Distribution of CO₂ in Western Pacific, Studied Using Isotope Data Made in Taiwan, OCO-2 Satellite Retrievals, and CarbonTracker Products

To assess sources and processes that affect the variability of CO₂ at local to regional scales, we have analyzed the mixing ratio [CO₂] and stable isotopic compositions (δ¹³C and δ¹⁸O) of atmospheric CO₂ for three years (2014–2016) in urban and sub-urban areas in Taipei, Taiwan. The data are compared with those from some background sites, viz., Lulin, Mauna Loa, and Minamitorishima, to evaluate how local emissions affect CO₂ level regionally. [CO₂] over the urban and sub-urban stations are significantly higher than that observed at the three aforementioned remote sites mainly due to local emissions, which partly mask the seasonal cycle caused by photosynthesis and respiration. Likewise, significantly low δ¹³C and δ¹⁸O values observed at two Taipei stations also point to anthropogenic emissions. The seasonal cycles in [CO₂] and in the isotopic compositions are retrieved using the ensemble empirical mode decomposition method. Regional impact is assessed using CO₂ products from the Orbiting Carbon Observatory-2 satellite, the NOAA/EARL CarbonTracker project, and meteorological data from European Centre for Medium range Weather Forecast-Interim. We found that besides local emissions, Taiwan is largely affected by external CO₂ in winter and spring originated from north, west and southwest landmasses. In winter air masses with elevated CO₂ concentrations, originated in eastern China influence Taipei. In spring season, about 2 ppmv enhancement in CO₂ observed at the top of Lulin, a high mountain station (2.8 km), could be linked to CO₂ produced by biomass burning in the southeast Asian countries and transported to the region by easterly winds.