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

Mole fractions of atmospheric CO₂ (XCO₂) 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 XCO₂ levels were highest in spring and winter, moderate in autumn, and lowest in summer. The diurnal XCO₂ was at a minimum from 1400–1600 LST (Local Standard Time) and a maximum at 0500 LST the next day. The increase of XCO₂ 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 XCO₂, suggesting an important potential source region.