A deeper knowledge of suspended particulate matter in the atmosphere is essential for modelers to increase the accuracy of their results. Most photochemical models currently in use do not take into account the solar radiation extinction by atmospheric aerosols. This can lead to incorrect results on atmospheric chemistry calculations. As the gas phase chemistry and the solar radiation affect the aerosol load, the link between the solar radiation, the gas phase and the aerosol chemistry processes should lead to important improvements of the air quality models. In order to implement these interactions, solar radiation, gas phase and aerosol chemistry modules are used together in a new model called TAPOM (Transport and Air POllution Model). As usual In a 3D air quality model the modules must be accurate enough to give reasonable results but must need low computational time: -The solar radiation module calculates the actinic fluxes and the photolysis rate constant. -The gas phase chemistry module calculates the chemical transformation of the gas phase species. -The aerosol module calculates chemical equilibrium between the gas and the aerosol phase.
A new model has to be validated by comparison with measurements before one can use its results. For that purpose we simulated the South Californian Air Quality Study episode of August 1987 on the Los Angeles basin. A large amount of data (emissions and atmospheric concentrations) is available for this episode, including aerosol measurements. We first proceeded different gas phase chemistry runs, without aerosol calculation. These runs were performed In order to validate the gas chemistry calculations as well as the wind fields. Our results for photochemical chemistry show a good agreement with the measurements. These results validate the transport1 solar radiation and gas chemistry modules of TAPOM. Aerosols calculations still have to be compared to measurements, and therefore are not yet validated. The first runs including aerosol calculations do not show significant changes on ozone concentrations. The main effects are seen on aerosol precursors such as nitric acid which is almost totally consumed when aerosol calculation is performed. The interactions between aerosol concentrations and solar radiation will be studied as soon as the aerosol results are validated.
The Lidar group has participated to the international PAUR II (see:
http://Iap.physics.auth.grlpaurl) campaign, in Crete, may 99. This campaign was devoted to the study of long range transport of aerosols over the Mediterranean Sea and southem Europe and its influence on UV radiation. Different international teams were participating, with UV meter, balloon, DOAS, in various places in Crete and around the Mediterranean basin. The EPFL lidar group participated with the mobile ozone lidar, which have been operated in the north-west coast of Crete, in Kolimbari. During this campaign, the lidar team performed measurements of ozone and aerosols vertical and temporal distribution. Range resolved ozone and aerosol depth have been used for interpreting the observed processes. An article presenting typical results and comparison with balloon measurement has been submitted to the international peer reviewed Journal of Applied Optics. The lidar data have been processed and used into the PAUR II database, and another paper related to our measurement will soon be submitted.
