Biogenic iodine emissions and identification of end‐products in coastal ultrafine particles during nucleation bursts

Abstract

[1] Ultrafine particles sampled during new particle formation bursts observed in the coastal zone were studied with transmission electron microscopy (TEM) and elemental analysis using energy-dispersive X ray (EDX). It was observed that both iodine and sulphur were present in the new particles with diameter below 10 mn. Gaseous emissions of halogen compounds from seaweeds were also measured at the same location during low-tide particle nucleation episodes. Based on the presence of iodine in the particle phase during low-tide nucleation bursts, and the significant emission of iodine compounds from the seaweeds during these periods, it is apparent that part of the biogenic iodine species emitted from the seaweeds end up in the ultrafine particulate phase. It was not possible to quantitatively determine the iodine content in the particles; however, in most cases the relative contribution from iodine and sulphate was similar, while some cases indicated no sulphate. On larger sized particles the contribution of sulphate was significantly higher than iodine. It appears that the condensable species leading to the appearance of new particles in the coastal atmosphere is an iodine species. Whether or not this iodine species also participates in the nucleation of new stable clusters could not be completely verified.

Marine particle nucleation: Observation at Bodega Bay, California

“…We have deduced previously that the nucleation precursor and nucleation processes occur near the coast only, so it is unlikely that sulfuric acid is the precursor. Field measurements at Mace Head, Ireland, and lab studies indicate that CH 2 I 2 [Makela et al, 2002;Hoffmann et al, 2001;Jimenez et al, 2003] or I 2 [Saiz-Lopez and Plane, 2004;McFiggans et al, 2004] out gassed from the ocean may be precursors for nucleation.…”

“…[16] The studies at Mace Head, Ireland [Makela et al, 2002], show that iodine species could be the precursor species leading to the new particle formation in the coastal atmosphere. The results presented here, though insufficient to pinpoint a chemical species, nevertheless suggest that nucleation is correlated to the coastal biogenic activity.…”

Marine Organic Halide and Isoprene Emissions Near Mace Head, Ireland

“…[7,8] The absorbent collection and analysis techniques are similar to those used previously to measure alkyl halides at MH. [3] Samples volumes were of the order of 6 L. Compounds routinely monitored for this experiment included CH 3 CH 2 Br, CH 3 CH 2 I, CH 2 Br 2 , CH 2 ICl, CH 2 BrI, CHBr 3 , CH 2 I 2 , isoprene, and monoterpenes.…”

“…However, in coastal areas, sulfuric acid does not correlate with new particle formation or tidal cycles. [1,2] The measurement of iodine in the ultrafine particle composition [3] during coastal nucleation events has focused attention on organic and inorganic emissions from seaweed as potential iodine sources. Molecular iodine [4] and CH 2 I 2 [5] are likely precursors, since they rapidly photolyze to give iodine atoms, which are converted to the IO radical by reaction with ozone.…”

“…IO is further oxidized to higher iodine oxides which are less volatile and can either condense on pre-existing stable clusters or form new particles. [5] Macroalgae emissions of alkyl iodides were measured at Mace Head, Ireland [3] from enclosures of several species, but the plant-level emissions were not extrapolated to an area source. Other possible sources were not identified.…”