Experiments with the assimilation of fine aerosols using an ensemble Kalman filter

In a series of experiments we issue forecasts of fine aerosol concentration over the coterminous USA and southern Canada using the Weather Research and Forecasting – Chemistry model initialized with 3D-VAR or ensemble Kalman filter (EnKF) assimilation methods. Assimilated observations include surface measurements of fine aerosols from United States Environmental Protection Agency AIRNow Data Exchange program. Evaluation statistics calculated over a month-and-half-long summer period demonstrate the advantage of EnKF over 3D-VAR and point to the limitations of applying a simple aerosol parameterization for predicting air quality over the forecast area. Strategies for further improvement of forecasting aerosol concentrations are discussed.