Abstract
Abstract. Simultaneous measurements of atomic iodine (I), molecular iodine (I2) and ultrafine particles were made at O Grove, Galicia (42.50° N, 8.87° W), on the northwest coast of Spain. The observations show a strong tidal signature, and indicate that the most probable sources of reactive iodine species are the exposed macroalgae during low tide. For the first time, I2 and I were concurrently measured revealing a high average I2/I ratio of ~32, which is higher than previously inferred by modelling studies. A 1-dimensional photochemical model is employed to simulate the observations showing that the high I2/I ratio can be reproduced in the presence of fast vertical mixing close to the surface, or using an extra chemical loss for I atoms with an unknown species. There is a lack of strong correlation between the I2/I and ultrafine particles, indicating that although they both have macroalgal sources, these were not at the same location. The model simulations also suggest that the source of the observed ultrafine particles is likely not very close to the measurement site, in order for the particles to form and grow, but the source for I and I2 must be local. Finally, the effect of NOx levels on iodine oxides, and the conditions under which iodine particle bursts will be suppressed, are explored.
Highlights
Measurements of reactive iodine species (RIS) in the marine boundary layer (MBL) were initiated by the detection of iodine monoxide (IO) (Alicke et al, 1999), iodine dioxide (OIO) (Allan et al, 2001) and I2 (Saiz-Lopez and Plane, 2004)
In this paper we present the first concurrent observations of I2, I and ultrafine particles in a semi-polluted coastal environment, and use these observations to test the current knowledge of iodine chemistry
We report the first concurrent observations of I, I2 and ultrafine particles in a coastal environment, which extend the relatively small available dataset of iodine, especially in semipolluted environments
Summary
Measurements of reactive iodine species (RIS) in the marine boundary layer (MBL) were initiated by the detection of iodine monoxide (IO) (Alicke et al, 1999), iodine dioxide (OIO) (Allan et al, 2001) and I2 (Saiz-Lopez and Plane, 2004). In the coastal marine environment, emissions of I2 from exposed macroalgae, such as Laminaria digitata and Laminaria hyperborea (McFiggans et al, 2004; Ball et al, 2010), have been shown to be the main source of RIS, resulting in an anti-correlation with tidal height (Saiz-Lopez and Plane, 2004; Peters et al, 2005; Mahajan et al, 2009). Iodine-induced ultrafine particle formation has only been reported to occur in two locations so far, i.e. Mace Head, Ireland (O’Dowd et al, 2002; McFiggans et al, 2004) and Roscoff, France (McFiggans et al, 2010) where high particle concentration of >105 particles cm−3 have been observed. Mahajan et al.: Concurrent observations of atomic iodine, molecular iodine and ultrafine particles
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