Atmospheric CO2 and 14CO2 observations at the northern foot of the Qinling Mountains in China: Temporal characteristics and source quantification

Wanyu Liu; Zhenchuan Niu; Xue Feng; Weijian Zhou; Dan Liang; Mengni Lyu; Guowei Wang; Xuefeng Lu; Lin Liu; Jocelyn C Turnbull

doi:10.1016/j.scitotenv.2024.170682

Atmospheric CO₂ and ¹⁴CO₂ observations at the northern foot of the Qinling Mountains in China: Temporal characteristics and source quantification

Sci Total Environ. 2024 Apr 10:920:170682. doi: 10.1016/j.scitotenv.2024.170682. Epub 2024 Feb 5.

Authors

Wanyu Liu¹, Zhenchuan Niu², Xue Feng³, Weijian Zhou⁴, Dan Liang³, Mengni Lyu³, Guowei Wang³, Xuefeng Lu⁵, Lin Liu⁶, Jocelyn C Turnbull⁷

Affiliations

¹ State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; Interdisciplinary Research Center of Earth Science Frontier, Beijing Normal University, Beijing 100875, China.
² State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an 710049, China; Open Studio for Oceanic-Continental Climate and Environment Changes, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266061, China; National Observation and Research Station of Regional Ecological Environment Change and Comprehensive Management in the Guanzhong Plain, China. Electronic address: niuzc@ieecas.cn.
³ Xi'an Institute for Innovative Earth Environment Research, Xi'an 710061, China.
⁴ State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; Open Studio for Oceanic-Continental Climate and Environment Changes, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266061, China; Shaanxi Provincial Key Laboratory of Accelerator Mass Spectrometry Technology and Application, Joint Xi'an AMS Center Between IEECAS and Xi'an Jiaotong University, Xi'an 710061, China.
⁵ State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; Shaanxi Provincial Key Laboratory of Accelerator Mass Spectrometry Technology and Application, Joint Xi'an AMS Center Between IEECAS and Xi'an Jiaotong University, Xi'an 710061, China.
⁶ Interdisciplinary Research Center of Earth Science Frontier, Beijing Normal University, Beijing 100875, China.
⁷ National Isotope Center, GNS Science, Lower Hutt 5040, New Zealand; CIRES, University of Colorado, Boulder, Colorado 80305, USA.

PMID: 38325447
DOI: 10.1016/j.scitotenv.2024.170682

Abstract

A two-year (March 2021 to February 2023) continuous atmospheric CO₂ and a one-year regular atmospheric ¹⁴CO₂ measurement records were measured at the northern foot of the Qinling Mountains in Xi'an, China, aiming to study the temporal characteristics of atmospheric CO₂ and the contributions from the sources of fossil fuel CO₂ (CO_2ff) and biological CO₂ (CO_2bio) fluxes. The two-year mean CO₂ mole fraction was 442.2 ± 16.3 ppm, with a yearly increase of 4.7 ppm (i.e., 1.1 %) during the two-year observations. Seasonal CO₂ mole fractions were the highest in winter (452.1 ± 17.7 ppm) and the lowest in summer (433.5 ± 13.3 ppm), with the monthly CO₂ levels peaking in January and troughing in June. Diurnal CO₂ levels peaked at dawn (05:00-07:00) in spring, summer and autumn, and at 10:00 in winter. ¹⁴C analysis revealed that the excess CO₂ (CO_2ex, atmospheric CO₂ minus background CO₂) at this site was mainly from CO_2ff emissions (67.0 ± 26.8 %), and CO_2ff mole fractions were the highest in winter (20.6 ± 17.7 ppm). Local CO enhancement above the background mole fraction (ΔCO) was significantly (r = 0.74, p < 0.05) positively correlated with CO_2ff in a one-year measurement, and ΔCO:CO_2ff showed a ratio of 23 ± 6 ppb/ppm during summer and winter sampling days, much lower than previous measurements and suggesting an improvement in combustion efficiency over the last decade. CO_2bio mole fractions also peaked in winter (14.2 ± 9.6 ppm), apparently due to biomass combustion and the lower and more stable wintertime atmospheric boundary layer. The negative CO_2bio values in summer indicated that terrestrial vegetation of the Qinling Mountains had the potential to uptake atmospheric CO₂ during the corresponding sampling days. This site is most sensitive to local emissions from Xi'an and to short distance transportation from the southern Qinling Mountains through the valleys.

Keywords: Atmospheric carbon dioxide; Biological CO(2); Fossil fuel CO(2); Radiocarbon; Temporal characteristics; The Qinling mountains.