Urban-scale variational flux inversion for CO Using TROPOMI total-column retrievals: A case study of Tehran

Emission inventories of trace gases and aerosols are a key input for air pollution modelling, yet are subject to significant uncertainties. The aim of this study is to refine urban-scale, gridded estimates of carbon monoxide (CO) emissions for Tehran, Iran; this was done using an inverse-modelling approach. We assimilated total column mixing ratios of CO retrieved from the TROPOspheric Monitoring Instrument (TROPOMI) using a four-dimensional variational assimilation system based on the Community Multi-Scale Air Quality Model. The inversion system allows for two representations of the temporal profile of emissions at each grid-point: scaling a fixed diurnal profile, or with separate, constant estimates spanning four diurnal time-categories. We evaluate the inversion capability by applying independent surface measurements.