Regional‐Scale Ozone Deposition to North‐East Atlantic Waters

Abstract

A regional climate model is used to evaluate dry deposition of ozone over the North East Atlantic. Results are presented for a deposition scheme accounting for turbulent and chemical enhancement of oceanic ozone deposition and a second non-chemical, parameterised gaseous dry deposition scheme. The first deposition scheme was constrained to account for sea-surface ozone-iodide reactions and the sensitivity of modelled ozone concentrations to oceanic iodide concentration was investigated. Simulations were also performed using nominal reaction rate derived fromin-situozone deposition measurements and using a preliminary representation of organic chemistry. Results show insensitivity of ambient ozone concentrations modelled by the chemical-enhanced scheme to oceanic iodide concentrations, and iodide reactions alone cannot account for observed deposition velocities. Consequently, we suggest a missing chemical sink due to reactions of ozone with organic matter at the air-sea interface. Ozone loss rates are estimated to be in the range of 0.5–6 ppb per day. A potentially significant ozone-driven flux of iodine to the atmosphere is estimated to be in the range of 2.5–500 M moleccm−2 s−1, leading to a mixing-layer enhancement of organo-iodine concentrations of 0.1–22.0 ppt, with an average increase in the N.E. Atlantic of around 4 ppt per day.

A revised global ozone dry deposition estimate based on a new two-layer parameterisation for air–sea exchange and the multi-year MACC composition reanalysis

“…Sarwar et al (2016) included ozone reactions with iodide, dissolved organic carbon (DOC) (a measure of DOM), DMS, and bromide in their ozone modelling for summer months in the Northern Hemisphere and found that the impact of DOC on the simulated deposition velocity was comparable to that of iodide, with the other reactions contributing much less. Coleman et al (2010) showed that in addition to iodide the inclusion of DOC in their empirical scheme described daytime deposition observations better in coastal wa- Massicotte et al (2017) gives an average DOC value of 52 µM for oceans.…”

“…Coleman et al (2010) empirically derived k = 3.44 × 10 6 M −1 s −1 based on data fitting, whereas Sarwar et al (2016) used k = 4.0 × 10 6 M −1 s −1 , noting that this value together with their selected DOC concentration yields a firstorder rate constant of ∼ 268 s −1 that lies between the two values 100 s −1 (open ocean) and 500 s −1 (coastal waters) used by Carpenter et al (2013) based on the modelling by Ganzeveld et al (2009). This reactivity value lies within the range of reactivity plotted in Fig.…”

The influence of model spatial resolution on simulated ozone and fine particulate matter for Europe: implications for health impact assessments

“…3e). Some of these positive differences are clear around the coastal regions which is likely due to differences in the land/sea mask at the two resolutions, which leads to less deposition over oceanic grid-cells at the coarse resolution and higher simulated O 3 concentrations compared to the same locations that are designated as land at the finer scale (Coleman et al, 2010). In addition, large positive differences in simulated O 3 concentrations between the two resolutions occur over the Alps, whereby simulated O 3 concentrations are higher at the finer scale ( Fig.…”

The influence of model spatial resolution on simulated ozone and fine particulate matter: implications for health impact assessments

“…3e). Some of these positive differences are clear around the coastal regions which is likely due to differences in the land/sea mask at the two resolutions, which leads to less deposition 235 over oceanic grid-cells at the global resolution and higher simulated O3 concentrations compared to the same locations that are designated as land at the regional scale (Coleman et al, 2010). In addition, large positive differences in simulated O3 concentrations between the two resolutions occur over the Alps, whereby simulated O3 concentrations are higher at the regional scale ( Fig.…”