The climatology of ambient CO2 concentrations from long-term observation in the Pearl River Delta region of China: roles of anthropogenic and biogenic processes
△CO 2 and △CO showed significant positive correlation. • Respiration released more CO 2 relative to photosynthesis. • Anthropogenic sources were the largest contributor to CO 2 . • Fossil fuels from power and industries controlled the level of anthropogenic CO 2 . • Vehicles were the main source of diurnal variations of CO 2 . A B S T R A C T The global/regional background CO 2 has been investigated extensively. However, the monitoring of CO 2 concentration remains sparse in the megacities of
... the megacities of China. Understanding the ambient CO 2 in urban areas and how it is influenced by meteorological conditions, anthropogenic emissions, and biogenic processes may shed light on improving the carbon evaluation. The climatology of ambient CO 2 is reported for the period 2014-2017 at the Guangzhou Panyu Atmospheric Composition Site (GPACS), a suburban site in the Pearl River Delta (PRD) region of China. The ambient CO 2 ranged from 420.50 ± 14.87 × 10 − 6 mol mol − 1 (ppm) in the summer to 431.94 ± 15.13 ppm in the winter and had an annual mean of 428.16 ± 16.26 ppm. The high CO 2 concentrations during the winter were a consequence of anthropogenic emissions and low solar radiation against mixing layer height (MLH). The diurnal variability of CO 2 exhibited two peaks: one peak occurring at 0500-0700 and another at 2100-2200 LST (Local Standard Time), which roughly corresponds to local rush hour. CO 2 decreased with nearsurface wind speed (WS), most of which was constrained to WS less than 2.0 ms − 1 . Carbon monoxide (CO) concentrations were simultaneously measured to distinguish between biogenic and anthropogenic sources of CO 2 . △CO 2 and △CO showed significant, positive correlations (r = 0.77-0.78, p < 0.001) in winter and autumn, reflecting common sources under synoptic air transport from the northwest and northeast directions. The correlation was lower in spring (r = 0.62, p < 0.001), possibly because the vegetation photosynthesis was stronger. A regression analysis of △CO 2 against △CO showed that the intercepts varied between 4.3 and 10.3 ppm, indicating that respiration released more CO 2 relative to photosynthesis. The mean diurnal slope (△CO 2 /△CO) ranged from 54.27 ± 5.36 to 71.07 ± 10.30 ppm ppm − 1 , indicating that the anthropogenic sources were the largest contributor to CO 2 compared to biogenic processes. The fossil fuels from power and industries are responsible for the level of anthropogenic CO 2 , while vehicles are the main source of diurnal variations. The ratio of △CO 2 to △CO was lower in winter, which indicates the contribution of CO emissions from traffic sources 2 were associated with the lower ambient temperature. More fossil fuel combustion to heat buildings together with reduced biospheric respiration can also explain the lower △CO 2 /△CO ratios during the winter.