Evaluation of OMI operational standard NO<sub>2</sub> column retrievals using in situ and surface-based NO<sub>2</sub> observations

Abstract

Abstract. We assess the standard operational nitrogen dioxide (NO 2 ) 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 NO x emission inventory over the continental US. Despite considerable sampling differences, NO 2 vertical column densities from OMI are modestly correlated (r = 0.3-0.8) with in situ measurements of tropospheric NO 2 from aircraft, ground-based observations of NO 2 columns from MAX-DOAS and Pandora instruments, in situ surface NO 2 measurements from photolytic converter instruments, and a bottom-up NO x 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 NO 2 validation. Since validation data sets are scarce and are limited in space and time, validation of the global product is still limited in scope by spatial and temporal coverage and retrieval conditions. Monthly mean vertical NO 2 profile shapes from the Global Modeling Initiative (GMI) chemistry-transport model (CTM) used in the OMI retrievals are highly consistent with in situ aircraft measurements, but these measured profiles exhibit considerable day-to-day variation, affecting the retrieved daily NO 2 columns by up to 40 %. This assessment of OMI tropospheric NO 2 columns, together with the comparison of OMI-retrieved and model-simulated NO 2 columns, could offer diagnostic evaluation of the model.

Hotspot of glyoxal over the Pearl River delta seen from the OMI satellite instrument: implications for emissions of aromatic hydrocarbons

“…We exclude observations from the first and last cross-track positions, those that fail the retrieval algorithm statistical quality checks, and those impacted by the row anomaly (http://www.knmi.nl/omi/research/product/ rowanomaly-background.php). Validation with aircraft data indicates that the OMI HCHO and NO 2 retrievals are accurate within 20 and 30 %, respectively (Lamsal et al, 2014;Zhu et al, 2016). CHOCHO/HCHO column ratios from OMI are consistent with aircraft observations (Kaiser et al, 2015), whereas previous SCIAMACHY retrievals showed large discrepancies (DiGangi et al, 2012).…”

The Ozone Monitoring Instrument: overview of 14 years in space

“…This is the case for NO 2 , SO 2 , and HCHO as their chemical lifetimes are short and their primary sources are located near the Earth's surface. As an example, Lamsal et al (2015) show that the long-term trends and short-term monthly variations in OMI NO 2 column densities from 2005 to 2013 compare well (e.g., r = 0.68 for trends) with those from the majority of surface concentration observations from the U.S. Environmental Protection Agency's (EPA) Air Quality System (AQS). Lamsal et al (2015) argue that the spatial coverage afforded by the OMI satellite data in combination with the maturity of the current retrieval algorithm allows for a more representative estimation of NO 2 trends within a city than observations from a sparse network of surface monitors.…”

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

“…GEOS-Chem concentrations of NO 2 and H 2 O 2 (proxy for HO 2 ) have been evaluated successfully in a number of aircraft campaigns (Martin et al, 2006;Hudman et al, 2007;Singh et al, 2007;Lin and McElroy, 2010;Mao et al, 2010;Travis et al, 2016). GEOS-Chem NO 2 columns have also been evaluated against satellite observations over China (Lin et al, 2012), North America (e.g., Lamsal et al, 2014), and Africa (Marais et al, 2012). Fast Hg 0 oxidation in the polar spring boundary layer is simulated by specifying high BrO concentrations when conditions for temperature, sea ice cover, sunlight, and atmospheric stability are met .…”