Golam Sarwar, U.S. Environmental Protection Agency
Halogen chemistry can be an important sink for ozone over oceanic areas from interactions with sea spray. A simple halogen-mediated first-order ozone loss was initially developed by using hemispheric CMAQ results obtained with and without detailed bromine/iodine chemistry for summer months. The detailed bromine/iodine chemistry has recently been updated and hemispheric model simulations were completed with and without the updated bromine/iodine chemistry for an entire year. The simple halogen-mediated first-order ozone loss is developed using the annual hemispheric CMAQ results obtained with and without full bromine/iodine chemistry. The revised halogen-mediated first-order rate constant for ozone loss (units=s‑1) as a function of atmospheric pressure P (units=atm) is:
These reactions are applied to grid cells over oceanic areas.
Model sensitivity runs were completed with the existing and updated simple first order ozone loss (continental U.S. domain) for a 10-day summer period. The updated simple first-order ozone loss reduces 10-day average ozone by up to 4.0 ppbV over sea water and by up to 2.0 ppbV over some coastal areas. There is no impact on model run time.
Figure 1: Impact of updated simple first-order ozone loss.
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UTIL/chemmech/src/wrt_reactions_module.f
Sarwar, G.; Gantt, B.; Schwede, D.; Foley, K.; Mathur, R.; Saiz-Lopez, A., 2015: Impact of enhanced ozone deposition and halogen chemistry on tropospheric ozone over the Northern Hemisphere, Environmental Science & Technology, 49(15):9203-9211.
Sarwar, G.; Gantt, B.; Foley, K.; Fahey, K.; Spero T. L.; Kang, D., Mathur, Rohit M., Hosein F.; Xing, J.; Sherwen, T.; Saiz-Lopez, A., 2019: Influence of bromine and iodine chemistry on annual, seasonal, diurnal, and background ozone: CMAQ simulations over the Northern Hemisphere, Atmospheric Environment, 213, 395-404.
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