Twenty years of CO 2 , CH 4 and CO greenhouse gas atmospheric concentration measurements at Finokalia station on Crete in the Eastern Mediterranean region are presented. This dataset is the longest in the Eastern Mediterranean, based on bi-weekly grab sampling since 2002 and continuous observations since June 2014. CO 2 concentrations increase by 2.4 ppm·y -1 since 2002, in agreement with the general north hemisphere trend as derived by worldwide NOAA observations. CH 4 showed a mean increasing trend of 7.5 ppb·y -1 since 2002, a rate that has accelerated since 2018 (12.4 ppb·y -1 ). In contrast, CO has decreased by 1.6 ppb·y -1 since 2002, which resulted from a strong decrease until 2017 (2.5 ppb·y -1 ), followed by a small increase in the last 3 years (0.2 ppb·y -1 ). Both CO 2 and CH 4 present maxima during winter and minima during summer, in general agreement with the observations at the ICOS stations in Europe. CO also presents the highest values in winter and the lowest values in summer during June, while a secondary maximum is seen in August, which can be attributed to open fires that often occur in the area during this period. The mean summertime diurnal cycles of CH 4 and CO agree with a 24-h mean OH radical concentration of the order of 0.3-1 × 10 7 molecules·cm -3 over the region, in general agreement with the only existing in-situ observations at Finokalia for 2001.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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