Mathematical modeling of the formation and transport of ammonium nitrate aerosol

Abstract

A mathematical model describing the transport and formation of aerosol NH 4NO 3 is presented. Based on a vertically resolved Lagrangian trajectory formulation incorporating gas phase kinetics, NH 4NO 3 concentrations are computed at thermodynamic equilibrium with precursor HNO 3 vapor and NH 3 concentrations. Sensitivity analysis shows that NH 4NO 3 concentration predictions are strongly influenced by ambient temperature and NH 3 levels. A brief description of the NH 3 emissions inventory used in this study is included to indicate the important sources. The model was tested by comparison to ambient NH 3, NH 4 + and NO 3 − concentrations measured at El Monte, California during June 1974. Model results compare favorably with the ambient measurements and are used to explain trends in those measurements. An early morning nitrate peak develops as HNO 3 produced soon after sunrise reacts with NH 3 accumulated overnight. A second peak in nitrate concentration is predicted and observed at El Monte later in the day. Potential applications of this model to control strategy decisions and to study the fate of NO x are discussed.