The chemical nocturnal rate of ozone removal in a downtown location in the city of Santiago de Chile was evaluated during March (end of summer), and May and June (autumn) of 2005. In all the measured days, ground level ozone concentrations drop below 1 ppb during night-time. The simultaneous measurements of NO and VOCs concentrations allows an estimation of the chemical rates of ozone removal by these pollutants. Calculated chemical removal rates are considerably larger than those experimentally determined. The main chemical ozone removal process is its reaction with NO. This process is partially compensated by ozone transport, most probably from the residual layer and / or advection of ozone enriched air masses.