The optimal spatial resolution for top-down/bottom-up integration of time-resolved urban fossil fuel CO2 emissions

The `Hestia Project' uses a bottom-up approach to quantify fossil fuel CO2 (FFCO2) emissions spatially at the building/street level and temporally at the hourly level. Hestia FFCO2 emissions are provided in the form of a group of sector-specific vector layers with point, line and polygon sources to support policy-making through spatial analysis. The spatial resolution is crucial to representing the heterogeneity and effective information content of the original Hestia FFCO2 emissions. From the perspective of a data provider for bottom-up/top-down integration, we need to find a balance between spatial resolution and data volume so that the gridded data product retains the maximum amount of information content while maintaining an affordable data volume. In this paper, we present an analysis of the Shannon entropy of the gridded FFCO2 emissions with varying resolutions in four Hestia study areas and find that the optimal resolution of these cities ranges from 80-200m. The following conclusions were drawn from this study: (1) The total emissions grid, which is the sum of several sector-specific grids, requires a finer grid cell resolution than each of these sector-specific grids; (2) The residential building emissions requires a finer grid cell resolution than the commercial and the industrial emissions grids; (3) The optimal resolution of the onroad emissions grid is largely dependent on the density of the road network; (4) The optimal resolution of the building emissions grid is related primarily to the compactness of the built-up area and the average size of the building footprints.