Tropospheric OH and Cl levels deduced from non-methane hydrocarbon measurements in a marine site
1Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, 71003 Heraklion, Greece
2Inorganic and Analytical Chemistry Department, Faculty of Chemistry, Al.I Cuza University of Iasi, 700506 Iasi, Romania
3Laboratoire des Sciences du Climat et de l'Environnement, CNRS/CEA, 91191 Gif-sur-Yvette Cedex, France
Abstract. In situ continuous hourly measurements of C2–C8 non-methane hydrocarbons (NMHCS) have been performed from March to October 2006 at two coastal locations (natural and rural) on the island of Crete, in the Eastern Mediterranean. Well defined diel variations were observed for several short lived NMHCS (including ethene, propene, n-butane, n-pentane, n-hexane, 2-methyl-pentane). The daytime concentration of hydroxyl (OH) radicals estimated from these experimental data varied from 1.3×106 to ~4.0×106 radical cm−3, in good agreement with box-model simulations. In addition the relative variability of various hydrocarbon pairs (at least 7) was used to derive the tropospheric levels of Cl atoms. The Cl atom concentration has been estimated to range between 0.6×104 and 4.7×104 atom cm−3, in good agreement with gaseous hydrochloric acid (HCl) observations in the area. Such levels of Cl atoms can be of considerable importance for the oxidation capacity of the troposphere on a regional scale.