Observation of slant column NO2 using the super-zoom mode of AURA-OMI

Abstract

We retrieve slant column NO₂ from the super-zoom mode of the Ozone Monitoring Instrument (OMI) to explore its utility for understanding NO_x emissions and variability. Slant column NO₂ is operationally retrieved from OMI (Boersma et al., 2007; Bucsela et al., 2006) with a nadir footprint of 13 × 24 km², the result of averaging eight detector elements on board the instrument. For 85 orbits in late 2004, OMI reported observations from individual “super-zoom” detector elements (spaced at 13 × 3 km² at nadir). We assess the spatial response of these individual detector elements in-flight and determine an upper-bound on spatial resolution of 9 km, in good agreement with on-ground calibration (7 km FWHM). We determine the precision of the super-zoom mode to be 2.1 × 10¹⁵ molecules cm⁻², approximately a factor of √8 lower than an identical retrieval at operational scale as expected if random noise dominates the uncertainty. We retrieve slant column NO₂ over the Satpura power plant in India; Seoul, South Korea; Dubai, United Arab Emirates; and a set of large point sources on the Rihand Reservoir in India using differential optical absorption spectroscopy (DOAS). Over these sources, the super-zoom mode of OMI observes variation in slant column NO₂ of up to 30 × the instrumental precision within one operational footprint.