Title: Urban air pollution monitoring at micro-, local and meso- scales using Pandora instrument

Increasing urbanization worldwide raise serious concerns about urban air quality and its effects on large human populations. This study presents application of the Differential Optical Absorption Spectroscopy technique to multi scale urban air quality (NO₂) monitoring. A Pandora spectroscopic instrument (SciGlob Inc) has been deployed on top of a 30 m building in Boston, MA, USA, since September 2019. It performs over the roof sky scans (local to meso scales), into the street canyon "target" (micro-scale), and direct sun measurements. In situ NO₂ measurements are also being conducted on top of the roof (co-located with Pandora) and at the street level near the "target" building. NO₂ spatial and temporal heterogeneity within different scales is discussed.