Iodine-mediated coastal particle formation: an overview of the Reactive Halogens in the Marine Boundary Layer (RHaMBLe) Roscoff coastal study
1Centre for Atmospheric Sciences, School of Earth, Atmospheric & Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
2School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK
3Department of Chemistry, University of Leicester, Leicester, LE1 7RH, UK
4School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
5Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
6Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
7National Centre for Atmospheric Sciences, University of Manchester, Manchester, M13 9PL, UK
8Station Biologique, Université Pierre et Marie Curie-Paris 6 CNRS UMR 7139, Roscoff, France
9National Centre for Atmospheric Sciences, University of York, Heslington, York, YO10 5DD, UK
10School of Environmental Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, UK
11National Centre for Atmospheric Sciences, University of Leeds, Leeds, LS2 9JT, UK
*now at: School of Geography, Earth Environmental Sciences, Univ. of Birmingham, Edgbaston, Birmingham, B152TT, UK
†sadly passed away 28 July 2009
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.