Since the industrial revolution, human activities have modified climate and weather; the most
notable example is global warming caused by the emission of greenhouse gases. The formation of
condensation trails, as a result of gases resulting from combustion in jet aircraft turbines, is one of
the most visible and well-known modifications. Indeed, the high density of flights at high levels of the
troposphere facilitates the formation of these trails, depending on the environmental conditions,
which, if they persist over time, are considered anthropogenic clouds.
This work aims to study the condensation trails in the sky of Girona, from a double perspective. On
the one hand, to obtain a quantification of the frequency of this phenomenon. On the other hand, to
verify the conditions in the atmosphere that allow (or not) the formation of contrails. With these
objectives in mind, a review of the existing literature on the conditions under which these
condensation trails are produced and their effects has been carried out. An exhaustive review of the
images provided by a hemispherical vision camera of the Environmental Physics Group (GFA) of the
University of Girona, corresponding to 10 years (2013-2022), has also been carried out. Finally, these
observations have been combined, with atmospheric conditions in the upper troposphere, given by
radiosondages performed in the city of Barcelona by the Meteorological Service of Catalonia (SMC)
and with information from commercial flights that passed over Girona during some days of the year
2022.
The results indicate that a little more than one in four days, at some time of the day, condensation
trails can be observed in the sky of Girona. It is more common in winter than in summer, and in the
morning or midday than in the afternoon. On the other hand, all observations of contrails (or their
absence) correspond correctly with the passage of aircraft at levels where the environmental
conditions, given by the Schumann diagram, justify their formation (or non-existence)
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