Reactive iodine species in a semi‐polluted environment

Abstract

[1] Iodine chemistry in the marine boundary layer has attracted increasing attention over the last few years because iodine oxides cause ozone destruction, change the atmospheric oxidising capacity, and can form ultrafine particles. However, the chemistry of iodine in polluted environments is not well understood: its effects are assumed to be inhibited by reactions involving NO x (NO 2 & NO). This paper describes Differential Optical Absorption Spectroscopy (DOAS) observations of iodine species (I 2 , OIO and IO) and the nitrate radical (NO 3 ) at a semi-polluted coastal site in Roscoff, France. Significant concentrations of IO and I 2 were measured during daytime, indicating efficient recycling of iodine from iodine nitrate (IONO 2 ). I 2 , IO, OIO and NO 3 were observed at night. These observations are interpreted using a one dimensional model to demonstrate that iodine plays an important role even in polluted environments due to recycling mechanisms not considered previously.

Coastal measurements of short-lived reactive iodocarbons and bromocarbons at Roscoff, Brittany during the RHaMBLe campaign

“…It is apparent that due to its very short photolytic lifetime (see Table 3) and yield of 2 I atoms per molecule photolysed, CH 2 I 2 accounts for the majority of I atom production from dihalomethane photolysis, even though gure 7. it was present in lower concentrations than CH 2 IBr and CH 2 ICl. We calculate a combined average midday (11 a.m.-2 p.m. local time) I atom flux from dihalomethanes of around 4.7×10 3 molecules cm −3 s −1 , which is considerably lower than the rate of I atom production from photolysis of I 2 , which we estimate to be roughly 7×10 7 molecules cm −3 s −1 (based on a mean I 2 concentration between 11 a.m. and 2 p.m. of 13 ppt, determined by long path DOAS measurements during the RHaMBLe campaign at Roscoff, Mahajan et al, 2009). Due to the rapid removal of photolabile I atom precursors during the daytime (photolysis lifetimes were ∼10 s and ∼4 min for I 2 and CH 2 I 2 respectively, see Table 3) it is likely that a significant fraction of these trace gases would have been removed before the point of measurement ).…”

“…Due to the rapid removal of photolabile I atom precursors during the daytime (photolysis lifetimes were ∼10 s and ∼4 min for I 2 and CH 2 I 2 respectively, see Table 3) it is likely that a significant fraction of these trace gases would have been removed before the point of measurement ). As such, it may be appropriate to use average night time concentrations in conjunction with midday photolysis rate constants to estimate upper limit I atom fluxes from these species, which would increase the I atom flux from I 2 to ∼3×10 8 molecules cm −3 s −1 (assuming an average nocturnal mixing ratio of 60 ppt, Mahajan et al, 2009). However, the same approximation cannot be made for the iodocarbons, since this assumes a constant emission rate between day and night, and the maximum observed concentrations of the dihalomethanes typically coincided with daytime low tide (see Fig.…”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…may increase ozone depletion by up to 60 % (Mahajan et al, 2009). The interaction between iodine and ozone also leads to the formation of ultra-fine particles under certain conditions (e.g.…”

In situ measurements of molecular iodine in the marine boundary layer: the link to macroalgae and the implications for O<sub>3</sub>, IO, OIO and NO<sub>x</sub>

“…To date the only unambiguous daytime OIO measurements is made in the Gulf of Maine (Stutz et al, 2007). At Mace Head (Peters et al, 2005;Saiz-Lopez et al, 2006a), Cape Grim (Allan et al, 2001), and Roscoff (Mahajan et al, 2009), OIO has been observed during the nighttime but never in the daytime.…”