Comparison of spatial patterns of pollutant distribution with CMAQ predictions

To evaluate the Models-3/Community Multiscale Air Quality (CMAQ) modeling system in reproducing the spatial patterns of aerosol concentrations over the country on timescales of months and years, the spatial patterns of model output are compared with those derived from observational data. Simple spatial interpolation procedures were applied to data from the Clean Air Status and Trends Network (CASTNet) and Speciation Trends Network (STN) monitoring networks. Species included sulfate PM, total nitrate (NO3-+HNO3), and ammonium PM. Comparisons were made for the annual average concentrations for 2001, and for one lunar month (4 weeks), where the month chosen for each species represents the highest concentrations of the year. Comparisons between the modeled and interpolated spatial patterns show very good agreement in the location and magnitude of the maxima and minima, as well as the gradients between them. Some persistent biases are identified and noted. Limitations on our ability to describe the spatial pattern from sparse data as well as the limitations of the networks are briefly discussed.