Carbon dioxide exchange across water–air interface and its influencing factors in middle reaches of Yellow River during winter

River systems strongly contribute to CO2 emissions. However, despite numerous reports on gas emissions from ice, the current understanding of CO2 exchange of rivers in winter and the factors affecting it is still relatively limited. To shed light on CO2 exchange and the factors influencing it for rivers during winter. Based on intensive field measurements using floating chambers, riverine CO2 exchange in middle reaches of Yellow River in China was examined. Our results showed net emissions of CO2 across the ice-free interface (51.874∼162.478 mg/m²·h). Compared with other rivers worldwide, the CO2 exchange is higher than most major rivers, such as the Lena and Kolyma Rivers. However, at the ice-covered river monitoring site, CO2 exchange across the water–air interface exhibited a net uptake, ranging from −36.336 to 0 mg/m²·h. Furthermore, the relationships between CO2 exchange and relevant physicochemical variables showed that CO2 emissions negatively correlated with pH and ice thickness and positively correlated with water velocity, wind speed, water temperature, atmospheric temperature, ammonia nitrogen levels, and total phosphorous content. This study is scientifically valuable as the findings provide insight into the CO2 exchange pattern that occurs at the water–air interface of rivers during winter both ice-covered and ice-free sites.