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How Have Divergent Global Emission Trends Influenced Long-range Transported Ozone to North America?
Citation:
Mathur, R., D. Kang, S. Napelenok, J. Xing, C. Hogrefe, G. Sarwar, S. Itahashi, AND B. Henderson. How Have Divergent Global Emission Trends Influenced Long-range Transported Ozone to North America? JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES. American Geophysical Union, Washington, DC, 127(16):e2022JD036926, (2022). https://doi.org/10.1029/2022JD036926
Impact/Purpose:
Employing multi-decadal model simulations of the changes in tropospheric O3 distributions across the Northern hemisphere from a comprehensive atmospheric modeling system in conjunction with detailed sensitivity calculations characterizing the response of tropospheric O3 to NOx and VOC emissions from source regions across the Northern hemisphere, we estimate that on a seasonal-mean basis, during the 1990-2010 period, long-range transported O3 (LRT O3) to regions across the Continental U.S. steadily increased by 0.06-0.2 ppb yr-1 in response to changes in precursor emissions outside North America. This net trend, in turn, arises from superposition of unequal and contrasting trends in contributions from different emission source regions across the Northern Hemisphere. Both the amount of long-range transported O3 and the magnitude of its trend vary spatially and are larger in the western U.S. than those in the east. Accurately quantifying the impacts of changes in emissions in distant continents on amounts of pollution imported is becoming as important as domestic control measures at receptor continents. Analyzing the impact of well documented and contrasting multi-decadal (1990-2010) changes in emissions across the Northern Hemisphere helped better explain the dominant source regions that drive the noted changes in observed O3 mixing ratios across the U.S. During the 2005-2010 period and perhaps even in the contemporary atmosphere, the contributions of shipping emissions to O3 imported to the U.S. troposphere are comparable to those from transport of O3 attributable to East Asian emissions and suggest possibly even higher contributions in the future if NOx emissions from commercial shipping operations were to increase in response to anticipated growth in seaborne trade. In addition to the O3 attributable to emissions from the source regions across the Northern Hemisphere, model calculations also suggest that air masses entering the North American domain have sizeable contributions of O3 that is of stratospheric origin. Our estimates suggest that O3 that is of stratospheric origin could constitute 29-78% of the estimated Spring time background O3 across the continental U.S. This highlights the need for improved quantification of the variability and amount of O3 in surface air that is attributable to the stratosphere in background O3 assessments and policy deliberations.
Description:
Several locations across the United States in noncompliance with the national standard for ground-level ozone (O3) are thought to have sizable influences from distant extra-regional emission sources or natural stratospheric O3, which complicate the design of local emission control measures. To quantify the amount of long-range-transported O3 (LRT O3), its origin, and change over time, we conduct and analyze detailed sensitivity calculations characterizing the response of O3 to emissions from different source regions across the Northern Hemisphere in conjunction with multidecadal simulations of tropospheric O3 distributions and changes. Model calculations show that the amount of O3 at any location attributable to sources outside North America varies both spatially and seasonally. On a seasonal-mean basis, during 1990–2010, LRT O3 attributable to international sources steadily increased by 0.06–0.2 ppb yr−1 at locations across the United States and arose from superposition of unequal and contrasting trends in individual source-region contributions, which help inform attribution of the trend evident in O3 measurements. Contributions of emissions from Europe steadily declined through 2010, while those from Asian emissions increased and remained dominant. Steadily rising NOx emissions from international shipping resulted in increasing contributions to LRT O3, comparable to those from Asian emissions in recent years. Central American emissions contribute a significant fraction of LRT O3 in southwestern United States. In addition to the LRT O3 attributable to emissions outside of North America, background O3 across the continental United States is composed of a sizable and spatially variable fraction that is of stratospheric origin (29%–78%).
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DOI: How Have Divergent Global Emission Trends Influenced Long-range Transported Ozone to North America?