An Online Downscaling Method to Simulate High Resolution Atmospheric Concentrations of Pesticides with the 3D Chemistry-Transport Model CHIMERE: Application and Evaluation

High resolution databases on atmospheric concentrations of pesticides are necessary in order to perform epidemiological studies but there is currently no modeling method to provide high resolution mapping of pesticides concentrations over a whole region. In this study, we propose an online downscaling method for CHIMERE to perform simulations at a sub-kilometer resolution. The main idea of this downscaling approach is to redistribute or interpolate some information simulated on the coarse grid to simulate the transport over a finer subgrid. The performance of the downscaling is analyzed by comparing the CHIMERE nested simulation results at 0.02 degrees and CHIMERE simulation results downscaled from 0.1 degrees to 0.02 degrees. By applying this method to S-metolachlor, we diagnosed an error generated by the downscaling of a few percents on both background and hotspot concentrations. The method was used to simulate concentrations over France at a resolution of 0.004 degrees with a limited increase of the computational time. Based on these simulations, we estimated that around 3 000 inhabitants were exposed to concentrations of S-metolachlor above 10 ng/m3 from April 15th to May 15th 2014.

Automated summary

In this study, an online downscaling method for simulating pesticide concentration at a sub-kilometer resolution is proposed. The method redistributes or interpolates information from coarse grid simulations to simulate the transport over finer subgrids. Applying this method to S-metolachlor, a few percent error was diagnosed, and accurate concentration distribution over France was successfully simulated.