Model study with UAM-V in the Milan area (I) during PIPAPO: simulations with changed emissions compared to ground and airborne measurements

The three-dimensional photochemical Urban Airshed Model with variable grid (UAM-V) is used to investigate the temporal and spatial dynamics of the photooxidant production in the highly polluted Milan area (Italy). A simulation of the 13 May 1998 event is presented, when peak ozone levels of 190 ppb were measured in the urban plume. A large field campaign provided data of numerous chemical species and meteorological quantities from ground based and airborne platforms. The highest measured ozone mixing ratios occurred in the urban plume, where a local peroxide decrease was found simultaneously. The model base case is able to reproduce the ozone concentration but more peroxide is formed in the centre of the plume than in the adjacent areas. This can be interpreted as a tendency of the model towards a stronger NOx sensitivity compared to observation. Modification of the emission inventory, which is based on observed discrepancies between inventory and measurements, lead to a better agreement with respect to peroxide formation and NOx removal in the urban plume. It seems that the different rearrangement of the emissions in urban and non-urban areas are important for the improved response of the model. Ozone levels did not differ much between the base case simulation and those with a modified emission inventory, while peroxide formation and NOx concentrations in the urban plume did.