Quantification of the rate of gas exchange across the air-water interface is essential in understanding the biogeochemical cycling of carbon in aquatic ecosystems. Estimating the gas transfer velocity (k) in alpine streams is uncertain, however, due to high turbulence and subsequent bubble-mediated gas transfer. Schmidt scaling is often used to estimate gas transfer velocities of climate relevant gases (e.g. CO2) from tracer gases (e.g. argon (Ar)), but this method has high uncertainty when scaling between gases of different solubilities (as is the case for Ar to CO2) in steep-slope streams with bubble-mediated gas transfer. Here I explore a method for the estimation of gas exchange of CO2 from Ar by performing dual tracer gas additions in mountain streams. Ar and CO2 gas were simultaneously and continuously injected into streams and gas exchange rates were estimated using an exponential decline model. The mean ratio of gas exchange of Ar (a) to CO2 (a) was 1.7 (95% credible interval of 1.3 to 2.3) and was approximately equal to the theoretical value of 1.7 based both on Schmidt scaling and solubility, showing that Ar can be used to estimate gas transfer of CO2 with scaling but with some uncertainty.