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<p>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 US, during April 2010. The results of this analysis are presented in two parts. In the previous paper (Part 1), model evaluation for tropospheric ozone (<span class="inline-formula">O₃</span>) 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 the surface <span class="inline-formula">O₃</span> mixing ratio over the US. In this subsequent paper (Part 2), 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 <span class="inline-formula">NO_<i>x</i></span>-sensitive regime during April 2010 over most of the Northern Hemisphere. By defining emission source regions over the US and east Asia, impacts from these emission sources are examined. At the surface, during April 2010, the emission impacts of the US and east Asia are comparable over the western US with a magnitude of about 3&thinsp;ppbv impacts on monthly mean <span class="inline-formula">O₃</span> all-hour basis, whereas the impact of domestic emissions dominates over the eastern US with a magnitude of about 10&thinsp;ppbv impacts on monthly mean <span class="inline-formula">O₃</span>. The positive correlation (<span class="inline-formula"><i>r</i>=0.63</span>) between surface <span class="inline-formula">O₃</span> mixing ratios and domestic emission impacts is confirmed. In contrast, the relationship between surface <span class="inline-formula">O₃</span> mixing ratios and emission impacts from east Asia exhibits a flat slope when considering the entire US. However, this relationship has strong regional differences between the western and eastern US; the western region exhibits a positive correlation (<span class="inline-formula"><i>r</i>=0.36</span>–0.38), whereas the latter exhibits a flat slope (<span class="inline-formula"><i>r</i> <i>&lt;</i> 0.1</span>). Based on the comprehensive evaluation of H-CMAQ, we extend the sensitivity analysis for <span class="inline-formula">O₃</span> aloft. The results reveal the significant impacts of emissions from east Asia on the free troposphere (defined as 750 to 250&thinsp;hPa) over the US (impacts of more than 5&thinsp;ppbv) and the dominance of stratospheric air mass on upper model layer (defined as 250 to 50&thinsp;hPa) over the US (impacts greater than 10&thinsp;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 US <span class="inline-formula">O₃</span> levels was insignificant at the surface level and was small (less than 1&thinsp;ppbv) over the free troposphere.</p>