Fig. 4.

Simulated percentage change in 2006 surface air pollution due to Chinese export of goods to the United States versus producing the same goods in the United States for (A) sulfate, (B) ozone, (C) BC, and (D) CO. Results are shown for annual mean concentrations in the lowest model layer (0–130 m), presented as (simulation 1 − simulation 6)/simulation 1 in the SI Appendix, section 6. The color scale is nonlinear to better present the wide range of impacts over different regions. The China-to-US export of goods results in enhanced (production-based) emissions of China with a reduction in US emissions. Air quality in China worsens as a result of these additional emissions. Over the western United States, concentrations of sulfate, ozone, and CO also increase because the elevated transport of Chinese pollution overcompensates for the effect of reduced US emissions. Meanwhile, concentrations of sulfate, BC, and CO decrease over the eastern United States, a beneficial effect particularly given its high population density.