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.

Research highlights► Mid-IR laser spectroscopy was applied for differentiation of CO2 sources in urban air. ► High-frequency isotopic CO2 measurements (δ13C and δ18O) were performed. ► Relative contribution of CO2 sources showed short-term and seasonal variations. ► Relative contribution of CO2 sources changed in different atmospheric conditions. ► A quantum cascade laser was used for the Mid-IR laser spectroscopy.