QA0 (Quality-Assurance stage 0) is a near-real-time verification of data quality performed at the time of data taking. It reflects the quality of the calibrations included in the Scheduling Block (SB) as well as other basic parameters of the observations.
If data do not meet the QA0 criteria (e.g. by lacking a detectable calibration source) but appear to contain otherwise valid data, they are classified as "QA0 SemiPass".
Such data are not subject to QA2, in which full calibration and generation of products are done. "QA0 SemiPass" data are, however, available for download as ASDMs (raw data) from the ALMA Science Archive. For more detail on the criteria of quality assurance, please refer to the ALMA Technical Handbook, available via the Documents page in the Science Portal.
The QA0 and QA2 statuses for all archived ALMA science data are displayed for each Member ObsUnitSet (see ALMA QA2 Data Products for details, available via the Documents page in the Science Portal) on the Archive query results pages.
Note that the QA2 status only reports about whether or not the data in Member ObsUnitSet did allow to reach the PI's science goal. Therefore, it is well possible that a Member ObsUnitSet has a "QA2 pass" status although not all of the ASDMs it contains have "QA0 Pass".