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The Mediterranean summertime ozone maximum: Global emission sensitivities and radiative impacts

by N. A D Richards, S. R. Arnold, M. P. Chipperfield, G. Miles, A. Rap, R. Siddans, S. A. Monks, M. J. Hollaway
Atmospheric Chemistry and Physics ()
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The Mediterranean troposphere exhibits a marked and localised summertime ozone maximum, which has the potential to strongly impact regional air quality and radia-tive forcing. The Mediterranean region can be perturbed by long-range pollution import from Northern Europe, North America and Asia, in addition to local emissions, which may all contribute to regional ozone enhancements. We ex-ploit ozone profile observations from the Tropospheric Emis-sion Spectrometer (TES) and the Global Ozone Monitoring Experiment-2 (GOME-2) satellite instruments, and an offline 3-D global chemical transport model (TOMCAT) to inves-tigate the geographical and vertical structure of the sum-mertime tropospheric ozone maximum over the Mediter-ranean region. We show that both TES and GOME-2 are able to detect enhanced levels of ozone in the lower tropo-sphere over the region during the summer. These observa-tions, together with surface measurements, are used to eval-uate the TOMCAT model's ability to capture the observed ozone enhancement. The model is used to quantify sensi-tivities of the ozone maximum to anthropogenic and natural volatile organic compound (VOC) emissions, anthropogenic NO x emissions, wildfire emissions and long-range import of ozone and precursors. Our results show a dominant sensi-tivity to natural VOC emissions in the Mediterranean basin over anthropogenic VOC emissions. However, local anthro-pogenic NO x emissions are result in the overall largest sen-sitivity in near-surface ozone. We also show that in the lower troposphere, global VOC emissions account for 40 % of the ozone sensitivity to VOC emissions in the region, whereas, for NO x the ozone sensitivity to local sources is 9 times greater than that for global emissions at these altitudes. How-ever, in the mid and upper troposphere ozone is most sensi-tive to non-local emission sources. In terms of radiative ef-fects on regional climate, ozone contributions from non-local emission sources are more important, as these have a larger impact on ozone in the upper troposphere where its radia-tive effects are larger, with Asian monsoon outflow having the greatest impact. Our results allow improved understand-ing of the large-scale processes controlling air quality and climate in the region of the Mediterranean basin.

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