DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) is a research campaign that took place from mid November to mid December at the atmospheric research station "El Arenosillo" operated by INTA (National Institute for Aerospace Technology, Spain). A complete suite of measurements needed to study the oxidation chemistry in ambient air has been conducted by an international team of scientists. The "El Arenosillo" station is located in the nature preserve Parque Natural del Entorno de Doñana near the cities of Seville and Huelva in Spain. The focus of this special issue is the study of atmospheric oxidation chemistry based on the data from the DOMINO campaign during the entire diel cycle, dominated by OH radicals during daytime and NO₃ radicals during nighttime, in air masses of various origins. A predominant wind direction during this time of year is from the northeast, transporting air from Seville (ca. 70 km distance) over the pine and eucalyptus forests in the national park. Air from the northwest transported fresher industrial and urban emissions from the city of Huelva (ca. 25 km), while air from southwesterly directions was of relatively clean marine origin.