The isotopic composition of carbon dioxide in the atmosphere is a powerful tool for constraining its sources and sinks. In particular, the ¹⁷O oxygen anomaly [Δ¹⁷O = 1000 × ln(1 + δ¹⁷O/1000) - 0.516 × 1000 × ln(1 + δ¹⁸O/1000)], with a value > 0.5‰ produced in the middle atmosphere, provides an ideal tool for probing the exchange of carbon dioxide between the biosphere/hydrosphere and atmosphere. The biosphere/hydrosphere and anthropogenic emissions give values ≤ 0.3‰. Therefore, any anomaly in near surface CO₂ would reflect the balance between stratospheric input and exchange with the aforementioned surface sources. We have analyzed Δ¹⁷O values of CO₂ separated from air samples collected in Taipei, Taiwan, located in the western Pacific region. The obtained mean anomaly is 0.42 ± 0.14‰ (1-σ standard deviation), in good agreement with model prediction and a published decadal record. Apart from typically used δ¹³C and δ¹⁸O values, the Δ¹⁷O value could provide an additional tracer for constraining the carbon cycle.