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Chemical nonlinearities in relating intercontinental ozone pollution to anthropogenic emissions

Model studies typically estimate intercontinental influence on surface ozone by perturbing emissions from a source continent, often times turning off completelythe anthropogenic emissions. The non-linear dependence of ozone production on its NOx and VOC precursors make it difficult to generalize results from the literature. We investigate this issue for intercontinental transport between North America (NA), Europe (EU), and Asia (EA) with sensitivity simulations in three global chemical transport models.

The figure above shows the changes in seasonal mean surface ozone over NA and EA due to perturbations (20% vs. 100% reduction) in EU anthropogenic NOx emissions simulated by three models. All models show little nonlinearity in summer but large non-linearity in other seasons. The strongest non-linearity is in winter for all three models. We also find that, in contrast, the NMVOC perturbations in source continents do not produce significant nonlinearities over the receptor continents year-round. This implies that the perceived relative benefit of controlling NOx vs. NMVOCs increases with the magnitude of reductions from current emission levels.