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Contributions of Source Regions to Changes in Long-Range Transported Ozone to North America during 1990-2010: A Modeling Analysis
Citation:
Mathur, R., D. Kang, S. Napelenok, C. Hogrefe, G. Sarwar, B. Henderson, J. Xing, AND S. Itahashi. Contributions of Source Regions to Changes in Long-Range Transported Ozone to North America during 1990-2010: A Modeling Analysis. International Technical Meeting on Air Pollution Modeling and Its Applications, Barcelona (and virtual), N/A, SPAIN, October 18 - 22, 2021.
Impact/Purpose:
Though implementation of control measures and technological advances have reduced ground-level ozone pollution across the United States, increasing amounts of ozone pollution inter-continentally transported from other world regions with increasing emissions, combined with changing and uncertain amounts of natural ozone from variability in stratosphere-troposphere exchange processes, can confound design and implementation of local air pollution abatement strategies. “Background” or amount not produced locally, constitutes a larger fraction of the ozone pollution at a location as local control measures are implemented. Detailed model calculations are analyzed to explain the role of the dominant source regions that drive the 1990-2010 changes noted in observed ground-level ozone measurements across the U.S. In recent years, the contributions of shipping emissions to ozone imported to the U.S. troposphere are comparable to those from transport of ozone attributable to East Asian emissions and could be higher in the future if commercial shipping operations were to increase in response to anticipated growth in seaborne trade. In addition to the O3 attributable to emissions from different world regions, air-masses entering the North American domain have sizeable contributions of natural ozone of stratospheric origin, variability in which needs improved quantification to guide background ozone assessments and policy deliberations.
Description:
As measures to limit the impacts of domestic emissions on surface-level ozone pollution are implemented, the increasing contributions ozone pollution transported from other regions become more influential in shaping local ozone levels and confound implementation of abatement measures to meet more stringent air quality standards. We investigate the contributions of emission changes from 7 source regions, as well as the stratosphere, on the change in tropospheric ozone burden across the Northern Hemisphere and its influence on long-range transport (LRT) of ozone to North America from 1990 to 2010. Sensitivity calculations are conducted with the Hemispheric Community Multiscale Air Quality (HCMAQ) model to estimate the response of O3 to emissions from different source regions across the Northern Hemisphere. The seasonal variations in source region contributions to O3 distributions will be discussed. Changes in NOx and VOC emissions from the 7 source regions are then combined with these sensitivity calculations and multi-decadal HCMAQ calculations to analyze the relative importance of the different source regions to the inferred long-range transported O3 to North America. The role of relatively poorly quantified sources such stratosphere-troposphere exchange and sectors such as commercial shipping in influencing lower tropospheric ozone distributions will be discussed.
