The second point is that urban air quality analyses require urban emissions inventories. As described above, we use spatial surrogates-mainly based on OpenStreetMap data-to allocate 0.5×0.5 degree CEDS emissions to much smaller InMAP grid cells. This spatial downscaling is important: in an analysis comparing InMAP and GEOS-Chem predicted contributions of withincity emissions for a subset of five of the 96 cities studied here (i.e. Johannesburg, Buenos Aires, Addis Ababa, Chengdu, and Guadalajara), we found that the r 2 value between GEOS-Chem and InMAP predictions when InMAP used emissions at their native resolution was 0.67, but when InMAP used the same emissions downscaled with the spatial surrogates described above, the r 2 value decreased to 0.2 (Figure , methods in supporting text). This implies that the use of highresolution emissions provides information that couldn't be reproduced by-for exampleapplying a correction factor to simulation results based on low-resolution emissions.