Quite high values of aerosols concentration were registered up to about 1 km altitude during the day. Interestingly, the lidar revealed a descent of the highest aerosol loads towards the ground during the morning. Corresponding to this descent, particulate matter (PM) mass measurements performed at the JRC-EMEP station revealed a doubling of PM10 levels at the ground.
A series of numerical simulations were performed (using the weather numerical mesoscale model MM5 in high resolution) to understand to which extent the lidardetected evolution of the particles distribution along the vertical could be explained by the boundary layer and/or horizontal transport processes. A particular stress was put on investigation of boundary layer parameters.
Configuration of the simulation domains
In order to investigate the boundary layer development, three simulations were performed using the MM5 code [1, 2]. The configuration of the domains was as follows:
- the central point was put at the location (8.6E, 45.8N),
- four nested domains with two-way option were used with grid steps respectively: 27 km, 9 km, 3 km and 1 km in both directions,
- the sizes of the domains were approximately: 2160 km, 1080 km, 486 km and 180 km,
- the nested domains were located centrally in the mother domains.
The USGS datasets for elevation, land use, vegetation and soil data were applied with the following resolutions: 10 min (~ 19 km), 5 min (~ 9 km), 2 min (~ 4 km) and 30 sec (~ 0.9 km) for the defined four domains respectively. The
white spots on the picture correspond to glacier or ice/snow cover. The biggest red one in bottom part of the picture indicates the city of Milan.