Background Characteristics of Atmospheric CO2 and the Potential Source Regions in the Pearl River Delta Region of China

Abstract

Mole fractions of atmospheric CO 2 (XCO 2) have been continuously measured from October 2014 to March 2016 at the Guangzhou Panyu Atmospheric Composition Site (23.00°N, 113.21°E; 140 m MSL) in the Pearl River Delta (PRD) region using a cavity ring-down spectrometer. Approximately 66.63%, 19.28%, and 14.09% of the observed values were filtered as background, pollutant source, and sink due to biospheric uptake, respectively, by applying a robust local regression procedure. Their corresponding mean values were 424.12 ± 10.12 ppm (×10 −6 mol mol −1), 447.83 ± 13.63 ppm, and 408.83 ± 7.75 ppm. The background XCO 2 levels were highest in spring and winter, moderate in autumn, and lowest in summer. The diurnal XCO 2 was at a minimum from 1400-1600 LST (Local Standard Time) and a maximum at 0500 LST the next day. The increase of XCO 2 in spring and summer was mainly associated with polluted air masses from south coastal Vietnam, the South China Sea, and the southeast Pearl River Estuary. With the exception of summer, airflow primarily from marine regions southeast of Taiwan that passed over the Pearl River Estuary had a greater impact on XCO 2 , suggesting an important potential source region.

A benchmark dataset of diurnal- and seasonal-scale radiation, heat and CO<sub>2</sub> fluxes in a typical East Asian monsoon region

“…11b. Positive nocturnal values, reaching 6.4, 8.2, 8.2, and 4.5 µmol m −2 s −1 for the SX-cropland, DT-cropland, XZ-suburb, and DS-suburb sites, respectively, were mainly related to the poor nighttime atmospheric mixing (Cheng et al, 2018), a lower boundary layer height (Hassan, 2015), plant respiration (Mai et al, 2020), and anthropogenic sources (Hu et al, 2018). The mid-afternoon negative CO 2 fluxes (about −8-29 µmol m −2 s −1 , where negative values refer to the fact that the ecosystem absorbs CO 2 from the atmosphere) at the SX-cropland, DT-cropland, XZ- suburb, and DS-suburb sites were due to the active biospheric photosynthesis and favorable dispersion conditions (Grimmond et al, 2002).…”

A benchmark dataset of diurnal- and seasonal-scale radiation, heat, and CO2 fluxes in a typical East Asian monsoon region

“…A marked and significant diurnal cycle of CO2 flux is shown in Figure 11b. Positive nocturnal values, respectively reaching at 6.4, 8.2, 8.2, 4.5 μmol m -2 s -1 for SX-cropland, DT-Cropland, XZ-suburb, and DS-suburb sites, which were mainly related to the poor night-time atmospheric mixing (Cheng et al, 2018), lower boundary layer height (Hassan, 2015), plant respiration (Mai et al, 2020), and anthropogenic sources (Hu et al, 2018). Mid-afternoon negative CO2 fluxes (about -8-29 μmol m -2 s -1 , negative values refer that the ecosystem absorbs CO2 from the atmosphere) at SX-cropland, DT-Cropland, XZ-suburb, and DS-suburb sites were due to the active biospheric photosynthesis and favorable dispersion conditions (Grimmond et al, 2002).…”

Analysis of the temporal variability of CO₂, CH₄ and CO concentrations at Lamto, West Africa

“…This signal can be explained by the combination of the variability of CO 2 fluxes exchanged between the vegetation, and the ABL (Putaud, 2019). Generally, ABL height increases after sunrise, reaches a maximum during noon, and decreases from sunset (Mahalakshmi et al, 2011;Mai et al, 2020). The accumulation of CO 2 at the surface stops abruptly after 7 hr, which result on the one hand from the radiative soil heating effects, which break up the inversion layer established during the night to mix vertically the trapped gases, and on the other hand reversal from CO 2 fluxes that become negative because of photosynthesis.…”

“…The accumulation of CO 2 at the surface stops abruptly after 7 hr, which result on the one hand from the radiative soil heating effects, which break up the inversion layer established during the night to mix vertically the trapped gases, and on the other hand reversal from CO 2 fluxes that become negative because of photosynthesis. CO 2 uptake by plants induces a slight decrease in CO 2 concentrations of $4 ppm between 12 hr and 18 hrs when the atmospheric boundary layer is developed to altitudes between 1 and 2 km (Goudie and Middleton, 2001;Aryee et al, 2020;Mai et al, 2020;Pedruzo-Bagazgoitia et al, 2020). The highest amplitudes of the CO 2 diurnal cycle (peak to peak amplitude greater than 40 ppm) are observed during the rainy season GSP and PSP (Table 3).…”

“…The choice of separating night and day is based on the variations of the ABL (Atmospheric Boundary Layer) diurnal cycle. The ABL is practically in a stable state during the night (not very turbulent) while it is most often unstable (turbulent) during the day(Fern andez-Duque et al, 2017;Mai et al, 2020) resulting in different vertical dilution of local fluxes and influence from more remote fluxes.…”