Abstract
Abstract. This paper presents a summary of the measurements made during the heavily-instrumented Reactive Halogens in the Marine Boundary Layer (RHaMBLe) coastal study in Roscoff on the North West coast of France throughout September 2006. It was clearly demonstrated that iodine-mediated coastal particle formation occurs, driven by daytime low tide emission of molecular iodine, I2, by macroalgal species fully or partially exposed by the receding waterline. Ultrafine particle concentrations strongly correlate with the rapidly recycled reactive iodine species, IO, produced at high concentrations following photolysis of I2. The heterogeneous macroalgal I2 sources lead to variable relative concentrations of iodine species observed by path-integrated and in situ measurement techniques. Apparent particle emission fluxes were associated with an enhanced apparent depositional flux of ozone, consistent with both a direct O3 deposition to macroalgae and involvement of O3 in iodine photochemistry and subsequent particle formation below the measurement height. The magnitude of the particle formation events was observed to be greatest at the lowest tides with the highest concentrations of ultrafine particles growing to the largest sizes, probably by the condensation of anthropogenically-formed condensable material. At such sizes the particles should be able to act as cloud condensation nuclei at reasonable atmospheric supersaturations.
Highlights
Research into marine atmospheric halogens has recently focused on two major implications: i) participation of reactive halogen species in catalytic ozone destruction cycles including heterogeneous reaction in or on seasalt aerosol and ii) the formation of new aerosol particles in the coastal boundary layer and their potential to act as cloud condensation nuclei (CCN)
The sampling inlet for NO and NO2 was on the same mast as the CMAX-differential optical absorption spectroscopy (DOAS) instrument and, at 3.5 m, at the same height as the IO measurement by Laser Induced Fluorescence (LIF)
This location ensured that when the wind was from 90 to 270◦it was crossing the town of Roscoff before being sampled and from all other directions, the air had not passed over the town but came directly from the sea
Summary
Research into marine atmospheric halogens has recently focused on two major implications: i) participation of reactive halogen species in catalytic ozone destruction cycles including heterogeneous reaction in or on seasalt aerosol and ii) the formation of new aerosol particles in the coastal boundary layer and their potential to act as cloud condensation nuclei (CCN). Whilst the primary source of inorganic chlorine and bromine species in the remote MBL is likely to be their release from the significant seasalt halide reservoir in atmospheric aerosol, the direct emission of organic precursors (Carpenter et al, 1999, 2000) from intertidal macroalgal species (Palmer et al, 2005) has been well established and will contribute significantly to the coastal atmospheric burden of RHS. Halocarbons ( iodocarbons) were shown to exhibit a tidal signature, with enhanced low tide abundances This might be expected following macroalgal exposure at low tide. The self-reaction of IO yields OIO; the reaction with HO2 and NO2 yielding HOI and IONO2 respectively The latter two compounds may be taken up by aerosol particles, releasing the dihalogen species IBr, ICl or I2 on aqueous reaction with available Br−, Cl− or I− respectively in the presence of sufficient acidity
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