High precision, absolute total column ozone measurements from the Pandora spectrometer system: Comparisons with data from a Brewer double monochromator and Aura OMI

We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground‐based direct‐sun irradiance measurements using our recently deployed Pandora single‐grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air‐shed and development of a ground‐based monitoring network for studying small‐scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid‐ to high‐latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double‐grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15–80°), indicating adequate Pandora stray light correction. A small (1–2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3°K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura‐OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI‐measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short‐term (hourly) temporal changes in TCO, not possible to capture by sun‐synchronous satellites, such as OMI, alone.