D-4 Report on the inter-comparison campaign within the BAQUNIN supersite in Rome

Third document of the ESA project WPs-2250-2251: "DOAS-BO: Towards a new FRM4DOAS-compliant site" in the frame of the QA4EO activities. This document is the report of the activities performed in the frame of WP 2251-3 of the IDEAS-QA4EO WPs-2250-2251 "DOAS-BO: Towards a new FRM4DOAS-compliant site''. The WP 2251-3 is centered on the inter-comparison campaign performed at La Sapienza University in Rome, part of the BAQUNIN supersite. In May 2021, the ISAC-CNR institute acquired (in the frame of a national funded project "Programma biennale degli investimenti del CNR") a new MAX-DOAS system, the SkySpec-2D. This system took part in several FRM4DOAS inter-comparison campaigns (e.g., CINDI) and full fills all the FRM4DOAS requirements. The SkySpec-2D final destination is the San Pietro Capofiume (BO) "Giorgio Fea" ISAC-CNR observatory in the Po Valley. Due to its full compliance with FRM4DOAS requirements and its more advanced technology, we decided to use the SkySpec-2D instrument instead of the TROPOGAS for the BAQUNIN campaign. However, before traveling to Rome, the SkySpec-2D was employed in an inter-comparison campaign with the TROPOGAS instrument in Bologna, in order to compare the performances of the two MAX-DOAS systems in the same conditions. In this report, we briefly describe the SkySpec-2D system and report the results of the Bologna and BAQUNIN inter-comparison campaigns.