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Impact of Halogen Chemistry on Ground-LEvel Ozone Levels in Europe
Citation:
Sarwar, G., R. Borge, Q. Li, D. de la Paz, C. Cuevas, AND A. Saiz-Lopez. Impact of Halogen Chemistry on Ground-LEvel Ozone Levels in Europe. 2019 Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes (Harmo 19), Burges, BELGIUM, June 03 - 06, 2019.
Impact/Purpose:
CMAQv52 model contains detailed halogen chemistry. The impact of the halogen chemistry on ozone over Europe is examined using the CMAQ model.
Description:
Oceans are the main emission source of halogens (Cl, Br and I). These species modify the oxidation capacity of the atmosphere and have an impact on the formation of secondary species, including organic aerosols and tropospheric ozone (O3). However, chemical-transport models used for regulatory purposes have not considered halogens until very recently. In this study, we apply the multi-scale WRF-SMOKE-CMAQ (v5.2) modelling system to understand the role of halogens on O3 levels in Europe. We perform a one-month simulation for July 2006 that reflects the typical summer conditions using 12-km horizontal grids and 35 vertical layers. We compare two versions of the Carbon Bond 2015 (CB05) chemical mechanism. One version includes a full description of the halogen gas-phase chemistry through 26, 39 and 53 reactions involving chlorine, bromine and iodine, respectively. The second version, used as a reference, does not include any of these reactions. Both simulations used boundary conditions generated from the corresponding hemispheric CMAQ model results. We compare O3 predictions from both model simulations to identify the impacts of including halogens into regulatory simulations. In addition, we compare our modelling results with the observations from more than 450 air quality monitoring stations all over Europe, both inland and in coastal areas. The combined halogen chemistry reduced the concentration of O3 by as much as 15 µg/m3 and improved model performance, especially at those monitoring stations close to the seashore (<24 km). Our results indicate that the index of agreement increases from 0.690 to 0.705 and the average bias decreases from 2.8 to -1.4 µg/m3 in these locations. Our results suggest that the inclusion of marine halogens into regional chemical-transport models for regulatory purposes is important, at least in coastal areas since they may play a relevant role in the formation and destruction of O3 and thus, should be considered when designing air quality plans and measures.
