Impact of Enhanced Ozone Deposition and Halogen Chemistry on Tropospheric Ozone over the Northern Hemisphere

Abstract

Fate of ozone in marine environments has been receiving increased attention due to the tightening of ambient air quality standards. The role of deposition and halogen chemistry is examined through incorporation of an enhanced ozone deposition algorithm and inclusion of halogen chemistry in a comprehensive atmospheric modeling system. The enhanced ozone deposition treatment accounts for the interaction of iodide in seawater with ozone and increases deposition velocities by 1 order of magnitude. Halogen chemistry includes detailed chemical reactions of organic and inorganic bromine and iodine species. Two different simulations are completed with the halogen chemistry: without and with photochemical reactions of higher iodine oxides. Enhanced deposition reduces mean summer-time surface ozone by ∼3% over marine regions in the Northern Hemisphere. Halogen chemistry without the photochemical reactions of higher iodine oxides reduces surface ozone by ∼15% whereas simulations with the photochemical reactions of higher iodine oxides indicate ozone reductions of ∼48%. The model without these processes overpredicts ozone compared to observations whereas the inclusion of these processes improves predictions. The inclusion of photochemical reactions for higher iodine oxides leads to ozone predictions that are lower than observations, underscoring the need for further refinement of the halogen emissions and chemistry scheme in the model.

Modeling intercontinental transport of ozone in North America with CAMx for the Air Quality Model Evaluation International Initiative (AQMEII) Phase 3

“…Global modeling studies have reported high-O 3 bias simulated in air arriving along the Texas coast (Fiore et al, 2002(Fiore et al, , 2014McDonald-Buller et al, 2011;Zhang et al, 2011). The high-O 3 bias over 10 ppb has been reported by a regional modeling study (Sarwar et al, 2015;Smith et al, 2015). Adding reactions of halogens (especially iodine; Smith et al, 2015) to the O 3 chemistry in CAMx mitigated (e.g., ∼ 3 ppb reduction of MDA8 O 3 at coastal sites) but did not eliminate this bias.…”

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

“…Halogens from inorganic (sea-salt) and organic (photodissociation of biogenic compounds) sources, particularly of marine origin, are thought to be important for the tropospheric ozone budget, as they take part in efficient ozone loss catalytic cycles (Read et al, 2008;Saiz-Lopez and von Glasow, 2012;Wang et al, 2015). Studies with single models have shown that this chemistry may have a notable impact on the ozone budget and associated radiative forcing in the troposphere Sarwar et al, 2015;Schmidt et a., 2016;Sherwen et al, 2016aSherwen et al, , 2016b, and the inclusion of tropospheric bromine chemistry has been suggested as a way of partially accounting for the low preindustrial ozone levels suggested by the measurements (Parrella et al, 2012) (although these measurements are uncertain; see TOAR-Observations).…”

Extending the Community Multiscale Air Quality (CMAQ) modeling system to hemispheric scales: overview of process considerations and initial applications

“…The halocarbon emissions are esti-mated using monthly average climatological chl a concentrations derived from the Moderate Resolution Imaging Spectroradiometer (MODIS). Sarwar et al (2015) provide details on estimating halogen emission and comparisons with other existing estimates.…”

“…In expanding CMAQ to hemispheric scales, particular attention was devoted to the role of deposition and halogen chemistry in marine environments, which can serve as sinks for O 3 exported from continental outflow and in transit to other regions via long-range transport. An enhanced O 3 deposition treatment that accounts for the interaction of iodide in seawater with O 3 was implemented (Sarwar et al, 2015) and found to increase deposition velocities in marine environments by an order of magnitude. In addition, the gas-phase chemical mechanisms were expanded to include 25 chemical reactions involving 7 chlorine species , 39 chemical reactions involving 14 bromine species, and 53 chemical reactions involving 17 iodine species (Sarwar et al, 2015).…”

“…However, efforts linking regional-and global-scale models have met with mixed success because biases in the global model can propagate and influence regional calculations and often confound interpretation of model results (e.g., Tang et al, 2008;Schere et al, 2012). Additionally, inconsistencies in process representations, species mapping, and grid structures could also introduce errors in the model linkage if not examined and handled carefully.…”