The objectives of the S5PVAL-TRANS campaign are twofold:
1) Testing a different S-5p airborne validation strategy based on transect flights instead of mapping flights. In contrast to mapping flights with airborne imaging systems, consisting of many adjacent flight lines over a certain industrial or urban hotspot, a transect flight consists of a set of segments or straight lines with major sources of NO2 (and HCHO and SO2) as waypoints. Instead of mapping one complete city or industrial area and its plumes, a transect flight can target many different hotspots and background areas. However, just a part of its emissions are captured during one overpass due to the restricted field-of view of airborne imagers. Transect flights allow that more S-5p/TROPOMI pixels can be covered during a flight, and subsequently more pixels can be intercompared for validation purposes. However, the TROPOMI pixels will be undersampled to a certain extent, leading to the issue of spatial representativeness. The (dis-)advantages of this flight strategy will be tested when compared to mapping flights and also the impact of undersampling the TROPOMI pixels will be assessed.
2) Validation of the TROPOMI HCHO product based on airborne SWING and AirMAP mapping. The TROPOMI HCHO product (as well as anthropogenic SO2) is challenging to validate based on daily airborne flights as atmospheric concentrations are typically low. Both the satellite and airborne observations are usually close to the detection limit and contain high noise. To increase the HCHO signal, acquisitions will be performed over some of the strongest HCHO hotspots in Europe during the summer period with airborne imaging systems with a high SNR.
Both the Bremen AirMAP instrument and a thermally stabilised version of SWING+ will be deployed from the FUB Cessna T207A D-EAFU over selected regions in the Po Valley in Summer 2022 or 2023. Several major NO2 and HCHO hotspots have been identified in TROPOMI data in this area.
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Nowlan, C. R., Liu, X., Janz, S. J., Kowalewski, M. G., Chance, K., Follette-Cook, M. B., Fried, A., González Abad, G., Herman, J. R., Judd, L. M., Kwon, H.-A., Loughner, C. P., Pickering, K. E., Richter, D., Spinei, E., Walega, J., Weibring, P., and Weinheimer, A. J.: Nitrogen dioxide and formaldehyde measurements from the GEOstationary Coastal and Air Pollution Events (GEO-CAPE) Airborne Simulator over Houston, Texas, Atmos. Meas. Tech., 11, 5941–5964, https://doi.org/10.5194/amt-11-5941-2018, 2018.