Results from a 1-D coupled air-snowpack model to investigate HONO concentrations in the planetary boundary layer during ANTCI 2003 at South Pole are presented. The model is a development of a multiphase physicochemical model for HONO in snowpack. The snowpack component of the model has large uncertainties arising from assumptions involving the surface nature of the snow grains and the concentrations of snow-phase precursors. Boundary layer observations of HONO concentrations are used to help constrain these uncertainties.