The absorption of NOX gases in water and alkalies [NaOH, NH4OH, Ca(OH)(2))] provides commercially important products nitric acid and salts (nitrates and nitrites), respectively. This complex phenomena of mass transfer with chemical reactions is described quantitatively in terms of [HVroot(kD)](j) values for J = N2O3, N2O4. However, the reported value of HVroot(kD) for N2O3 absorption in strong alkaline solution was 50 times its value in water. For the inten-nediate case of NOX absorption in weak alkali Ca(OH)(2), it was necessary to have a mathematical model which incorporated the HNO2 decomposition, as well as neutralization by alkali. This led to a unified model for NO, absorption, which can be used for predicting point rates of NOX absorption as well as selectivity, for various gas compositions and liquid-phase pH. Parametric sensitivity has been reported. A comparison of the model predictions with data from patent on Ca(NO2)(2) manufacture has been made to test the model validity.