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Halogen Chemistry in the CMAQ Model
Citation:
Sarwar, G., K. Foley, R. Mathur, H. Simon, J. Xing, AND K. Fahey. Halogen Chemistry in the CMAQ Model. 15th Annual CMAS Conference, Chapel Hill, NC, October 24 - 26, 2016.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Computational Exposure Division (CED) develops and evaluates data, decision-support tools, and models to be applied to media-specific or receptor-specific problem areas. CED uses modeling-based approaches to characterize exposures, evaluate fate and transport, and support environmental diagnostics/forensics with input from multiple data sources. It also develops media- and receptor-specific models, process models, and decision support tools for use both within and outside of EPA.
Description:
Halogens (iodine and bromine) emitted from oceans alter atmospheric chemistry and influence atmospheric ozone mixing ratio. We previously incorporated a representation of detailed halogen chemistry and emissions of organic and inorganic halogen species into the hemispheric Community Multiscale Air Quality model. We performed simulations without the halogen chemistry as well as with the halogen chemistry without and with the photolysis of higher iodine oxides. The halogen chemistry without the photolysis of higher iodine oxides lowered summertime mean ozone by ~15% over marine environments; while the halogen chemistry with the photolysis of higher iodine oxides lowered ozone by ~48%. Here, we revise the halogen chemistry by (1) updating all photolytic reactions involving halogen species, (2) incorporating several heterogeneous reactions, and (3) revising organic and inorganic halogen emissions. We perform model simulations without and with the halogen chemistry for the summer months. We use the first month as model spin-up and analyze the results for the remaining months. Our model results confirm that the halogen chemistry effectively reduces ozone not only over surface marine environments but also aloft. However, the spatial impact on ozone varies substantially, and the accompanying paper presents a detailed analysis of the spatial impacts. We compare our current model results to those obtained with previous simulations and also with available observations.
