The climatology of ambient CO2 concentrations from long-term observation in the Pearl River Delta region of China: Roles of anthropogenic and biogenic processes

Abstract

The global/regional background CO2 has been investigated extensively. However, the monitoring of CO2 concentration remains sparse in the megacities of China. Understanding the ambient CO2 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 CO2 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 CO2 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 CO2 concentrations during the winter were a consequence of anthropogenic emissions and low solar radiation against mixing layer height (MLH). The diurnal variability of CO2 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. CO2 decreased with near-surface 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 CO2. △CO2 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 △CO2 against △CO showed that the intercepts varied between 4.3 and 10.3 ppm, indicating that respiration released more CO2 relative to photosynthesis. The mean diurnal slope (△CO2/△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 CO2 compared to biogenic processes. The fossil fuels from power and industries are responsible for the level of anthropogenic CO2, while vehicles are the main source of diurnal variations. The ratio of △CO2 to △CO was lower in winter, which indicates the contribution of CO emissions from traffic sources were associated with the lower ambient temperature. More fossil fuel combustion to heat buildings together with reduced biospheric respiration can also explain the lower △CO2/△CO ratios during the winter.