Regular airborne mapping of NO2 above Berlin and Bucharest

BIRA-IASB equipped research aircraft in Germany and Romania with several versions of the in-house developed imaging instrument SWING. We used these airborne devices to produce regular mappings of the NO2 fields above Berlin and Bucharest in 2021 and 2022. These measurements reveal the urban emissions of NOx at a high spatial resolution, enabling scientists to distinguish hotspots such as power plants from the more diffuse traffic and heating sources, in order to study the yearly variations of the NOx fluxes, and to validate the TROPOMI air quality satellite.

Air pollution seen from a satellite …

NO2 is an atmospheric pollutant with direct adverse effects on human health. Through its role in atmospheric chemistry, it is also a precursor of other key air quality indicators such as surface (‘bad’) ozone and particulate matter. In mid-latitude urban areas, NO2 mainly originates from:

  • combustion engines
  • fossil fuel-based production of heat and electricity.

Due to its absorption in the visible spectrum, it is possible to remotely quantify NO2. This is done from ground, from aircraft, or from space, using the so-called DOAS (Differential Optical Absorption Spectroscopy) technique.

The DOAS method is used to produce daily global NO2 maps with the TROPOMI satellite instrument onboard the S5p satellite. Such maps shed light on the NO2 distribution at the global scale, yet the spatial resolution is coarse (5.5x3.5 km2).

Moreover, the calibration and validation of the satellite measurements are crucial for optimizing the data quality and thus for taking informed decisions to improve air quality.

… appears clearer from an aircraft

In the context of the validation of TROPOMI/S5P, BIRA-IASB developed the compact SWING instrument. This device acquires nadir UV-visible spectra, scanning the air under the aircraft perpendicularly to the flight direction, following the whiskbroom principle.

Using the same DOAS technique as TROPOMI, it also produces maps of NO2, but at a much higher spatial resolution of typically 150 m. SWING was developed for the weight and volume requirements of Unmanned Aerial Vehicles (UAVs) and is hence very compact. This eases its integration in larger manned aircraft, possibly with a set of other scientific instruments.    

We have equipped several research aircraft with in-house developed SWING-type of instruments:

  • a Cessna-207 and a motor glider from the Free University of Berlin (FUB, Germany),
  • a Britten-Norman 2 from the National Institute for Aerospace Research "Elie Carafoli” (INCAS, Romania).

In 2021 and 2022, ESA supported SWING experiments for regular airborne mappings of NO2 over Berlin (12 flights) and Bucharest (18 flights).

This unique dataset covers the four seasons. This makes it particularly valuable for TROPOMI validation but also for other applications such as the quantification of the urban NO2 flux, as the latter significantly varies across the year.

Map of NO2 12/11/2022
SWING map of NO2 from the FUB motorglider, superimposed with the TROPOMI map of the same day (12 November 2022). The higher resolution of the SWING map enables to see in particular the plume from the Reuter West power plant (northern dot).
SWING maps of NO2 over Bucharest 2021
SWING maps of NO2 from the INCAS BN-2 over Bucharest for 6 days between July and November 2021. The levels of NO2 vary with the seasons, increasing in winter due to the larger sources (heating and electricity production) and longer lifetime of NO2 at lower temperatures.