The Ammonia-Nitric Acid-Water System

Ammonia and nitric acid can react in the atmosphere to form ammonium nitrate, NH4NO3  

Ammonium nitrate is formed in areas characterized by high ammonia and nitric acid concentrations and, as we will see in the next section, low sulfate concentrations. 

The dissociation constant, Kp(T), is therefore equal to the product of the partial pressures of NH3 and HNO3. Kp can be estimated by integrating the van t Hoff equation (Denbigh 1981). The resulting equation for Kp in units of ppb2 (assuming 1 atm of total pressure) is 

FIGURE 10.19 NH4NO3 equilibrium dissociation constant as a function of temperature at RH = 50%. 

FIGURE 10.20 NRjNCMs) concentration as a function of temperature for a system containing 7 pgm-3 NHj and 26.5 pgm 3 HN03 at 30% RH. The difference between the total available mass (dashed line) and the NH4N03 mass remains in the gas phase as NHj(g) and HNOj(g). 

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