Photochemical modelling of the Barcelona area under weak pressure synoptic summer conditions

摘要

The city of Barcelona and its surrounding area, located in the western Mediterranean basin, can reach high levels of O_3 in summertime under weak pressure synoptic conditions. To study the origin of this photochemical pollution, the episode that took place between the 3 and 5 August 1990 was chosen. The main meteorological mesoscale flows that take place in the region, such as sea and land breeze, convection cells and topographic injections, were reproduced with the meteorological non-hydrostatic mesoscale model MEMO for 5 August 1990. Industrial and commercial activity on 5 August 1990 was very low because it was a Sunday in the summer holiday period. Therefore, the emissions inventory calculated for this day in an area of 80×80 km~2 around Barcelona showed that the main sources of VOC were traffic (51%) and vegetation (34%), while NO_x were mostly emitted by traffic (88%). Photochemical simulation with the MARS model has shown that the combination of mesoscale circulations and local emissions is crucial in the production of O_3. For instance, NO_x inland transport towards regions where biogenic VOC are emitted causes the formation of O_3, while topographic injections cause the formation of elevated O_3 air layers. The synoptic wind, coming from the northeast in this case, also played an important role in advecting the air masses with local generated O_3 away from their precursor emission sources. Evaluation of the model simulations is also performed and discussed by means of comparison of meteorological measurements in 9 surface stations and concentration measurements in 5 surface stations.