Deployment and Evaluation of a Low-Cost Sensor System for Atmospheric CO₂ Monitoring on a Sea-Air Interface Buoy

Abstract. Direct in-situ observation of marine CO₂ concentrations is, crucial for estimating air-sea CO₂ fluxes, yet such observations remain scarce. Drawn on experiences from urban CO₂ monitoring and buoy-based measurements, this study deployed a sea-air interface buoy platform in the northern South China Sea, near Maoming, Guangdong Province, China. This platform was equipped with three low-cost SenseAir K30 sensors to enable continuous atmospheric CO₂ measurement. This paper presents the first detailed account of the methodology, encompassing hardware design, environmental corrections, land-based validation tests, offshore deployment procedures, and initial observational results. These findings thus provide valuable insights for advancing marine CO₂ observations practices. To mitigate the impacts of temperature, humidity, and pressure on sensor readings – while simultaneously compensating for zero-drift – an environmental correction method was implemented. This approach significantly improved data accuracy: in land tests, the root mean square errors was reduced from 8.03 ppm to 3.64 ppm; in marine observations, the root mean square errors decreased from 24.26 ppm to 1.59 ppm. Importantly, this level of precision meets the requirements for resolving sea surface CO₂ dynamics (~420–480 ppm). Observed concentrations were consistent with HYSPLIT-simulated long-range atmospheric transport, revealing the stable and homogeneous nature of the marine atmospheric boundary layer, with diurnal variations of approximately 3 ppm, and capturing localized or short-term fluctuations due to terrestrial carbon sources. These results demonstrate the effectiveness of the method, offering a low-cost, high-density solution for marine atmospheric CO₂ monitoring and providing key inputs for inversely estimating ocean carbon sink.