A Model Study of Hydrogen Cyanide formation Under Reducing Conditions

Abstract

Hydrogen cyanide (HCN) may have been present in the Archean atmosphere, which was anoxic, reducing, and received less solar radiation than today. HCN likely played a key role in prebiotic chemistry and the origin of life. To understand how an atmosphere rich in CO2, CO, and CH4 influenced HCN levels on early Earth, this study investigates HCN formation in the Archean using a one-dimensional photochemical model. The model, named PATMO[1], includes 65 chemical species and 480 reactions, and simulates atmospheric processes from the surface up to 100 km over 100 years. Assuming a CH4 mixing ratio of 100 ppmv, two Archean atmospheric scenarios were examined: a CO2-dominated atmosphere with 1000 ppmv CO, and a N2-dominated atmosphere. While HCN concentrations differed significantly above 75 km between the two cases, the variation near the surface was minimal. Surface HCN levels could have reached up to 0.35 ppm, consistent with the findings of Tian et al. (2011)[2]. We concluded that the abundance of CO2 and CO had little impact on surface HCN levels.