ALBERT

Description: [1]  Observations of gas-phase iodine species were made during a field campaign in the Eastern Pacific marine boundary layer (MBL). The Climate and HAlogen Reactivity tropicaL EXperiment (CHARLEX) in the Galápagos Islands, running from September 2010 to present, is the first long-term ground-based study of trace gases in this region. Observations of gas-phase iodine species were made using Long Path Differential Optical Absorption Spectroscopy (LP-DOAS), Multi-axis DOAS (MAX-DOAS) and Resonance and Off-resonance Fluorescence by Lamp Excitation (ROFLEX). These measurements were supported by ancillary measurements of ozone, nitrogen oxides and meteorological variables. Selective halocarbon and ultrafine aerosol concentration measurements were also made. [2]  MAX-DOAS observations of iodine monoxide (IO) display a weak seasonal variation. The maximum differential slant column density was 3.8 × 10 13 molecule cm -2 (detection limit ~7 × 10 12 molecule cm -2 , or ~0.8 pptv). The seasonal variation of reactive iodine IO x (= I + IO) is stronger, peaking at 1.6 pptv during the warm season (February-April). This suggests a dependence of the iodine sources on the annual cycle in sea surface temperature, although perturbations by changes in ocean surface iodide concentration and solar radiation are also possible. An observed negative correlation of IO x with Chlorophyll indicates a predominance of abiotic sources. The low IO mixing ratios measured are not consistent with satellite observations, if IO is confined to the MBL. The IO x loading is consistent with the observed absence of strong ozone depletion and nucleation events, indicating a small impact of iodine chemistry on these climatically relevant factors in the Eastern Pacific MBL.