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Are Changing Emission Patterns Across the Northern Hemisphere Influencing Long-range Transport Contributions to Background Air Pollution?
Citation:
Mathur, R., D. Kang, S. Napelenok, C. Hogrefe, AND J. Xing. Are Changing Emission Patterns Across the Northern Hemisphere Influencing Long-range Transport Contributions to Background Air Pollution? 2017 AGU Fall Meeting, New Orleans, Louisiana, December 11 - 15, 2017.
Impact/Purpose:
With more stringent NAAQS threshold values, the accurate characterization of the amount of pollution transported to the U.S. or background pollution is becoming increasingly important. Sensitivities of hemispheric ozone to source region NOx and VOC emissions calculated with the decoupled direct method (DDM) in CMAQ are combined with multi-decadal simulations across the northern hemisphere to characterize the changing contributions of different source regions to background O3 levels across North America during the 1990-2010 period. These calculations quantitatively demonstrate that during 1990-2010, the amount of long-range transported O3 to North America has increased and that the relative importance of the various source regions to this O3 varies seasonally. Additionally, the results reveal the increasing contributions of emissions from international shipping to estimated LRT & background O3 and emphasize the need for improved quantification of emissions from this sector.
Description:
Air pollution reduction strategies for a region are complicated not only by the interplay of local emissions sources and several complex physical, chemical, dynamical processes in the atmosphere, but also hemispheric background levels of pollutants. Contrasting changes in emission patterns across the globe (e.g. declining emissions in North America and Western Europe in response to implementation of control measures and increasing emissions across Asia due to economic and population growth) are resulting in heterogeneous changes in the tropospheric chemical composition and are likely altering long-range transport impacts and consequently background pollution levels at receptor regions. To quantify these impacts, the WRF-CMAQ model is expanded to hemispheric scales and multi-decadal model simulations are performed for the period spanning 1990-2010 to examine changes in hemispheric air pollution resulting from changes in emissions over this period. Simulated trends in ozone and precursor species concentrations across the U.S. and the Northern Hemisphere over the past two decades are compared with those inferred from available measurements during this period. Additionally, the decoupled direct method (DDM) in CMAQ, a first- and higher-order sensitivity calculation technique, is used to estimate the sensitivity of O3 to emissions from different source regions across the Northern Hemisphere. The seasonal variations in source region contributions to background O3 are then estimated from these sensitivity calculations and will be discussed. These source region sensitivities estimated from DDM are then combined with the multi-decadal simulations of O3 distributions and emissions trends to characterize the changing contributions of different source regions to background O3 levels across North America. This characterization of changing long-range transport contributions is critical for the design and implementation of tighter national air quality standards
