Monitoring air quality and the impact of environmental policies at the needed scales
Processes controlling Air Quality (AQ) cover a wide range of scales, from point-like emissions to intercontinental transport, and so do the regulations enacted by public authorities to manage air quality over their domain of legal competence. AQ monitoring has been hitherto relying mostly on in-situ measurements of surface concentration, with geographical gaps between observations filled in with numerical modelling.
New generation satellite sounders on sun-synchronous Low Earth Orbits (LEO) – like the Copernicus Sentinel-5(p) series started in 2017 – perform now daily global mapping of air pollution down to the 3-km scale.
Soon this daily global mapping will be complemented with geostationary instruments (GEO) observing the diurnal cycle of pollutants, although over the limited geographical area accessible from a geostationary viewpoint: European AQ will be observed hourly by the Sentinel-4 satellites, while other GEO sounders will point to North-America and East-Asia.
Key challenges to realize the full potential of the Air Quality satellite constellation
To realize the full potential of the constellation of LEO and GEO satellites being assembled, and to make their observations fit-for-purpose for air quality applications at the different scales, several challenges need to be addressed, among others:
- Enhance to sub-city scales the resolution of satellite data, typically from 3-4 km down to 1 km, to make them better suited for the monitoring of e.g. the Low Emission Zones enforced in several Belgian cities,
- Determine the non-trivial relation between the column amount of pollutant measured by a satellite and the surface concentration measured by in-situ networks,
- Determine how the different LEO and GEO vantage points lead to a different perception of atmospheric and surface details and how we can benefit from or correct for these differences.
LEGO-BEL-AQ: Pioneering an integrated LEO+GEO AQ monitoring system for Belgium
Funded by the Belgian Federal Science Policy Office under the BRAIN-Be 2.0 programme, and carried out in collaboration with IRCEL-CELINE, the LEGO-BEL-AQ project (for Low-Earth and Geostationary Observations of BELgian Air Quality) pioneers the synergistic use of the Copernicus LEO+GEO AQ Sentinels in support of Belgian air quality policies.
Figure 1 illustrates over the Brussels area the sub-city scale capacity of the system by showing contrasts in nitrogen dioxide (NO2) between the summers of 2019 and 2020. Further particulars and illustrations are available on the LEGO-BEL-AQ project website at https://lego-bel-aq.aeronomie.be.