QA4EO DOAS-BO: Towards a new FRM4DOAS site in the Po Valley

Pollutant gases information can be retrieved from ground-based and satellite visible and UV spectra, exploiting the Differential Optical Absorption Spectroscopy (DOAS) technique. The validation of the satellite NO2 tropospheric column shows the particular importance that should be given to measurements acquired in polluted regions. As the Po Valley (Italy) is one of these regions, it often experiences very high NO2 concentrations due to industrial, agriculture and urban activities and to the fact that the surrounding mountains protect the valley from winds that might otherwise disperse such pollution plumes. Despite this, an instrument compliant with the Fiducial Reference Measurements for Ground-Based DOAS (FRM4DOAS) standards is not yet present in Po Valley. Hence, the purpose of the DOAS-BO WPs within the QA4EO ESA project, that we will present, is to make a step to close this gap. We started using an existing custom spectrometer, named TROPOGAS and located in Bologna, that exploits the heritage of CNR-ISAC in spectrometers development. It operated with a measurement configuration that is as much as possible compliant with FRM4DOAS requirements. We assessed the performances of the TROPOGAS spectrometer during a measurement campaign held in Bologna at CNR-ISAC premises. The campaign focused on the evaluation of the synergies between ground-based remote sensing, in-situ near-surface (NOx Chemilunescence analyzer) and satellite data (TROPOMI). A second campaign, to inter calibrate the TROPOGAS with other ground-based instruments (i.e., PANDORSA 2S spectrometer, Brewer spectrophotometer), was foreseen within the Boundary-layer Air Quality-analysis Using Network of Instrument (BAQUNIN) supersite located in Rome. Recently the CNR-ISAC acquired two SkySpec2D spectrometers. One will be located at the CNR-ISAC Rome Atmospheric obServatory (CIRAS) and the other one at the San Pietro Capofiume (SPC) "Giorgio Fea" station. This type of instrument is fully compliant with FRM4DOAS requirements. For this reason, after an inter comparison with the TROPOGAS, the SkySpec2D of SPC will be used for the BAQUNIN campaign. The objectives of the QA4EO DOAS-BO WPs are to demonstrate the importance of the DOAS measurements in the Po Valley, re-enforce the Italian know-how on Multi-Axis (MAX)-DOAS technique and go towards the provision of standardized data for validation networks.