Quantification of emission estimates of CO₂, CH₄ and CO for East Asia derived from atmospheric radon-222 measurements over the western North Pacific

Emissions of CO, CH₄ and CO₂ in East Asia were estimated using the atmospheric concentration of ²²²Rn measured at Minamitorishima (MNM) and Yonagunijima (YON) with a high-precision ²²²Rn measuring system. The ²²²Rn measurements showed a distinct seasonal variation, as well as enhanced ²²²Rn (ERN) events associated with high-frequency synoptic variations. The enhancements of CO, CH₄ and CO₂ coincided with the ERN events at MNM and YON. The enhancement ratios ΔCH₄/ΔRn, ΔCO₂/ΔRn and ΔCO/ΔRn calculated for the ERN events and corrected for the radioactive decay of ²²²Rn during the transport were used to estimate the emissions of CO, CH₄ and CO₂ by multiplying a constant ²²²Rn exhalation rate of 1.0 atom cm⁻² s⁻¹ and the associated catchment area estimated by a 3D transport model. By modifying the categorisation of the sources, the ²²²Rn-derived emissions of CO₂ and CH₄ were found to be in agreement with the published emission databases. As for the CO emission, results of our study were consistent with the REAS CO emission database but showed that the EDGAR database underestimates the CO emission over East Asia by about 44%. It is demonstrated that the ²²²Rn tracer method used in this study could provide a useful and independent tool to verify the trace gas emissions in East Asia.