HONO formation in the troposphere

Atmospheric Chemistry Nitrous acid (HONO) is an important tropospheric intermediate. Current atmospheric models, which assume its formation in the heterogeneous reaction of nitrogen dioxide (NO2) and water, fail to correctly predict the high concentrations of HONO that are detected in the troposphere. Using subnanosecond first-principles molecular dynamics simulations, Martins-Costa et al. show that HONO forms from NO2 preferentially in bulk water with very low probability of its desorption from the surface of liquid water. The present results call into question the catalytic role of the air-water interface and suggest that further studies that take into account various tropospheric chemical species adsorbed on the aqueous droplets are required to elucidate the mechanism of this important atmospheric chemistry. J. Am. Chem. Soc. 142 , 20937 (2020).