A fast air quality model using Look-up tables to address integrated environmental assessment model requirements.

The use of integrated assessment models (IAM), which combine models from different fields, raises the need for developing specific modelling concepts in order to provide results to support policy decisions within a reasonable time frame. Air quality policy support systems have been evolving towards the use of integrated assessment models that relate technologies (emitting sources) with air quality levels. Existing photochemical air quality models are not directly suitable for integrated assessment as they are time intensive in terms of input preparation and simulation speed. The objective is to present a methodology to reduce the computational burden of photochemical models, using pre-tabulated values of first order reaction rates. This approach was designed for the Luxembourg Energy and Air Quality (LEAQ) assessment model. It combines the air quality model with a technoeconomic model which computes ozone precursors emissions coming from energy consumption (e.g. traffic). The models are coupled via an optimization approach, which minimizes the total energy cost for a given ozone level. We have used an adapted version of AUSTAL2000, as a transport calculator and coupled it with a fast photochemical module, the AsYmptotic Level Transport Pollution (AYLTP). AYLTP consists of a Look-Up Table (LUT) of linear reaction coefficients. The LUT has been built using a box model by simulating a large set of possible combinations of meteorological variables and precursor concentrations. The ozone concentration variations are then obtained using the rate coefficient that is utilized to affect the mass carried by the Lagrangian particles. The loss of accuracy inherent to this approach is acceptable given the reduction of CPU time. The development of such methodologies is important when considering IAM. The use of linear reaction rates obtained with the help of the LUT represents an innovative step towards the use of simplified air quality models that involve complex chemistry.