This study focuses on broadening the knowledge of a fluorometric index to improve the detection of oil substances present in the marine environment. It is assumed that the value of this index will provide information about a possible oil discharge at some distance from the sensor. In this paper, the detection of oil present in seawater as a mixture of oils such as fuel, lubricate oil, or crude oil based on a fluorescence indicator-fluorometric index (FIo/w) is discussed. FIo/w was defined based on specific excitation and emission wavelengths coming from the obtained excitation-emission spectrum (EEM) of oil-free seawater and, in parallel, the same water but artificially polluted with oil. For this, measurements of a mixture of oils in seawater for an oil-to-water ratio in the range from 50 × 10-9 to 200 × 10-9 as well as oil-free seawater were performed. Laboratory measurements continued five times in months in the summer season with the coastal waters of the southern Baltic Sea (last spring, summer, and early autumn). The dependence of FIo/w on the presence of oil in seawater, the oil-in-water ratio, as well as months of the considered season has been demonstrated.
Keywords: excitation–emission spectra; fluorometric index; oil detection; oil fluorescence; oil pollution in seawater; seawater fluorescence.