ARGONAUT

Due to the large industrialization and urbanization, Air Quality (AQ) has been degraded worldwide, leading to more than 7 million premature deaths annually and Climate Change (CC) is becoming a reality with the five warmest years measured in the 2010s. The society is facing major environmental challenges: developing coordinated monitoring and mitigation strategies leading to optimal reduction of both AQ and CC impacts. Providing a response at the finer scale of territories is also critical to ensure efficient reduction policies. The primary objective of ARGONAUT is to provide new estimates of French anthropogenic emissions of the main AQ pollutants (nitrogen oxides - NOx, carbon monoxide - CO and non-methane volatile organic compounds - NMVOCs) and carbon dioxide (CO2) at high resolution, based on the atmospheric inversion and the last generation of satellites (Sentinel-5P/TROPOMI, CO2M). We will exploit the multiple-species high resolution imaging to exploit the local correlations between the various species and co-assimilate them to better constrain their emission estimates. Indeed, information on jointly observed pollutants, such as nitrogen dioxide (NO2) and CO, which have a long history of measurement from space, will add an additional valuable constraint on the emission inversion of co-emitted species that are more difficult to measure to useful levels, such as CO2 and NMVOCs. Highly resolved images are essential in this context to reveal the high correlation between the concentrations of different species locally, and then to clearly separate the anthropogenic sources, to quantify their emissions and to monitor their temporal evolution. Making a step forward in the joint assimilation of relevant pollutants and CO2 together, and addressing the correlation between them, will improve the emission inventories and their consistency across species and, more generally, should help addressing AQ and CC related emissions at the national to subnational scales. With the recent availability of TROPOMI colocalized images of NO2, CO and formaldehyde (HCHO), and in the future of CO2 and NO2 from CO2M, implementing such an approach becomes possible, as will be explored by ARGONAUT. ARGONAUT will put efforts to develop a highly sophisticated inverse modeling system, able to benefit from this high resolution imaging at the national level. A parallel objective of the project is to demonstrate the potential for addressing the city/plant scale with a zoom or dedicated systems downstream the national scale inversion. This bears additional challenges, because it requires the modeling and inversion systems to match the local fine scale atmospheric plumes from these sources despite a high and complex uncertainty in the meteorological simulation at this scale. Traditional atmospheric inversion techniques, which assume that transport modeling errors can be summarized as a statistical noise that has no temporal or spatial correlations are not adapted to tackle such a challenge. To overcome this issue and make the emission inversions much more reliable, we propose in the ARGONAUT project to move from classical statistical indicators to new non-local metrics. Finally, the project aims at quantifying the added value of atmospheric inversion approaches constrained by the assimilation of satellite images and of the derived optimized emission inventories in downstream operational products such as AQ forecasts or exposure assessments, and local CO2 emission monitoring. ARGONAUT will contribute (i) to define the potential elementary components for such a future national operational system and/or downstream services, and (ii) to consolidate the visibility and position of the French scientific community of inverse modeling as key players for satellite-based European operational services.