Theoretical investigation of the relative impacts of water and ammonia on the tropospheric conversion of NO to HNO.

Reaction of ammonia with NO, without and with the assistance of water, in the troposphere has been investigated by electronic structure and chemical kinetic calculations. The whole process has been compared against the hydrolysis reaction, uncatalyzed as well as water and ammonia catalyzed. A comparative study between hydrolysis and ammonolysis based on relative rates has been extensively carried out. The analysis reveals that ammonolysis has negligible practical atmospheric implication compared to hydrolysis. The former could have a significant contribution in tropospheric HNO formation only at 0 km altitude under two conditions: either on a local scale, where ammonia concentration could reach around a thousand times its global average value, or under very low humidity and at a lower temperature. Relative rate studies also suggest that the catalytic effect of both ammonia and water is negligibly small in determining the atmospheric fate of NOvia gas phase hydrolysis and ammonolysis.