A low-cost in-situ CO2 sensor based on a membrane and NDIR for long-term measurement in seawater

The multi-point simultaneous long-term measurement of CO2 concentration in seawater can provide more-valuable data for further understanding of the spatial and temporal distribution of CO2. Thus, the requirement for a low-cost sensor with high precision, low power consumption, and a small size is becoming urgent. In this work, an in-situ sensor for CO2 detection in seawater, based on a permeable membrane and non-dispersive infrared (NDIR) technology, is developed. The sensor has a small size (Þ 66 mm×124 mm), light weight (0.7 kg in air), low power consumption (<0.9 W), low cost (<US$1 000), and high-pressure tolerance (<200 m). After laboratory performance tests, the sensor was found to have a measurement range of (0–2 000)×10−6, and the gas linear correlation R2 is 0.99, with a precision of about 0.98% at a sampling rate of 1 s. A comparison measurement was carried out with a commercial sensor in a pool for 7 days, and the results showed a consistent trend. Further, the newly developed sensor was deployed in Qingdao nearshore water for 35 days. The results proved that the sensor could measure the dynamic changes of CO2 concentration in seawater continuously, and had the potential to carry out long-term observations on an oceanic platform. It is hoped that the sensor could be applied to field ocean observations in near future.