Picarro | Regional effect as a probe of atmospheric carbon dioxide reduction in southern China

Based on the World Meteorological Organization (WMO) data, the global average mole fraction of atmospheric CO₂ was 405.5 ± 0.1 parts per million (ppm) as of 2018, which was 146% of the pre-industrial (before 1750) level (WMO, 2018). To mitigate climate change, China is striving to reduce its carbon dioxide (CO₂) emissions before 2030 and has derived a series of national environmental policies to advocate green development. However, the implications of these measures on the mole fraction of the regional atmospheric CO₂ remain ambiguous and whether carbon emission has been alleviated or even reversed as intended in key areas. Hence, it is necessary to accurately evaluate the regional variation of ambient CO₂ to describe the interaction characteristics between regional sources and sinks of the carbon cycle, and to explore the connection with the vigorously enforced sustainable development policies of China.

Based on this, in this article, a group of Chinese scientists from Jinan University conducted a three-year continuous observation campaign of the atmospheric CO₂ mole fraction at the summit of the Nanling Mountains, southern China in 2015–2017 to probe the timely feedback of the implementation of the green policies of the government. They combined meteorological and statistical methods to extract the background time series of CO₂ from the in situ observational data. The obtained time series was further smoothened and separated using the fast Fourier transform and low-pass filter, which provided detail of atmospheric CO₂ variability. Additionally, climate-related sustainability issues encompassing the government policies and societal impacts were discussed to determine the cause of short-term variation in the atmospheric CO₂.

[CO₂ mole fraction measurement]: For continuous sampling and measurements of ambient CO₂, an analyzer (G2301, Picarro Inc., USA) based on fourth-generation wavelength scanning cavity ring-down spectroscopy technique was employed. This type of instrument introduces a near-infrared laser for specific recognition through a high-precision sensor with both highly linear and steady-state responses for automatic mole fraction analysis according to the international standard for CO₂ monitoring set by the WMO.

[Results]:

Fig. 1 Average CO₂ amplitude pattern for diurnal cycles as a function of different months.

Fig. 2 (a) and (b) Monthly average CO₂ concentration (solid-line) and corresponding de-seasonalised long-term trend (dotted-line). (c) and (d) Rate of change of atmospheric CO₂ mole fractions.

g. 3 (a) Variations of monthly CO₂ concentrations. (b) Annual summer atmospheric CO₂ mole fraction and corresponding growth rate.

Fig. 4 Potential source regions of background CO₂ during different seasons. The red triangle represents the Nanling site.

The authors concluded that after excluding the impact of weather conditions, the analyses revealed that changes in CO₂ source and sink characteristics jointly dictated the decrease in atmospheric CO₂ concentration in the Nanling area through the complicated two-way interaction of the carbon cycle. The three-year lasting decline of the atmospheric CO₂ concentration in the Nanling area, which acted as a probe, provided timely positive feedback of the existing green policies of the government. Although there were some limitations to the study, the connection between the atmospheric CO₂ concentration variations and natural-anthropogenic drivers has been established by our analyses and suggests further research on the atmospheric CO₂ dynamics. As the mole fraction of the atmospheric CO₂ continues to rise globally, this study may aid the people in reducing CO₂ emissions.