Abstract
[1] Measurements of OH and HO2 concentrations were made at the surface of the eastern coast of the Hudson Bay during the COBRA campaign from February 18th to March 8th 2008. Diurnally averaged OH and HO2 concentrations peaked at 1.16 (±1.02) × 106 molecule cm−3 and 1.42 (±0.64) × 108 molecule cm−3 respectively. A box-model, constrained to supporting observations, is used to access the radical budget in this cold, northerly environment. Formaldehyde (HCHO) photolysis is found to be the dominant daytime radical source, providing 74% of the observed HOx. A considerable (>80% of the total source) surface HCHO source is required to reconcile the model and observed HCHO concentrations. Model simulations also suggest significant roles for the heterogeneous loss of HO2 and for halogen chemistry in the cycling of HO2 to OH. The formation of HO2NO2 is identified as an important radical reservoir, reducing HOx concentrations during the day and enhancing them at night. This impacts both local oxidizing capacity and reduces local ozone production by approximately 30%. The sensitivity of the local chemistry to uncertainties in these processes is explored. The majority of these processes are not currently represented in global chemistry models.
Highlights
A box‐model, constrained to supporting observations, is used to access the radical budget in this cold, northerly environment
This local chemistry is generally considered to be controlled by the chemistry of oxides of hydrogen (OH and HO2 ≡ HOx) and oxides of nitrogen (NO and NO2 ≡ NOx)
In this paper we investigate the processes controlling HOx at the surface using observations of OH and HO2 during a surface field campaign in the Canadian high latitudes during the spring of 2008
Summary
[2] The largest recent changes in surface air temperatures have been seen at the poles [Solomon et al, 2007]. [6] Halogens (Cl, Br, I) have been found to significantly impact high latitude boundary layer chemistry, notably during the spring [Barrie et al, 1988; Fried et al, 2004; Bloss et al, 2007, 2010; Saiz‐Lopez et al, 2008] These species (predominantly I and Br) influence HOx concentrations through the reaction of XO (generic halogen oxide) with HO2 to form HOX (reaction (10)). Through the use a box model constrained to supporting measurements, the observations are assessed and the processes important in controlling the HOx budget in this environment are investigated. Simulations were constrained to average diurnal cycles of observed O3, NO2, CO, HCHO, H2O vapor and temperature All these data were first filtered to remove periods where the sampled air mass was being influenced by the site power generator. To separate the processes controlling the daytime and nighttime chemistry, we first analyze the processes occurring at local noon and at local midnight
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