Impact of halogen monoxide chemistry upon boundary layer OH and HO₂ concentrations at a coastal site

Abstract

[1] The impact of iodine oxide chemistry upon OH and HO 2 concentrations in the coastal marine boundary layer has been evaluated using data from the NAMBLEX (North Atlantic Marine Boundary Layer Experiment) campaign, conducted at Mace Head, Ireland during the summer of 2002. Observationally constrained calculations show that under low NO x conditions experienced during NAMBLEX (NO 50 pptv), the reaction IO + HO 2 ! HOI + O 2 accounted for up to 40% of the total HO 2 radical sink, and the subsequent photolysis of HOI to form OH + I comprised up to 15% of the total midday OH production rate. The XO + HO 2 (X = Br, I) reactions may in part account for model overestimates of measured HO 2 concentrations in previous studies at Mace Head, and should be considered in model studies of HO x chemistry at similar coastal locations.Citation: Bloss, W. J., et al. (2005), Impact of halogen monoxide chemistry upon boundary layer OH and HO 2 concentrations at a coastal site, Geophys. Res. Lett., 32, L06814,

Peroxy radical chemistry and the control of ozone photochemistry at Mace Head, Ireland during the summer of 2002

“…OH and HO 2 model/measurement comparisons are reported in Smith et al (2006), Sommariva et al (2006a) and nighttime HO 2 and RO 2 in Sommariva et al (2006b). Model results at NAMBLEX for HO 2 were in much better agreement with the measurements when the model was additionally constrained to measured halogen oxides (Sommariva et al, 2006a;Bloss et al, 2005c).…”

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

“…The introduction of halogen chemistry, using differential optical absorption spectroscopy (DOAS) measurements of BrO and IO (Saiz-Lopez et al, 2006) to constrain the model, increased the modelled OH concentrations by up to 15 % and decreased HO 2 by up to 30 % owing to reactions of HO 2 with XO radicals to form HOX which subsequently photolysed to X + OH . Bloss et al (2005a) indicated that up to 40 % of the instantaneous HO 2 loss could be attributed to HO 2 + IO, and that photolysis of HOI was responsible for 15 % of the noontime OH production.…”

“…In general, observationally constrained box model simulations suggest that halogens in the troposphere will increase OH concentrations, primarily because of a change in the HO 2 to OH ratio occurring as a result of reactions of halogen oxides (XO) with HO 2 to produce a hypohalous acid (HOX) which photolyses to give an OH radical and a halogen atom (Kanaya et al, 2002(Kanaya et al, , 2007Bloss et al, 2005a;Sommariva et al, 2006Sommariva et al, , 2007Whalley et al, 2010). Other impacts on the HO x photochemical system are observed (impacts from changes to NO x chemistry etc.…”

“…Observations of BrO and IO radicals within the MBL have demonstrated widespread impacts on atmospheric composition and chemistry (Alicke et al, 1999;Sander et al, 2003;Leser et al, 2003;Saiz-Lopez and Plane, 2004;SaizLopez et al, 2004SaizLopez et al, , 2006Peters et al, 2005;Whalley et al, 2007;Mahajan et al, 2010a;Commane et al, 2011;Dix et al, 2013;Gomez Martin et al, 2013;Le Breton et al, 2017), including significant effects on HO x concentrations and on the HO 2 : OH ratio in coastal and marine locations (Bloss et al, 2005a(Bloss et al, , 2010Sommariva et al, 2006;Kanaya et al, 2007;Whalley et al, 2010).…”

“…Simultaneous measurements of OH and HO 2 by laserinduced fluorescence (LIF) (Bloss et al, 2005a;Smith et al, 2006) and halogen species by a combination of DOAS (for BrO or IO, OIO and I 2 ) and broadband cavity ring-down spectroscopy (BBCRDS) (for OIO and I 2 ) (Bitter et al, 2005) during NAMBLEX enabled box model calculations to fully explore the impacts of halogens on the local composition. A box model without halogen chemistry was able to reproduce the NAMBLEX OH observations to within 25 %, but HO 2 observations were overestimated by up to a factor of 2 .…”