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Discussion papers
https://doi.org/10.5194/acp-2019-718
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-718
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Aug 2019

Submitted as: research article | 26 Aug 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Modeling Trans-Pacific Transport and Stratospheric Intrusion of Tropospheric Ozone using Hemispheric CMAQ during April 2010: Part 2. Examination of Emission Impacts based on the Higher-order Decoupled Direct Method

Syuichi Itahashi1, Rohit Mathur2, Christian Hogrefe2, Sergey L. Napelenok2, and Yang Zhang3 Syuichi Itahashi et al.
  • 1Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), 1646 Abiko, Abiko, Chiba 270–1194, Japan
  • 2Environmental Protection Agency (EPA), Computational Exposure Division, National Exposure Research Laboratory, Office of Research and Development, Research Triangle Park, NC 27711, USA
  • 3Department of Marine, Earth, and Atmospheric Sciences (MEAS), North Carolina State University (NCSU), Campus Box 8208, Raleigh, NC 27695, USA

Abstract. The state-of-the-science Community Multiscale Air Quality (CMAQ) Modeling System which has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ), is applied to study the trans-Pacific transport, a phenomenon recognized as a potential source of air pollution in the U.S.A., during April 2010. The results of this analysis are presented in two parts. In the previous part 1 paper, model evaluation for tropospheric ozone (O3) was presented and an air mass characterization method was developed. Results from applying this newly established method pointed to the importance of emissions as the factor to enhance surface O3 mixing ratio over the U.S.A. In this subsequent part 2 paper, emission impacts are examined based on mathematically rigorous sensitivity analysis using the higher-order decoupled direct method (HDDM) implemented in H-CMAQ. The HDDM sensitivity coefficients indicate the presence of a NOx-sensitive regime during April 2010 over most of the northern hemisphere. By defining emission source regions over the U.S.A. and East Asia, impacts from these emission sources are examined. At the surface during April 2010, the emission impacts of the U.S.A. and East Asia are comparable over the western U.S.A. with a magnitude of about 3 ppbv impacts on a monthly mean of all hours basis whereas the impact of domestic emissions dominates over the eastern U.S.A. with a magnitude of about 10 ppbv impacts on a monthly mean basis. The positive correlation (r = 0.63) between surface O3 mixing ratios and domestic emission impacts is confirmed. In contrast, the relationship between surface O3 mixing ratios and emission impacts from East Asia exhibits a flat slope when considering the entire U.S.A. However, this relationship has strong regional differences between the western and eastern U.S.A.; the western region exhibits a positive correlation (r = 0.36–0.38) whereas the latter exhibits a flat slope (r < 0.1). Based on the comprehensive evaluation of H-CMAQ, we extend the sensitivity analysis for O3 aloft. The results reveal the significant impacts of emissions from East Asia on the free troposphere (defined as 750 to 250 hPa) over the U.S.A. (impacts of more than 5 ppbv), and the dominance of stratospheric intrusions on upper model layer (defined as 250 to 50 hPa) over the U.S.A. (impacts greater than 10 ppbv). Finally, we estimate changes of trans-Pacific transport by taking into account recent emission trends from 2010 to 2015 assuming the same meteorological condition. The analysis suggests that the impact of recent emission changes on changes in the contribution of trans-Pacific transport to U.S.A. O3 levels was insignificant at the surface level and was small (less than 1 ppbv) over the free troposphere.

Syuichi Itahashi et al.
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Status: open (until 21 Oct 2019)
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Syuichi Itahashi et al.
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Short summary
The state-of-the-science Community Multiscale Air Quality model extended for hemispheric applications (H-CMAQ) has been applied to trans-Pacific transport which recognized as a potential air pollutants source over the U.S.A. In part 2, the higher-order decoupled direct method (HDDM) is applied to investigate the emission impacts from East Asia and U.S.A. during April 2010. Furthermore, changes in trans-Pacific transport caused by the recent emission variations are examined.
The state-of-the-science Community Multiscale Air Quality model extended for hemispheric...
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