Long-term atmospheric NOx/CO enhancement ratios in megacities provide evaluations of emission inventories. A fuel-based emission inventory approach that diverges from conventional bottom-up inventory methods explains 1970–2015 trends in NOx/CO enhancement ratios in Los Angeles. Combining this comparison with similar measurements in other U.S. cities demonstrates that motor vehicle emissions controls were largely responsible for U.S. urban NOx/CO trends in the past half century. Differing NOx/CO enhancement ratio trends in U.S. and European cities over the past 25 years highlights alternative strategies for mitigating transportation emissions, reflecting Europe's increased use of light-duty diesel vehicles and correspondingly slower decreases in NOx emissions compared to the U.S. A global inventory widely used by global chemistry models fails to capture these long-term trends and regional differences in U.S. and Europe megacity NOx/CO enhancement ratios, possibly contributing to these models' inability to accurately reproduce observed long-term changes in tropospheric ozone.
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Hassler, B., McDonald, B. C., Frost, G. J., Borbon, A., Carslaw, D. C., Civerolo, K., Granier, C., Monks, P. S., Monks, S., Parrish, D. D., Pollack, I. B., Rosenlof, K. H., Ryerson, T. B., von Schneidemesser, E., Trainer, M. (2016): Analysis of long-term observations of NOx and CO in megacities and application to constraining emissions inventories. - Geophysical Research Letters, 43, 18, p. 9920-9930.DOI: http://doi.org/10.1002/2016GL069894
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- Three-Dimensional Observation of Atmospheric Processes in Cities