Aerobiology at regional scale

One of the big issues in aerobiology is short term forecasting of airborne particles concentrations. The efficiency of traditional statistical models is localized and often limited, in particular under changing climatic conditions such as those that occurred in the last decades and because they do not take into account the airborne particles movements. Transport can well be traced with the help of trajectories models, as will be illustrated by events of chestnut pollen over the Alps and of ragweed pollen over the western Switzerland. Dispersion models, linked to meteorological models based on the physics of the atmosphere, are in theory best suited for describing and forecasting particles concentrations. However, their application at regional scale faces to several problems, when one wants to use them for regular and generalized applications. Two sets of information that would be required by these models are often lacking: 1) the initial conditions (concentration of particles in the air at time zero), and 2) the location and timing of particles emission (which implies e.g. adequate vegetation and land use maps). The first one is related to aerobiological measurement technology and the second either to the absence or insufficient availability of the data. Another difficulty lies in the size of the mesh used by the models, and/or the computer time required for high resolution calculations. A mesh of 20 to 50 km can be well suited for flat areas, but totally inefficient for regions with a more complex topography. Aerobiological data - such as the extended pollen season in the Jura Mountains and the comparison between imported versus local ragweed pollen in Geneva - suggest interesting interpretations that still need to be confirmed and let hope a wider use and rapid development of dispersion models validated for the regional scale.