Recommendation. Improve our ability to quantify the impacts of long-range transport of POPs on human and ecosystem health and to predict how this might change in the future. This requires efforts to

• develop hemispheric emission inventories and projections for POPs (especially PAHs and PCDD/Fs).

• parameterize and validate hemispheric transport models for POPs. Future research on global transport of POPs should focus on bringing together modeling and observation specialists during the design and execution of field campaigns to identify the most important parameters to measure and therefore reduce model uncertainties.

• better quantify the current U.S. inflow and outflow of POPs through measurements and modeling. This includes the continuation of long-term atmospheric monitoring programs, which can aid our ability to track how POPs are redistributed due to climatic and global emission changes.

• estimate future U.S. inflow and outflow based on projected changes in source regions and global climate change, using hemispheric transport models.

• expand our understanding of the photochemical processes that affect POPs during transport.

• evaluate long-range transport potential in the initial assessment and regulatory approval of new chemicals.