A new gridding method for zonal travel activity and emissions using bicubic spline interpolation

For air quality dispersion models, mobile source emissions, including both link- and traffic zone-level emissions, must be disaggregated into grid cells. Current gridding methods assign all traffic analysis zone level emissions to the single grid cell containing the TAZ centroid. In this study, we propose a new approach for disaggregating traffic analysis zone-level emissions using a bicubic spline interpolation function and activity and roadway densities. The new approach, which better replicates the heterogeneity associated with travel activities, distributes zone-level emissions into the grid cells contained within the zone boundary. When results are compared to the current methods, we find that fewer grid cell misallocations occur and that emissions from TAZs overlapping multiple grid cells are apportioned correctly. The gridded emissions inventory developed using the new approach will result in better data inputs for air quality modeling, and in particular can significantly improve the sensitivity of transportation conformity analysis.