Tropospheric OH and Cl levels deduced from non-methane hydrocarbon measurements in a marine site

Abstract

Abstract. In situ continuous hourly measurements of C 2 -C 8 non-methane hydrocarbons (NMHC S ) 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 NMHC S (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 1.3×10 6 to ∼4.0×10 6 radical cm −3 , in good agreement with boxmodel 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 0.6×10 4 and 4.7×10 4 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.

A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation

“…A recent study reported similar Cl concentrations in the marine boundary layer (e.g. Arsene et al, 2007). Including Cl chemistry at those levels leads to a decrease of 4‰ in the isotopic composition of the H 2 reservoir whereas the contribution of O 1 D oxidation was found to be negligible.…”

The significance of atmospheric inputs of soluble and particulate major and trace metals to the eastern Mediterranean seawater

“…Apart from the main sampling site at Finokalia, wet deposition samples were also collected at a secondary station situated at the University of Crete, 6 km south of Heraklion (35°20′N, 25°07′E). Further description of the site and the prevailing meteorology can be found in Arsene et al (2007). The sediment traps were moored for seven years (1999)(2000)(2001)(2002)(2003)(2004)(2005) in the southern Cretan Sea (along 45°06′E, 500 m and 1715 m depth, Kouvarakis et al, 2001).…”

Chlorine activation by N<sub>2</sub>O<sub>5</sub>: simultaneous, in situ detection of ClNO<sub>2</sub> and N<sub>2</sub>O<sub>5</sub> by chemical ionization mass spectrometry

“…While Cl-atoms have not been directly observed, labile sources in addition to ClNO 2 , such as Cl 2 , have been observed (Spicer et al, 1998). Regionally averaged Cl abundances have been inferred from observational analyses of hydrocarbons (Arsene et al, 2007;Cavender et al, 2008), but due to the limited spatial and temporal coverage of such measurements, the global Cl-atom source term remains largely unconstrained (Platt et al, 2004). Second, since ClNO 2 is not a terminal NO x sink, production via N 2 O 5 heterogeneous reaction represents a reduction, by as much as 50%, in the amount of NO x removed during night by NO 3 and N 2 O 5 chemistry, effectively enhancing the NO x -lifetime because Reaction (R8) ultimately returns one NO x .…”