By means of life cycle modeling and Latin hypercube sampling, uncertainties in ozone concentrations downwind of London have been estimated for the first time in photochemical models, albeit with the involvement of a substantial element of subjective judgement. The analysis has led to a clear definition of which areas of model input determine the greatest contribution to the uncertainties in the calculated distribution of a wide range of secondary pollutants generated downwind of London. These calculations show that the initial concentrations of hydrocarbon emissions are heavily dominated by uncertainties in wind speed, photolysis rates, and hydroxyl radical sinks. Each secondary pollutant is influenced to different extents by the different model input areas. However, when ozone control strategies are evaluated, these uncertainties are no longer significant, and other parameters dominate. Accurate prediction of ozone concentrations at a specific location does not necessarily guarantee accurate prediction of the model responses to ozone control strategies. ¿ American Geophysical Union 1988