Science Inventory

Impact of intercontinental pollution transport on North American ozone air pollution: an HTAP phase 2 multi-model study


Huang, M., G. Carmichael, B. Pierce, D. Jo, R. Park, J. Flemming, L. Emmons, K. Bowman, D. Henze, Y. Davila, K. Sudo, J. Jonson, M. Lund, G. Janssens-Maenhout, F. Dentener, T. Keating, H. Oetjen, AND V. Payne. Impact of intercontinental pollution transport on North American ozone air pollution: an HTAP phase 2 multi-model study. Atmospheric Chemistry and Physics. Copernicus Publications, Katlenburg-Lindau, Germany, 17:5721-5750, (2017).


This paper presents a number of modeling experiments that were performed as part of the Hemispheric Transport of Air Pollution phase 2 (HTAP2). This study aims to address (1) the comparison of the O3 sensitivities generated from the HTAP2 and HTAP1 experiments, which could help address how the LRT impacts on NAM changed through time; (2) how the refined modeling experiment design in HTAP2 can help advance our understanding of the LRT impacts on NAM, particularly the involvement of regional models and the inclusion of small spatial–temporal scale analyses during high O3 episodes that are more relevant to air quality management; and (3) the usefulness of satellite observations for better understanding the sources of uncertainties in the modeled total O3 (e.g., from the emission and regional models’ boundary condition inputs) as well as for reducing the uncertainties in some of these model inputs via chemical data assimilation.


The recent update on the US National Ambient Air Quality Standards (NAAQS) of the ground-level ozone (O3/ can benefit from a better understanding of its source contributions in different US regions during recent years. In the Hemispheric Transport of Air Pollution experiment phase 1 (HTAP1), various global models were used to determine the O3 source–receptor (SR) relationships among three continents in the Northern Hemisphere in 2001. In support of the HTAP phase 2 (HTAP2) experiment that studies more recent years and involves higher-resolution global models and regional models’ participation, we conduct a number of regional-scale Sulfur Transport and dEposition Model (STEM) air quality base and sensitivity simulations over North America during May–June 2010. STEM’s top and lateral chemical boundary conditions were downscaled from three global chemical transport models’ (i.e., GEOS-Chem, RAQMS, and ECMWF C-IFS) base and sensitivity simulations in which the East Asian (EAS) anthropogenic emissions were reduced by 20 %. The mean differences between STEM surface O3 sensitivities to the emission changes and its corresponding boundary condition model’s are smaller than those among its boundary condition models, in terms of the regional/period-mean (<10 %) and the spatial distributions. An additional STEM simulation was performed in which the boundary conditions were downscaled from a RAQMS (Realtime Air Quality Modeling System) simulation without EAS anthropogenic emissions. The scalability of O3 sensitivities to the size of the emission perturbation is spatially varying, and the full (i.e., based on a 100% emission reduction) source contribution obtained from linearly scaling the North American mean O3 sensitivities to a 20% reduction in the EAS anthropogenic emissions may be un-condition models’ mean O3 sensitivities to the 20% EAS emission perturbations are _8%(May–June 2010)/_11%(2010 annual) lower than those estimated by eight global models, and the multi-model ensemble estimates are higher than the HTAP1 reported 2001 conditions. GEOS-Chem sensitivities indicate that the EAS anthropogenic NOx emissions matter more than the other EAS O3 precursors to the North American O3, qualitatively consistent with previous adjoint sensitivity calculations. In addition to the analyses on large spatial–temporal scales relative to the HTAP1, we also show results on subcontinental and event scales that are more relevant to the US air quality management. The EAS pollution impacts are weaker during observed O3 exceedances than on all days in most US regions except over some high-terrain western US rural/ remote areas. Satellite O3 (TES, JPL–IASI, and AIRS) and carbon monoxide (TES and AIRS) products, along with surface measurements and model calculations, show that during certain episodes stratospheric O3 intrusions and the transported EAS pollution influenced O3 in the western and the eastern US differently. Free-running (i.e., without chemical data assimilation) global models underpredicted the transported background O3 during these episodes, posing difficulties for STEM to accurately simulate the surface O3 and its source contribution. Although we effectively improved the modeled O3 by incorporating satellite O3 (OMI and MLS) and evaluated the quality of the HTAP2 emission inventory with the Royal Netherlands Meteorological Institute–Ozone Monitoring Instrument (KNMI–OMI) nitrogen dioxide, using observations to evaluate and improve O3 source attribution still remains to be further explored.


Impact of intercontinental pollution transport on North American ozone air pollution: an HTAP phase 2 multi-model study   Exit


Record Details:

Product Published Date: 05/08/2017
Record Last Revised: 04/10/2018
OMB Category: Other
Record ID: 339573