This dataset collects ACTRIS/EARLINET data collected during the Jan-May 2020 period expect for the May 2020 special measurement campaign (for those data and for having the complete coverage of the Jan-May 2020 we invite to use both the datasets).

The January-May 2020 dataset is based on measurements performed and processed at the individual stations, with standard operation procedures. Measurements are collected following the EARLINET schedule (three times per week: Monday around local noon; Monday after local sunset; Thursday after local sunset).

Data is processed in a decentralized way by each station, using their own algorithms or the Single Calculus Chain (SCC), and submitted to the EARLINET/ACTRIS database. Quality Control procedures are applied automatically on the data during the submission of the data to the EARLINET/ACTRIS database (https://www.earlinet.org/index.php?id=293).

Data is classified as Level 1 and Level 2 data. Level 2 data is compliant to all the QC procedures currently working on the ACTRIS/EARLINET database. Level 1 data is data of lower quality since they fail at least 1 of the advanced quality controls running on the ACTRIS/EARLINET database. Particular attention should be paid using Level 1 data.