Preprints
https://doi.org/10.5194/egusphere-2023-1059
https://doi.org/10.5194/egusphere-2023-1059
05 Jun 2023
 | 05 Jun 2023

To new heights by flying low: Comparison of aircraft vertical NO2 profiles to model simulations and implications for TROPOMI NO2 retrievals

Tobias Christoph Valentin Werner Riess, Klaas Folkert Boersma, Ward Van Roy, Jos de Laat, Enrico Dammers, and Jasper van Vliet

Abstract. The sensitivity of satellites to air pollution close to the sea surface is decreased by scattering of light in the atmosphere and low sea surface albedo. To reliably retrieve tropospheric nitrogen dioxide (NO2) columns using the TROPOspheric Monitoring Instrument (TROPOMI), it is therefore necessary to have good a priori knowledge of the vertical distribution of NO2. In this study, we use an aircraft of the Royal Belgian Institute of Natural Sciences, which was already equipped with a sniffer sensor system, measuring NOx (= NO + NO2), CO2 and SO2. This instrumentation enables us to evaluate vertical profile shapes from several chemical transport models and to validate TROPOMI tropospheric NO2 columns over the polluted North Sea in the summer of 2021.We observe multiple clear signatures of ship plumes from seconds after emission to multiple kilometers downwind. Besides that, our results show that the chemical transport model TM5-MP, which is used in the retrieval of the operational TROPOMI NO2 data, tends to underestimate surface level pollution while overestimating NO2 at higher levels over the study region. The higher horizontal resolution in the regional CAMS ensemble mean and LOTOS-EUROS model improve the surface level pollution estimates, but the models still systematically overestimate NO2 levels at higher altitudes, indicating exaggerated vertical mixing in the models over the North Sea. When replacing the TM5 a priori NO2 profiles with the aircraft-measured NO2 profiles in the air mass factor (AMF) calculation, we find smaller recalculated AMFs. Subsequently, the retrieved NO2 columns increase by 20 %, indicating a significant negative bias in the operational TROPOMI NO2 data product (up to v2.3.1) over the North Sea. This negative bias has important implications for estimating emissions over the sea. While TROPOMI NO2 negative biases caused by the TM5 a priori profiles have also been reported over land, the reduced vertical mixing and smaller surface albedo over sea makes this issue especially relevant over sea and coastal regions.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Share

Journal article(s) based on this preprint

08 Nov 2023
To new heights by flying low: comparison of aircraft vertical NO2 profiles to model simulations and implications for TROPOMI NO2 retrievals
Tobias Christoph Valentin Werner Riess, Klaas Folkert Boersma, Ward Van Roy, Jos de Laat, Enrico Dammers, and Jasper van Vliet
Atmos. Meas. Tech., 16, 5287–5304, https://doi.org/10.5194/amt-16-5287-2023,https://doi.org/10.5194/amt-16-5287-2023, 2023
Short summary
Download

The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
Satellite retrievals of trace gases require prior knowledge of the vertical distribution of the...
Share