A twenty year record of greenhouse gases in the Eastern Mediterranean atmosphere.

ABSTRACT

Twenty years of CO2, CH4 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. CO2 concentrations increase by 2.4 ppm·y-1 since 2002, in agreement with the general north hemisphere trend as derived by worldwide NOAA observations. CH4 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 CO2 and CH4 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 CH4 and CO agree with a 24-h mean OH radical concentration of the order of 0.3-1 × 107 molecules·cm-3 over the region, in general agreement with the only existing in-situ observations at Finokalia for 2001.