The three-dimensional photochemical model UAM-V is used to investigate the effects of various meteorological conditions and of the coarseness of emission inventories on the ozone concentration and ROG/NO_x limitation of the ozone production in the Po Basin in the northern part of Italy. As a base case, the high ozone episode with up to 200 ppb on 13 May 1998 was modelled and previously thoroughly evaluated with measurements gained during a large field experiment. The performed variations in meteorology are applied to mixing height, air temperature, specific humidity and wind speed. Three coarser emission inventories are obtained by resampling from 3×3 km² up to 54×54 km² emission grids. The model results show that changes in meteorological input files have the largest effect on peak ozone. In the modelled ozone plume a slope of 10.1 ppb ozone/°C and in Milan of 2.8 ppb ozone/°C were found. The net ozone formation in northern Italy is more strongly temperature than humidity dependent, while the humidity is very important for the ROG/NO_x limitation of the ozone production. For each of the meteorological variations (e.g. doubling the mixing height), the modelled ozone plume remains ROG limited for this case. A strong change towards NO_x sensitivity in the ROG limited areas is only found if much coarser emission inventories were applied. Increasing ROG limited areas with increasing wind speed are found, because the ROG limited ozone chemistry induced by point sources is spread over a larger area. Simulations without point sources tend to increase the NO_x limited areas.