to differentiation of CO₂ sources. High-frequency isotopic CO₂ measurements (δ¹³C and δ¹⁸O) in urban air in Nagoya allow for the contributions of anthropogenic and biogenic CO₂ sources to be differentiated. The laser spectroscopic method, using a Mid-IR quantum cascade laser, provides us with the advantage of higher temporal resolution of the data compared to traditional isotope ratio mass spectroscopy. The relative contribution of CO₂ sources in Nagoya was found to be roughly 0.42, 0.33 and 0.25 for natural combustion, gasoline combustion and biogenic respiration in the spring, but with large short-term (hourly) variations dependent on wind direction, and long-term variations dependent on heating demand and biological seasonality.