10.26165/JUELICH-DATA/GK7PJQ Cho, Changmin0000-0002-5977-2705(Forschungszentrum Jülich GmbH, IEK-8)Hofzumahaus, Andreas0000-0003-2876-0880(Forschungszentrum Jülich GmbH, IEK-8)Fuchs, Hendrik0000-0003-1263-0061(Forschungszentrum Jülich GmbH, IEK-8)Dorn, Hans-Peter0000-0001-5945-7708(Forschungszentrum Jülich GmbH, IEK-8)Glowania, Marvin0000-0001-5434-531X(Forschungszentrum Jülich GmbH, IEK-8)Holland, Frank0000-0002-2278-4761(Forschungszentrum Jülich GmbH, IEK-8)Rohrer, Franz0000-0003-3436-3419(Forschungszentrum Jülich GmbH, IEK-8)Vardhan, Vaishali(Forschungszentrum Jülich GmbH, IEK-8)Kiendler-Scharr, Astrid0000-0003-3166-2253(Forschungszentrum Jülich GmbH, IEK-8)Wahner, Andreas0000-0001-8948-1928(Forschungszentrum Jülich GmbH, IEK-8)Novelli, Anna0000-0003-2077-7573(Forschungszentrum Jülich GmbH, IEK-8) Jülich DATA 2021 Laser-induced fluorescence (LIF) is a widely used technique for the measurement of ambient hydroxyl (OH) radicals and was used for the majority of field campaigns and chamber experiments. Recently, most LIF instruments in use for atmospheric measurements of OH radicals introduced chemical modulation to separate the ambient OH radical concentration from possible interferences by chemically removing ambient OH radicals before they enter the detection cell. This data contains the application and characterization of a chemical modulation reactor (CMR) applied to the Forschungszentrum Jülich LIF (FZJ-LIF) instrument in use at the SAPHIR (Simulation of Atmospheric PHotochemistry In a Large Reaction Chamber) atmospheric simulation chamber. Besides dedicated experiments in synthetic air, the new technique was extensively tested during the yearround Jülich Atmospheric Chemistry Project (JULIAC) campaign, in which ambient air was continuously flowed into the SAPHIR chamber. The four files include measurements during winter, spring, summer and fall 2019. Fuchs, Hendrik(Forschungszentrum Jülich GmbH, IEK-8)