We evaluate InMAP model prediction accuracy on total PM2.5 concentration by comparing against measurements from the WHO ambient (outdoor) air pollution database (WHO, 2016), which provides PM2.5 measurements for 53 of the 96 cities studied here. We assess performance using metrics including mean bias (MB), mean error (ME), mean fractional bias (MFB), mean fractional error (MFE), and coefficient of determination (r²). Definitions of these metrics are in Table . We also use the same metrics to evaluate the global GEOS-Chem model predictions as configured and run by against the same PM2.5 measurements in the same cities. In addition, we compare InMAP model predictions of total PM2.5 concentrations against satellite-based predictions of PM2.5 concentrations in 91 global cities , and predictions by in 43 global cities.