Evaluation of OMI operational standard NO₂ column retrievals using in situ and surface-based NO₂ observations

We assess the standard operational nitrogen dioxide (NO₂) data product (OMNO₂, version 2.1) retrieved from the Ozone Monitoring Instrument (OMI) onboard NASA's Aura satellite using a combination of aircraft and surface in~situ measurements as well as ground-based column measurements at several locations and a bottom-up NOx emission inventory over the continental US. Despite considerable sampling differences, NO₂ vertical column densities from OMI are modestly correlated (r = 0.3-0.8) with in situ measurements of tropospheric NO₂ from aircraft, ground-based observations of NO2 columns from MAX-DOAS and Pandora instruments, in situ surface NO₂ measurements from photolytic converter instruments, and a bottom-up NOx emission inventory.

Overall, OMI retrievals tend to be lower in urban regions and higher in remote areas, but generally agree with other measurements to within ± 20%. No consistent seasonal bias is evident. Contrasting results between different data sets reveal complexities behind NO₂ validation.