Informing Near-Airport Satellite NO2Retrievals Using Pandora Sky-Scanning Observations

Abstract

Airports are a large and growing source of NOx. Tracking airport-related emissions is especially difficult, as a portion of emissions are elevated above the surface. While satellite-based NO2 observations show hot-spots near airports, near-source retrievals often have large biases related to uncertainties in the NO2 vertical distribution and resultant air mass factors (AMF). Here we use observations from UV–vis spectrometers (Pandora 1S, SciGlob) deployed near the Atlanta Hartsfield-Jackson International airport from April 2020–May 2021 to assess the impact of aviation on NO2 vertical profiles. We show the first near-airport sky-scanning Pandora observations, which are used to distinguish the airport plume from the urban background. We find that increasing aviation leads to higher NO2 over the airport, and the enhancement is distributed across the mixed layer near-equally. We compare observed profiles with those modeled by the Goddard Earth Observing System composition forecast (GEOS-CF) system. We find that modeled profiles attribute a larger portion of the column closer to the surface and underestimate the NO2 mixing height. Observed profiles typically exhibited greater NO2 concentrations up to 2.5 km above ground level. Air mass factors (AMF) calculated using observations (AMFFused) are similar over Hartsfield-Jackson to those calculated using GEOS-CF (AMFGEOS-CF). The unexpected similarity in alternative AMFs is attributed to the altitude-dependent sensitivity of AMFFused to changes in NO2 concentration. Using either AMFFused or AMFGEOS-CF to evaluate TROPOMI NO2 against independent direct-sun observations produces consistent normalized mean differences of −22% and −29%, respectively. Overall, these results demonstrate the benefits of a combined ground and satellite-based approach for probing a complex distribution of NOx emissions in an urban area.