Long-term Measurements of CO₂, CH₄, and Isotopic Ratios of CO₂ in the Western Pacific: Trends, Variations, and Implications

C. Ou-Yang^1,2, J. Wang², W. Liu³, C. Chang⁴, D. Neff^5,6, E. Dlugokencky⁶, S.E. Michel⁷, B.H. Vaughn⁷, J. White⁷, R.C. Schnell⁶ and N. Lin^1,2

¹National Central University, Department of Atmospheric Sciences, Chung-Li, Taiwan; +886-3-4227151 ext.65543, E-mail: cfouyang@cc.ncu.edu.tw
²National Central University, Department of Chemistry, Chung-Li, Taiwan
³National Central University, Center for Environmental Monitoring and Technology
⁴Academia Sinica, Research Center for Environmental Changes, Taipei City, Taiwan
⁵Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO 80309
⁶NOAA Global Monitoring Laboratory (GML), Boulder, CO 80305
⁷Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO 80309

This study demonstrates the long-term behaviors of CO₂, CH₄, δ¹³C and δ¹⁸O of CO₂ measured at a high-altitude site (Lulin Atmospheric Background Station, LLN, 23.47°N, 120.87°E, 2862 m ASL) and a sea-level maritime site (Dongsha Island, DSI, 20.70°N, 116.73°E, 8 m ASL) in the western Pacific as being participated in the NOAA/CCGG network since April 2006 and March 2010, respectively. Our data suggest that the mean growth rates at LLN and DSI are close to those at MLO over the monitoring period. However, significantly elevated acceleration rates of CO₂ (0.166 ppm yr^-2) and CH₄ (1.321 ppb yr^-2) are found at DSI compared to those at LLN (0.098 ppm yr^-2 for CO₂ and 0.558 ppb yr^-2 for CH₄) and MLO (0.072 ppm yr^-2 for CO₂ and 0.227 ppb yr^-2 for CH₄). Cluster analysis of backward trajectories has been performed at both sites, indicating distinct influence features between the free troposphere and surface in the western Pacific over a year.

Continuous measurements of CO₂ and CH₄ were also performed at LLN using a CRDS since December 2010, showing coherent trends and seasonal variations with the CCGG flask air samples. By comparing to the concentrations in the air masses from the Pacific, the impact of biomass burning on CO₂ and CH₄ from continental Southeast Asia are calculated to be approximately 1.9 ppm and 24.3 ppb, respectively, based on the nighttime CRDS data in spring (mid-February to mid-April). This estimation excluded 2015-2018 due to the majority of springtime air masses arriving at LLN were not originated from this region in these years.

Figure 1. Temporal variations of (a) CO₂, (b) CH₄, (c) δ¹³C and (d) δ¹⁸O of CO₂ measured at LLN, DSI and MLO.